# 600v 600a service, do I need non ferrous straps?



## jza (Oct 31, 2009)

Ran a new service, 500 ft long of single conductor 500mcm teck, 3ph. Looked in the CEC but can't find anything, do I need non-ferrous straps?

I'm in Canada but wouldn't mind knowing how it would be done in the USA.


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## jza (Oct 31, 2009)

Nvm, 12-106 (5).

But does this apply to teck?


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## don_resqcapt19 (Jul 18, 2010)

If the ferrous support will completely encircle the single conductor, there will be heating at that point. It is possible with that size conductor fully loaded to create enough heat to damage the insulation. A one hole type strap would not cause this problem. A ferrous strut strap on ferrous strut would.


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## jza (Oct 31, 2009)

The teck is mounted on ferrous strut and strapped with a ferrous cobra strat. The teck however is armored, with aluminum.


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## don_resqcapt19 (Jul 18, 2010)

jza said:


> The teck is mounted on ferrous strut and strapped with a ferrous cobra strat. The teck however is armored, with aluminum.


 The aluminum armor does not change anything. You will have a heating issue at each strap with that installation...that is assuming that a cobra strap has electrical contact with the strut on both sides of the cable. I don't know what a cobra strap is.


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## oliquir (Jan 13, 2011)

is that a teck cable with 3 conductor or only one?


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## don_resqcapt19 (Jul 18, 2010)

oliquir said:


> is that a teck cable with 3 conductor or only one?


 The original post says single conductor. My comments are based on that and would not apply to a cable that has all 3 phases in the same cable.


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## oldtimer (Jun 10, 2010)

oliquir said:


> is that a teck cable with 3 conductor or only one?


He mentioned it was single conductor. Corflex maybe?


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## Mike in Canada (Jun 27, 2010)

Single-conductor cables carrying more than ~200A (from memory) must not be completely encircled by ferrous material. You can either use aluminum straps or aluminum uni-strut. I suppose you could use both, but that would be ridiculously expensive. If you're running the cable through a roof deck or anything like that then you have to make sure that the metal cladding has been cut away in such a way that it doesn't encircle single conductors. As long as all three phases go through the same hole you're okay. This isn't really covered by the CEC properly... it's covered by CSA standard C22.2 No. 131-07. The standard allows for using larger cable and de-rating it to 70% to avoid doing all of the extra work to avoid sheath currents, but the last installation I did went sour because the inspector didn't allow the de-rating. I had to go back and cut roof-decks with the cable already through them to get rid of the metal. He even made me jack-hammer the concrete out between the cables just in case there was a re-enforcing grid in there (there wasn't... I knew there wasn't...).
Don't forget the switchgear and panel have steel skins. You need to cut it out and use an aluminum plate at the source end and a fibre-board plate at the load end. Don't try to use a knock-out punch on either. You have to use a hole-saw.

If you need any more details, just ask.


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## Mike in Canada (Jun 27, 2010)

oldtimer said:


> He mentioned it was single conductor. Corflex maybe?


 They make single-conductor TECK, too. It still has a bonding conductor, unlike coreflex.


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## don_resqcapt19 (Jul 18, 2010)

Mike,
Does the CEC permit you to cut a slot between the cable entry holes in a ferrous enclosure like the NEC does? 


> 300.20(B) Individual Conductors. Where a single conductor carrying alternating current passes through metal with magnetic properties, the inductive effect shall be minimized by (1) cutting slots in the metal between the individual holes through which the individual conductors pass or (2) passing all the conductors in the circuit through an insulating wall sufficiently large for all of the conductors of the circuit.


This applies in the NEC no matter what the current is, as opposed to the CEC rule that does not apply unless the current is 200 amps or more.


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## Mike in Canada (Jun 27, 2010)

Strictly speaking, slotting is not enough. It depends on the discretion of the inspector, though. If you had a 3/4" wide slot through 1-1/4" KO's then you'd probably be fine, but a hack-saw slot wouldn't pass (even though it might actually do the job just as well). The problem is that the inspectors often don't actually know more about the situation than the journeymen, so they just go by 'feel'. When I'm doing something that isn't adequately covered by the CEC then I try to have a copy of the applicable CSA code with me at the time of inspection, or at least a copy of the installation instructions from the manufacturer.
As far as the panels and gear are concerned, since you need to put a non-ferrous plate in there, anyway, you have to have the material removed such that the connectors don't touch the body of the enclosure at all. I sometimes use over-sized knockouts and then cut between them, but it's faster to use a zip-cut disc in a grinder and cut a rectangle then mount your aluminum or fibre-board.
When running parallel runs you are allowed to use multiple openings in the interest of maintaining strength in the material you are going through, so instead of a slot 2' long you can have three slots 8" long with a few inches of material between each, and you have three legs completing a phase going through each slot. As long as you complete the phase (L1, L2, and L3) then it's not a problem.
Oh, and when going over ceiling joists make damn sure you don't get one of your cables on one side of a joist riser and the others on the other. They can consider that 2' triangle of metal to be ferrous material encircling your conductor, and they can nail you on it. Just imagine how much fun it is to cut and splice one of those suckers, particularly given the irritating rules on doing it. Pricey? Oh, yeah!

Oh, and I tried using the 70% opt-out once, and the inspector didn't go for it. He made me go back and do all of the non-ferrous stuff after the fact when I had already up-sized the cable so that it was de-rated to 70%. That was a bad day.


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## jza (Oct 31, 2009)

End result, straight from ESA:

Over 425a, aluminium plate at line side, fibre glass plate on load side. Non ferrous strapping throughout (conductor may not be surrounded by ferrous material unless all the other conductors are surrounded with it. The phenomenon at play is called a sheath/eddy current.


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## Mike in Canada (Jun 27, 2010)

jza said:


> End result, straight from ESA:
> 
> Over 425a, aluminium plate at line side, fibre glass plate on load side. Non ferrous strapping throughout (conductor may not be surrounded by ferrous material unless all the other conductors are surrounded with it. The phenomenon at play is called a sheath/eddy current.


 Just to clarify, it doesn't necessarily need to be 'all other conductors', you just need a complete phase. If you have a parallel run of A B C C B A then you can have two slots, one for A B C and one for C B A and since each slot contains a complete phase there is no eddy-current nonsense. Similarly if A B C is on one side of a joist riser and C B A is on the other side you're still okay because there is a complete phase on each side.
The job that I referenced before was 600A with a parallel run. That means only 300A per cable, but the inspector insisted on the fibre and aluminum. It's worth calling the inspector first and finding out what they're after. It sucks rocks to have to change it after the fact.


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## don_resqcapt19 (Jul 18, 2010)

Mike in Canada said:


> ...That means only 300A per cable, but the inspector insisted on the fibre and aluminum... .


I thought the rules for this in the CEC started at currents of 200 amps? Unlike the NEC where they apply no matter what the current is.


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## RePhase277 (Feb 5, 2008)

Why does it have to be ferrous vs. non-ferrous? I mean, I have seen it in the NEC but this is the first time asking. ANY metal is subject to inductive heating, not just ferrous metals.


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## jza (Oct 31, 2009)

don_resqcapt19 said:


> I thought the rules for this in the CEC started at currents of 200 amps? Unlike the NEC where they apply no matter what the current is.


You have to start taking precautions at 200amps, but only at 425amps do you need to go all out.

Mike, at one point in the run A and B go through a wall, and C does not. Do you think this is going to be a problem? The wall is framed with metal stud, so A and B are going to be encircled as they pass through the wall.


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## don_resqcapt19 (Jul 18, 2010)

InPhase277 said:


> Why does it have to be ferrous vs. non-ferrous? I mean, I have seen it in the NEC but this is the first time asking. ANY metal is subject to inductive heating, not just ferrous metals.


The effect is very minor with non-ferrous metals.


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## johnsonr1 (May 29, 2011)

jza said:


> End result, straight from ESA:
> 
> Over 425a, aluminium plate at line side, fibre glass plate on load side. Non ferrous strapping throughout (conductor may not be surrounded by ferrous material unless all the other conductors are surrounded with it. The phenomenon at play is called a sheath/eddy current.


The other item that I do not see mentioned when using teck cable runs over 200 A is that the load needs to be floated. The bond is connected at the line side and cut off at the load side. Also ensure your lock nuts are Aluminum. Had issue with 600V/600A runs where supplier sent me steel lock nuts and didnt catch it till the guys had it installed in switchgear; had to remove and replace.


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## user4818 (Jan 15, 2009)

jza said:


> Ran a new service, 500 ft long of single conductor 500mcm teck, 3ph. Looked in the CEC but can't find anything, do I need non-ferrous straps?


Sub the job to someone on Craigslist next time.


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## HARRY304E (Sep 15, 2010)

Peter D said:


> Sub the job to someone on Craigslist next time.


He can't ..

You may answer the phone...:laughing:


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## Mike in Canada (Jun 27, 2010)

jza said:


> You have to start taking precautions at 200amps, but only at 425amps do you need to go all out.
> 
> Mike, at one point in the run A and B go through a wall, and C does not. Do you think this is going to be a problem? The wall is framed with metal stud, so A and B are going to be encircled as they pass through the wall.


 The inspector that I had on that job would have had kittens over this situation. Another inspector might not. If you can somehow replace part of one of the metal studs with a wooden stud then you can circumvent the problem. With suspended ceilings this actually wouldn't be *that* miserable to do. However, it may be that the inspector you have won't have a problem with it. Or perhaps your best bet will be to put in a junction box and oversize the conductors in that section. If you can de-rate them to 70% then you can bypass the problem. So sayeth the code:

4-008 Sheath currents in single-conductor metal-sheathed cables (see Appendix B)
(1) Where sheath currents in single-conductor cables having continuous sheaths of lead, aluminum, stainless
steel, or copper are likely to cause the insulation of the conductors to be subjected to temperatures in
excess of the insulation ratings, the cables shall be
(a) derated to 70% of the current-carrying rating that would otherwise apply;
(b) derated in accordance with the manufacturer’s recommendations and in compliance with
Rule 2-030; or
(c) installed in a manner that prevents the flow of sheath currents.


So, de-rating is supposed to be a get-out-of-jail-free card, but it didn't work for me. It's all about the discretion of the inspector...


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