Strange Electrical Issue

kakampers · Jun 28, 2019

OK...electrical gurus...we have a really odd situation we cannot figure out...

This only happens here at our son's house where we had a 50amp plug professionally installed. No matter where we are we have no issues with 50 amp incoming power...we can run both AC's etc., even had no problem the night before we arrived here.

We have 123 volts on all legs at the plug, but when we plug in and check the EMS we are only getting 111-113 volts per leg...where the heck is this massive voltage drop. We can run one AC, but the load of a second one drops us down below the 104 cutoff on the Progressive EMS...

Anyone have any idea, we are checking all connections within the rig, but don't understand why it only happens here???

PS we plugged in our Hughes Autoformer, which is old and not sure it was working, and it burnt at the neutral leg...we had to replace the plug..but still only getting 111-113 volts

danemayer · Jun 28, 2019

You should check for loose wire connections in that 50 amp box and back to the breaker in the house panel.

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kakampers · Jun 28, 2019

danemayer said:
You should check for loose wire connections in that 50 amp box and back to the breaker in the house panel.

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Ken just replaced to the 50 amp plug and is now checking the house panel that it is run off of...stay tuned...

kakampers · Jun 28, 2019

Dan....how much voltage drop should be expected under normal circumstances??

kakampers · Jun 28, 2019

Ken just check the 50amp breaker in the house panel..all is tight and no indication of a problem or heating up....sigh...

Silverado23 · Jun 28, 2019

How long of a run is the wiring from the breaker box in the house feeding to the RV Box where your plugged in then add the length of wiring run to your RV.
Either the wiring size is undersized at some point or the length is excessive.

Another possibility is if a long cable run was used, was a splice used someplace that could be causing excessive voltage drop under load.
Poor connections someplace either in the box or with breaker?

Have you tried a different breaker, even though it does not appear bad?

danemayer · Jun 28, 2019

kakampers said:
Dan....how much voltage drop should be expected under normal circumstances??

If a voltmeter reads 123 but the EMS shows 113 before you apply a load, either you've got bad wiring/contacts or one measuring device is wrong. But when the 2nd AC unit causes voltage to drop below 104, I vote for bad wiring/contacts.

The meter reading suggests that there's no significant drop until even a light load is placed on the circuit. If it was a normal drop from distance/type of wire, I'd expect meter and EMS to agree.

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avvidclif · Jun 28, 2019

kakampers said:
Ken just check the 50amp breaker in the house panel..all is tight and no indication of a problem or heating up....sigh...

What kind of drop at the house panel? Divide and conquer. Measure drop under 1 ac load at the input to the main breaker panel, then at the output of the breaker, then at the input to the receptacle on the house. Somewhere in there is the problem Between the main breaker panel and the EMS.

jnbhobe · Jun 28, 2019

I would hope that both legs were wired to different sides of the main box. Just a thought.

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kakampers · Jun 28, 2019

OK...this is what we discovered so far, after a call to Progressive. Did not know that you can adjust what the remote reads, as it can vibrate and need to be recalibrated. We checked the voltage at both incoming legs and discovered we were getting just under 120 volts to the EMS, however the monitor was only ready around 113 on each leg. Progressive talked us through adjusting what the monitor reads to match the actual incoming voltage.

Now, however, when we turn on one AC the voltage immediately drops down to around 113-114 (and we verified this at the incoming lug on the EMS)...add the second AC and now we're down to 104-105 and not long before the EMS cuts us off...

How much should the AC's draw down the voltage?? Are these units getting ready to go??

danemayer · Jun 28, 2019

If your EMS was accurate everywhere in the past, I don't know why you would suddenly have to calibrate it by 10V. Maybe, but that doesn't sound quite likely.

I just looked at our EMS which is outside at the pedestal. L1 = 123V with 23 amps. L2 = 122V with 0 amps. I've never seen any voltage drop from putting a load on the leg.

If your EMS is inline, the problem could also be at your cord connection to the trailer, or cord reel if you have that. Or depending on location, it could be the transfer switch, if you have that.

kakampers · Jun 28, 2019

We checked the cord voltage in and out...was getting just over 120 volts...a 3 volt drop from the 50 amp connection. Then checked the incoming voltage on lines one and two at the lugs in the EMS(ours is hardwired)...it was jus under 120 volts, not even a full volt drop... adjusted the remote to reflect true incoming voltage. Progressive says this is not uncommon.

Holds fine until we turn on the AC...drops dramatically at the EMS incoming lines...and remote reads the drop correctly....

I'm sure the EMS was off but we didn't realize until we got here and the voltage from the house was lower to start with...

avvidclif · Jun 28, 2019

Use this calculator to figure "Perfect" voltage drop under load. https://www.rapidtables.com/calc/wire/voltage-drop-calculator.html

A piece of 6ga wire 50' long. 120v AC and 20A current will drop .79v All of your wiring should be 6ga.

I have 3 AC's and Progressive EMS hardwired. With a 30 ft cable to rv. L1 Normal 3-4A 122v. Turn on 1 AC and L1 current goes to 19A and voltage drops to 120. For the calculator figure each AC at 15A. Use the current numbers off the EMS.

You have a wiring problem at the house.

kakampers · Jun 28, 2019

Still don't understand why the ACs are causing such a drop in voltage?

kakampers · Jun 28, 2019

avvidclif said:
Use this calculator to figure "Perfect" voltage drop under load. https://www.rapidtables.com/calc/wire/voltage-drop-calculator.html

A piece of 6ga wire 50' long. 120v AC and 20A current will drop .79v All of your wiring should be 6ga.

I have 3 AC's and Progressive EMS hardwired. With a 30 ft cable to rv. L1 Normal 3-4A 122v. Turn on 1 AC and L1 current goes to 19A and voltage drops to 120. For the calculator figure each AC at 15A. Use the current numbers off the EMS.

You have a wiring problem at the house.

Ok...not sure off the gauge, but it was wired by a licensed electrician...

danemayer · Jun 28, 2019

A 10V drop is signalling a problem.

Is your EMS before the transfer switch? If so, the voltage drop is in your cord reel, or the receptacle or house. If the EMS is after the transfer switch, it could be the transfer switch. Pitted contacts, a loose wire, or failing contactors are all possible.

Don't put too much faith in the electrician. A license doesn't keep them from making mistakes. Ask my generator how it felt when the electrician miswired the transfer switch at the house.

Can the 50 amp box cover be removed so you can check for a voltage drop there when the 2nd AC kicks in?

One other thought: are the 2 A/C units on different power legs. Turn on A/C 1 and look at the EMS monitor to see which leg is carrying the load. Turn it off and turn on A/C 2 and see if it's on the other leg. They should be on different legs. Even so, if on the same leg, that would only possibly cause a drop if you're around 50 amps on 1 leg, meaning other things would be sharing the same power leg.

TedS · Jun 28, 2019

Is the house in fact wired for 2 50-amp circuits or maybe only 1 50-amp circuit feeding the two legs of the outlet?

kakampers · Jun 28, 2019

TedS said:
Is the house in fact wired for 2 50-amp circuits or maybe only 1 50-amp circuit feeding the two legs of the outlet?

Yes...two 50 amp breakers...

danemayer · Jun 28, 2019

TedS said:
Is the house in fact wired for 2 50-amp circuits or maybe only 1 50-amp circuit feeding the two legs of the outlet?

Good point. What's the voltage reading across L1 and L2 at the 50 amp receptacle?

wdk450 · Jun 28, 2019

I would troubleshoot this PURELY with a good AC Digital Voltmeter, testing trailer voltages at the inside breaker panel incoming feed wires. The DVM is purely an electrical troubleshooting tool; the EMS voltage readout is a monitoring convenience for the RV owner.

Apples and Oranges can make a lousy fruit salad.

Strange Electrical Issue

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