50 amp question

[pawpaw47]

I had a situation at an RV park the other day and I need some help to understand what happened. Of course, this happened late at night.
My surge protector showed low voltage (108 volts) on one of the incoming legs of the park's 50 amp service (the other leg was normal 120 volts) and eventually my surge protector shut down everything connected to that leg. The other leg was working normally. After a little while, the voltage on that leg returned to normal level and the items that were shut down began working again. A little later the same thing happened, but this time the voltage didn't return to the normal level. My wife suggested that I try hooking up to the 30 amp connection on the pedestal (I carry both 30 and 50 amp cords). I unhooked the 50 amp cord and connected the 30 amp cord and everything worked normally.
I'm no electrician, and I'd like to know how the 30 amp and 50 amp services operate. Please keep your explanations simple and in layman's terms so this old fart can understand.
Thanks in advance for your help.
__________________

[Jframpey]

enblethen wrote:
Fifty amp is two legs of 120 volts. It should read 240 volts between the two parallel blades in the receptacle.
When installed the system should have an equal amount of load on each leg.
A common problem in parks is there is more 30 amp, single 120 volt leg, are plugged into the circuit. This causes the voltage to drop on that leg.

For that reason I rotate L1 and L2 between each power pedestal. If everyone used 30 plugs I'd have a balanced load on each leg.

It sounds as if the 108v leg has a poor connection somewhere adding a lot of resistance and causing the low voltage... or several nearby trailers are pulling from one leg causing a voltage drop.

My power company had a bad neutral several months ago, causing my tenants to see 135 volts on one leg, 105 on the other... and 15 volts neutral to ground! Squirrels!

[pawpaw47]

Thank you for all the info guys.
I now have a better understanding of the difference between 30 and 50 amp service.

[pianotuna]

Best way to avoid brown outs is to add an autoformer.

[enblethen]

Fifty amp is two legs of 120 volts. It should read 240 volts between the two parallel blades in the receptacle.
When installed the system should have an equal amount of load on each leg.
A common problem in parks is there is more 30 amp, single 120 volt leg, are plugged into the circuit. This causes the voltage to drop on that leg.

[RoyB]

Bad neutral connections at the source sure gives off some strange readings on the typical two zones of circuits. When the current rises on the neutral leads it takes away from one zone and adds to the other zone... They all use aluminum wiring now in the feeders and corrosion sets in by having two different type of metal being used. They use a special greese around those aluminum connections that helps big time... It all tries to equal out to the 240VAC source voltage with 120VAC on each leg and zero volts on the neutral being the desired outcome.

Indeed your surge protector device may have saved you some high dollar expenses by shutting down for the unbalanced conditions you was seeing.

Roy Ken

[azrving]

30 amp is one leg supplying 120 volts. 50 amp is two legs supplying 120 volts onn each leg. If you check the voltage from leg to leg you will see 240 but nothing in the RV operates on 240. The danger with 50 amp RV service is that if the neutral is lost 240 volts can be fed to some appliances causing a cloud of smoke. Often times us 30 amp RV owners will adapt to 50 amps because our 30 amp rig is now riding on a heavier gauge wire to the pedestal. On the other hand 50 amp RV owners could be somewhat safer by operating on the 30 amp circuit because it doesn't have the ability to cause damage if neutral is lost. You could also make a 50 amp adapter to only power one leg which might carry your main ac unit.

That didn't help did it? 🙂

[Old-Biscuit]

50A RV Service....
TWO 50A power leads---L1 & L2 each capable of 50A/6000 watts
Main AC Panel has 2 busses...each protected/fed power via 50A circuit breakers
RV equipment split between those 2 busses with individual circuit breakers

30A to 50A adapter
Only ONE power lead
Inside adapter that lead feds 2 power leads on output side of adapter so BOTH leads in the 50A service get energized

30A only can supply 3600 watts total
So power supply is limited.
Only ONE high amp draw device at a time (A/C unit OR Microwave)
Best if fridge and water heater are on Propane vs Electric so demand is lessened

[mtofell1]

From what you describe it sounds like a problem with the park's supply of power. The low voltage could be due to a variety of factors but that really isn't important. It sounds like your rig did exactly what it was supposed to do. And so did you 🙂

The 50A service is 2 - 120V "pipes" of power and it sounds like 1 of them had a problem. The 30A service is 1 - 120V "pipe" and it was clean in your situation. Keep an eye on things your next time plugged in to 50A service to be sure there isn't something wrong with your equipment. From what you describe a problem with the park power is by far the most likely.