100 amp Sub Panel...


Old 10-23-10, 06:18 AM
Thread Starter
Join Date: Oct 2010
Location: usa
Posts: 3
100 amp Sub Panel...

I need to run a sub panel to a detached garage about 30' away. The main panel is 100 amp Pushmatic. The panel is almost full with breakers. I have a hot tub, dryer, stove/frig/microwave, hot water heater, and ele. baseboard heaters along with several recep's - basic lighting in the panel. In the summer the ac is run.
The questions I have are:
1.Can I run a 100 amp sub panel off my 100 amp main panel?
I need to supply power to two ele. baseboard heater 120v, twelve recep.s, five basic light fixtures, three desktop computers, tv, one ac unit 120v

2.What gauge wire should I use(6,4, or 2)? This is going underground in conduit.
Sponsored Links
Old 10-23-10, 06:33 AM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,968
You have the worst scenario of all. Under amped panel and a pushmatic to boot. I would seriously consider upgrading my service, since 100 amp panels just aren't even installed in residences much anymore. Of course it isn't for the faint of heart. Your POCO may have to run new entrance and from there down everything must change. A new 200 amp panel will service all your needs without the need to worry about new circuits. I know it isn't what you wanted to hear, but it's there. Others may have better solutions, so hang in there.
Old 10-23-10, 08:52 AM
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Sorry to be a bearer of bad news but the way you describing the exsting situation and you are pretty much right the limit of exsting 100 amp service but you have to upgrade the service and normally this will not a DIY item unless you are super seasoned and if your local area do allow homeowner do it own upgrading it can be done but otherwise majorty of the time the Electrician will deal with it.

I have done this all the time for last 20+ years so it will be like semi brezze with me but there are few pointers here you have to understand what will happend with this set up.

You will have to get permit for this (I will fill in the details along the way )

You will have to get ahold of POCO and they will look at your exsting location to see if your overhead drop zone still meet their requirement otherwise they will ask you to move to differnt location ditto with underground lateral runs { they will tell which way they will run the lateral }

Once the POCO unhook the drop or disconnect the lateral expect power outage anywhere from half to full day { few case longer } {most electricians will able swap this and will have everything done in 4 to 6 hours ave time but special situation may will warrant longer time period so we will let you know ahead of time by bring the generator or other means }

I know few DIY's did scucessed with service change but majorty of the time Electrician do this { apartment and condos and commercal buildings are automatic done by electricians per code and laws }

Pushmatic genrally not a major issue but only weak qurik is P2100 breaker ( 100 amp breaker it can be used as main breaker or feeder breaker ) and they are not cheap anyway and they pretty much out of production for a while but can still get replacement breakers but they are not cheap anymore so really I recomend that you get modern load centre.

For your subpanel you will need 4 wire feeder { code do not allow 3 wire feeder anymore } which it will have two hot conductor and netural and ground { typically green conductor } but size will depending on load.

Normally I useally recomened 50 or 60 amp subpanel size ( unless you have 200 amp service or larger then we can go much larger subpanel size )

Is your exsting circuit in detached garage is single circuit or MWBC ??

and once you start run the subpanel route you have to ditch the exsting circuit.

The code do not allow more than one MWBC to the detached structures.

I will fill in more details little later { I am on European time zone }

Old 10-24-10, 07:51 PM
Thread Starter
Join Date: Oct 2010
Location: usa
Posts: 3
lol thats what i thought! #%!it. I have done several panel swaps to 200 amps. Just was hoping there was an easy way out because the panel is in a closet with tight space. Looks like i'm tearing two walls open and buying alot of junction boxes. I appreciate your help.

Thank You,
Old 10-24-10, 08:02 PM
Thread Starter
Join Date: Oct 2010
Location: usa
Posts: 3
Do you think I could run a 50 amp sub to supply power to two ele. baseboard heater 120v, twelve recep.s, five basic light fixtures, three desktop computers, tv, one ac unit 120v?? I wouldn't be running everything at once ever. Summer time ac winter the heat. The majority of the recep's are for code and not used. The lights will never be used all at once. Im powering everything now with a heavy duty ext. cord. Minus the heaters of coarse. A 15 amp breaker is feeding it now. Don't laugh it's all I got for now. hehe
Old 10-24-10, 10:56 PM
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,399
Without knowing the wattage requirements of the equipment it cannot be stated with certainty that a 50 ampere sub-panel would be sufficient. You need to do a demand load calculation on those circuits that would be fed from the sub-panel.

That stated, if you are running everything on a 15 ampere circuit now the 50 ampere sub would probably be fine.
Old 10-25-10, 10:49 AM
Forum Topic Moderator
Join Date: Feb 2005
Location: Near Lansing, Michigan
Posts: 10,515
I'd say you could do it, but pretty much everyone here doesn't think you should. In fact, you probably should have upgraded the service before the addition of the hot tub given that you have all-electric appliances and air conditioning.

The 50A feeder to the garage sounds more than adequate (12,000 W). I don't see a problem with going ahead and doing the garage correctly with a proper feeder and subpanel; it's a big step up from the extension cord. Consider a full 200A service upgrade as you next big project to plan for. The most you will be out is the cost of the Pushmatic 50A breaker which is probably less than $50, and you can resell it on eBay when you replace the panel.

Underground in 1-1/4" PVC conduit buried 18", use #6 copper THHN black and red for the hots, white for the neutral, #10 green for the ground. This is good for up to 60A. You'll need ground rods and an isolated ground/neutral in the garage panel. Bruto's subpanel sticky thread provides more details.

You have the worst scenario of all.
Could always be worse...he could have FPE.
Old 10-25-10, 11:21 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 33,058
You have the worst scenario of all.
Could always be worse...he could have FPE.
Or Zinsco.


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes