Topic: 120 vac Shore Power Wiring (Read 2725 times) previous topic - next topic

2014 Unity 24MB. 30A capacity is overloaded when roof AC, electric water heater or microwave (shared circuit), electric fridge are operating. The coffee maker was idle. The coach batteries were fully charged, so the coach converter was not loaded.
I just purchased the coach and was blindly oblivious to the problem until I installed the Progressive Industries 30A surge and electrical monitoring device. Now, I see about 38-40 amps combined loads. A reasonable solution would be to turn off the roof AC when running the microwave. At this current, the inverse trip rate for the 30amp main breaker in the coach and 30amp park supply should usually allow for short term overloads. That's with new breakers that function correctly.
A reasonable approach would be to manipulate equipment usage to control current flow.
The coach has a 3200 watt, diesel Onan, so I am limited there. Usually, many parks have 50 amp, 240 volt / 30 amp, 120 volt / 20 amp, 120 volt pedestals. With a 50amp to 30amp adapter, there is a 50a, 120v supply to the shore power cable.
Solution:
Fabricate or purchase a 6 gage, 3 wire cable from the 50/30 adapter to the coach shore power input. Inside the coach, change the #10 shore power input to the changeover switch to #6, then change the main breaker from 30 amp to 40 amp.

Safety: As the input is now protected by a 50amp breaker on the pedestal, the #6 wire is protected. I do not have to apply for UIL approval, yet know from experience that the 30amp male plug at the pedestal and 30amp shore power connector and receptacle at the coach have ample ampacity up to 50amps. They could be upgraded to 50 amp devices. The bus capacity of the installed coach circuit breaker box is adequate as each circuit is still individually protected. So, with 50amp shore power, I can be lazy and safe.

Limitations:
1. RV Park has only 30 amp available.
2. Onan DG has only 30 amp available

NOW. MY QUESTION: (That took long enough to get to)
Has anybody found the physical route of the #10 cable inside the coach from the shore power receptacle to the change over switch on the rear of their breaker load center?
I am fairly sure it is under the under sink cabinet floor on the driver's side. Before I start taking things apart, I just thought I would ask.

You may also want to visit the coach transfer switch to see if its contacts are rated for higher current, plus the wire coming from the coach transfer switch to the main breaker.

ETA - after reading hdtvluvr's response below, it also raises the question of the 50/30 adapter AND your shoreline cord.  The wire gauge in those might be sized for 30 amp, not 50, so pulling more than 30 might turn it into a fuse or a fire hazard.

I found it was easy just to manipulate the loads.
Only really long term large load is the A/C everything else is fairly short and easy to turn off when close to 30 amps.

That 50 Amp is 240 volts and the 30 is 120.  The 50/30 adapter just takes one leg of the 240 thus giving you approx 30 amps.

Lots of rewiring to do.  Better to manipulate the loads.

Yes, but a 50 amp hookup SHOULD be 2 50 amp legs, so if it takes one leg and distributes it to the coach, the shore breaker would be capable of 50 amp.

The OP's shoreline cord and the adapter, however, might only be rated for 30 amps, and if so will overheat if more than that is being pulled.  The 50 amp campground breaker will not protect the coach from such a condition.

Thanks for that correction.

Good thought on the transfer switch continuous current capacity. I looked it up. The T-30 is rated for circuits of 105-130 vac, 60 hz, 30Aac. Noted also that when used with a 50 amp circuit breaker, the transfer switch is suitable for withstanding a fault current of 5000 rms, symmetrical amps. Max 240vac. I feel confident, in my coach, to utilize 30-40 continuous amps with 50 amp protection.
The shore power cord will be upgraded to a 6-3 SO. The 50amp pedestal breaker, although 2 pole, does protect both legs.
The 6-3 SO at 25’ length has the capacity for 50amps continuous, so it is protected.
I am trying to justify utilizing the 30amp, 3-wire connector and the 30amp, shore power connector to 60% above their stated capacity. Also, if you look at the male (pedestal) or female (shore power) connectors on many coaches, they are damaged and have heat marks. This is probably due to worn connections on the pedestals and multiple insertions at the coach. So, I'll probably convert both to 50amp connectors. The only change is the connector on the coach. 50amp, 4-wire cables are standard. I'll just utilize 1 leg after the RV Shore Power connector.
I appreciate all your comments and suggestions.