Let say I wanted some power out in my shed. I ran just 14 gauge wire thinking I won't blow the 15A breaker with just lights and the occasional smaller power tools. For the most case this is true... but lets say occasionally I use a heater or an air compressor and then not thinking I run another power tool and blow it. The breaker is not in that easily accessible location.

I had a bright idea to install another breaker box in the shed with a 15A breaker as well so I can just switch it back on in the shed. Sometimes it breaks the one in the shed but other times it still breaks the one in the house.

Anyway that I can make it always break the one in the shed first? I want to buy like 15.1A breaker for the house, but it looks like they don't make those... Do GFCI Breakers or another type break quicker than another?


  • I don't know this for sure, but because of the distance, the breaker in the house will always break first unless you heavy up the wire and breaker to go along with it, then the lighter breaker will trip first. The distance the line runs from the house makes the wire/breaker work harder to get power out to the other breaker. The phenomena is called voltage drop or what I have called line drop. That's my terminology, it may not be accurate. – Jack Jan 8 '16 at 4:43
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    You've essentially created a subpanel. Did you install it accordingly? You'll need to be sure that the neutral and ground are not bonded or you have a potentially very dangerous situation. The right solution would've been a 60 or 100A subpanel. – isherwood Jan 8 '16 at 4:44

Fastest way to make the shed breaker trip first is downgrade it to 10A.

Also you have a subpanel now, make sure you configure the neutrals and grounds to code.

I can't help noticing that 5 kva transformers (240/480 jumpable, to 120-240 split phase) are regularly available on the used market. That could provide very safe 3600w (30A) over the existing 14ga. to the shed's panel, which would become a main panel with its own ground rod, solving any code issues with neutrals/grounds and helping with phase balance. You'd want a pro electrician to install or at least bless that setup.

  • This is genius pending a proper install overseen by a professional. – Damon Jan 9 '16 at 16:48

If you have two breakers of the same type, the one in the house is much more likely to trip, because current is pulled through that one to get to the other one. Breakers trip on heat, so it's a race between the two, and the one feeding the second gets a head start.

There are other things to consider, too - it's generally a great idea to run power tools from a GFCI protected receptacle. This saves you if something goes wrong with the tool causing parts of it you might touch to become energized.

What I recommend you do is run a new 20A circuit to your shed for convenience receptacles, and make sure to use a GFCI receptacle (you could go for a GFCI breaker, but you're back in the boat of having to run inside to reset it if it trips). This allows you to install even more receptacles from the load side of the GFCI for convenience, and makes things safer overall.

With what you have, you're good for lighting and probably some chargers for cordless tools and such, but any circular / reciprocating saw is going to trip it if it binds (and gets closer to the listed locked-rotor amperage).

If this means some digging, you could also go for a 30A sub panel in the shed that would meet current and future needs (any time you dig, it's good to future proof a bit, makes the time spent trenching more valuable). There's no real good way to fix this without heavying-up what you've got.

Short addendum

A great way to plan for what you've got is to take the LRA (locked-rotor amperage) of the biggest motor you intend to power and multiply that by 1.25. In this case, it's going to be either your compressor, or possibly circular / miter saw, depending on what you have. This should be stated on any UL listed tool.

For most household compressors, you're going to end up somewhere around 24 to 27 amps pulled if the motor is energized and completely seized, so a 30 amp sub panel would probably be your best bet to run a few tools at normal (non-locked) operation, while providing some allowance for blades binding a little, or the compressor recovering pressure while other things run.

But, run the LRA of the stuff you want to use together typically, and you'll get a pretty good idea of what you'll need to pull out to the shed to support it. Your normal continuous load won't be nearly as high as the LRA, but you've got to plan for the occasional peaks.

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    If the OP is in the United States, in an area covered by the NEC, I believe it is against code to pull multiple circuits to an out-building. The correct way, as suggested by @isherwood's comment, is to put a sub-panel in the shed and run larger gauge wiring with a larger breaker in the main panel. Make sure you understand the correct way of wiring a sub-panel. – DoxyLover Jan 8 '16 at 6:57

Breakers protect from gradual overloads like the ones you are causing on a time curve. In fact, a 15 amp breaker won't disconnect the circuit until you've spend many seconds, perhaps minutes above 15 amps.

Breakers do exist with different time curves. The more lenient curves are meant for extremely large motors in factories for example that might take a minute to get up to speed. In theory you might be able to shop around and find two differently curved breakers, but they are not meant for what you're wanting.

I would recommend instead that you use an audible alarm in the shed that measures current used with a Current Transformer that clips around the hot conductor. I've had much success with the Efergy Elite True Power Meter doing exactly this to keep a breaker from tripping that's behind a door I'm not supposed to have easy access to, but there are other brands/models that do the same thing.

Good luck hearing its tiny beeper over an air compressor or power tool though.

An even better option of course would be to run a bigger service to the shed. I would recommend a two pole 30A circuit for your shed. This would roughly quadruple the capacity you have at the shed.

If running new underground/overhead cable is absolutely not possible, then the only other option you have would be to get a 240-to-120 step-down transformer, and use the existing 15A line for 240V instead of 120V. You would also need to get a double pole breaker for the circuit of course. This would roughly double the capacity you have at the shed, but the transformer is going to cost a fortune, and very likely is not supposed to be used outdoors.

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