Wiring RV service for one 30 amp plus one 20 amp breaker using 10-3 wire

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andonso

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Apr 9, 2018
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I'm installing a 30 amp subpanel outlet from a 200 amp subpanel using direct burial 10-3 wire, which has two hots, one neutral and one ground. (4 wires)

I've read it's possible according to NEC to share a neutral between two hots using 4 wires.

One hot going to the 30 amp single pole breaker, the other hot to the 20 amp single pole breaker and pigtails from each outlet (30 and 20 amp) to the (10-3) neutral and pigrails to the ground.

From what I've read so far both the neutral and ground wires need to be rated for the capacity of the connected breakers.

GFI doesn't allow to share a protected neutral, but I'm not planning on adding any GFI to the outlet and subpanel. There are a couple of gfi outlets in the motorhome that aren't part of the 10-3 feed circuit.

One reason I'm using two separate breakers, a 30 amp and 20 amp is the RV is wired for 30 amp service and the 20 amp circuit with a dedicated 20 amp breaker will be connected only to a Rheem 110 Volt 2000 watt 20 gallon water heater that draws a max. ~17 amps.

So one side of the 10-3 will feed the  motorhome while the other side will feed the water heater

I suppose technically the 20 amp breaker should be 25 amps to compensated for surges. However I wasn't able to find any Square-D HOM breakers which my 200 amp panel uses. I did find some 25 amp square-d QO breakers which I believe are thicker?

 
You really should not share a neutral among two different branch circuits (the 30 and the 20). A shared neutral is used with 240v service where the two hots are out-of-phase with each other.

If you did share the neutral it would need to be rated for the combined amperage, i.e. 50A in this case. Standard 10/3 wire doesn't do that - the neutral is 10 gauge just like the hots.

If you want to do this, use a 30A/240v (2-pole) breaker in the load center, not a separate 30 & 20.  The common neutral works in that configuration. That gives you a 30A trip for each hot.  The best bet would be to use the 10/3 feeder to a subpanel and then put a 30A outlet and a 20A outlet in the subpanel, with breakers for each.  That way your well pump stays independent of the RV outet.
 
The method Gary outlined gets around all the issues.  Run 240V 30A to the outside sub box.  At that point, feed the RV 120V 30A breaker and plug from one side and the 120V 20A breaker and plug from the other side.  This is similar to how 50A RV's are wired.  240V 50A runs to the main panel.  There it is split, going through separate 120V 50A breakers, then to breakers for the sub circuits.
 
The multi wire branch circuit would work OK with the 10/3 cable. The neutral will only carry the difference in current between the two legs so the most current on the neutral would be 30 amps from the RV circuit. It will be reduced by any current on the 20 amp circuit. This circuit was common in homes before all of the arc fault breakers were required by code.

You need to use two single pole breakers with an approved handle tie connecting the breakers to make a common trip so you're safe when you work on the circuit. The breakers need to be next to each other so they are on opposite legs of the panel.
A GFCI receptacle will work as long as it's installed at the RV end of the circuit.
QO and HOM breakers are not interchangeable. They have different mounting configuration.
 
The multi wire branch circuit would work OK with the 10/3 cable. The neutral will only carry the difference in current between the two legs so the most current on the neutral would be 30 amps from the RV circuit. It will be reduced by any current on the 20 amp circuit.

That's true ONLY if the two hots are out of phase with each other. There is no guarantee of that if two separate (non-adjacent) breakers are tied together.

Andonso stated only that he was using separate 30A & 20A breakers, so the phase match-up is an unknown.  If the branch breakers are adjacent, he may as well use a twin-30 breaker, which is fine even though the well pump only requires 20A. The breaker protects the (10 gauge) wire, not the pump itself.
 
That was the reason for the handle tie to connect adjacent breakers. They are out of phase on breaker panels.
 
That was the reason for the handle tie to connect adjacent breakers. They are out of phase on breaker panels.

Probably, but there are load centers that do not support 240v breakers at all, so being adjacent isn't quite fool-proof.  I'll agree those 120v-only panels are not common and are typically sub-panels, but making an assumption about it could be dangerous.

Yes, I'm nit-picking!    ::)
 
The easiest and best way to "Share a neutral" between two hots is if the two hots are L-1 and L-2 of 120/240 volt service.  This way the currents in teh two legs SUBTRACT on the neutral
The current in the neutral is the difference between L-1 and L-2

If they are both the same leg then the currents add and you need to upgrade the neutral wire for safety.
 
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