Installing a Sub-Panel

[JTS]

I am building a new 40X50 with 14' eve height shop and now I'm down to electrical.

My house has 400 amp service and I am planning on putting a 100 amp sub-panel in the shop. I am having trouble figuring the right size copper wire to put in for the hots/neutral and ground. I already installed 2" pvc conduit from the house to the shop and pulled a string though it. Total distance is 160'.

Any input on the electrical is appreciated.

Attached are some pictures of the shop being built.

 

[Jagmandave]

The electrical wholesaler you're going to buy the wire from will know what you need.

How many amps are you going to pull to the sub, 100? 200? Single phase or 3 phase? That and the distance will tell them what size wire you need. Your 2" pipe should be big enough...

I find that when I'm buying bulk like this, my elec wholesaler was often less expensive than buying from the big blue or orange box store.

Nice shop!

 

[Jim Johnstone]

The electrical wholesaler you're going to buy the wire from will know what you need.

How many amps are you going to pull to the sub, 100? 200? Single phase or 3 phase? That and the distance will tell them what size wire you need. Your 2" pipe should be big enough...

I find that when I'm buying bulk like this, my elec wholesaler was often less expensive than buying from the big blue or orange box store.

Nice shop!

I totally agree with his statement on electrical wholesalers, and not just on big bulk purchases. There were things in small quantities that my local wholesaler totally smashed home depot or lowes on pricing.

 

[pattenp]

My advice would be to use aluminum wire, copper is very expensive. AL will be around $2 a foot compared to copper at $5 a foot. That's a ballpark park price for the size needed for 100A service.

 

[climbabout]

#3 copper THHN is rated for 110 amps per table 310.15 of the NEC - use 3 legs of this for the hots and neutral. #8 will be fine for the ground. Going up one size, #2 is rated 125 amps. 2" conduit is plenty large enough for either size.

 

[pattenp]

I think you'll have a hard time finding #3 copper. If you want copper use #2. If you use AL you could get by with #1 but I'd go with #1/0. This is to get the full 100A I assume you are looking for.

 

[climbabout]

Ditto on the advice for buying from a supply house, and not just because my family owns one. The big box stores lure you in with a few loss leaders per department, knowing what prices you are likely to check, then zing you on all the other peripheral parts you need to complete a job. My price on 14/2 romex will always be higher than them because we can't buy it as well as they do and cannot afford to give it away, but we'll beat them overall on an entire bill of material EVERY time.
Tim

 

[JTS]

You guys are great!


I called the local electrical supply house and the guy on the phone seemed pretty sharp.

He said to use #3 copper with #8 ground, all of which he has in stock for me to pick up.

Cost for #3 copper is $1.54 per foot.

I'll buy the sub-panel and breakers while I am there.

The first task is getting the sub-panel in!

 

[climbabout]

I think you'll have a hard time finding #3 copper. If you want copper use #2. If you use AL you could get by with #1 but I'd go with #1/0

#3 copper should be available at any medium size supply house - we routinely sell it, but as pattenp suggests - no harm in using #2.
Tim

 

[pattenp]

If #3 copper is in stock where you are then get it. The electrical supply place I deal with has to order #3 because it not a common seller. They always have plenty of #2.

 

[BigJohn20]

#3 copper THHN is rated for 110 amps per table 310.15 of the NEC - use 3 legs of this for the hots and neutral. #8 will be fine for the ground. Going up one size, #2 is rated 125 amps. 2" conduit is plenty large enough for either size.

With 2008+ NEC, you cannot use 310.15(B)(2)(6) to size subpanels. You must use 310.16, which still gives an ampacity of 100A for 3AWG and 115A for 2AWG.

 

[sberry]

I will get some argument here but its not a sub, its a service to a detatched structure from an existing service. If I was going to the expense of copper (wouldnt) but would spring for number 2 at that distance. I believe you need a 6 ground with the 2???
My main comes in to my shop but in this case if it was mine it would get a number 6 grounding the frame of the building to the ground in this panel.

 

[pattenp]

You guys are great!


I called the local electrical supply house and the guy on the phone seemed pretty sharp.

He said to use #3 copper with #8 ground, all of which he has in stock for me to pick up.

Cost for #3 copper is $1.54 per foot.

I'll buy the sub-panel and breakers while I am there.

The first task is getting the sub-panel in!

The 3 #3 copper conductors to run 160' at $1.54 per foot is going to cost you $740 and that doesn't count the ground. Is there a reason you don't want to use aluminum? Aluminum will cost you less than half that amount.

 

[BigJohn20]

I will get some argument here but its not a sub, its a service to a detatched structure from an existing service. If I was going to the expense of copper (wouldnt) but would spring for number 2 at that distance. I believe you need a 6 ground with the 2???
My main comes in to my shop but in this case if it was mine it would get a number 6 grounding the frame of the building to the ground in this panel.

You're going to get an argument because the situation isn't a service as defined by the NEC:

Service. The conductors and equipment for delivering electric
energy from the serving utility to the wiring system of
the premises served.

Unless he's coming off of a meter with dual-lugs right to the shop, this is not a service. One it lands on the main disconnect(s), it is no longer a service.

 

[Gary S]

I ran #2 copper to the 100amp box in my garage. I got a fantastic price on the wire at Menards. Menards didn't have #3 on hand, so buying #3 somewhere else would have cost me more than the #2 from Menards.

 

[sberry]

It has all the elements of a service, disconnect, ground rods. Bob Keis at the elect tool box forum calls it a service. Is the word sub even used in the coxe book?

 

[BigJohn20]

It has all the elements of a service, disconnect, ground rods. Bob Keis at the elect tool box forum calls it a service. Is the word sub even used in the coxe book?

It is after the main disconnect, which means it is no longer the supply from the POCO to the house, so by the definition in the NEC, it is not a service.

In the 2008, they removed lighting and appliance panelboards. Subpanel has one instance of use in the 2008 NEC. Feeder, however, is in the NEC:

Feeder. All circuit conductors between the service equipment,
the source of a separately derived system, or other
power supply source and the final branch-circuit overcurrent
device.

 

[Aceman]

It has all the elements of a service, disconnect, ground rods. Bob Keis at the elect tool box forum calls it a service.

Sounds like someone needs to tell him it's not a service either then...

 

[JTS]

I noticed in the Main house panel that the ground bars aren't used, only the neutral bar is.

In the new sub-panel/service panel/Load center I need to install a ground bar and keep the neutral wires separate from the grounds correct?

Here is the panel I bought.
http://www.homedepot.com/buy/electr...om20m100c-main-breaker-load-center-48371.html

 

[BigJohn20]

I noticed in the Main house panel that the ground bars aren't used, only the neutral bar is.

In the new sub-panel/service panel/Load center I need to install a ground bar and keep the neutral wires separate from the grounds correct?

Here is the panel I bought.
http://www.homedepot.com/buy/electr...om20m100c-main-breaker-load-center-48371.html

Spot-on. PK23GTA is the ground bar you need for that panel.

 

[nany2204]

I noticed in the Main house panel that the ground bars aren't used,

 

[BigJohn20]

I noticed in the Main house panel that the ground bars aren't used,

Not uncommon. Since the ground and neutral bars are bonded together at the main service, you don't have to land the neutrals and grounds on separate bars. It does make for a much cleaner install and easier service in the future.

 

[sberry]

I am not sure, not that it matters much but wonder how one of those code guru types like Holdt would describe it? I read it described as a service by Bob Keis, if I am not mistaken he is on the board that does the book?

 

[Charles (in GA)]

If Home Depot has the wire you need, and it is more convenient, they will match any local competitor. I know of one HD who has a retired commercial electrician working in the elect dept and he is constantly calling the supply houses and matching prices if the supply houses are cheaper. Many times the HD is the cheapest. My experience with supply houses in the Atlanta area is that they are quite high on everything, including the stuff HD sells. This may not be true elsewhere but here, you go to HD first, then the supply house.

Charles

 

[Charles (in GA)]

Here is the panel I bought.
http://www.homedepot.com/buy/electr...om20m100c-main-breaker-load-center-48371.html

If you haven't opened, used, molested, the new panel (and if they won't R*pe you on restocking fees), Personally, I would take it back, and get a 40 space, 40 circuit panel. You can never have too much panel, and the extra space is a dream to work in. Square D with aluminum bus bars........ I thought everyone said they were so great? Siemens uses solid copper, GE uses tin plated solid copper.

Charles

 

[JTS]

Personally, I would take it back, and get a 40 space, 40 circuit panel.
Charles

I couldn't find a 100A panel that had more spaces, the only ones they had in stock with more spaces were 150-200A panels. I really want to get this thing mounted this weekend. If I need more space later I'll just add another panel on the other side of the shop.

 

[BigJohn20]

I couldn't find a 100A panel that had more spaces, the only ones they had in stock with more spaces were 150-200A panels. I really want to get this thing mounted this weekend. If I need more space later I'll just add another panel on the other side of the shop.

As long as it's being fed by a 100A breaker, you can use a panel with a higher main breaker in it without a problem. The main breaker in the new subpanel becomes a disconnect as opposed to providing overcurrent protection, which is done at the main panel.

 

[Charles (in GA)]

The rating of a panel is the MAXIMINUM rating of the panel, you can run less current thru it, but not more.

Charles

 

[JTS]

The main breaker in the new subpanel becomes a disconnect as opposed to providing overcurrent protection, which is done at the main panel.

That makes sense.