Parallel Equipment grounding conductor size

[tramike]

If you have a 2000 amp feeder with parraleled 10 times, each conduit has 3/0 conductors per phase, what size equipment grounding conductoor do you need?

 

[dereckbc]

Re: Parallel Equipment grounding conductor size

250 KCM copper or 400 KCM AL in each conduit. Are you saying you have 10 parallel conduits containing 3/0 phase conductors?

[ February 23, 2004, 04:07 PM: Message edited by: dereckbc ]

 

[tramike]

Re: Parallel Equipment grounding conductor size

yes, each conduit has 3 - 3/0 conductors plus an equipment ground.

 

[dereckbc]

Re: Parallel Equipment grounding conductor size

See anything wrong with the design? 3/0 phase and 250 KCM ground.

 

[iwire]

Re: Parallel Equipment grounding conductor size

I would be thinking 5 sets of 600s for this.

Cheaper in time & materials.

Also the more pipe runs the more difficult it is to keep them the same length.

 

[russ]

Re: Parallel Equipment grounding conductor size

250.122(F) is the article for grounds run in parallel raceways.

It doesn't seem practical to install the 10 raceways your planing, if, this is a new installation

 

[don_resqcapt19]

Re: Parallel Equipment grounding conductor size

(A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122 but shall not be required to be larger than the circuit conductors supplying the equipment.

Can we apply the above and use a 3/0 EGC in each of the conduits?
Don

 

[iwire]

Re: Parallel Equipment grounding conductor size

Originally posted by don_resqcapt19:

(A) General. Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122 but shall not be required to be larger than the circuit conductors supplying the equipment.

Can we apply the above and use a 3/0 EGC in each of the conduits?
Don

Don I thought of that too, but I would say no as I believe the group of paralleled conductors makes one circuit conductor.

What do you think?

Bob

 

[russ]

Re: Parallel Equipment grounding conductor size

Seemed like 250KCM was too big to me, until I read 250.122(F)(1).
Here's one place where the ground conductor is based on the over-current device.

 

[don_resqcapt19]

Re: Parallel Equipment grounding conductor size

Bob,
And the 10 paralleled EGCs are one conductor equal to the size of the ungrounded conductors.
Don

 

[wanderer20001us]

Re: Parallel Equipment grounding conductor size

If this is a 150V-600V wye connected system, then 240.13 applies(it will have ground fault protection). If the ground fault is set to meet 250.122(F)(2) along with meeting the other conditions, then you can use 3/0 egc in each pipe.

But why would use use 10 - 3/0 in the first place?

 

[dereckbc]

Re: Parallel Equipment grounding conductor size

Originally posted by wanderer20001us:
[QBBut why would use use 10 - 3/0 in the first place? [/QB]

Seems like I asked that already.

Is ther some reason why 10-runs of 3/0 were used?

 

[tramike]

Re: Parallel Equipment grounding conductor size

That is what the cotractor wanted to install. No particular reason for having it paralled 10 times

 

[wanderer20001us]

Re: Parallel Equipment grounding conductor size

Must be T&M

 

[eonebrandon]

Re: Parallel Equipment grounding conductor size

Have you seen the price of copper lately..
also, if you have an estimating program, run both ways through. the smaller the conductor, the less resistivity lost, the easier to pull, no tugger etc. how many amps is a 500 kcmil good for? now look at a 1000 kcmil, notice a problem. Now, in 96' and older NEC, there was a specific exception that stated the grounding conductor shall not be required to be larger than the ungrounded conductor. It was not until 99' that it was restructured to the "general" note that now covers all area A-F including motors. I think the guy is ahead of the curve.

 

[tramike]

Re: Parallel Equipment grounding conductor size

250.122 F 2 applies to multiconductor cable

 

[dereckbc]

Re: Parallel Equipment grounding conductor size

Originally posted by eonebrandon:
the smaller the conductor, the less resistivity lost

Does 10 parallel runs of 3/0 AWG = .0076 ohms/kft, and 5 parallel runs of 500 KCM = .00516 ohms/kft?

Does 1000 feet of 3/0 awg cost less than 500 feet of 500 KCM?

What are the installation/material cost of 10 runs of 2 inch RMC, and 5 runs of 3-1/2 RMC?

[ February 24, 2004, 04:00 PM: Message edited by: dereckbc ]

 

[eonebrandon]

Re: Parallel Equipment grounding conductor size

resistivity from a loss of amps stand point (ie. surface skin effect, as in more of it) did you run it thru a estimating program yet? if you run 100' both ways you save at least $2,500 and if the run is longer, start multiplying....$$$$

 

[hurk27]

Re: Parallel Equipment grounding conductor size

By eonebrandon: ie. surface skin effect, as in more of it

I don't think skin effect comes into play at the low frequency's our power supply is at (60hz's)
Now at 400 HZ's?

 

[eonebrandon]

Re: Parallel Equipment grounding conductor size

Here I go making assumptions, but isnt that amoung other reason why you loose so many amps the larger your conductor becomes?