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Old 07-12-2011, 11:10 PM   #1
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Default Parallel feeders

I want to size parallel feeders for a 400 amp main breaker panel. Where in the NEC does it give you sufficient information to do this?

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Old 07-13-2011, 12:03 AM   #2
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I want to size parallel feeders for a 400 amp main breaker panel. Where in the NEC does it give you sufficient information to do this?

Thanks,
Blastphemer
The NEC assumes that you know how to do it and provides references for the minimum required installation.

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Old 07-13-2011, 12:30 AM   #3
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I want to size parallel feeders for a 400 amp main breaker panel. Where in the NEC does it give you sufficient information to do this?

Thanks,
Blastphemer


Table 310.15(B)(16)




310.10

(H) Conductors in Parallel.
(1) General.
Aluminum, copper-clad aluminum, or copper
conductors, for each phase, polarity, neutral, or grounded circuit
shall be permitted to be connected in parallel (electrically
joined at both ends) only in sizes 1/0 AWG and larger where

installed in accordance with 310.10(H)(2) through (H)(6).


Exception No. 1: Conductors in sizes smaller than 1/0
AWG shall be permitted to be run in parallel to supply
control power to indicating instruments, contactors, relays,
solenoids, and similar control devices, or for frequencies of
360 Hz and higher, provided all of the following apply:
(a) They are contained within the same raceway or
cable.
(b) The ampacity of each individual conductor is sufficient
to carry the entire load current shared by the parallel
conductors.
(c) The overcurrent protection is such that the ampacity
of each individual conductor will not be exceeded if one
or more of the parallel conductors become inadvertently
disconnected.
Exception No. 2: Under engineering supervision, 2 AWG
and 1 AWG grounded neutral conductors shall be permitted
to be installed in parallel for existing installations.
Informational Note to Exception No. 2: Exception No. 2 can
be used to alleviate overheating of neutral conductors in existing
installations due to high content of triplen harmonic
currents.
(2) Conductor Characteristics.
The paralleled conductors
in each phase, polarity, neutral, grounded circuit conductor,
equipment grounding conductor, or equipment bonding
jumper shall comply with all of the following:
(1) Be the same length
(2) Consist of 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
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Old 07-15-2011, 05:13 PM   #4
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I want to size parallel feeders for a 400 amp main breaker panel. Where in the NEC does it give you sufficient information to do this?

Thanks,
Blastphemer
400 amp, I always pull parallel 4/0 and #4 ground in (2) 2" conduits. 3/0 are good for 200amp but 99.9999999% of everthing I do is for motor loads and it covers the 125% factor. Just take the ampacity of the wire and double, triple quadruple.... etc. The only reason I dont run a 3 or 3 1/2" and pull 500MCM is the greenlee 555 (triple nickle) only goes to 2" and the large table bender and threader (for rigid)are a pain in the ass.
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Old 07-15-2011, 05:30 PM   #5
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400 amp, I always pull parallel 4/0 and #4 ground in (2) 2" conduits. 3/0 are good for 200amp but 99.9999999% of everthing I do is for motor loads and it covers the 125% factor. Just take the ampacity of the wire and double, triple quadruple.... etc. The only reason I dont run a 3 or 3 1/2" and pull 500MCM is the greenlee 555 (triple nickle) only goes to 2" and the large table bender and threader (for rigid)are a pain in the ass.
What's the 125% factor...That seems like a waste of money, if you need a 400 amp ocp device use 2 sets of 3/0 copper, you aren't doing yourself any favors...You would also need a #3 cu ground in each pipe also.
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Old 07-15-2011, 05:36 PM   #6
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I want to size parallel feeders for a 400 amp main breaker panel. Where in the NEC does it give you sufficient information to do this?

Thanks,
Blastphemer
Read 310.4 and 300.3 of the 2008 NEC
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Old 07-15-2011, 05:39 PM   #7
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400 amp, I always pull parallel 4/0 and #4 ground in (2) 2" conduits.
Hows that been working out for ya?
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Old 07-15-2011, 06:07 PM   #8
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Hows that been working out for ya?
Good question.

Chris
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Old 07-15-2011, 06:30 PM   #9
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Hows that been working out for ya?
Ok... maybe i need to be more clear for the commercial <electricians>.... 3 phase motor loads that reqrequire a 400amp disconnect and get fused down to whatever the FLA is of the motor ALWAYS get fed with parallel 4/0 and a ground per conduit. Thats.... 3 conductors and a ground per pipe. So if you see something wrong and why it may not work.... please fill me in.

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Old 07-15-2011, 06:41 PM   #10
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Ok... maybe i need to be more clear for the commercial <electricians>.... 3 phase motor loads that reqrequire a 400amp disconnect and get fused down to whatever the FLA is of the motor ALWAYS get fed with parallel 4/0 and a ground per conduit. Thats.... 3 conductors and a ground per pipe. So if you see something wrong and why it may not work.... please fill me in.
Fused down?...Not sure why you need 4/0 cu...It's overkill and not needed for a 400amp ocp device. Your ground size is also too small ...A #4 cu is not large enough. You need a #3 cu in each pipe based on a 400 ocp device...
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Old 07-15-2011, 06:42 PM   #11
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Ok... maybe i need to be more clear for the commercial <electricians>....
What?

First of all a 400A feeder with two sets of 3/0 would require a #3 in each conduit. 250.122(F). Secondly, you have increased the ungrounded conductor size. 250.122(B).
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Old 07-15-2011, 06:49 PM   #12
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Old 07-15-2011, 07:17 PM   #13
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Mill, what Chris K is talking about is art. 250.122(B). 3/0 is all that is necessary but if you upsize the ungrounded conductors then you must upsize the EGC.

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