I need to wire a subpanel in my addition. I’m familiar with electrical work, and understand at least the basics of subpanel wiring. I know I need four conductors, and the ground / neutral are not bonded at the subpanel (they aren’t even bonded in my main panel since I have an outdoor meter socket/breaker panel combo).
I need help in getting from theory to reality. I’d like to use a 200A 40/40 panel, which is typically used as a main panel (my main panel is a Siemens 200A 40/40). I want to use this panel so I can just home run lots of circuits. It’s easier when remodeling since I don’t have to go opening boxes to extend the loop etc. I’d like to breaker this subpanel at 100A or 200A (probably 100A to keep the feeder smaller). The subpanel feed is around 75 feet. The subpanel is going to carry substantial load: two bathrooms (with whirlpool tub), kitchen (less oven), dining room, lighting/plugs in additional 1800 sq ft. My meter base/breaker panel combo has four open slots so I plan on feeding from there.
The issues:
1. No Siemens 100A breaker at Lowes. No 200A breaker either – will the 200A panel have the breaker already installed as the main breaker?
2. What wire to use? 4-3 SE copper cable doesn’t exist at Lowes and I’d probably want 2-3 because of the long distance. Sounds like a brutal cable to work with. Lowes has THHN in various sizes, but that needs to be run in conduit which would make this job substantially harder (lots of snaking around). So do I use Al SE cable?
As a side note, HD has bundled wire called “Mobile Home Feeder” that sounds pretty scary, but maybe that’s what I need (it’s Al). It looks just like the cable the power company used when they buried my service. They had it various gauges. I will also be computing voltage drop on the cable to make sure voltage drop stays under 3% (maybe even 2%) at full load. If I do go this route, these cable are too large to put under breaker terminals, so do I just buy some new lugs that attach to the bars in my outdoor breaker panel?
Any help appreciated. This is an inspected job so no need to worry about me putting some junk together. Just trying to figure out how it’s normally done.
MERC.
Replies
"1. No Siemens 100A breaker at Lowes. No 200A breaker either - will the 200A panel have the breaker already installed as the main breaker?"
Depends. Panels come in all flavors. Some with and some without the main breaker. But those at the home horror stores will more than like come with the main breaker.
BTW, there is no need for "main" breaker in the sub-panel. It is protected by the feeder breaker in the upstream panel. However, you might want one for convience so that you work on the panel without runign back and forth to the main panel.
" So do I use Al SE cable?"
No problem, just use the anti-oxidation stuff on the connections.
"The subpanel is going to carry substantial load: two bathrooms (with whirlpool tub), kitchen (less oven), dining room, lighting/plugs in additional 1800 sq ft. "
If you go to the FHB main page and then the additional stuff on the left side, under mechanical you will find a worksheet where you can do a load calculation.
Bill gave good advice.
Personally, I prefer the breaker at the subpanel for easy disconnect, as well as for a few other reasons.
Cliff Popejoy had a nice article a while ago...maybe 2 years back...about wiring a subpanel. If I recall, there was good info on cable and sizing.
While I'd prefer CU, the pocketbook prefers Al. As Bill mentioned, use the anti-oxidant paste when using Al.
If your connecting cable is good sized, which it will be...you might have trouble connecting the neutral to the neutral bar without an adaptor or connector of some sort. Make sure you leave the supply house with the parts you need so you don't get slowed down mid-stream.
I remember doing a house where the main was in the garage (200A 40 breakers) and we also wanted a 40-breaker panel in the basement of the house. Ran into some rule about the number of successive breakers and the capacity of the sub panel. The inspector made us run the house panel all the way back to the primary disconnect rather than through the main panel in the garage. Could not be connected as a sub off the main panel. It was not really any more difficult one way or the other, but it had to be configured as two main panels. Anyway, this is something you need to ask your inspector.
This is actually what I was leaning towards doing. I don't know all the code, but it seems to make some amount of sense to wire the 200A 40/40 just like my other 200A 40/40 is wired. That will require me to find some new lugs for my outdoor box that will allow me to connect two large wires to each hot leg and the neutral. I think the ground wire is smaller and can just go under an empty screw terminal.
I will go visit my local supply house and see what parts they have that might make this easier. I will also dig up the FHB article on the subpanel, I do remember the article.
MERC.
I'm sure one of the electricians will chime in, but if you're going to run the additional panel as a 200A panel, I think it would make better sense to run it directly off the meter (or off an additional meter, depending on what this addition will end up as...MIL apartement, etc) than to try running a 200A sub off a 200A main.
You may need your service off the grid upgraded as well.
My service off the grid is the biggest cable my power company installs (a 350 mil cable I believe). It was fun to wrestle with at any rate. It's the grid here that is in bad shape, but at least my drop is solid. It's also directly off of a transformer so that helps some.
I am going to look into tapping straight off the meter base or breaker panel next to the meter base. Like you said, I don't think it's prudent to try to pull the 200A off my existing main panel.
Thanks
MERC.
350 CM is good for 300 amps (AL) and 350 (CU) unless there is a long run.
"I am going to look into tapping straight off the meter base or breaker panel next to the meter base. Like you said, I don't think it's prudent to try to pull the 200A off my existing main panel."
I don' know what it would cost or if it is practical to change it, but they make 320 amp meter and the bases are tapped for multiple lugs for applications where they run multiple main pannels.
In any case if you come off the meter that you need to install another weather proof 200 amp disconnect. All disconnects need to be in the same immediate area.
Also you might want to run a total load calculation to see how close you are getting to 200 amps total to see if there is a need up the total service (and disconnects).
" Ran into some rule about the number of successive breakers and the capacity of the sub panel."
There is nothing in the code about the number of successive breakers. And even if there was that does not require the use of a 2nd "main" pannel. You can use pannels with feed through lugs on the main bus.
However, the load might have been load might have been too high. In that case the service needed to be upgraded also. And it is not practical to use a single main disconnect. (more than 200 amps is not readily available in residential appications).
"The inspector made us run the house panel all the way back to the primary disconnect rather than through the main panel in the garage. Could not be connected as a sub off the main panel. It was not really any more difficult one way or the other, but it had to be configured as two main panels. "
DANGER WILL ROBINSON.
If you had a main disconnect them neither of these where main pannels, they where sub-pannels.
If there is no separate main disconnect and the main breaker is to act as the main disconnect then the pannels need to be in all in one immediate location.
Well, the two panels are about 100 feet apart. I guess thats why we needed a main disconnect. I do remember we had to do it twice and the inspector changed his mind a couple times. We did ask for the inspector's opinion before we started but it still got confused. The place had 400 amp residential service which confused just about everybody. Its a really big house. I ran the conduit, but the electrician connected all the heavy stuff. We have the meter, main disconnect, one panel in the garage (with main breaker). Main disconnect also feeds cable to the basement with second panel, also with main breaker. There is a second breaker/disconnect in the garage between the main and the cable to the basement. The basement panel has a couple subs of its own. I'm reasonably clear about everything except the second disconnect. Anyway, the inspector is satisfied so its fine with me.
My inspector told me #2 AWG for 100A subpanel, #1 AWG if it's AL. But actually 60A was really sufficient, I'm wiring upstairs (AFCI) and AC air handler, 6 AWG is okay for that. #2 AWG cable is very very heavy. I'm using Square D QO for subpanel, it is not possible to separate ground and neutral, you have to add a separate ground bus bar.
Do you really need 200A? I read somewhere that an all-electric house is normally only pulling max 40A at any one time (with electric stove, dryer etc). People are putting in 200A because they know future house buyers will expect it.
Though I haven't done a load calculation yet, I don't believe I need 200A. My house has mostly gas appliances, only the oven and AC (two of them) are the major electrical draw. However I want the 40/40 panel and that generally comes in only 200A. I realize I could convert the 200A panel to main lug only and breaker it at 100A on the other end, but at that point, I'm wondering why? Why not just run 200A wire.
I'll have to see how it works out.
MERC.
> Why not just run 200A wire.
Try lifting 100' of #1 or #2 wire. Now imagine fishing that through the house. Convinced me to go with 60A....
Edit: whoa, make that 25'....I was thinking of the price.....
Edited 9/30/2004 11:47 pm ET by Taylor
Well my electrician called me the other day to say "I haven't forgotten about you" (he's a pretty busy guy). We agreed that I would do most of the work including procuring some of the material and he would come over for a 1/2 day or so and I would help him get it all working (read: pull the big wire, hook up to main panel).
He's away for the weekend though, so I have a question maybe somebody here can answser. I bought a Siemens 40/40 200A main breaker panel. Can I mount it so it's a bottom-feed...in other words the main breaker will be on the bottom?
As a side note, I have an existing Siemens 200A 40/40 from about 4 years ago. In the new panel, the ground and neutral bars only extend about 1/2 way down where the breakers sit, whereas the old one has full length bars. Amazing what these jerk off companies will do to save 5 cents on a $150 unit. I know I can put additional bars in, but GIVE ME A BREAK.
MERC.
I don't know about that pannel.
But I know that the SQ QO and maybe Homeline say that you can remove the guts and remount them upside down.