ECN Forum Forums General Topics of the Trade General Discussion Area Canada vs. USA.Parrallel runs in the same conduit

you raise a good point, why no derating if you ran this as three conductors of equivalent ampacity but derating for 6 conductors? the assumption is the same heat is generated by the 3 conductors as the 6 conductors or even triple and quad feeders.

Also, since your install starts in one jurisdiction and ends up in another, would you need to comply with CEC at one end and NEC at the other, with two permits, and two inspections?

Skin effect is huge as the conductors get huge. Unless spec'd the larger conductors are uneconomic.

Paralleling a fist full of 1/0s will give you maximum un-derated capacity.

The rules exist based upon heat buildup/ radiation. In underground/piped systems there is a limit as to how fast the heat can bleed off. While aboveground conduit would seem to have advantage -- remember that air temperatures of 100 F are possible. This means that worst case calculations show either route rate limited.

Since these conductors are crossing the border -- I'd hand the issue off to an EE and get him to take the exposure.

I can't see anyone paying an EC for his professional expertise in such matters. Think of yourself as a general practitioner and the EE as a surgeon. No one wants your opinion on heard operations. They certainly aren't going to pay for it.

Concentrate on what you can get paid for -- not on what piques your professional interest. Keep that as a hobby -- and don't expose yourself to professional liability.

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I've had instances where I was right and the 'expert' was wrong. It went his way all the way down the line. I had no business being that knowledgeable. My boss was not interested in defending my position in the slightest.

Being correct -- but beyond your credentials -- will get you killed, professionally.

Copper conductors, underground.

I think the cross section area of 500 mcm is double 250 mcm. It looks like it has half the resistance.

http://www.nexans.ca/eservice/Canada-en_CA/navigate_235212/Soft_Bare_Copper.html#top

Conductors don't cross the border. They supply power to the toll booths, shop and security building on the Canadian side. The bridge spans the border, has lights etc on it but the wires I'm dealing with are the main service wires.

Wires to first disconnect are 3 x 350MCM R90 copper ran underground to a 400amp fused disconnect. (3" rigid stubs up and comes in the building above ground and you can see 3" conduit going up a near by pole)
From there 6 x 4/0 R 90 copper conductors in a rigid 3" underground a short distance to main 400amp distribution panel. Was origionally fused at 300amps, they want more. Actually one fuse was 300amps and the other was 330amps?

Underground conductors are Diagrams B4-1 to B4-4 and Tables D8A to D15B in the Canadian Code.

Can someone with the NEC give me a hand on this one?

310.16 says 310 amps for copper, and 250 for aluminum reading from the 60 degree c table.

You should be able to use the 75c column.