We are installing conductors into a large switch gear unit at work. They are terminating into 2 of 600 amp switches and 1 of 800 amp switch. The wires are 500 kcmil 4 conductor cable parallel feeds( 28 conductors total. We are tie wrapping all 28 conductors together for approximately 1.5 meters together(all touching) in the switchgear along the side of the unit.

The debate we are having is:
Is there a derating factor b/c of the bundling of the 28 conductors along 1.5 meters?

What is code rule on this?

Hey Cinner...

I see several issues with this idea.

1) 12-108(2) manadates that the spacing and alignment of conductors in parallel are maintained in such a way as to reduce inductive reactance between conductors to ensure the proper division of currents between the cables. See Appendix B for suggested cable arrangements.

A byproduct of ensuring that alignment of conductors is maintained is that the effect of induced heating in the structural steel of the switchgear will be minimized. See 4-008.

2) The correction factors of Table 5C are mandated in this instance by rules 4-004 (1c) or (2c) and (10).

I would reject this install as you described it if it came my way. Having said that, check with the AHJ in your area for a way to do this job in a way that meets the code's requirements.

You may have to think about bringing the cables into the switchgear from different directions.

Rick...


[This message has been edited by Rick Kelly (edited 06-14-2006).]

Is there a switch gear made that has space enough to separate the wires? The wiring space is usually so small that it's necessary to plan the layout so the wires will nest tightly together.

I don't think those rules apply to enclosures containing overcurrent devices or splitters.

Of course they apply. Because a conductor is inside a switchgear enclosure or in a splitter does not mean it is safe from the effects of inductive reactance or mutual heating.

I would expect that all such installs would be planned in such a way as to ensure that proper cable spacing, as much as possible, is maintained, as mandated by 12-102(2).

We are only talking about two cable diameters between bundles of conductors, as in...

The diameter of 500 kcm is (as per Table 10) is 24mm, so 48mm or 2 inches between a bundle of phase conductors is what is required. Might look like this...

A A
(B C) 2" (B C)
| 2"
A A
(B C) 2" (B C)
| 2"
A A A
(B C) 2" (B C) 2" (B C)

(The "A" conductors are supposed to be over the "BC" pairs but the site won't show them that way)

You might have to construct racks to support the cables.

Neutrals can be placed where convenient.

If you can not fit this into the existing switchgear enclosure, in this manner, then the switch gear is to small and someone needs to do some engineering on it.

The code does take into consideration the reality that sometimes cables will be bundled together over short disctances. Hence 4-004(10), where contact between multiple cables for less then 600mm is considered acceptable. Over 600mm you need to derate the ampacity of the cables as per Table 5C. So... your 500kcm cables get derated to 237 amps (395 * .60).

In the example given... 28 conductors bundled together for 1.5 meters without derating them... no way, at least IMHO no way.

The above mentioned conditions are part of the reality of conductors in parallel and bundled together that can not be avoided.

Don't want to do the above... bring out 1250 kcm for the 600 amp feeds and 2 parallel runs of 600kcm or bus duct for the 800 amp feed.

For what it is worth... I would recommend having an Electrical Engineer bless this setup then have your AHJ nod approval as well.

Why not run this idea by the your local AHJ and let us know what was said by them about this install. I am curious to see if they raise the same points I did.

These are not trivial issues. Please do not ignore them. Or... have your liability insurance up to date and current.

[This message has been edited by Rick Kelly (edited 06-15-2006).]

Thanks Rick for your participation sure is great to have another knowledgeable Canadian electrical code person on this forum

Join a forum and jump in I always say. The wireing to the switch board is governed by part 1 of the CEC. Cable spacing and derating are covered there. Inside the cabinet is part 2 of the CEC and the code is pretty loose here. Manufactured products are approved from Canadian Standards, where one exists, and the internal wiring of the feeder cables is prescribed by those standards. As an inspector I am aware of the mutual heating of 1 cable by another where spacing is not maintained and will require a contractor to maintain cable separations until the wires get into the cabinet. Now I don't have any rules to enforce except those supplied from the manufacturer or if I did field product evaluations I might have some authority or expertise to qualify how the internal wiring is done. The internal cable spacing is important but the CEC part 1 does not prescribe the internal wiring of panels. Don't believe that means I'll tolerate a mess. Hope that confuses the situation.

The common sense answer is try the best you can to maintain spacing but without air circulation there reaches a point where all the wires are at or near the same temperature.

Hey Mike... welcome aboard.

Under our act and regulations, in my region of operation, we have jurisdiction on all installed equipment other than equipment owned by the supply authority and used in their function as a "Utility".

As to the Part 2 issue, OEM equipment from a manufacturer would have had the required internal supports needed to ensure that proper cable spacing was maintained. That the manufacturer observed proper cable support and spacing would be a requirement of them before they were granted certification on the equipment in the first place.

Given the info that Cinner offered, it appears that there are no internal supports for his outgoing conductors to the down stream equipment. As such, he needs to provide support for them in a manner that meets the engineering need. The fact that the required cable supports were missing does not allow him to ignore the need for them.

Your point about air temperature is valid, though switchgear manufacturers do take those issues into consideration when they design the "heat loading" of the structure.

I can pretty well guarantee, however, that none of the switchgear manufacturers would bundle 28 conductors together for 1.5 meters.

[This message has been edited by Rick Kelly (edited 06-16-2006).]

Rick I agree with all you points and we do on occasion reject approved equipment if it appears that there is a mis application or someone is using it inapropriately. Lets look at a simple 42 circuit house panel and how an electrician usually finishes the internal wiring. Separate all the bonds and route them along the outside of the can to the bonding terminals. Then the neutrals (grounded circuit conductors) are grouped and terminated last the hots to the o/c devices. all these wires typically get grouped together for neatness and visual appeal. Generally the only thing I like to prevent here is the use of ty raps to tightly bundle these groups of wires. So that is a typical panelboard with a lot of #14, and #12,
We dont have any fault bracing nor I suspect need any but once we get to 500mcm we want spacing? and Bracing. OK the bracing I understand but I cannot remember seeing bracing installed in any panel for load circuits. I have seen a lot of feeders braced but never have I seen braces installed for load conductors. I have seen lots of load conductors ty wraped to frame members of the switchboards but never a bar or rack or frame specfically installed to attach the outgoing cables. So I am wondering what you have in mind for internal wire management of a disribution panel?
Can you tell I am a S*** Disturber?
Again I agree that all you say is logical and a good idea. I would ask an electricain to respect spacing or even demand it inside the switchboard but I really don't believe that the internal wiring of a panel is governed by part 1 of the CEC but part 2 which we don't have direct authority. Yes we always have authority to challenge or reject anything that our experience would judge a hazard or substandard. I am just offering that it might not actually be a violation to allow intimate contact of the conductors within the panel.

Quote by mikesh
Join a forum and jump in I always say


Hey we have a Friday night chat on this forum starts about 6 pm PDT if you get a chance come and join us BTW usually theres a group chatting each night and we have a few Canadians participating also.

Rick
I hope we didn't offend you with some comments that were made on the chat about northern lifestyles I thank you for pointing out that it wasn't polite to mention some folk tales about our northern Canadian friends.

Not sure what it is you are refering to Doug.

I was not in any chat this Friday???

All 28 conductors aren't in contact for the whole 1.5 meters, but the last 6 are in a bundle for almost that distance. The architects squeeze the electrical equipment into ever shrinking spaces and the engineers specify the smallest equipment, so the manufacturer with the smallest wiring space supplies the equipment. The wiring space along side of the breakers, in a 2000 amp gear, can be as small as 6 inches by 12 inches. Add in enough space to bend a 300 MCM, and the wires are bundled together, tight. Forget spacing.

I have yet to see an engineer increase the wire size to accomodate the switch gear, nor an inspector challenge an engineer on this.

After the engineered installation, to change the application of the rules so the last breaker space is unusable (without increasing the size of every existing conductor), would be viewed dimly by most everyone. We can follow any rules than can be dreamed up; but, we must have adequate notice and the rules must be applied fairly - even to engineers.

Can we take a break from reading the code book like it was the bible, written by the all seeing and all knowing? I agree that it's a legal document (the code) and, in the end, must be applied strictly as read, but, I've never seen a heating problem from bundling cables in any equipment. Yes, in a conduit, but not in equipment. True on parallel runs in the wrong conduit, but not in a panel. I've done thermal imaging in a place were marrettes melt, but haven't seen a problem in a CDP.

We load circuits to 80% unless the load is cycling or the breaker has a 100% rating. I think the issue is already dealt with. e.g. 8-104.

I see twh has some interesting perspective on the internal wiring of a panel and you might see that I Kinda agree in that I don't think the code book extends to the inside wiring of the panelboard as that is a part 2 requirement. Interesting statement in that we should not take the code book as the bible. Frankly and i apologise in advance to those of you that will be offended by this statement but I prefer to say you should not read the Bible like it is a code book. The Code weather it is building, elevator, or electrical is the lowest standard that any regulated product is to be installed and there lies the challenge in interpretations. In the case of this discussion I don't think that the internal cable routing is governed by section 4, 8, 12 or 26.

Hi Guys...

I have not had, nor will have, the time to reply to this thread for a few days. I do have some points I wish to discuss with the group and will get back to you later on this week.

[This message has been edited by Rick Kelly (edited 06-20-2006).]

Good Day Cinner!

I sent you an E-Mail at you're listed address with a EL drawing attached (MY APPOLOGIES FOR THE CRUDE PENCIL TYPE DRAFT AS I COULD BUT WHAT THE HEY IT WAS ONLY 3:00AM), but I was wondering as to what kind of set up was being implemented here. Was it a 25KV wye Vault type to 600V with remote EL rooms outfitted with 25, 50 ect KVA with 600V in and 208 & 120V out fed to the EL rooms, or was it a panel board used with the XFMR's on the poles and the 208 120 3 Phase brought through to the pull box, to the Main SW, to the Meter Stack tap box, and out to the meter centers as required then sub fed from there?
Then I would like to ask one of my friends who is the head examiner for the ones challenging the TQ at the moment and ask for his input as to you’re question!
I hope that this will help in any way for a more direct answer to you're question!

Have a good day, and to all on the EL Forum!

Robert Wagner.