Copper Service to Subpanel

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msext

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Can anyone help me out? I have a customer that is requesting a subpanel in a detached garage (easy no problem) but wants copper feeders to panel. All work is in PVC pipe and is apporx 20' to the other building.

Im so used to running AL feeders which size copper do I need for 200Amp? I have seen several things 2- 3ott 1- 1ott(neutral) which is correct?

Thanks guys
 
Re: Copper Service to Subpanel

A garage is not a dwelling unit so that rules out Table 310.15(B)(6).

That leaves us to use Table 310.16

If the customer is requesting 200 amps the minimum size copper conductor will be 3/0 for the ungrounded conductors.

Section 220.22 explains the requirements for reducing the neutral size if you want.

I think it is safe to say you could drop back to a 1/0 neutral without any code or usability issues.

That said I do not think I have ever used a reduced neutral other than in some SE cables. In pipe I just match the neutral to the ungrounded conductors.

The EGC size is found in Table 250.122, for 200 amps that is a 6 AWG copper.

If I was doing the job and the distance was not an issue I would run three 3/0 AWG and one 6 AWG AWG.
 
Re: Copper Service to Subpanel

Also read 230.40 Exception 3, It could save you money. :D

Bob I have never figured out why on a 200 amp circuit, a EGC can be a #6 but a GEC or a bonding conductor has to be a #4 and based on table 250.66 Bonding would be for fault current also. :confused:
 
Re: Copper Service to Subpanel

Originally posted by hurk27:
I have never figured out why on a 200 amp circuit, a EGC can be a #6 but a GEC or a bonding conductor has to be a #4 and based on table 250.66 Bonding would be for fault current also. :confused:
Click to expand...
I am interested in this also. My thought is that it is because when the EGC is working the voltage applied is the service voltage 240 for example.
When the GEC is working the voltage is from a lighting strike and is a much higher voltage, therefore it can overcome the resistance more easliy.

Maybe one of the smarter people from this site can clear me up on this.

I am also wondering if the GEC serves as a drain to prevent the lighting strike or not?
 
Re: Copper Service to Subpanel

When we use Table 250.122 it is on a circuit that has overcurrent protection.

When we use Table 250.66 the circuit has no overcurrent protection.

A 6 AWG is adequate to open a 200 amp breaker.

On the other hand the 4 AWG run to a metal underground water line has to be able to take whatever current can pass through the service conductors from the power company.

If the metal water service is common with other services in the neighborhood and if you have a service conductor fault to the grounding electrode system the GEC will be subject to many thousands of amps until something burns open.

The only thing that really limits the full current available from the power company is the impedance of the service conductors. I believe that is why 260.66 is based on the size of the service conductors but that is an assumption.
 
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