A DATE WITH TRAINING IN MARCH

CENTRE FOR STUDIES IN ELECTRICAL ENGINEERING
PRACTICES & STANDARDS

(CESEEPS International Association, Inc.)


MODULE 2.0:

MEDIUM VOLTAGE SYSTEMS

& APPLICATIONS IN INDUSTRIES

Date: March 5 – 7, 2008
Venue: SUGBAHAN Food Center
A. S. Fortuna St., Mandaue City, Philippines


SEMINAR INFORMATION

CESEEPS’ Module 2.0 known as “MEDIUM VOLTAGE SYSTEMS & APPLICATIONS IN INDUSTRIES” is the second of a series of five seminars composing the training program “DESIGN PRACTICES IN INDUSTRIAL ELECTRICAL SYSTEMS”. Accompanying the course is The BLUE BOOK aimed as a reference material for electrical design engineers. As a sequel to Book 1, The Blue Book provides demonstrations for the medium voltage segment in the design process for the industrial power system in concept.






As a training phase, Module 2.0 covers the development of single line diagrams, system dimensioning, medium voltage fuses & power circuit breakers, overview of system fault duties, power distribution systems and a glimpse of an entire system configuration of the industrial plant or commercial complex. It also covers power transformers, medium voltage cables, cable terminations and power centers - all from the viewpoint of the medium voltage side.

(Part of the 42 participants of Module 1.0 conducted in February 2008)

Envisioned as a design guide, Module 2.0 contains in detail how electrical systems are dimensioned from the LV Switchgears to the Power Centers, to the Primary Unit Substations, Medium Voltage Distribution System Configurations and to the Power Generating Plants. Devised to be simplistically understandable to any engineer/participant, this seminar module book attempts to achieve the design of a model medium sized-industrial plant in the Philippine setting. It likewise exposes traditional folklores in component designing where provisions of the IEEE/ANSI, IEC and other International Standards are cited as reference.

The seminar also includes the highlights of the Grid & Distribution Codes of the Philippines and Power Plant Operations both in Island Generation and Grid Connected modes. To demonstrate how a manufacturing plant is designed from scratch, a thick chapter on “Electrical System Design for a Manufacturing Plant” is included in the Blue Book.

(Another pictures of Module 1.0 Seminar held last month)

While The BLUE BOOK focuses on Medium Voltage Systems, the rest of electrical engineering “must-know” competencies are covered in other books that CESEEPS International Association Inc. had produced. This is where the electrical engineer in totality is treated with global standards and how leading countries are performing their electrical engineering.

It is then assured that practice designing with CESEEPS POWER BOOKS SERIES as guide provides the necessary understanding on the real electrical engineering in industrial plants. This will help catapult the Filipino electrical engineer into the level of a truly world-class technocrat. That’s the greatest legacy that CESEEPS can offer.

This therefore is truly addressing the gap between the academe and the industry.

COURSE OBJECTIVES:

At the end of the module, the participants are expected to be able to:

a) Develop & apply Detailed System Single Line Diagrams related to MV Systems,

b) Design & Apply Dimensioning Processes for Electrical Systems of Industrial Plants,

c) Design & Apply Power Transformers, Power Centers & Primary Substations,

d) Understand the Application of Power Generation Systems both in Island & Grid -Paralleled Modes,

e) Understand the Application of MV System Configurations in Power Plants, Substations and Distribution Systems,

f) Design, select & apply the proper protective devices such as circuit breakers & power fuses,

g) Establish benchmarks for Power System Audit.


TRAINING COVERAGE:

The following topics will be covered in the training module: (click to enlarge pix)

FAULTY ELECTRICAL WIRINGS - PART 6

GOING BACK TO BASICS

FAULTY ELECTRICAL WIRINGS – A CLOSER LOOK
(Last Part of a Series of Six)

By Doods A. Amora, PEE 1821
(February, 2008)

10) SIZING THE FEEDERS, LV/LV TRANSFORMERS & POWER CENTERS

In reality, whenever there’s a major renovation done on a building electrical system, it usually becomes a condition leading to faulty electrical wiring. As feeders & sub-feeders already exist in a building, they could not just be torn-down as so much money had already been spent on these parts of the system. Hence, as a result of the surprises in new load requirements; new feeders or sub-feeders had to be inserted into terminals of existing circuit breakers, its subsequent conduits (if there are any) squeezed in whatever available space in a crowded room, or just plain naked cables tied to existing conduits runs. Some cases may have resorted to the usual “skin, splice and tape” method. These “ragtag, make-do” additions to the system always make the otherwise neat & workmanlike original installations into messy and faulty conditions.


For example:

Somewhere in the country, a new office building has just been inaugurated for business. A few months thereafter, the building management became frantic to install an additional power center and subsequently the new distribution feeders to satisfy clients’ needs who happen to lease half of the building. In the end, it was the client who financed and installed its own power center in an already cramped & messy room allocated supposedly for electrical services. And this is not even an Internet Hotel, the building is just an edifice built for corporate office clientele.

The building owner or its representative architects did not recognize that today, there are new electrical footprints that have to be dealt with in designing power systems for buildings. Computers, IT peripherals & office electronic equipments and the harmonics they bring – they are not loads in the past, but now are eating more power than that of the traditional plug-in appliance loads. This is not an isolated case. It’s happening anywhere else in the world.

How are the “one-time components” in the electrical system of a commercial building designed? Should the electrical design engineer wait for the architects & mechanical engineers to complete their respective designs as inputs? And from there, the electrical engineer usually counts the loads, make circuit arrangements and determine the panelboards, MCC’s, etc. From these arrangements will subsequently shape the sub-feeders, the feeders and eventually, the transformers. Such is the usual practice, of course…

If such is the case, the electrical designer would have to base his system from the loads given by the architects (lighting, GPR’s, etc) & mechanical engineers (air-conditioning). With some allocation for future loads, then presto – all’s well and the building is energized. Fine…

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(The "One-Time Events" in the electrical system of a building: the Power Center, the Feeders, the Busways, the LV/lv Transformers and the Distributors)

But then, what if in reality, the lessee’s business has a different hunger for loads? Does it mean that the electrical system (the feeders/sub-feeders, the LV/lv transformers and even the main service substation transformers) now embedded in the building has to be overhauled to fit the load?

Certainly not! By plain logic, the building electrical system must be all time ready to provide clients what they need; whoever and whatever they are – without overhauling the system.

But how are these done?


11) THE LOAD DENSITY METHODOLOGY

In the USA and other parts of the world, the sizes of feeders/sub-feeders and the transformers are mandated to be based on the Load Density Methodology.

“But Sir, following this Code methodology will cost a fortune. It will result to large feeders and transformers than what are actually needed!”

NEC Table 220-3(b) lists certain occupancies (types of buildings) for which load densities (lighting & general-purpose outlets) specified in volt-amperes per square foot. The PEC also lists down the lighting load densities in terms of volt-amperes per square meter. Both Codes have a purpose.

In each type of occupancy, there must be adequate feeder circuit capacity to handle the total load that is represented by the product of volt-amperes per unit area times the area of the building. The KVA load derived from these computations shall then be multiplied with a demand factor in order to approximate the maximum demand load ever possible that soon to be served by feeders or sub-feeders. The maximum demand plus a load growth factor of 20% to 30% is recommended imbedded in the design until the ultimate service transformer. In design practice, a 65%-70% loaded feeder or transformer in a brand new office building is usually acceptable.

Aside from lighting & general purpose receptacles in office occupancy, a substantial load of 55% - 65% of the whole building load happens to be the ventilating and air-conditioning loads. The same is true to manufacturing concerns whose production lines are air-conditioned. Load densities for air-conditioning systems are also provided by the Code and IEEE publications. Thus the engineer can approximate safely the air-conditioning loads even if the mechanical group has not yet completed their designs.

Let us now look closer at modern office buildings. The new computer age has also brought along the much needed transformation in the power system landscape that the design of office building wants to achieve. Computer loads are special as they require special treatment, too. They also generate harmonics that makes power systems not only dirty but also cause to reflect more loads into the system. As they themselves are vulnerable to system disturbances they help create, they therefore need to be isolated. These special pieces of office equipment even have special plugs thus needing special outlets. But then in the past and even in the present time, these special loads are not getting the attention they deserve from electrical designs.

Traditionally, computers & peripherals are not recognized as loads with “new identity”. They are just considered as part of the general purpose receptacles usually provided by traditional designs. But then, recent experiences show that computers and electronics equipment in offices now eat up more power than the traditional “plug-in” & appliance loads.

Using load densities intended for GPR’s (general purpose receptacles) with the thinking that computer and IT loads are part of it; is ‘highly arguable’ for reasons that the load densities recommended by the Electrical Code for GPR’s were established long before the advent of computers. Moreover, IEEE recommends that these loads shall have dedicated 3-wire single phase circuits, home-running to dedicated 3-phase, 5-wire panelboards, to be fed by the so-called PDU’s (Power Distribution Units) and to be served by dedicated delta-wye isolating transformer with a sufficient factor in sizing system components to address harmonics.

Modern corporate offices today are expected to be replete with office computers and peripherals that would fill up 85% to 90% of the entire office desks of the building. But alas, the most recent PEC or NEC hasn’t established yet load densities for office computers & peripherals. It has been learned that today, authorities & experts in the USA are still in the process of surveying or making census on usages of computers in offices. But then, even though load densities for computer loads in offices are not yet available in the present Electrical Code, power allocation for office IT equipments has to be inputted in any office building design. Otherwise then, will be the frantic calls for the ragtag cure to overload conditions.

The Seemingly Large Feeders

According to the IEEE Gray Book, “In many modern buildings, the actual maximum demand loads will be substantially less than that calculated under the NEC methodology; but where the NEC or equivalent Code is in effect, the Code calculations using the load density method must be used in sizing service, feeders, switchboards and panelboards”.

Admittedly, the resulting feeders calculated or derived through Load Density Method would seem to appear significantly larger than the actual count of demand loads based on the actual circuits drawn on plans. However, this NEC Methodology has a purpose. Again, in the USA, this method is imposed over & above any other method for feeders and the subsequent transformers.

But why the Load Density Method results to larger feeders than what appears needed? Why these feeders have to terminate in Distributors? Why do sub-feeders have to terminate in Sub-Distributors, and so on and so forth?

Let us remember that feeders are supposed to be ‘one-time-event’ installations. The feeders derived from the Load Density Method are usually larger than the actual count of demand loads based on the actual layouts on a plan. This is so because the commercial building must be ready enough to accommodate surprises in load demands brought by assorted clients’ appetite for power. Whatever happens, the feeders must be there available and ready.

The Distributors & Sub-Distributors along with panelboards designed under the Load Density method usually provide ready-to-use circuit breakers that can be utilized anytime when the event comes, without disturbing the embedded feeders and sub-feeders. In effect, messy additions into the system would be avoided and the original well-installed system would be preserved, no matter who and what businesses the clients are.


Feeder Oversizing

Again, in real-life system designing, feeders and sub-feeders are usually oversized to accommodate present load conditions, the anticipated load growth but as well, the surprises in client’s peculiarity in demand. Load Growth Factors imbedded in cabled feeders usually ranges from 20% - 30%. If the feeder is a busway system; the more that it must be oversized (normally at 25% to 35%) - because should it happen that the bus ducts would be short of capacity in the future, can you imagine replacing them?

“But Sir.., is oversizing not a violation of the Code?”

Let’s take a look at some relevant provisions of the Code.

“The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the non-continuous load plus 125 percent of the continuous load. [NEC 215.2 (A)(1)]”. For general service feeders, the Code further said, “the computed load of a feeder or service shall not be less than the sum of the loads on the branch circuits supplied, after any applicable demand factors permitted (NEC 220.10)”.

For feeders serving group motors, the Code says: “Motor loads shall be computed in accordance with NEC 430.24, 430.25 (NEC 220.14)”. To continue, “Conductors supplying several motors, or motors and other loads, shall have an ampacity not less than 125 percent of the full-load current rating of the highest rated motor plus the sum of the full-load current ratings of all the other motors in the group, as determined by 430.6(A), plus the ampacity required for the other loads (NEC 430.24)”.

Hence, designing sizes of circuits or feeders ends up in the ampacities of cables or bus. Protecting these circuits by OCPD’s must match these ampacities because after all, the protective devices are supposed to protect circuit conductors. As NEC 240-3 says: “Conductors shall be protected against over-current in accordance to their ampacities, but where the ampacity of the conductor does not correspond with the standard ampere rating of a fuse or a circuit breaker, the next higher rating shall be permitted only if this rating does not exceed 800 amperes”.

But, “where feeder conductors have an ampacity greater than required by 430.24, the rating or setting of the feeder overcurrent protective device shall be permitted to be based on the ampacity of the feeder conductors (NEC 430-62(b)”.

Therefore, oversizing a feeder (larger than the minimum requirements) is permitted for as long as it is protected properly by protective devices with sizes or settings that match the ampacity of the conductors used. Note that oversizing the feeders above the minimum requirements is a normal event in designing. These are due to the following factors:

a) Anticipation to future loads or load growth,

b) Compensation to voltage drops, necessitating larger cables,

c) Compensation for derating conditions, like too many conductors in a raceway or cable trays,

d) Compensation to correction factors in ambient temperatures,

e) The usual assumption that the loads are all continuous in anticipation to future change of use.


12) THE CONCLUDING PART

Statistics showed that the month of March tops the number of fire incidents in the Philippines compared to other periods in a year. Thus in an effort to raise consciousness prompted the authorities to declare it as the “Fire Prevention Month”. But why is the month of March laden with most incidents of fires? Is it because it’s summer time and the environment is hot?

Probably yes! Dry combustible materials are easy to ignite when the environment is hot and the air abundant. On the other hand, ventilating and cooling comfort appliances as air-conditioners, electric fans are in full blast during these times and the electrical loads are high. Ripe for overloads…, huh? - as many observers say.

Again back to square one, why the overload when there are OCPD’s installed?

The more troubling question is: “Has it occurred to us that the hotter ambient temperature makes the conductor derating conditions in full effect? What if the OCPD’s are sized without considering the derating factors?” (Remember Part 5 of this series).

As pointed out in the earlier episodes; there really exist faulty wirings. The conditions for electrically-started fires cited in this series are only a tip of the iceberg. There are still mountains of issues wanting to be discussed. But to this author, it is now a matter of lifting people’s consciousness - the level of awareness that these articles hope to help achieve.

Although much had been said about “faulty wirings” by the media, significant number of fires are caused by carelessness on the part of the occupants. Aside from these obvious causes, it’s however very difficult to establish faulty electrical wiring as the cause of a fire.

That’s why in these modern times, like the ‘new medical detectives’ we usually see on TV, we need forensic electrical engineers. In the USA, the forensic engineers are not just ordinary ones. They are a select breed of highly experienced PhD’s, complete with laboratories and all having the credentials to represent in court proceedings. Like any medical detectives or forensic pathologists, the forensic engineers reconstruct and establish the interwoven sequence of events that lead to electrical fires.

In the Philippines, we have yet to hear one of this kind. Wishful thinking as it may, such forensic engineers are highly wanting in the recent Glorietta blast controversy.

In the end, Flawed Design, Unworkmanlike Installations, Substandard Electrical Components & Devices, and Cheap Engineering; all of them contributing to each other, constitute to evolve into what we call as: FAULTY ELECTRICAL WIRING.

The Electrical Engineer: The engineering community now faces the task of selecting the correct power-system topology for new building environments. By evaluating popular power-system topologies, there has to emerge a shift in paradigm as deviations from the traditional way of systems designing has dramatically changed.

It is then necessary that we, Filipino electrical engineers have to investigate our traditional electrical practices from that of global standards. Again, there must be a paradigm shift from what was thought of as “traditional practices” to what are global; otherwise the electrical engineer will become irrelevant in these modern times.

What is globalization for?


Doods A. Amora, PEE
February, 2008

FAULTY ELECTRICAL WIRINGS - PART 5

GOING BACK TO BASICS

FAULTY ELECTRICAL WIRINGS – A CLOSER LOOK
(Fifth Part of a Series of Six)

By Doods A. Amora, PEE 1821
(February, 2008)

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9.0) THE FEEDERS & SUB-FEEDERS
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As one looks into the upstream of the system, there are lots of feeders & sub-feeders that have to be dealt with along the way. Several articles in the Electrical Code are devoted in sizing feeder conductors necessary for the safety and operability of electrical systems.

“Feeders” are conductors which carry electric currents from the service switchgear (or generator switchboard) to the distributors, or groups of distributors, or groups of MCC’s, or load centers supplying bulk loads. “Sub-feeders” originate from distribution centers and supply one or more other sub-distribution boards, motor control centers or panelboards. Code rules on feeders also apply to sub-feeders.

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(Examples of Good & Workmanlike Distribution Feeder Installations)
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At the onset, feeders and sub-feeders must be capable to carry the amount of current required by the present load, plus any current that may be required in the future. Selection of the sizes of a feeders depends on the magnitude and nature of the known loads as computed from the branch circuits, the unknown but anticipated loads, the voltage drop as well, and more importantly, the surprises in future loads.

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• LV Feeders in commercial buildings usually originate from the main LV Switchgear of the Power Center to Distributors or group of Distributors (First Frame).


• MCC’s as in the above picture usually are powered by Sub-Feeders coming from Distributors or Sub-Distributors (Second Frame).
  
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As feeder circuits are usually not within visual sight (beneath walls or ceilings most of the time), conductor overheating that results in insulation breakdown or meltdown always go unnoticed. Feeder circuits are usually protected by over-current devices (as fuses or circuit breakers), but then in many cases, these same over-current devices had given user-occupants the wrong security that the circuits are adequately protected.

Now note that the situation in the industrial plant is much better than that of a commercial building. The operation & maintenance in industrial plants usually are supervised by electricians and engineers in shifts. Any unusual manifestations on the system are most likely detected and fixed promptly. That explains why seldom that we hear an industrial plant burned out because of electrically-started fires.

On the other hand, most commercial buildings in the country are not supervised by qualified personnel – in fact, a majority of them (except for the large shopping malls & high-rise buildings) don’t have electrical operation & maintenance personnel at all. Electrical problems like blown-off fuses or tripped circuit breaker are generally attended to by an ‘all-around utility guy’ who may have dangled with electricity before.


The Threat of Feeder Burn-Outs
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Feeders and Sub-Feeders in commercial buildings or industrial plants are considered ‘one-time events’, as such these circuits are usually forgotten over the years - thus the danger of unnoticed feeder overloading to occur.

The fact that feeders/sub-feeders are inherently carrying heavy or high ampere loads, most electrical fires in buildings originate from these circuits. As we say, electrical fires usually happen after several years of operation when loads are added indiscriminately and capacities of feeder cables went overloaded.

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1) A Picture of an overloaded Sub-Feeder
2) Note the imminent insulation breakdown of the overloaded Sub-Feeder Conductor
3) A burned out MV/LV Transformer due to overloading

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Now remember that commercial buildings are open to lessees or locators. The lease could be the entire building or may be a floor or several floors in the building. Note that loads proportionately cater to the appetite of the lessee’s business. A commercial bank of course significantly differs from a hardware store, or a fine-dining restaurant from an ordinary office.

For instance, a change of client from a motel business to a high-end heavily air-conditioned & exotically lighted disco joint may mean tripling of continuous loads. Because capacities of feeders & sub-feeders are not fully consumed in the beginning, then there seem to be no problem. ‘Business as usual’ has now been on-stream and nobody cares - after all, there was no tripping off circuits.

Normally, the new lessee would bring along his contractor to renovate the system to suit to the new business. However, note that the contractor doing a renovation on a building space previously occupied by someone else is only concerned on his scope - which is only confined within the interest leased by his client. New branch circuits and even new panelboards may have been installed for the new client and there seem to be no problem.

Meanwhile the electrical system of the disco joint may have increased the load of the building system significantly but remember that the contractor doing the renovation job has no business on the system of the entire building. Again, the contractor’s interest is only “where to tap”. As feeders & sub-feeders are not readily & physically visible, what if these have been overloaded and have already started to melt-down? Yes, there was no circuit tripping off because the over-current protection may have happened to be oversized. Who really knows?

Worse, how many commercial buildings in the country use industrial fans placed in front of distribution panels to cool off the protective devices in an effort to prevent them from tripping off? If the panelboards are unusually hot, what’s happening then to the non-visible feeder & sub-feeder conductors?

The Threat of LV/LV Transformer Burn-Outs
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Like feeders & sub-feeders, LV/LV transformers when installed & energized are considered permanent fixtures in a system. They are usually oversized above the present load conditions and are expected to carry future additional loads. But then a number of electrical fires are pinpointed unto them.


Relatively large commercial complexes power its buildings with 480v, 3-phase, 60 Hz. The 480v takes care of the centralized air-conditioning system, the ancillary pumps, elevators, escalators & other motor loads. Several sub-systems downstream are the common LV/LV transformers transforming voltage to 240v for general lighting, store lighting and offices’ loads. In the Philippines, sizes ranging from 25 to 300 kVA are common installations. And there are several of them scattered within the building.

But an innocent-looking LV/LV transformer installed in a messy corner of a stock room or in whatever space available in some floors of an old building that is converted into an apartelle, bank or department store rolled into one; could be a candidate culprit to ignite a full-blown fire. As pointed out earlier, LV/LV transformers as “one-time events” are usually oversized above the present load conditions and are expected to carry future additional loads. Why then and in what instance shall an oversized transformer burn out?

Oversized from the beginning, transformers like the feeders are usually forgotten as years go by - even as loads keep on increasing and increasing. If electrical operation of the building is not supervised by qualified electrical practitioners (as in many commercial establishments), chances are, the transformer burns out without even knowing that same transformer had already been overloaded. The question is why, when there are protection devices installed? Here lies the issue! How can a transformer be protected from overloading?

This leads to one of the many reasons why there is a need for protection of transformers. But protecting transformers vary in sophistication as to the voltages involved, the size and the degree of importance. Probably if the transformer is LV/LV, then this could be the reason why less serious attention is given to these types of apparatuses.

LV/LV transformers may not be so expensive pieces of equipment compared to others in the system but its value can be very significant because they might be powering essential loads, computer loads & other IT business tools. Moreover, these transformers usually make the lighting systems and general purpose loads in a business operable. Its value in the electrical system is equally important because of the interruption it brings during failures.


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Sidebar 1: By the way, how do we electrical engineers provide overloading protection to LV/LV transformers? Simple..., huh? But not quite because it could be tricky. Consult the Code, then make a scenario and try placing OCPD’s on the transformer circuit. Then analyze/simulate if the transformer can be protected from overloading. Better still, consult books by Joseph MacPartland where good sample scenarios are presented.

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Sidebar 2: At this point, it is worthwhile to mention one common mistake in electrical systems of buildings - the installation of outdoor type oil-immersed transformers inside the building. Although a mortal sin, bringing inside the building oil-immersed transformers (whether MV/LV or LV/LV) is a practice not so uncommon in the Philippines. To recall, the oil used in this type of transformer is mineral oil - a highly flammable liquid. As the transformer burns out (as seen in the picture at the right), ignition into a full-blown fire is a sure formula.

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Derating of Conductors
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Most buildings were burned not because of short circuits, but by overloads. A short circuit being in the kilo-ampere magnitude will surely trip even an oversized continuous ampere-rated circuit breaker somewhere, that is, assuming that the short circuit current does not outsize the interrupting rating of the circuit breaker. Fact is, a breaker with KAIC rating not outsized by the fault current interrupts the fault without damage to itself.

On the other hand, overloads mean overheating. And overheating if sustained for long will start a fire. Of course circuits do have protection, but what if the circuit breaker continuous ampere-trip rating happens to be oversized viz-a-viz the feeders and the transformer they are protecting? Engineers therefore are supposed to be concerned in overloads as well because an overload coupled with an incorrectly sized thermal ampere-trip rating of a molded case circuit breaker is also a sure formula for melt-downs and eventually the fire.

But how come when the circuit breakers placed in the system matched with the ampacity of the conductors?

That brings us to the subject of derated ampacities of conductors.

Although conductors do have published current-carrying capacities but they are so rated at the ambient temperature of 30 deg C. Also, these ampacities are true only if the are no more than three current-carrying conductors in a raceway or cable. Conditions other than these specifications reduce the capacities of conductors - such derating pushes the conductors to lower net ampacities. Now the question: “Is placing OCPD’s based on the published ampacities of conductors correct?” Maybe yes, maybe not!

Note that placing OCPD’s based on the published ampacities of conductors are correct only if the conditions on “ambient temperature” and the “no more than three current-carrying conductors in a raceway or cable” are met. If not, then the OCPD’s must be sized based of the net ampacity of the wires & cables after being derated.

Does it make sense? Of course, Yes! Because in this case; the OCPD will provide correct protection to the derated cables.

One thing more: The Electrical Code states that in high capacity circuits of 800 amperes & larger, the use of the “next higher protective device ratings” is not permitted. This is so because the ampere increment of protective devices on these levels are already large. Using the “next higher rating” would place the feeder conductors in danger. Worse, some designers & contractors usually don’t consider derating the conductors because these would mean bigger cables and ergo, higher cost. Now, therefore; using the 'next higher rating' OCPD to protect a derated feeder conductor would go farther away from its intended protection.

The secret therefore in high capacity feeder circuits is that the design engineer must place feeders in bigger sizes while maintaining the size of over-current protection. This strategy will take account the voltage drop requirements and the derating factors that lead to overloading of the conductors, as well. Otherwise, what could have been a quality feeder installation will retrogress into faulty electrical wiring!

(To be continued…)

Next Episode: HOW ARE FEEDERS & TRANSFORMERS SIZED?

FAULTY ELECTRICAL WIRINGS - PART 4

GOING BACK TO BASICS

FAULTY ELECTRICAL WIRINGS - A CLOSER LOOK
(Fourth Part of a Series of Six)

By Doods A. Amora, PEE 1821
(February 2008)

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6.0: INTEGRITY OF ELECTRICAL INSTALLATIONS

“Poor workmanship or Un-workmanlike installations” are ‘substandard practices’.

When we declare something as “substandard”, it predicates that there should be some sort of a standard.

As standards shape the integrity of any system, what then is the electrical standard? In the Philippines, is it not the Philippine Electrical Code? The National Building Code (under the watch of the Office of the Building Official) and the Fire Code of the Philippines (Bureau of Fire Protection) - two of other community-related safety codes are in fact citing & referring to the Philippine Electrical Code in so far as electrical installations are concerned.

The term standard refers to design & installation norms or procedures set forth by an authority. In the Philippines, the Philippine Electrical Code (PEC) is the acknowledged standard reference for electrical installations in buildings & industrial plants. The Electrical Code covers rules in design process and the ways of installation. While the National Electrical Code (NEC) of the USA is sponsored by the National Fire Protection Association of America (NFPA), the PEC is published by the Institute of Integrated Electrical Engineers of the Philippines (IIEE).

Competent electrical practitioners are aware that fundamental rules and standards are needed to ensure safety to persons and properties from the hazards arising from the use, misuse, abuse & misapplication of electricity. That is the intent of any Electrical Code, the IEEE Recommended Practices and the IEC Design Guide, among other publications. Conforming to these rules or standards along with proper maintenance will result to electrical systems relatively free from hazards.

Although the aforementioned references include provisions for permissible methods of installation, as any electrical code says, they are not intended as a design or construction manual to untrained persons. Experts say that sound engineering practice, quality workmanship and good sense of economics along with flexibility, reliability and provisions for future growth are equally important considerations.

Again note that the “flaws & defects” constituting faulty electrical wirings are electrical installations that are not of standard. As construction defects are not always easy to identify, there are numerous things that can go wrong in a building, amongst them maybe the results of soil settling or just the expected wear & tear. In the case of electrically started fires, the culprit could be faulty wiring. That’s why in the USA, electrical inspectors are not just appointed - they are certified as inspectors. They’ve got to pass the training, tests and certification process by the National Fire Protection Association (NFPA).

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(Do you want these installations in your own home or building?)

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Integrity of Design & Construction

It should be noted that safety in homes and buildings begins at the drawing boards & design sheets. As pointed out earlier, a faulty electrical wiring could start from a faulty design. Thus the engineer must see to it that his design not only makes sense but of standards. But it must be emphasized that a design (in terms of Code Rules & International Standards) might be perfect on paper but could be horrible in the way the design is implemented.

Implementation is another field of expertise and the Code attempts to include some in its provisions. Therefore, in designing and its subsequent interpretation into reality, it is not of the business to just any person (‘do-it-yourselfers’, ‘cemetery electricians’ or the ‘street disco electricians’) – it must be a work of experienced professional engineers & registered master electricians who understand the responsibility of providing mankind with safe environment in the whole lifetime of a building or industrial plant.

Safety of life and preservation of property are two of the most important factors in the design of the electric system. Conforming to established codes & standards in the selection of the material and equipment is imperative. Professional & workmanlike installations are equally important because no matter how perfect the designs on paper are, it becomes useless when not implemented professionally. Most electrical disasters are caused by either poor design or due to the ignorance of correct installation practices.

To recall, a system might work out operationally as intended to but the same system might be violations of the Code. In situation like this, the Code being devoted to safety must never be compromised because electrical disasters don’t happen in just a few years from the first energization. Like a thief in the night, it usually happens when every one is not expecting.

And faulty wiring is not something an ordinary person should ever to try to fix. It needs professionals to correct it!

Thus, a safe, good and reliable building electrical wiring is a product of both design and execution of the plans into reality that are of standards. Not even value engineering can shatter the intent of the Code & Standards.

7.0) SUBSTANDARD DEVICES & MATERIALS

More often than not, too much cheap engineering is in fact, costly. By making the first cost not objectionable, it does not mean that the engineer shall use cheap, undersized and substandard materials or equipment. Applying correct Value Engineering, the design must fundamentally conform to good engineering practice, codes and standards. This fundamental requisite must not be compromised under the “cloak of costs”. Again, isn’t it that minimum standards must still stand-out even after any “value engineering” is applied..?

(Pictures of Substandard Installations Resulting to Fires)
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Reliability starts with the design engineer’s good sense of selection of electrical equipments & components that would soon compose a continuously operating system. It needs deep knowledge of the various electrical products available and good experience on the performance of these products.

Now note that aside from the National Building Code (c/o OBO) and the Fire Code of the Philippines (c/o BFP), the Bureau of Product Standards (BPS) is another standard-safeguarding agency overseeing the integrity of electrical devices, wires, apparatuses and equipment. But then, without a competent electrical practitioner around specifying and approving wiring devices (for a house or building under construction) may pose huge problems later on.

The Incandescent Lamp Socket

For instance, the incandescent bulb receptacles proliferating in shopping malls nowadays are of cheap “sardine-tin-like” (lata ng sardinas) socket material – too hot even to touch. If operated continuously non-stop for days, it becomes hot enough to melt the insulation at the terminals of conductors.

The Fluorescent Lamp Ballast

And the ballast cores - “sardine-tin-like” too. And if these ballasts burned, the house becomes a candidate for burning, too. Unlike the UL listed & other internationally renowned ballasts, these cheap ones don’t contain fire retardant elements.

The Adapters

In the past, if there were adapters, they were Mogul to E-27based sockets. Now, you can find E-27–to-Mogul adapters in shopping malls. Imagine the overheating that can result if we connect the sardine-tin-like socket of an ordinary E-27 base to mogul adapters to light up a 400w mercury or metal halide lamp? The overheating would not even trip the circuit because the circuit may not yet in over-loaded condition but the sardine-tin socket has already melted!

Studies of electrical fires in homes in the USA show that many problems are associated with improper use of electrical devices by do-it-yourselfers. Common practices that can lead to fires include the use of improperly rated devices such as switches or receptacles and loose connections at these devices. Both can lead to overheating and arcing that can start fires.


8.0: ABUSE & MISUSE OF ELECTRICITY

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Sidebar:

Arcing by the way could be series or parallel. The parallel arcing is actually a short circuit or a ground fault while a series arcing is like a loosely connected switch (in this case, not a short circuit).

Have you experienced lighting a cigarette using the line series to a lamp through the wet tip of the cigarette? The wet tip of the cigarette acts as a switch that provides a loose path of current to the lamp. The current passing through the wet tip heats up – then finally igniting the cigarette.

Or a sausage heated for lunch by the same way as in the picture? The sausage when over-cooked becomes carbonized. Once carbonized, it ignites a fire.

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Of course, abuse & misuse of electricity certainly contribute to electrically started fires. Abuse & misuse of electricity is a given fact in a society populated by the common tao, who are yet to be guided on the safe use of electricity.

But let me ask these questions:

For instance, in the much ballyhooed “octopus wiring”, how can it ignite a fire when the circuit is protected by a circuit breaker..?

Overloading? If the circuit happens to be overloaded, isn’t it that the over-current protective circuit breaker trips off? That of course granting that the circuit breaker is correctly sized viz-a-viz the conductors.

“But the circuit breaker did not trip? Aha! The circuit breaker must have been oversized! There you are again - the oversizing made it faulty”.

But then in reality, there are normally a number of outlets in the same circuit with no loads or not in use at any given time. Chances are, the loads in the octopus connections may not reach the tripping threshold of the circuit breaker and thus, no breaker trips because there was no overload – as far as the circuit is concerned.

The danger actually lies at the point of connection, where the multiple outlets are tapped. For instance, an E27 base lamp socket is fitted with a screw base outlet which in turn multiple outlets are connected into it, the overload or overheating happens not in the circuit but in the socket itself. The same is true if the octopus wiring is derived from a wall outlet of low capacity. That for sure is a recipe for electrically-started fires.

Fires are also caused by people using the wrong size fuse or even putting a coin (in case of the glass fuse) behind a fuse when they don't have a spare.

As electricity and water are a bad combination, there are several cases that indoor type devices are installed outdoors.

But then, isn’t it that abuse or misuse of electricity will result to “faulty electrical wiring”?


(To be continued…)

Next Episode: THE FEEDERS & SUBFEEDERS