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Feeding a sub panel with breakers at both ends, which one will trip first?

Feeding a sub panel with breakers at both ends, which one will trip first?


  #1  
Old 06-08-19, 08:15 AM
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Feeding a sub panel with breakers at both ends, which one will trip first?

I've got kind of a weird situation, I'm wiring up a small backyard tiny house for use as a rental. Main power will be supplied by a 30A breaker and 10/2 wire coming from the main house, to an RV box, then to an RV plug, then into the sub panel in the tiny house where it feeds a couple of 20A circuits.

So heres the issue, with this amount of power, popping the breaker will happen from time to time, and I want the person in the house to be able to reset it there. If I didn't care about electrical code, I'd just go ahead and put an oversized breaker at the main panel and backfeed the sub panel through a 30A single pole breaker. I like to keep things as compliant as I can though, so I'm trying to figure out if there is a different way to do this. It's too bad they don't make 29 amp breakers or I could just backfeed the subpanel with one of those and the problem would be solved! Maybe it's not an issue? in this scenario if I had a 30 amp breaker on BOTH ends of the 100' 10/2 line, which breaker would trip first, the one in the main panel or the one in the sub panel? Any ideas for how to do what I'm trying to do here?

thanks for any replies!
 
  #2  
Old 06-08-19, 11:00 AM
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Welcome to the forums.

By code...... you must protect the wire from the main panel to the sub panel. Since #10 is rated for 30A...... you cannot use anything larger than a 30A breaker. Since you've run 10-2...... the little house will be running on a maximum of 120v @ 30A.

No two 30A breakers will trip at the same exact time.
 
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Old 06-08-19, 03:00 PM
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Why the RV hookup? Is the tiny house mobile?
 
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Old 06-08-19, 03:09 PM
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Supply the 30A RV box 40A using #8. The 30A will trip before the 40A feed.
 
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Old 06-08-19, 03:28 PM
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The "tiny house" rental sounds like a residence so has lots of NEC and other codes. Should do a load calculation and based on that put in a new feeder/supply as mentioned.

To address original question: Use a 30 amp fuse at house as a fuse will normally blow before a breaker.
 
Zorfdt voted this post useful.
  #6  
Old 06-10-19, 07:49 AM
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To address original question: Use a 30 amp fuse at house as a fuse will normally blow before a breaker.
I like Astuff's answer. A fast-acting fuse will most always blow before a circuit breaker except possibly in the case of a direct-short. If you turn on too many items and pull 32A, the fuse will blow quickly while it may take minutes for the breaker to trip.
 
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Old 06-10-19, 08:25 AM
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If you know the service overloaded why not install a larger one? For example 50A 120/240 typical on larger RVs?
 
 

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