sub panel question

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Old 07-25-08, 07:21 PM
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sub panel question

hi all! I have a question I'm a little unsure about. If I wanted to add a 60 amp subpanel, I would need a 60 amp main breaker. Let's say I wanted to add electric heat to my air handler which means I need another 60 amp breaker, can I use a 60 amp load breaker with a 60 amp main?? I know y'all are gonna ask why I don't just add 70 amp or 100a, this question is to satisfy a curiosity that I haven't been able to find an answer to. Thanks in advance for any responses.
 
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Old 07-25-08, 08:03 PM
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Originally Posted by blackwater View Post
hi all! I have a question I'm a little unsure about. If I wanted to add a 60 amp subpanel, I would need a 60 amp main breaker. Let's say I wanted to add electric heat to my air handler which means I need another 60 amp breaker, can I use a 60 amp load breaker with a 60 amp main?? I know y'all are gonna ask why I don't just add 70 amp or 100a, this question is to satisfy a curiosity that I haven't been able to find an answer to. Thanks in advance for any responses.
The panel must be sized to the load, thats all thats required.
 
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Old 07-25-08, 08:13 PM
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The sub panel you are adding if it is small enough (8 or less circuits, double pole counts as 2) then it would not need a main. The whole thing is ultimately protected by the breaker you put in your main box to serve this connection to the sub.

The sub box must be connected with 4 wire cable - 2 hot, neutral, and ground. SER cable is often used to provide service to a remote box. It has the required 4 conductors. The wire size depends on the current and length of the run.

Someone else can chime in on how to rate the panel. In your case the 60A is for a load that may draw 50A continuous for a long duration as opposed to a branch circuit that rarely draw there rated full current. A mixture of 15A and 20A circuits in a panel can add up to much more than the panel rating becasue of this.

It seems you really do not need to put in a sub panel in the case you mentioned as there may be no capacity left in the panel. If you do not intend to connect anything else to the panel then just a wire dedicated circuit with a disconnect at the device would suffice. There are disconnect boxes with single two pole breaker that would serve this purpose. It would be wired to the main the same way a sub panel would. Also it sounds like this heater may be a 220 only device. if it does not need a neutral then a 3 wire - 2 hot and ground - cable could be used, but ONLY if it were wire directly with the disconnect, not via sub panel.
 
 

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