Subpanel protection

If I want to add a small 30amp subpanel in the basement of a single family home, and it is fed from the panel that is in the attached garage about 75' away, do I need a main breaker or a disconnect or will a main lug panel suffice? Please cite appropriate code articles. Thanks!

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
If I want to add a small 30amp subpanel in the basement of a single family home, and it is fed from the panel that is in the attached garage about 75' away, do I need a main breaker or a disconnect or will a main lug panel suffice? Please cite appropriate code articles. Thanks!

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If the subpanel is fed from an appropriately sized breaker in the MDP, an MLO sub with no disco between it and the MDP is fine. Sorry, I don't have time to slog through my code book for you.
 

dema

Senior Member
Location
Indiana
I agree with ggun. You basically need a main disconnect or a main breaker if you are entering a building or structure or if you are on the secondary side of a transformer - provided the panel is fed from a properly sized breaker.
 

charlie b

Moderator
Staff member
Location
Seattle, WA
Occupation
Electrical Engineer
The code does not recognize the notion of a "sub panel." 408.36 says that a panelboard (i.e., your 30 amp "sub panel") must have overcurrent protection of a value not greater than the rating of the panelboard. It goes on to say the overcurrent device can be within, or at any point upstream of, the panelboard. So as long as there is a breaker in the main panel serving the sub panel, and as long as that breaker is not higher than 30 amps, you satisfy the requirement.

Please note that it is important that the garage is "attached." You have a single building, and are not feeding one building from a separate building. If the garage were detached, then 225.31 and 225.32 would require a separate disconnecting means for the feeder from the garage to the sub panel. That need not be an overcurrent device; a non-fused disconnect would suffice. However, you would still need overcurrent protection, and the breaker in the garage panel would still suffice for that purpose.
 
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