I doubt this is legal for the most part, but I have a 240v subpanel on my insulated tiny house, shed whatever you wanna call it. Right now it's my office, but a while back I set it up with a 240v 30 AMP Generator Hookup. I made a 75ft 240f 10/3 extension cord that runs to a 30 240 AMP breaker that used to be the dryer as I don't use that anyways. The wires from the hookup is 10/3 indirect and everything inside is mostly 12/2 with a few short 14/2 on the 15amp side.

Inside the tiny house is a 20amp and 15amp breaker. I have a spare 15amp, as I think the return wire must equal 30amps. I did separate natural bar with a nylon screw from the case of the subpanel and screwed down the ground wire to the body of the subpanel under the 4 screws holding the subpanel to the wall, and so everything is 10/3 to the 30 amp hookups and subpanel with the 20amp and 15amp breakers being 12/2

Do I need to add a grounding rod to the tiny house since I already have a ground wire coming from the main house

Would this pass inspection?

Do I need to replace the 20 amp breaker with a 15 amp making both breakers 15 amp or can I keep the 20amp since if I used both at its max amps it would be 35amps total exceeding the 30amps or it would trip the main 30amp breaker?

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    Are the 20A and 15A 120V circuits or 240V? – manassehkatz-Moving 2 Codidact Jan 3 at 4:52
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    What make and model is the subpanel in question? Can you post photos of it please? – ThreePhaseEel Jan 3 at 5:02
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    4-Prong 30A dryer receptacle? Or not plugged in, just wired to that breaker? 10/3 with ground? i.e. 4 wires, not 3 wires? "Extension cord" is just laying on the ground? – Ecnerwal Jan 3 at 13:13

If your 15A & 20A circuits are 120V, you are not fully loaded on a 30A 240V feed IF they are on "opposite legs" - USA/Canada power is 120/240V and a 30A 240V feed can run 60A of 120V circuits fully loaded without tripping. Half the 120V circuits are on one hot "leg" and the other half are on the other hot "leg" and there is 240V between the "hots" of opposite legs, and 120V between the hots and Neutral. When oposite legs are loaded at the same time, neutral carries only the difference between them, not the sum - so it all stays below 30A in the wires.

But the broader concept there is that it's perfectly fine (and normal) to have breakers that add up to more than the feed amperage - of course, you'll trip the feed breaker if you use too many things at the same time, but that's also why it's OK - the main feed breaker will protect the wire. You may well have a 15A breaker on a lighting circuit that never draws more than 5A, (or 1A in a 10x12 shed with LED or florescent), for instance.

You should indeed have not one, but two grounding rods at the shed, 8 feet or more apart. The reason for two is that one grounding rod is acceptable if you do a test that costs more than a second grounding rod and 8 more feet of wire, but with the second rod you don't need the test.

There are some probable code issues with the power feed itself.

10/3 cable with 4 wires is not cordage (which for the same 4 wires would be marked 10/4) - it's wire that's intended to be installed and left in a protected situation, not moving.

If that cable is lying on the ground, it would need to move either underground into a conduit (where, in fact, you would not want cable, you'd want wires - cable is VERY hard to pull into conduit) or lashed onto a suspension cable overhead, out of reach. The cable or wires used must also be "suitable for wet locations."

For a "tiny house" on wheels that might move, you might want a flexible, tough cord that can be left on the ground - "cordage" - but that's really not appropriate for a shed that stays in one spot in the yard, and in most cases even with a "tiny house on wheels" or RV it's preferable from a damage point of view to run conduit out to a pedestal where a short cord can connect to the thing that may move.

  • The main Breaker is a 30amp Double Pole, and the 240 Extenstion has two hots, a neutral and ground so only one natural wire to and from the outside building, so I assumed the neutral wires has to be able to handles all the 120v Breakers amps, i plan to snake the extension cord thru some conduit for added protection from the elements and scrapes – Travis Rose Jan 4 at 14:45
  • No, the way that neutral works with 240/120 is that if you have 30A on one leg of 120V, and 0 on the other, the neutral carries 30A. If you add 5A on the other leg, the neutral carries 25A - 15A on the other leg, neutral 15A, 30A on the other leg, 0A on the neutral. Neutral carries only the difference between the hot legs. – Ecnerwal Jan 4 at 14:56

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