# 200 amp sub panel



## telsa (May 22, 2015)

Tmorrow4 said:


> I have a job coming up where I need to install a 200a, 277/480v three phase sub panel. It will have its own 200a breaker in the MDP and a conduit run of 150 feet. Am I right in using 3/0 copper for my feeders and neutral and 4 copper for my ground? Thanks!


Bump it to 4/0... that's the normal practice for 150 feet.


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## Tmorrow4 (Mar 29, 2017)

Should I also bump my ground size to 2?


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## Dennis Alwon (May 9, 2009)

Look at T250.122. The equipment grounding conductor only needs to be #6 however if you increase the size of the ungrounded conductors then you must proportionally increase the size of the equipment grounding conductor. A #4 equipment grounding conductor should be fine if you increase the ungrounded conductors.

It depends on the load as to whether or not you should increase the ungrounded conductors


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## Dennis Alwon (May 9, 2009)

I don't think it is necessary to increase the conductors to 4/0.


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## sbrn33 (Mar 15, 2007)

I would not upsize it either. Plus if money is a factor I am running that new simplull 4/0 alum. and pull it in pretty much by myself.


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## telsa (May 22, 2015)

I can't recall the last time I pulled 3/0 copper for a 200A panel.

Okay, I never did.

The prints ALWAYS spec'd 4/0 (copper).

A #4 bonding conductor IS bumped up a notch.

The spec's usually called out #6. I can't ever recall an EE going for #4.

You have #6 + the EMT as a bond.


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## HackWork (Oct 2, 2009)

telsa said:


> You have #6 + the EMT as a bond.


That doesn't count. If he runs an EGC conductor, it needs to be to code, a #4 for 4/0. 

I know it's odd, because he can forgo the conductor completely and use just the pipe as the EGC.


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## MXer774 (Sep 1, 2014)

3/0's with a #6 for this one!


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## telsa (May 22, 2015)

HackWork said:


> That doesn't count. If he runs an EGC conductor, it needs to be to code, a #4 for 4/0.
> 
> I know it's odd, because he can forgo the conductor completely and use just the pipe as the EGC.


It's all on the EE.

We build to spec.

NEVER had any AHJ call them ( the EE ) out on it.


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## HackWork (Oct 2, 2009)

telsa said:


> It's all on the EE.
> 
> We build to spec.


 You're supposed to build to code.

Could you have an EE spec a 20 Amp circuit run on #16 speaker wire?

I guarantee the plans you agreed to clearly said in it that you would do all installations according to electrical code.



> NEVER had any AHJ call them ( the EE ) out on it.


 They probably didn't look. Or didn't care. But you still shouldn't give advice to people here that is directly against code and could cost them a lot of money.


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## MechanicalDVR (Dec 29, 2007)

HackWork said:


> You're supposed to build to code.
> 
> Could you have an EE spec a 20 Amp circuit run on #16 speaker wire?
> 
> ...


Code is what it is and I've seen PE stamped plans with problems before.


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## active1 (Dec 29, 2009)

There are more factors that should be addressed.
Is the neutral considered a current carrying conductor?
Temperature?
What is the actual load?

310.15(5) Neutrals are not counted in 4 wire 3 phase unless it carries nonlinear loads, than it shall be counted.

if you count the neutral then you have 4 conductors in a conduit and need to de-rate 80%.

Using the 75 CU degree column 310.15 (assuming the OCP like most above 100 amps is rated for 75C) 

3/0= 200A x .8 = 160A
240.2(B)If the load does not exceed the wire ampacity you can go the next size up OCP.
240.6 lists 175A as the next size. It's not 200A.

4/0=230 x .8 = 184A
240.2(B)If the load does not exceed the wire ampacity you can go the next size up OCP. Your continuous load should not exceed this unless you have special 100% continuous rated gear. 
240.6 lists 200A as the next size.

That's why EE will spec out 4/0 CU for 4 wire 200A.

Voltage drop on 480v 3PH 150' is almost no difference.
3/0 @ 160A = 2.57v drop or 0.54%
4/0 @ 160A = 2.04v drop or 0.43%
A difference of 0.53v


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## active1 (Dec 29, 2009)

The EG would be a #6CU (250.122).
310.15(6) Adjustment factors shall jot apply to grounding bonding conductors.


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## manchestersparky (Mar 25, 2007)

Dennis Alwon said:


> Look at T250.122. The equipment grounding conductor only needs to be #6 however if you increase the size of the ungrounded conductors then you must proportionally increase the size of the equipment grounding conductor. A #4 equipment grounding conductor should be fine if you increase the ungrounded conductors.
> 
> It depends on the load as to whether or not you should increase the ungrounded conductors


This is an often overlooked or unknown rule in the NEC. I have had many EC look at me like I was crazy when I tell them !


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## active1 (Dec 29, 2009)

Ya, thinking about it more I agree with manchestersparky the EG should be #4cu if using 4/0.


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