Different Cables in same loop

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siva

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Hi
1) We have 12 nos 1500 KVA,11 KV/400 V transformers connected via ring main units using 3 core X 300 mm2 cable. It is supposed to feed from both sides like a ring (British standard). Now the issue is, in the first contract the scope was to energize these 12 transformers only. Now we are going to give another contract to complete this loop. The problem is 300 mm2 cable is not readily available. So can we use 2 nos of 120 mm2 in parellel to complete this loop. Is there any code violations?

2) The distribution panel boards we are using here do not use any GFCIs for receptacles circuits or not with main incoming breaker. Is there any code requirements for personnel protection?

Thanks in advance

Siva (Djibouti)
 
Siva...

You list your occupation as "inspector." In reviewing your posts you've asked numerous questions that indicate you completely lack even the most basic, common aspects of the NEC, acceptable wiring practices, or a common American electrical installation.

Of your 35 posts, 27 are thread-starting questions and in only 5 do you ever respond or clarify. I point this out to indicate that it appears you are working in an industry or an aspect of the industry you have no qualification to be involved in to the degree in which you claim (inspector) and are using this forum to cover up for this fact. IMHO, you're just as dangerous as a homeowner who seeks to use this forum as an instruction manual, only worse as you're apparently dealing with high potential installations.

It's troubling me because the sheer range of basic questions you pose, from the Kelvin output of lamps, to the testing of hi-potential cables, to voltage drop on lengthly circuits, to color coding an NEC installation in a foreign enviroment also leads me suspect that you're not at all familiar with even the basic apsects of the electrical industry in any other country as well.

I urge the moderators of this forum to review your posts and make a determination that the information you've been gleaning from this site isn't going to get somebody, especially our overseas naval servicemen, killed.
 
clarification

clarification

You misunderstood me...I know 2nos of 120 mm2 will carry more current than 1no 240 mm2....I am here for only six months ....I have british standard back ground .. NEC less...thats why I want to know is there any code violatins before doing an activity other than in the contract...thanks / Siva
 
The NEC is a code for electrical safety. It often allows for many ways to accomplish the same end result.

Your contract is something totally different from the NEC. Your contract can specify whatever the contracting parties agree to. If they want a certain size of wire for some reason and it is noted that way in the contract, you have to supply what is in the contract, unless you can get the contract amended. The fact that the NEC would allow something cannot be used as an excuse to cheat on your contract terms.

The NEC does not even recognize metric size wires.

Incidentally, I am not sure what you refer to as the Britsh (ring) system is actually permitted by the NEC. What is common is to have the distribution transformers wired in parallel from two different sources, something considerably different than ring wiring.
 
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The NEC permits conductors sized 1/0 and larger to be connected in parallel. 120 mm2 is a bit bigger than our 4/0 so the NEC would permit the 120 mm2 to be connected in parallel. The 300 mm2 is just a bit smaller than our 600 kcmil. Two 4/0 s in parallel have a higher ampacity than a single 600 kcmil.
As far as the loop circuit, the ones I have worked with have an open in the loop so it is not a ring circuit. In the event of a cable section failure, the connections at the transformers are reconfigured to deenergize the faulted cable section will still providing power to all of the transformers. Some pad mount transformers using load break elbow connection even had a "parking stand" for the loop cable that is not connected (the open section, used to prevent a ring circuit).
Don
 
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