Subpanel Right Below Main
I have run out of circuit breaker slots in my main breaker panel. I need to add a circuit for an electric dryer and am looking to add a subpanel directly below the main to add breaker capacity. The main panel does not allow the use of tandem breakers and as such, I am stuck with the subpanel as the only option to expand breaker count.
I wanted to double check on my understanding of a few things. First, since the subpanel is in the same dwelling as the main box, no additional ground rods are needed. Also, no matter the rating of the subpanel, the wire used to feed the subpanel only needs to support the load of the breaker used in the main panel provided the mains of the subpanel are rated for the wire gauge used.
To be detailed as to my intent...
I am looking to use this box as the subpanel...
1. I intend to run about 3 feet of 4 gauge wires for connection to the main lugs of the subpanel (smallest allowed from the pdf I read) for the hots.
2. 2 additional 6 gauge runs for the neutral and ground wires. These will both terminate to the same ground/neutral bar in the main panel, but to the separate bars in the subpanel.
3. Hots will be connected to a 60 amp double-pole THQL breaker in the main panel.
4. All wire will be THHN wire run from main to subpanel through flexible EMT conduit.
The big things that I am not sure about is whether the 60 amp breakers can properly take a 4 gauge wire feed and have been unable to find a reliable document to confirm. Can someone confirm whether or not this is acceptable?
Also, I am have the nuetral and ground connections thought out correctly right? They should not be bonded together in the subpanel, but they do attach to the same bar in the main panel. My concern is in verifying that the subpanel I chose does in fact have isolated neutral/ground bars. The picture makes it seem almost like the bars are connected together. Anyone familiar with this box to confirm that they are in fact isolated?
Other than that, if anyone sees any other problems with my thought process, please let me know...
If you're going through all this to use an electric dryer you probably don't have gas...
Q: What is your current service size (amps) and panel size (#of full sized breaker spaces)?
Q: Are any of the 120V circuits not being used?
iow... is there really NO OTHER WAY to accomplish this?
You're using two breaker spaces to find two more in another panel?
Otherwise you seem to have a good handle on things. A suggestion:
-install the new panel as close to the side of original as possible
-keep all the 240V circuits in the current panel...
and move only 120V circuits to the new panel
ps how about posting a picture of the current panel (w/deadfront off) ?
You don't need 4-gauge for the feeder if it's copper wire. #6 is fine. #6 for the two hots and the neutral, and a #10 ground. The 60A breaker should accept #6 wire without a problem. In the panel you have chosen, the right hand bar is the neutral bar. There is a metal strap used to bond the neutral to the metal enclosure, for your purpose you will remove that jumper.
To answer all questions posed....
Main panel is a 20 space, 20 circuit panel. No tandems/thin breakers are supported (as mentioned in original post). I have 2 spaces left in the box, however, I find it easier now to add a subpanel than to add the dryer circuit and then need to rearrange everything when I remodel the kitchen and need to bring it up to code (this will add about 3 circuits).
I am aware I can use #6 wire for a 60 amp breaker, however, the subpanel chosen only supports 1/0-4 copper wire. As such, the smallest I can use is #4 copper. I'd prefer to stay with a 60 amp breaker in the main panel if the breaker will accept #4 copper which is what I am hoping for some confirmation on.
I thought the ground could be smaller, but I forgot what the official ground sizing rule is/was. Can you elaborate on the "rule" that allows #10? Is it simply 2 gauges smaller than the hot wires?
Depending on what other remodeling you do you'll have AFCI space issues as well
Short term... I still say juggle the breaker space you have now until you're ready to do the service upgrade but if you MUST add the sub panel... then keep all the 240V circuits in the current panel and move only a few 120V circuits to the new panel.
I eventually plan to upgrade the service and am aware of the AFCI issues.
The reason i prefer not to juggle the breakers and keep all 240V in the main box is because of wire length. I only have 2 spaces left in the main box and I need to add 240V for the dryer. As such, I would need to move 2 of the 120V into the subpanel which would then both require pigtails in order to lengthen the wires to reach the subpanel. As such, I feel that simply adding the dryer circuit into the subpanel would leave a cleaner installation, unless there is a real electrical reason to only have 120V circuits in the subpanel.
A 60 amp GE THQL will accept #8 thru #3 conductors.
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