size of the ground wire

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Energy-Miser

Energy-Miser

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Maryland
Trying to wire a single phase 120/240 V, 35 kw generator into the house, inside 2" PVC. Using 4/0 XHHW Alum. for the hots and the neutral. Will number 4 bare do for ground for this system? Anything bigger I am afraid may put me over the fill limit of the PVC. What is the conventional wisdom? Thanks for your inputs in advance. e/m
 
3 4/0 XHHW=.9591
1 #4 XHHW=.0814
Thats 1.0405in.2

2" 80=1.725in2
2" 40=1.975in2

You got millions of square inches left:grin:
 
E.M., Bear in mind that you have increased your conductors 2 sizes larger,

ie. 2/0al. for resd. 150a 120/240v service, the EGC must reflect this increase

250.122(B)
 
benaround said:
E.M., Bear in mind that you have increased your conductors 2 sizes larger,

ie. 2/0al. for resd. 150a 120/240v service, the EGC must reflect this increase

250.122(B)
Click to expand...
So, what are you saying is the minimum size bare copper I can get away with (assuming still use of the 4/0 for the hots and the neutral)? e/m
 
chris kennedy said:
3 4/0 XHHW=.9591
1 #4 XHHW=.0814
Thats 1.0405in.2

2" 80=1.725in2
2" 40=1.975in2

You got millions of square inches left:grin:
Click to expand...
Thanks again Chris. I will probably use #6 copper, which will leave even more room. e/m
 
e/m, what is the application? 35 KW genny will probably have a 150A breaker. Is the existing service 200A? Service rated transfer switch?
 
chris kennedy said:
e/m, what is the application? 35 KW genny will probably have a 150A breaker. Is the existing service 200A? Service rated transfer switch?
Click to expand...
The house has 800 amp service. The generator does have a 150A breaker in it. The transfer switch is 200A and is not service rated, so we added a 200A disconnect ahead of it. Now we left out the ground wire, and had to pull out the three 4/0 wires and add the #6 THHN to it, and then re-pull it. Took four of us, two feeding it and two pulling on the fish tape. It took a couple of hours, and went much better than I had feared (the 2" pvc was already burried, with sod on top, the pull distance was around 70 feet, and there were at least two 90 degree truns in there, between the LB at the side of the house and the other end inside the gen). All went very well, and now we are ready for inspection once again. Thanks for your guidance with this, it is very much appreciated. e/m
 
Energy-Miser said:
Now we left out the ground wire, and had to pull out the three 4/0 wires and add the #6 THHN to it, and then re-pull it.
Click to expand...
Whaooo, Thats nuts. I sorry. How the heck did that get missed?
 
chris kennedy said:
3 4/0 XHHW=.9591
1 #4 XHHW=.0814
Thats 1.0405in.2

2" 80=1.725in2
2" 40=1.975in2

You got millions of square inches left:grin:
Click to expand...

Are you sure this calculation is correct?
 
chris kennedy said:
Whaooo, Thats nuts. I sorry. How the heck did that get missed?
Click to expand...
Oversight. The master electrician I had on the staff at the time was not very thorough, and I was totally pre-occupied with invoicing, material handling, etc. at the office, so it happened. He is gone now (not just for this, there were other reasons). I am checking and double checking more on our jobs, learned a couple of lessons! e/m
 
infinity said:
Are you sure this calculation is correct?
Click to expand...
Well Chris was looking at the 60% column in the table (table 4, chapter 9), instead of at the 40%. But his point is well taken, because even at the 40% there is room to spare:
Schedule 40 at 40%: 1.316 Sq. Inch.
Schedule 80 at 40%: 1.150 Sq. Inch.

e/m
 
Straighten Me out here!

Straighten Me out here!

Now I know I'm not the shapest tack here. I thought that while the NEC uses chapter 9 as Applicable as referenced 90.4 (05').

It just gets to me throwing out these numbers, in no case tonight has there been a mistake.

I guess its a case of new construction(i'm spoiled) and real world application of service and upfits.

Am I missing something between Service Entrance verses Mixed Branch services.

Isn't it the case that its only desirable to have an over-all fill of only 40% of the conduit space, for a particular service.
That the NEC uses the fill aspect of more wire and the derating is always (should) be determined. Lets not forget (talk) about voltage drop.

I can't recall that its a code to fill up a conduit to 98%, but if you do here's the limit to do it ? (based on 9-C). 60% for a 24" nipple I get that.

I have gotten use to it but never a good grip on that aspect and frankly while totally allowed and within the code, I don't have to practice this, much.
 
Energy-Miser said:
Trying to wire a single phase 120/240 V, 35 kw generator into the house, inside 2" PVC. Using 4/0 XHHW Alum. for the hots and the neutral. Will number 4 bare do for ground for this system? Anything bigger I am afraid may put me over the fill limit of the PVC. What is the conventional wisdom? Thanks for your inputs in advance. e/m
Click to expand...

Pipe fill calculator, choose XHHW-2 for Aluminum wire

http://www.boricuaonline.com/frankelectric/calculator-racefill.php
 
jrannis said:
Guys,
Am I getting that its OK to mix copper and Aluminum in the same raceway?
Click to expand...

why not? if the insulation is equal and you are not paralleling them...i am by no means definitive on this, haven't even contemplated looking it up...just thinking out loud
 
jrannis said:
Guys,
Am I getting that its OK to mix copper and Aluminum in the same raceway?
Click to expand...

Absolutely.

Even in parallel installations you could use different materials for individual phases in the same or individual conduits

Roger
 
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