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Wire sizing and conduit sizing

Asked Apr 10, 2007, 01:55 PM — 8 Answers
I am looking for confirmation on some of the info I have found and answers to a few missing pieces. This is regarding wire size and conduit size for service conductors from the meter to the breaker panel (about 30 ft away).

Wire Size:
125A service needs #2 copper or 1/0 aluminum -- #6 copper ground.
150A service needs #1 copper or 2/0 aluminum -- #6 copper ground.
200A service needs 2/0 copper or 4/0 aluminum -- #4 copper ground.

Is this correct? These would each be 3 wire services plus ground. Do all 3 wires have to be the same size or can the neutral be smaller? If so, how much smaller?

Conduit:
How deep does PVC conduit for this run need to be (no driveways involved)?
What diameter PVC conduit is needed for each of the services above?
Specifically I am looking at either 125A or 150A service and would like to use a conduit big enough so that someday in the future I could run another set of wire back through this conduit that would provide photovoltaic current back to an REC meter (and back to the grid). Is 2.5 inch conduit adequate for what I want now and in the future?

THANK YOU!

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8 Answers
tkrussell's Avatar
tkrussell Posts: 9,673, Reputation: 3698
Senior Electrical & Lighting Expert
  
#2

Apr 10, 2007, 05:03 PM


Wire Size:
125A service needs #2 copper or 1/0 aluminum -- #6 copper ground.
150A service needs #1 copper or 2/0 aluminum -- #6 copper ground.
200A service needs 2/0 copper or 4/0 aluminum -- #4 copper ground.

All correct.

These would each be 3 wire services plus ground.

Correct.


Do all 3 wires have to be the same size or can the neutral be smaller? If so, how much smaller?

The neutral can be 70 % of the line connected load amps rating.


Conduit:
How deep does PVC conduit for this run need to be (no driveways involved)?

Minimum is 18" deep, a warning tape 6-12 in below grade is not required but a cheap insurance to digging up a feeder later.

What diameter PVC conduit is needed for each of the services above?

No nit picking here, use 2" for all sets, and always use wire lube.

Specifically I am looking at either 125A or 150A service and would like to use a conduit big enough so that someday in the future I could run another set of wire back through this conduit that would provide photovoltaic current back to an REC meter (and back to the grid). Is 2.5 inch conduit adequate for what I want now and in the future?

I would not suggest large cable be pulled in later alongside existing cable. If both sets of cable will be drawing power at the same time, derating is needed, so the next size wire may be needed for some sizes. Sorry but a fair amount of calcs are need each size each wire.

3" is needed for #4/0's.

Sorry but Jennifer Lopez is on Idol, so I got to see this.

I will check back later.
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ptnoble's Avatar
ptnoble Posts: 42, Reputation: 1
Junior Member
  
#3

May 14, 2007, 09:32 AM
[quote=tkrussell]Wire Size:
125A service needs #2 copper or 1/0 aluminum -- #6 copper ground.
150A service needs #1 copper or 2/0 aluminum -- #6 copper ground.
200A service needs 2/0 copper or 4/0 aluminum -- #4 copper ground.

All correct.

These would each be 3 wire services plus ground.

Correct.


Do all 3 wires have to be the same size or can the neutral be smaller? If so, how much smaller?

The neutral can be 70 % of the line connected load amps rating.

SO, For a 100A service, can I have my two hots be #4 copper and the neutral be #6 copper?

THANKS
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ptnoble's Avatar
ptnoble Posts: 42, Reputation: 1
Junior Member
  
#4

May 14, 2007, 09:33 AM
SO, For a 100A service, can I have my two hots be #4 copper and the neutral be #6 copper?

THANKS
PTN
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tkrussell's Avatar
tkrussell Posts: 9,673, Reputation: 3698
Senior Electrical & Lighting Expert
  
#5

May 14, 2007, 04:06 PM


Only if doing the load calculations to arrive at the maximum unbalanced current and the load is no less than 65 amps for a #6 THHN/THWN wire.

Most likely it will be less, I have no idea of the loads, and I just didn't want to say yes without explaining why.
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abcsalem's Avatar
abcsalem Posts: 70, Reputation: 9
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#6

Oct 17, 2007, 08:19 AM
Quote:
Originally Posted by tkrussell
[i]Wire Size:
No nit picking here, use 2" for all sets, and always use wire lube.
Tk, do we need to use wire lube, if one is to use metal conduit?
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tkrussell's Avatar
tkrussell Posts: 9,673, Reputation: 3698
Senior Electrical & Lighting Expert
  
#7

Oct 17, 2007, 04:20 PM


The quality of wire lube nowadays, it is worth the cost and effort. The biggest risk to pulling wire is the friction,esp for long runs.
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Lola71078's Avatar
Lola71078 Posts: 1, Reputation: 1
New Member
  
#8

Apr 30, 2012, 10:32 AM
What size grey conduit do I need to run two 4/0 alluminum wire through?
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tkrussell's Avatar
tkrussell Posts: 9,673, Reputation: 3698
Senior Electrical & Lighting Expert
  
#9

May 1, 2012, 03:40 AM
Minimum size of Schedule 40 PVC conduit would be 1-1/2", assuming XHHW insulation on the 2- #4/0 Al.

Depending on length, it may be wise to upsize the conduit.

May I ask why only two conductors?
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