200 A panel

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shawn73

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I am installing a 200A 3 phase 208Y/110V panel in my factory. I was planning on using 4/0 THHN. It should be good to 260A X 80% (because with the neutral I will have 4 current carring conductors in my EMT) So, the wire should have 208A of Ampacity. The NEC states 4 conductors in a 2" piece of conduit. If I pull a #6 ground with that to be extra safe, will that exceed the capacity of the EMT?

I can't go up a size with my conduit because our bender stops at 2". Can I split up all the wires into 2 seperate EMT runs to power the panel? It doesn't really seem like a very professional way to do things. Is there a specific way to divide up the wires? Then I should be abe to use 3/0 instead of 4/0 too. Thanks
 
Re: 200 A panel

Since you are in a bit of a crunch, I would do a fill calculation instead of going off of Annex C to see if you have any extra wiggle room. Also, you did not state in your post why you are counting the neutral as current carrying conductor? You only need to count it if it meets the criteria in 310.15(B)(4)(c). i.e. a lot of non-linear loads on your circuit.

[ June 02, 2005, 11:14 AM: Message edited by: wirenut1980 ]
 
Re: 200 A panel

I agree with Dave that unless over half the load is nonliner, you don't have to count the neutral. So you could use 3/0 wire.

If you still want to use 4/0, I calculate that they just barely fit in the 2" conduit for THHN wire (about 2 tenths of one percent extra capacity).

You should verify this by doing the calc. yourself. And you might want to check the jambing ratio (its in the appendix.)

Steve
 
Re: 200 A panel

I would add that parallel raceways would require a minimum of 1/0 conductors in each raceway. Also, to be technical the system that you've mentioned is 208/120 volts not 110.
 
Re: 200 A panel

Originally posted by steve66:
I agree with Dave that unless over half the load is nonliner, you don't have to count the neutral. So you could use 3/0 wire.
Click to expand...
Where do you see that? I see:
(c) On a 4-wire, 3-phase wye circuit where the major portion of the load consists of nonlinear loads, harmonic currents are present in the neutral conductor; the neutral shall therefore be considered a current-carrying conductor.
Click to expand...
It's re-affirming that nonlinear loads need to be counted, not relieving the need to count them if the loads are shown not to be nonlinear. Contrast (A) with (C).

(A) flat out states that in that very special situation, you are permitted to overlook the neutral. If the code didn't say that, you'd have to count the neutral, despite the fact it's demonstratably not carrying current.

If his neutral is carrying an amp, it's carrying current. ;)

Steve, by my calculations, you'd be over if you had four 4/0's and a 6 in a 2" EMT.

According to Table 4, a 2" EMT has 866 square millimeters available (@ 40%, "over 2 wires").

By Table 5, a 4/0 THHN is 208.8 square millimeters.
A #6 THHN is 32.71 square millimeters.

So:
208.8 x 4 = 835.2 (Three 4/0 Phases & Neutral)
835.2 + 32.71 = 867.91
867.91 - 866.00 = (-1.91) sq. mm.

So, it's over on pipe fill.

Have you performed a load calc? Do you really have 200 amps of connected load? Can your neutral be derated? By just knocking that neutral down a size or two you're golden.

[ June 02, 2005, 07:24 PM: Message edited by: georgestolz ]
 
Re: 200 A panel

George, I think that you missed the point. What was said is that if the neutral is not a current carrying conductor than the feeder would not require derating, therefore 3/0 could be used instead of 4/0.
 
Re: 200 A panel

Originally posted by georgestolz:
If his neutral is carrying an amp, it's carrying current. ;)
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George, No that is not true to the NEC, the neutral can carry hundreds of amps and still not be counted as a current carrying conductor.


Check out 310.15(B)(4)(a)

310.15(B)(4) Neutral Conductor.

(a)A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(2)(a).
Click to expand...
You do not have to consider a neutral a current carrying conductor unless 310.15(B)(4)(b) or (c) apply.

A typical multiwire branch circuit in a 12/3 fed from a 240/120 service only contains 2 current carrying conductors. :cool:

[ June 02, 2005, 07:33 PM: Message edited by: iwire ]
 
Re: 200 A panel

George,
In general the grounded conductor of a 3 phase, 4 wire system is not required to be counted as a current carrying conductor per 310.15(B)(4)(a). Where a major portion of the load is nonlinear loads, then the grounded conductor must be counted as a current carrying conductor per 310.15(B)(4)(c). Note that if you use just two ungrounded conductors and the grounded conductor from a 3 phase, 4 wire system, the grounded conductor is always counted as a current carrying conductor.
Don
 
Re: 200 A panel

Sorry George,

I'm with David, Steve, Bob and Don on this one. If the load is linear the neutral doesn't count as a current carrying conductor.
 
Re: 200 A panel

And even if the load is non-linear, it has to be a major portion before the "neutral" is considered a C.C.C.
I take that to mean a major portion of the Art. 220 calculated load.
 
Re: 200 A panel

Shawn73
What will you be using this panel for? This will help everyone to figure out if there's nonlinear loads or possible harmonic currents that might be present here.
Jim
 
Re: 200 A panel

I stand corrected. :)

Edit to add: But my pipe-fill math was pretty good, ey? :D

[ June 02, 2005, 10:46 PM: Message edited by: georgestolz ]
 
Re: 200 A panel

Well, I thought this would be an easyone, but it seems I have cause quite some arguments! It will be powing assembly areas in our factory. (Many florescent lights, hot melt glue guns, a hand maybe 10 computers, Some low amperage machines with PLC's, steamers, etc)
Thanks for the help.
 
Re: 200 A panel

George,
Note that if you use just two ungrounded conductors and the grounded conductor from a 3 phase, 4 wire system, the grounded conductor is always counted as a current carrying conductor.
Don

George, the math for the above is shown in Mike Holts Understanding the NEC material.
 
Re: 200 A panel

Shawn73

It looks like to me you need to count the neutral wire. 4/0 is good to run for your conductors. It also looks like you need 2 1/2 inch conduit.
Jim
 
Re: 200 A panel

It looks like to me you need to count the neutral wire.
Click to expand...
Based on the original post why do you think that the neutral should be counted?
 
Re: 200 A panel

Originally posted by tom baker:


George, the math for the above is shown in Mike Holts Understanding the NEC material.
Click to expand...
Don't steal the mans glory. He spent some quality time on that im sure. :D
 
Re: 200 A panel

Originally posted by infinity:
Just wondering why you chose to use mm instead of inches?
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I kinda just went, hmm, which did I use last time I did this? Oh well, I'll just use the mm. :D

Originally posted by tom baker:
George, the math for the above is shown in Mike Holts Understanding the NEC material.
Click to expand...
Don't steal the mans glory. He spent some quality time on that im sure. :D
Click to expand...
Darn tootin'--and I didn't have to use a cheat sheet for once! :D

Oh, and Tom, you know I'm broke. I can't afford 'em books. I just hang around here and pirate knowledge. ;)
 
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