Table 250.66

[jemsvcs]

If I am following Table 250.66 correctly, when installing two sets of two 250 kcmil AL conductors for a service I could use a single 1/0 AL conductor for the grounded conductor?

 

[don_resqcapt19]

Re: Table 250.66

Only if both sets of 250 are in the same raceway and if the grounded load calculated per 220.61 is 164 amps or less.
Don

 

[FrancisDoody]

Re: Table 250.66

I agree 250.66 lets you parallel twin 250's and use a 1/0 AL conducter for your EGC

 

[Jhr]

Re: Table 250.66

Isn't the calculation used to arrive at the answer you seek is for copper conductors, so you would have to go to a 2/0 or 3/0 NEC 2005 Chap.9 Table 8 ?

 

[charlie b]

Re: Table 250.66

I must be missing something here. What I think is that the only "calculation" needed here is to add 250 plus 250, get 500 as an answer, and look that up in Table 250.66. The minimum size is then 1/0 copper or 3/0 aluminum.

This is a separate issue, but would I be right in saying you only need one of these GECs, that you don't have to put one in each of the two conduits?

 

[jemsvcs]

Re: Table 250.66

Charlie -

I would put all four 250 kcmil Al conductors and the single 1/0 Al conductor in a single 2 1/2" RMC - not running the parallels in separate conduits here.

 

[bphgravity]

Re: Table 250.66

The question is refering to the service grounded neutral, not to the required GEC size.

 

[jemsvcs]

Re: Table 250.66

and according to Table 250.66, two 250 kcmil Al conductors would only require a 1/0 Al grounded conductor and not a 3/0 (that is for OVER 500 kcmil).

 

[Jhr]

Re: Table 250.66

Table 250.66 is for sizing the GEC not the grounded/nuetral conductor. And also is it 2 sets of 2 or 2 sets of 3, speaking of conductors.

[ October 28, 2005, 03:34 PM: Message edited by: Jhr ]

 

[bphgravity]

Re: Table 250.66

Actually it is, sort-of. See section 230.42(C) which refers you to 250.24(B)(1).

 

[jemsvcs]

Re: Table 250.66

According to 250.24(C)(1), Table 250.66 is used to size the grounded service conductor.

And it is two sets of two conductors we are talking about.

 

[Jhr]

Re: Table 250.66

Those sections are saying that the nuetral shall not be smaller than the ground wire.

 

[websparky]

Re: Table 250.66

According to 250.24(C)(1), Table 250.66 is used to size the grounded service conductor.

No, it does not say that at all!
It does say that it won't be smaller than the GEC.

250.24(C) Grounded Conductor Brought to Service Equipment.
(1) Routing and Sizing. This conductor shall be routed with
the phase conductors and shall not be smaller than the required
grounding electrode conductor specified in Table 250.66 but
shall not be required to be larger than the largest ungrounded
service-entrance phase conductor.......

The code does say;

The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.22, and 230.42 are met.

 

[Jhr]

Re: Table 250.66

No, it does not say that at all!
It does say that it won't be smaller than the GEC.

Thats what I said in my last post so it does say that .