Using 50 amp service for a 30 amp TT

[BBQGUY]

Wires are sized for the max current load and the breaker is sized to protect the wires. The 50amp to 30amp dog bone is NEC complaint as long as the user is connected to a 30amp RV using a 30amp rated supply cord of the appropriated wiring size for the length of cord used. A current draw over 30amps from the RV will trip the RV's 30amp main breaker saving the supply cord.


In the presented scenario, you could use the readily available 50A x 30A x 30A "Y" Park Power Adapter and check the voltage of each 30amp plug with a volt meter. Choose the one with the higher voltage to plug into.

[JCDMeyer]

Looks like someone else had the same idea and have already made it. Thanks for your help. However $150 is a bit steep when I can make one for less than $50.

[itat]

Has anyone actually built a weatherproof box with a 30A breaker and male and female 30A plugs? That way you could connect it to a 50A to 30A dog bone and have 30A protection for your power cord. Seems like a fair bit of work and expense for such a small risk though.

[BBQGUY]

Originally Posted by itat

Has anyone actually built a weatherproof box with a 30A breaker and male and female 30A plugs? That way you could connect it to a 50A to 30A dog bone and have 30A protection for your power cord. Seems like a fair bit of work and expense for such a small risk though.

If your RV has a 30amp service there no need for the breaker box you mentioned because there is a 30amp main breaker in the onboard RV subpanel. This is the reason you can use a 50amp male to 30amp female adapter and not be concerned of overheating the power cord as long as the wire size is correct for the length of cord(s) being used. What fails in a wire is the insulation from excessive heat.

[OntarioFireFighter]

Originally Posted by timfromma

The only issue I have with adapting 50A service down to 30A is that in the event of a major electrical failure in your camper, the breaker on the box will not trip until you exceed 50A of current draw.

You (should) have a 30A input breaker on your converter/power distribution panel... That protects the 30A cord from the RV to the pedestal from overload damage.

The only way you'd have to wait for the 50A breaker in the pedestal to trip, is if the cordset between the RV and the pedestal shorted.

[5picker]

Originally Posted by OntarioFireFighter

You (should) have a 30A input breaker on your converter/power distribution panel... That protects the 30A cord from the RV to the pedestal from overload damage.

The only way you'd have to wait for the 50A breaker in the pedestal to trip, is if the cordset between the RV and the pedestal shorted.

But there are those who believe something is going to fall from the sky and short out the cord so they will advise you to never ever use a 50 to 30 adapter.

[325BH]

I have one of these for my friends to use (I no longer have a 30 amp rig):

https://www.amazon.com/ParkPower-Mar.../dp/B000NV2VN0

You can choose which leg to use... or have two 30 amp rigs share the 50 amp pedestal.

[itat]

My question for the extra 30A breaker box is related to the concern by some here that something might happen to the RV power cord (or the main line in the trailer before the breaker in the power center) that will draw more than 30A but not be an outright short which would trip the 50A breaker. It's a very small risk but I suppose it's still plausible. I'm just curious if anyone has felt compelled enough to rig something up to add a 30A breaker because I don't think any of the dogbone manufacturers offer a 50A to 30A dogbone with an built-in 30A breaker.

Here is Mike Sokol's take on the use of dogbone adapters. He doesn't seem to have a problem with the 50A male to 30A female dogbone as long as it's a good quality product, but he warns about using the hockey puck style adapters.

https://www.youtube.com/watch?v=VgDOa-dAxjc

[JCDMeyer]

I don't think you need it. Even if you plug you 30 amp rig into a 3000 amp 125 volt line your 30 amp breaker will pop long before you hurt your shore line.

[ScottBrownstein]

As many have already said, the concept of connecting a conductor to a current source where the source protection is GREATER than the conductor current carrying capability of the cord is a common occurrence...AS LONG AS THIS CONNECTION IS NOT PERMANENT. The code does not permit this in permanent wiring (mixed wire sizes) not for the reason you might expect. They are trying to avoid a future electrician looking at the circuit in the panel, seeing that it is say, 12 GA and then upping the breaker to 20 amps from its existing 15 amps. If there were 14 ga wire somewhere in the circuit, this would destroy the protection of the whole circuit.

As others has said, your panel in the RV is protected by a 30 amp breaker so the only exposure that you would have is the 30 amp cable between the panel and the pedestal. If this were not permissible, every appliance, light or even tiny piece of electrical equipment that had a plug would have to be wired with at least a 14 ga cord, or perhaps even a 12 ga cord since modern kitchen outlets are always fused at 20 amps.

It's safe...it's code... forget it.