My house has two utility 30 amp outlets (with 30 amp breakers at the main panel). I want to use from the house outlet, 30 Amp RV Extension Cord going into a 30A 125V RV Power Inlet (to be installed on the shed). All wiring up to that point is 10 AWG. After that it will be 12 AWG wiring. Do I need to use a Sub-Panel in the shed with 20/15 Amp breaker(s)? Can I use GFCIs instead? Suggestions?

The shed (10x14 Ft) will be use to run bench lights, bench outlet strip, light weight bench grinders/polisher, other hand tools like drills, vacuum cleaner, small mini fridge, fan (NOT Air Conditioner), maybe a coffee pot etc. Basically the main use is for Arts and Crafts. The use is intermittent and not intended for full time operations (so it will be disconnected when not in use).

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    Why are you wanting to wire the shed using an extension cord instead of using a permanent wiring method? Is decommissioning the 30A outlet in question an option? May 3, 2021 at 23:01
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    A GFCI only senses difference in outgoing and returning current. Please read the installation instructions for GFCI receptacles leviton.com/en/docs/GFTR1-5L.pdf Read under "1. What is a GFCI", third paragraph, "A GCFI receptacle does not protect against circuit overloads.." May 3, 2021 at 23:16

2 Answers 2


There are two three separate issues here:

Extension Cord

An extension cord is not supposed to be used for permanent wiring. You really should use a permanent wiring method - either cable designed for outdoor use or wires in conduit. Normally this involves buried cable or conduit, with specific minimum depth required depending on the type of cable or conduit.

Conduit may cost more initially (materials cost for conduit + wires is generally more than underground cable, but trenching cost/effort is lower for conduit) but has the advantage that you can start with 10 AWG and upgrade later if you need more power, and/or start with a single hot (120V, see below) and upgrade later to two hots (240V).

Breaker Size/Subpanel

If you have a 30A breaker, normally all wire in the circuit needs to be 10 AWG or larger. GFCI (which will be needed anyway) does not help protect against high current, only from unbalanced current.

The preferred solution, unless you only need one circuit (in which case you can switch to a smaller breaker) is a subpanel, with 30A coming in (or more if you install larger wire and breaker) and as many 15A or 20A circuits as you need to power lights, receptacles, etc.

There are a bunch of other things you will need:

  • GFCI - This can be in receptacles or as part of the breakers in the subpanel
  • Ground rods connected to the ground of the subpanel
  • Ground and neutral separate in the feed cable and in the subpanel
  • Shutoff switch - the easiest way to do this is a subpanel that has a main breaker. That breaker can be much larger than the feeder capacity - even 100A or more - as the breaker in the main panel will protect the wire (e.g., 30A for 10 AWG).

120V vs. 240V

I missed this until I read Harper's answer. You are referring to a 30A 120V circuit - i.e., a single pole. If you can manage it (two breaker spaces next to each other instead of just one) then a 2-pole breaker will serve you much better. Instead of 2 wires (hot/neutral) + ground, you run 3 wires (hot/hot/neutral) + ground. Depending on a bunch of factors, this will cost you a little more, but definitely not twice as much, and provide you with both twice as much total power and the ability to run 240V devices if you ever need to do so.


The 30A supply receptacle needs both neutral and ground

... so NEMA 14-30.

You cannot pull 120V power off a NEMA 10-30 (dryer) socket- no ground.

You cannot pull 120V power off a NEMA 6-30 welder/compressor/EVSE socket - no neutral.

A NEMA 5-30 or TT30 would also be acceptable, as they have both.

A subpanel is necessary

You cannot put common receptacles or lights on a 30A circuit. You will need a subpanel to derive 15A or 20A circuits. You can have as many circuits as you want, but if the loads you are actually using, together overdraw 30A the supply breaker will trip.

If there are more than 6 throws (hand motions) to shut off all power, then you need a master disconnect. The cheapest way to get that is a panel with a main breaker (of any size). That's an awfully good idea, since you may find 30A@120V stifling, and at the least upgrade it to 30A/240V, and maybe higher still with a hardwired connection.

You can throw 2 or 3 breakers with one hand motion, by getting retrofit handle ties that tie 2-3 breakers. The 3-breaker ties are for 3-phase power, but it's fine to use them for this.

You are better off having dual 20A on the 30A supply, because you'll get more out of your 30A if you do. It's easier to load them e.g. 18/12 than it is to load them perfectly dead-nuts on 15/15.

GFCIs have no ability whatsoever to act as breakers. Much the opposite in fact. You can pull 20A through a 15A GFCI and that's legal. (NEC 110.3(B)). .. you can even pull 30A and it won't complain, but that'll exceed its rating and so it might burn out.

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