Electrical question on wire size

[roger55]

I am wiring a 100 amp sub-panel in my new workshop.
What size wire should I use? The wire length from the main house panel will be 60 feet. My 24X48 shop will have a water heater, A/C and 5hp compressor. I only have a small 110V welder.

Reading all that I could find in Google searches said that only #4 is required but some recommend #3. I have already run 1" PVC conduit underground.
Pretty sure local codes would only require #4.
What about the type of wire? THHN or THWN?

Should the green be #6 or #8 in either case of the feed wire size?

Thanks,
Roger

 

[700jfm]

Sorry I would like to help you but I don't know the answer. But I will be doing almost the same thing but in reverse. I will be moving the main service breaker to the new garage and runing to the house, making the house the sub-panel. Im thinking #3 for me, But I have all electric heat A/C and every thing a 3,000sf house has so

 

[Aceman]

3-#3 THWN conductors
1-#8 THWN green equipment grounding conductor

Honestly, you could probably downsize the neutral to a #4 with no issues from the inspectors. Sometimes we pull full size neutrals and sometimes we drop it a size or two if they're aren't a lot of line-neutral loads.

 

[LoneGunman]

roger, #4 THHN is rated for 95 amps when you do not have more than 3 current carrying conductors which you do not. You can get away with the #4 in some areas but the right way to do it IMHO is to use #3. Your bigger problem is going to be your conduit size, 1" conduit is only allowed to have three conductors of #3 or #4, if this is being inspected and if it was in my area you would fail as the ground makes it four conductors. The code doesnt say 3 current carrying condictors (two hots and a neutral) it says 3 conductors, your ground is a conductor.

700jfm, Unless I'm misunderstanding something, you are going to feed your 3000 square foot house with a 100 amp breaker?

 

[LoneGunman]

Ace, we had it that way, no more though, we have to pull fullsize neutrals now.

 

[700jfm]

Roger55 I was not trying to steal your thread Just thought we had the same problem.
Lonegunman I think it's 100 amp. it's what was put in the house when it was built. The new service in the garage will be 200 amp. And I will be running from it to the house.

 

[LoneGunman]

700, okay, I thought you had a 200 amp in the house and were going to replace it with a 100 amp.

 

[CraigFL]

Will this be running through a hot attic in Texas where you might have to derate the wire due to ambient temperature? If so, you might even have to use #2....

 

[roger55]

Thanks to everyone who replied.

I did find some new information late yesterday.
San Angelo goes by 2002 National Electric Code and publishes their requirements for wire sizes on their web-site. For residential use, their requirement for 100A is #4.
Since my run is only 60 feet and is underground (temperature is not an issue), I will go ahead and run the #4.
I also talked to a local electrician who agreed to do a pre-inspection for me before the city comes to do their inspection. He told me to use 3 - #4s with a #8 ground wire. He also said my 1" conduit is fine. This is the same electrician I used to bring in the 400A service to my house last year.

 

[roger55]

3-#3 THWN conductors
1-#8 THWN green equipment grounding conductor

Honestly, you could probably downsize the neutral to a #4 with no issues from the inspectors. Sometimes we pull full size neutrals and sometimes we drop it a size or two if they're aren't a lot of line-neutral loads.

I guess I am still wavering on whether to go ahead and get the #3 instead of the #4.
I have already installed the 1" PVC conduit. ( I know, I should have put in 1 1/4.) I am going to buy the wire tomorrow.

Do you think I can pull 3 - #3s and a #8 through the 1 inch OK?
It's only 60 feet total with 2 - 90s and a 45. I'll figure on using lots of lube and stagger the wires on the connection to the pull tape.

Thanks,
Roger

 

[Stuart in MN]

Thanks to everyone who replied.

I did find some new information late yesterday.
San Angelo goes by 2002 National Electric Code and publishes their requirements for wire sizes on their web-site. For residential use, their requirement for 100A is #4.

Be careful on that...table 310.15(B)(6) in the 2002 NEC allows #4 copper for 100 amp residential service entrance conductors (the main wires coming from the electric utility to the house), but I don't think it applies for branch circuits on your side of the service entrance. They may still want you to use #3 copper for the run from the house to the shop, so it may be worth a call to the city engineering department before you go ahead.

 

[roger55]

Be careful on that...table 310.15(B)(6) in the 2002 NEC allows #4 copper for 100 amp residential service entrance conductors (the main wires coming from the electric utility to the house), but I don't think it applies for branch circuits on your side of the service entrance. They may still want you to use #3 copper for the run from the house to the shop, so it may be worth a call to the city engineering department before you go ahead.

Do you think I can pull 3 -3's and an 8 through that 1" PVC conduit?
As I said, it's only 60 feet with 2 - 90s and 1 - 45.

 

[Stuart in MN]

There are a number of conduit fill calculators online, just Google "conduit fill calculator" and a whole bunch of them show up. I ran the wire sizes and amounts through several of them and it looks like you can get away with 1" conduit and #3 wires, although just barely (remember that the NEC only allows 40% conduit fill - add up the cross section areas of all the wires and the sum must be less than 40% of the cross section area of the conduit.)

Again, check with the city inspector to make sure what he'll allow. Also, if you're pulling the wires yourself use plenty of lubricant, and be careful the wires don't saw grooves into the 90 and 45 bends in the PVC conduit.

 

[Charles (in GA)]

Do you think I can pull 3 -3's and an 8 through that 1" PVC conduit?
As I said, it's only 60 feet with 2 - 90s and 1 - 45.

Its gonna be a real bear, you can rest assured of that. Thats alot of wire for that small of a conduit, you are right at the fill limit if not over it, and lots of lubricant will help but you will need someone feeding and pushing and someone pulling..... hard, to get it thru.

Charles

 

[Palmetto]

I dont envy you. That is gonna be a tough pull, use lots of lube. Definetly not a one man job.

I put in 2" conduit to my shop. I had 140' to go, and pulled 3-#3's by hand, with no lube, no problem. I also put in 100amp service. I used #3 becuase I got a good deal on it.

 

[roger55]

I dont envy you. That is gonna be a tough pull, use lots of lube. Definetly not a one man job.

I put in 2" conduit to my shop. I had 140' to go, and pulled 3-#3's by hand, with no lube, no problem. I also put in 100amp service. I used #3 becuase I got a good deal on it.

I went with 3 - #4s and a #8 through my 55 feet of 1" conduit.
With the lube and with help from my wife, it wasn't too bad.

I talked to 2 other local electricians who said #4 was fine for what I was doing.