Electric subpanel/main panel question.
user-69084
| Posted in General Discussion on
I have a 200 amp main panel to the house (4 years old). The electrician that built the house ran a cable from the main panel to the basement for a future subpanel (ALCAN S stabiloy (R) AA-8000 AL type SE cable style R XHHW-2 600V 3 CDRS). I want to add a subpanel to the basement that I am finishing. The main panel has only one full size (1″) knockout that has not been used. All of the breakers are 1/2″ 15, 20, or 30 amp breakers (except the two 60 amp breakers for a heat pump). I was trying to add a 125 amp sub panel, where I will need 9 breakers. Am I out of luck? What are my options?
Suggestions or help will be greatly appreciated.
untjeb
Replies
First of all do you really need 125 amps for the sub-pannel. I don't know what brand of pannel that you have and I am not that familar with all of the different sizes of breakers. But I suspect that you can get a 70-100 amp breaker in the space that you have.
Also look at the label on your pannel and see what the maximun number of circuits are. There are some pannels are labled some thing like 30/40. That means that you can have 40 circuits, but there are only slots for 30 standard breakers. You have to use some tandem (2 breakers in the space of one) to get the 40 circuits. If that is the case then you need to re-arrange some of the circuits and breakers to make the space.
Other than that you can add a sub-pannel at the main pannel. You will move a few of the circuits from the main pannel to the new sub-pannel to make room in the main pannel for the breakers for the now 2 sub-pannels.
Also you might be able to move a couple of circuits from the main pannel to the basement sub-pannel.
Thank you for your suggestions. The main panel is a GE. I went ahead and bought a 125 amp GE for the subpanel. I can use it later for the detached garage. I will look for a 1" (full height) 75 - 100 amp breaker and buy a subpanel to match. I could also move a couple of circuits that are from the basement to the main to the sub to free up some room in the main.
Again thanks for the help.
untjeb
First,
I'm not an electrician, but let me throw some advice your way...
You have a 200 amp main service, now you've made reference to a 100 amp subpanel in the basement, and a future 125 amp panel in the detached garage.
If the 125 in the garage is going to be a sub run off the 200 main, it's time to call for help. I'm not saying you're not capable of doing the physical work...but you need to find out if your main service can handle the potential of 425 amps of panels. You may need to get your service upgraded.
Call your local inspector. Free advice.
Call your utility. Again, free advice.
Do it right so your next call isn't to the Fire Department.
FHB had a nice ditty by, I think, Rex Cauldwell, several months back regarding wiring up a subpanel. I encourage you to check it out for a bit of background information.
125 + 200 = 425? I assume a typo, not a math mistake.
It doesn't matter what the main panel can handle, it is the circuits that are wired that matter. Pulling off 100amps (I'd throttle down the sub to 100) would only mean that you are taking capacity away from the main panel in terms of circuit load to the house. The service itself is most likely capable of 240amps (standard 2 phase meter). Okay, so assume the house main panel is now a 100 amp panel... can someone show me a typical home that draws all 100amps at the same time?
Unless you go with a main disconnect with 2 sets of lugs, one for each panel, between the meter and the load centers. Then you would be pulling power to the sub without going through the main panel. Easier to setup, but the service drop may not be sized correctly, the local power company would be the people to call.
Regardless, this is a job that requires a permit from your local regulatory group, thought out design, and inspections. Coordination with the power company may be necessary as well.
I agree with the others as to why do you need 125 amps? I run a ful shop with a 60 amp circuit and have plenty left over. I would definately have a electrician come and look at it.
At Darkworks cut to size made to burn......Putty isnt a option
Jeff,
Yeah, a partial mind-fart.
The 425 came from his 200 amp main, plus his post where he mentioned using the 125 panel that he now has in his detached garage and buying another 100 amp panel to use as the subpanel in the basement. It should have been 325...a 200 main/sub in the house/basement, and a 125 in the garage.
It's the size and adequacy of the service drop and meter box itself in handling a total of 325 amps or panels that I was trying to address.
Good catch, thanks...
Regards, Mongo
Edited 10/28/2002 1:57:02 PM ET by Mongo
Mongo
If the 100 amd 125 amp pannels are SUB-PANNELS then they all feed through the main 200 amp breaker.
If there is any combination of loads that total more than 200 amps that main breaker goes, period!
It really does not matter where the loads come from. Most main pannels have this same "problem". Put in 40 20 amp breakers in the pannel. 1/2 of them will be on each leg so that gives you 400 amps possible load on the 200 amp main pannel.
Also just because a "100 amp" or "125 amp" sub-pannel is used that does not mean that they have that much maximum load. Those size pannels are often used as sub-pannels for two reason, commonaly available and large number of breaker spaces.
They are often feed with 60-80 amp feeders and breakers at the main pannel for say home workshops.
Bill,
I agree with what you wrote. I re-read my previous post and see where my words are muddled.
I never considered him running two subpanels off the 200 amp main for the following reason: In my town we can only have one subpanel run off the main. Any other additional panels have to be wired directly into the meter, or off an additional meter.
So, if he were building in my town, he could have the 200 main feeding the 100 subpanel. The extra 125 for the garage would have to be wired into the meter, or off of a secondary meter, for a total of 325 amps potentially drawn at the service drop.
He'd have to upgrade his meter and service to do that if it wasn't rated for that type of load. Which, apparently, he is planning on doing.
The decision to upgrade the meter and service to 400 amp is for a future workshop in a detached garage with an office. Since I was going to finish the basement with a subpanel off of the 200 amp main panel. Upgrading my meter and service to 400 amp was better than having a separate line and meter to the shop (I would need a 300 foot trench to the shop for the power). It seemed too much for a 200 amp service to handle a 2500 sq ft house + basement + shop, not that all of the outlets and lights would be used at the same time.
For the subpanel, I can move two of the 1/2" breakers from the main to the subpanel and use a double 100 amp breaker to hook up the subpanel to the main panel. Even though the subpanel is rated to 125 amp, I will not need that much with eight 15 amp breakers. Before you think that I will need a small nuclear reactor to power my house, I use about 1,100 kWh per month.
Thanks again for the help and input.
untjeb
> In my town we can only have one subpanel run off the main. Any other additional panels have to be wired directly into the meter, or off an additional meter.
Go figure. It's exactly the opposite here. They won't let you have more than one service on a single family residence, but you can have all the sub panels you want.
-- J.S.
Thanks for the comments. I should have described the future service into the house. I currently have 200 amp service to the house, at a future date (next year) I will upgrade to 400 amp service. I had our power company rep come out and look at our service. He said that with a meter up grade to 400 amps and a second main, my lines could bring in 400 amps. That is why I could use the 125 amp box at a later date.
Thanks again,
untjeb
It sounds like you've addressed what I was concerned with...the adequacy of the service and the meter.
Good luck with your project.
Did you get a spec sheet from your utility guy? That's a must. It can also be a surprise. Here in Los Angeles, the DWP only allows one make and model of main for 400 Amps, a Milbank that comes with two 200 Amp breakers. From there, your only option is to feed two 200 Amp subs.
-- J.S.
400 amp service - wow!
Are you sure it is a house and not a small factory?
You may want to make sure how large a subpanel circuit you can tap off your main panel....the local code may allow up to only 100-amps.
Best to check with your building inspector first before you proceed.
Why do you need 125 Amps in the basement? That seems like too much, unless the basement is huge or there will be a workshop or other big power-using item in the basement. A typical basement might only need one or two additional 15 Amp circuits and three 20 Amp circuits. You can add a small sub-panel right next to the main panel, then relocate some of the circuits from the main panel to that new sub-panel. You will then have plenty of space for a double breaker to feed your basement sub-panel. Be sure that the cable already in place can handle to load. Also, you need to check the load on the main panel. If you really need 125 Amps in the basement, you will probably have to upgrade the main panel and service. Any open breaker slots in any of the panels should be covered with the proper filler plug.