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AC Voltage question


John Laninga

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It's hot in Texas. Moved to a new park, had 50A pedestals so I ran all three roof top AC units to cool the rig down. After running a while, the circuit breaker tripped and power was off. I reset the breaker, but noticed the breaker was old and weak. It tripped again after only a few minutes of running. The park changed the breaker, noting that they were all some 7 or 8 years old and this type of failure was not uncommon.

 

But I decided just to run two AC units anyway. Noticed on my Progressive EMS unit that voltages were strange: L1 had 103V and 15A, L2 117V and 35A. Of course, the EMS tripped and when it reset it went to the same voltages and tripped again. I turned of one AC unit, now running only one and my voltages were L1 107V, L2 was 117V. I turned off all AC at night, since temps dropped way down.

 

This morning voltages were L1 122V 6A and L2 120V 0V. I powered up a space heater and turned on my electric water heater. Now I'm reading L1 112V 6A and L2 120V 20A.

 

I'm wondering if maybe the pedestal receptacle (which felt normally tight when plugging in) may be bad? Or any other suggestions? I'm leaving this park in 2 days, temps are dropping so I guess I can live with it but I would like to know what the problem is and maybe help the camp host with a positive suggestion.

 

Thanks, John

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Follow-up:

 

My neighbor has an external Progressive EMS, mine is builtin. Yesterday, when my system was reading 103V, he was running two AC units and his EMS did not shut down. It is now 8:30AM, and my readings vs. his:

 

Mine: L1 115V 7A L2 119V 11A

His: L1 116V 14A L2 123V 10A

 

Thought this might help in determining the problem...

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There are several possible causes and all of them are outside of your RV. It isn't at all uncommon in older RV parks for wiring to be old as well and that could mean a host of possible problems like poor connections at junctions, old power plugs, undersized wire, or a lot of other things. With most of those problems, the difference in voltage between L1 & L2 will typically follow the current load. The higher the current drawn from a leg the lower the voltage will fall, until it reaches the low voltage set point of your EMS and power is interrupted. When the problem is in the outlet due to poor connections there, you and usually tell that because the receptacle will be hot to the touch. Any time a connection or other problem in a circuit causes any significant resistance to current flow, that part will cause a voltage drop and the energy expended there is dissipated as heat. Even in normal circumstances you can experience some of that by using all of our a/c at the same time and feel the RV power cord and it will be warm to the touch, which is normal but it demonstrates the fact that power is lost when current flows through any medium.

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One of the things that scares me the most about the RV life is plugging in to a campgrounds pedestal...I spent 10 years inspecting meter loops/breaker boxes on poles, residential and commercial units and just about everything in-between...the wiring that we could inspect and turn down for various reasons stopped at the breaker box (main disconnect from our lines)...from that point on was the consumers responsibility...our service area consisted of 10 large rural counties (in Tx) that had hundreds of subdivisions and campgrounds that had no restrictions or inspections of house or campground wiring required...pretty much whatever the "electricians", and I use that term very loosely did was ok with the ones paying the bill. Pretty scary situation but one that was completely out of the electric company's jurisdiction...sooooo, and I know it has been said many times on this forum, but I want to repeat it one more time...GET A METER AND LEARN HOW TO USE IT!!!! It takes very little knowledge about electricity to use it correctly and can save you lots and lots of misery and money down the road...sorry for the rant, I will step off my soapbox now!!!!

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I agree with Kirk on this one. At our large Naval facility where I was an electrical engineer MOST ALL similar (low or different voltages) electrical problems could be traced back to what he mentioned: Loose burned carboned resistive connections and loose burned resistive Neutral connections. Temp changes humidity and use all add up to resistance at various locations causing low voltage at the load and/or different voltages. Its NOT just a circuit breaker were talking about, its the sum of all the wiring connections and splices and worn receptacles etc etc. What you are describing does NOT surprise me one bit. Of course, attaching a volt meter at say the pedestal absent a substantial load dosen't tell you the whole story. Theres no IR voltage drop across a loose resistive connection until theres current flow through it.

 

John T

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