Subpanel popping CB in main panel

Reply

  #1  
Old 08-28-08, 04:10 PM
Member
Thread Starter
Join Date: Aug 2008
Location: West Virginia
Posts: 3
Received 0 Votes on 0 Posts
Subpanel popping CB in main panel

Hello,

Have a (hopefully small) problem and would like some input.

The small building behind our house has a subpanel which is tied into a 30 amp breaker in the main CB box in our house.

This subpanel has:
1 - 30 amp double breaker for the dryer
1 - 30 amp double breaker for the hot water heater
1 - 30 amp single breaker for the lights and outlets

When the dryer and hot water heater are on at the same time, and everything else is off, the CB in the main box trips.

Shouldn't the CB in the main box be more then 30 amps? Any help or advice would be appreciated. Thanks.
 
Sponsored Links
  #2  
Old 08-28-08, 04:19 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,967
Received 2 Votes on 2 Posts
Welcome to the forums! 30 amp single breaker for lighting is too large, 'cause I bet you only have 12-2 wiring. It needs to be a 20 amp breaker, or 15, if you have 14-2 wiring.
As far as the tripping, it is simple math. You have the entire subpanel on a 30 amp breaker. You attempt to run a 30 amp water heater and 30 amp dryer at one time, it will overpower the 30 amp breaker in the main box. Now, in order to increase the size of the breaker in the main box (which is too small), you have to run larger wire to the outbuilding to handle the increased amperage draw. What size wire is being used to feed this subpanely?
 
  #3  
Old 08-28-08, 05:10 PM
Member
Thread Starter
Join Date: Aug 2008
Location: West Virginia
Posts: 3
Received 0 Votes on 0 Posts
Thank you for your time and the reply Chandler.

Checked the wiring going to the outbuilding it's #10-3/0.

Thanks again for the help!
 
  #4  
Old 08-29-08, 06:54 PM
Member
Thread Starter
Join Date: Aug 2008
Location: West Virginia
Posts: 3
Received 0 Votes on 0 Posts
What size CB should I use in the main box and do I need to run a new wire to replace the 10-3/0?
 
  #5  
Old 08-29-08, 07:08 PM
Member
Join Date: Mar 2006
Location: NE Wis / Paris France{ In France for now }
Posts: 4,808
Received 0 Votes on 0 Posts
It depending on how far the subpanel from the main breaker and also you mention that you have water heater and dryer on the same panel and the exsting wire is 10-3 W/G but which verison you have NM { romex } or UF { Underground Feeder } or in the conduit { pipe } ??

If this in the pipe it will be pretty easy to swap wire to larger diamater and the pipe shouldbe inch or larger with 60 amp breaker with #6{copper] or #4{Alum} wire or larger depending on the length.

Now with other issue you have to deal now is the 30 amp single pole breaker for lighting circuit that need to be change to 20 amp { with #12 wire size } or 15 amp { with #14 wire size }.

Hope this question should help you some of it.

Merci,Marc
 
  #6  
Old 08-29-08, 07:15 PM
Member
Join Date: Jul 2008
Location: USA
Posts: 376
Received 0 Votes on 0 Posts
10/3 has a maximum rating of 30A so the main is sized correctly but overloaded. If you wanted to up the size to say #8 or #6 copper. It would certainly be better for the load you have. BUT - make sure the sub panel has the proper rating also. You could use a 50A breaker in the main with #8 and a 60A with #6

The distance of the run also matters. It sounds like this building is close but wire distances can add up.

Also follow the code for sub panels. The neutral and ground should not be connected together anywhere outside of the main panel. In the sub panel you will need to isolate them. There is usually a jumper you can remove from the neutral to the case. You will need to buy a separate ground connection bar for your box. The sub panel should also be grounded locally with a ground rod or connection to a known good ground using at least #6 copper. This would connect to the sub panel case and ground coming from the main panel.

The dryer should have a 4 wire connection and plug and neutral and ground should not be connected together at the dryer. Again a jumper.
 
Reply

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
 
Ask a Question
Question Title:
Description:
Your question will be posted in: