Shore Power Question for the Sparkies - Montana Owners Club

dieselguy · 09-04-2020, 09:46 AM

This question is about taping off the 15 amp circuit in many 30 amp campground power pedestals to run a second 13500 BTU A/C. Yes, I'm aware that some 30 amp pedestals available wiring may not support tapping off the 15 amp plug.

I'm looking at adding a 15 amp Marinco plug in in the side of a fiver and running that separate line to a stand alone 15 amp receptacle in the storage bay near the A/C power line to the front air conditioner. That OEM A/C line will be interrupted by male and female 20 amp plugs so I can plug it in to the stand alone 15 amp receptacle when the need arises. With the fiver thermostat controlling both A/C's ... do you think there will be an issue with 2 separate inlet power feeds off the campground power pedestal as far as damaging the thermostat's common control to both A/C's?

Thanks in advance

Daryles · 09-04-2020, 01:52 PM

All I can say is I've read on RVELECTRICITY FB group, it is against code to run two electrical connections from the same pedestal to the same RV.
I have no idea why.
Would what you are proposing work?
Probably...
Is it safe???
No idea???

dieselguy · 09-04-2020, 03:33 PM

Well this seemingly quick and dirty project has became more complex ... I just realized IF I were to tackle this request, I'll need to add a small beaker box to fuse the circuit. It'll be more than just plugging and unplugging receptacle ends. I know owners have done this in the past, but with a stand alone front A/C. Daryles ... I'll research your point.

Slow Hand · 09-04-2020, 03:59 PM

I have seen 110 outlets on some RV pedestal at some campgrounds. Could you not add another breaker to your fuse panel?

dieselguy · 09-04-2020, 04:20 PM

The issue is as follows. The owner owns a 50 amp fiver and runs across campgrounds which generally are 30 amp. He would like to run both A/C's on extremely hot days without totally shutting everything else off to sqeak by. He's read on some RV forums where people run a separate extension cord from the 15 amp plug on the 30 amp pedestal, and in various ways powered their second air conditioner from that extension cord. This has nothing to do with power from the existing power center in your fiver. It has to do with separating one air conditioner to be able to run on the smaller circuit on a 30 amp power pedestal and still be able to return it back to normal operation for a 50 amp pedestal. He approached me to do it, but I'm concerned about the common thermostat control as his fiver sits now.

jetskier · 09-04-2020, 05:42 PM

Here's a thought:

Buy a 30A auto transfer switch. Take the feed for the second AC from the main panel and feed it into the shore power side so the 50A service takes priority over the 15A. Install your 15A plug on the side. Buy a cheap panel and run the 15A service into it and use a 15A breaker. Feed the output of that panel to the other input of the ATS. The output of the ATS goes to the AC direct. This would make it safe and automatic.

It would be better to try to run 12ga for all wiring and 20A breakers for an AC. You aren't supposed to go over 80% of the rated breaker for general loads in the real world.

**DQDick** · 09-04-2020, 06:26 PM

The third AC on our 2017 is run off a 30amp breaker in the basement that goes to a 30amp plug on the outside near the convenience center. I can run it off a 30 amp or 20amp from the pedestal depending on whats available using dog bones as necessary.

dieselguy · 09-04-2020, 07:37 PM

Hadn't thought about a transfer switch ... worth considering.
Dick ... so to run your 3 A/C's at once, you have 2 power cords running to your fiver? Regular 50 amp and then your secondary 30 amp plug? Just asking because of reply #2.

RMcNeal · 09-05-2020, 03:59 AM

I am considering a 3rd AC. Our unit came pre-wired for a 3rd unit in the kitchen where the Max Air fan is located. If I do decide to add it, I intend to run a separate circuit to power it with a 30 amp receptacle outside as Dick described. Since the 50 amp input is really 2-50 amp 110 volt circuits, and not a single 50 amp 220 volt circuit, I don't think this would cause any problems.

psomers · 09-05-2020, 06:41 AM

Back in the day when all campers were 30 A I had adapter to plug into 15 A to get refrigerator cool for trip. DW would want to cool camper to load. It wouldn't pop CB but receptacle would get to hot to be safe. I know that was AC and refrigerator both pulling amps.
Winter camping I have seen several 30 A campers with a 15 A power cord running in through slide opening to run additional heater.

BB_TX · 09-05-2020, 08:46 AM

While an auto transfer switch would be the ultimate solution, I don't see any problem with your "patch cord" approach for the likely few times you will need it.

As far as the thermostat, most home thermostats run on 24 vdc powered from a transformer at the heating/AC unit. But there are some thermostats that do run on 120 vac. I don't know what these in the RV are powered from. Would be interesting to know. But if the park pedestal is 30 amp only with a 15 or 20 amp second receptacle, then they almost for sure would both be the same phase and shouldn't be any problem there either. Wiring each from different phases would increase their wiring costs.

mhs4771 · 09-05-2020, 09:03 AM

I think you'll find that the T-stats in most RVs run off +12V, because they still need to be able to run the furnace without shore power.

RMcNeal · 09-06-2020, 02:58 AM

That's kinda what I was getting at BB-TX. Still single phase 110 volt whether using 15 or 50 amp. Our thermostats run off 12 volt DC. I would think that is the case with most since there is a 12 volt DC source all the time.

drjjj · 09-09-2020, 01:36 PM

I think I have seen dog bones that have 15 & 30 amp male ends wired to a single 50 amp female end. Would this work in a 30 amp campground?

jetskier · 09-09-2020, 01:52 PM

Quote:

Originally Posted by drjjj

I think I have seen dog bones that have 15 & 30 amp male ends wired to a single 50 amp female end. Would this work in a 30 amp campground?

The only problem I see with those combiners is you don't know which leg of the 50A connector gets the 15A and 30A feeds, respectively. You may have more loads on one side than the other and 15A may not cover it. I suppose the best adapter would be the dual 30A to 50A adapter and use a 15 to 30A adapter puck. You could swap it to either 30A connector depending on your load requirements on each leg of the 50A.

bcrvman · 09-09-2020, 02:14 PM

I don't understand how the AC power will affect a DC thermostat. The idea will work (no idea about local codes) as long as the 15 or 20 amp circuit is either dedicated (very unlikely) or tapped off one of the 50 legs while the 30 is tapped off the other 50 leg ideally. If the 15 or 20 is tapped off the 30 then there is no advantage.

jetskier · 09-09-2020, 02:27 PM

Quote:

Originally Posted by bcrvman

I don't understand how the AC power will affect a DC thermostat. The idea will work (no idea about local codes) as long as the 15 or 20 amp circuit is either dedicated (very unlikely) or tapped off one of the 50 legs while the 30 is tapped off the other 50 leg ideally. If the 15 or 20 is tapped off the 30 then there is no advantage.

There's no impact on the DC or thermostat side. I'm not sure how that even came up as an issue.

McRod · 09-09-2020, 02:49 PM

Quote:

Originally Posted by dieselguy

This question is about taping off the 15 amp circuit in many 30 amp campground power pedestals to run a second 13500 BTU A/C. Yes, I'm aware that some 30 amp pedestals available wiring may not support tapping off the 15 amp plug.

I'm looking at adding a 15 amp Marinco plug in in the side of a fiver and running that separate line to a stand alone 15 amp receptacle in the storage bay near the A/C power line to the front air conditioner. That OEM A/C line will be interrupted by male and female 20 amp plugs so I can plug it in to the stand alone 15 amp receptacle when the need arises. With the fiver thermostat controlling both A/C's ... do you think there will be an issue with 2 separate inlet power feeds off the campground power pedestal as far as damaging the thermostat's common control to both A/C's?

Thanks in advance

I purchased a 50 amp and 20 amp RV pedestal outlet for my land (same box) from Home Depot. The 20 amp is piggy backed off the 50 amp from the factory. There is no separate wiring for the 20 amp. It's only there for convenience. They both have their own breakers. Assuming you were maxing your 50 amp, there would be nothing to gain by plugging into the 20 amp other than popped breakers. If you know for a fact its wired separately then there should be no issues. I would not count on it.

RMcNeal · 09-09-2020, 02:53 PM

In addition, the 50 amp to 30/15 amp dogbone will not work if the 15 amp receptacle is GFCI. I have one and it will trip the GFCI outlet every time. I didn't realize that when I bought it.

BB_TX · 09-09-2020, 02:57 PM

Quote:

Originally Posted by RMcNeal

In addition, the 50 amp to 30/15 amp dogbone will not work if the 15 amp receptacle is GFCI. I have one and it will trip the GFCI outlet every time. I didn't realize that when I bought it.

A GFCI doesn't play well when it shares a neutral as it does in the case of that type adapter.

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