Parallel taps

[sevlander]

We have a 400a breaker feeding a trough with parallel 4/0 copper conductors. We need to tap a 200a breaker enclosure and (2) 100a breaker enclosures off of the load side of the 400a CB in the trough. The electrcian on site wants to take (1) set of the 4/0s directly into the 200a CB and tap the (2) 100a off the remaining 4/0 wires. We want him to tap all (3) CBs from both paralleled conductors together at the same point. I cannot find any code that would stop the electrician from doing it his way, but I do not think it is correct. Is there anything stopping him from doing it his way as far as the NEC is concerned? Thanks

 

[cripple]

Parallel taps

If you are asking each of the 4/0 conductors can be individually, no each tap conductor would have to be terminated to both paralleled 4/0. All paralleled conductors are required to comply with 310.4.
310.4(B) Conductor Characteristics. The paralleled conductors in each phase, polarity, neutral, grounded circuit conductor, or equipment grounding conductor shall comply with all of the following:
(1) Be the same length
(2) Have the same conductor material
(3) Be the same size in circular mil area
(4) Have the same insulation type
(5) Be terminated in the same manner

 

[charlie b]

I also thought about 310.4, but I'd like to think there is a stronger and clearer prohibition available somewhere else. The parallel conductors already exist. When they were installed (sometime in the past), I am sure they met all five of those conditions. So exactly which condition(s) would be violated, if you tapped off one parallel set and not the other? Item (5) is the only possibility, and I wouldn't call a "tap" a new "point of termination." I could not find any other article that would apply here, but I don't think 310.4 is enough.

 

[sevlander]

I believe 310.4 answers my question. I skipped right over that article...it is what i believed makes the individual conductor tap illegal. Thanks

 

[steve66]

FWIW: I also like the second sentance of 240.21:

Conductors applied under the provisions of 240.21 A through H shall not supply another conductor except through an overcurrent protective device meeting the requirements of 240.4.

If you tap into one of the 4/0's, the 4/0 are no longer in parallel (they won't carry the same current). Therefore, they become tap conductors. Then the wires to the 100A breakers would be tap conductors supplied from another tap conductor, which is not allowed per the paragraph above.

 

[LarryFine]

The electrcian on site wants to take (1) set of the 4/0s directly into the 200a CB and tap the (2) 100a off the remaining 4/0 wires.

If you do as you described, the conductors would not be paralleled, and standard tap rules for the lengths involved would apply.

However, tapping two conductors from a tap is still prohibited, so your two 100a disco's on the other 4/0's would be a problem.

It looks like you're back to paralleling every tap, unless you can replace the second set of 4/0's with two sets of 100a conductors.