Strange Electrical Issue

[kakampers]

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.

We're going to see if we have a drop at the 50 amp plug when AC is on in the morning... exhausted right now from the heat. We checked each AC separately and they are on separate legs. The EMS is after the transfer switch because of the generator. We just replaced the transfer switch last July as we had a loose connection and burned a lug on the generator side...every single connection was checked and tightened in the rig.

This is the most baffling thing we've ever dealt with

 

[kakampers]

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

It's reading 123v on each leg at the receptacle...

 

[danemayer]

It's reading 123v on each leg at the receptacle...

L1 to ground or neutral should be 123V. L2 to ground or neutral should be 123V.

L1 to L2 should be 246V. If it reads 0V, it's miswired.

 

[kakampers]

L1 to ground or neutral should be 123V. L2 to ground or neutral should be 123V.

L1 to L2 should be 246V. If it reads 0V, it's miswired.

We were here when it was wired...each leg runs off it's own 50 amp breaker from the panel box...

 

[mlpeloquin]

Have you check the voltage at the breaker box with load AC running? Rare, but just because it is new, it does not eliminate the new panel breaker.

 

[kakampers]

Have you check the voltage at the breaker box with load AC running? Rare, but just because it is new, it does not eliminate the new panel breaker.

Haven't done that yet, but will tomorrow...you do mean the breaker in the house panel, right? If the voltage drops at the breaker under load what is that telling us, bad breakers?

 

[danemayer]

Take a reading.

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[kakampers]

Take a reading.

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We will check at the receptacle and at the breakers in the morning under load...if the voltage is dropped there what is the issue?

 

[mlpeloquin]

Haven't done that yet, but will tomorrow...you do mean the breaker in the house panel, right? If the voltage drops at the breaker under load what is that telling us, bad breakers?

House panel. You know the input rail to the panel is good with 100 to 120A service. So first in the line is the breaker. Then work your way down the line. You got to know the gauge wire that was installed as well. Too small of gauge will have a big voltage drop. 50A breaker is to protect 6ga wire.

 

[kakampers]

House panel. You know the input rail to the panel is good with 100 to 120A service. So first in the line is the breaker. Then work your way down the line. You got to know the gauge wire that was installed as well. Too small of gauge will have a big voltage drop. 50A breaker is to protect 6ga wire.

Ok...DH says it's 8 gauge wire. He checked voltage at the breaker was 125 and at the receptacle was 123, but that was before we plugged the RV up.

 

[danemayer]

We will check at the receptacle and at the breakers in the morning under load...if the voltage is dropped there what is the issue?

What we're trying to poke at is whether the two 50 amp lines are actually different phases. If they are the same phase you will have problems. That's why you need to verify that the voltage reading between L1 and L2 is 240V.

8 gauge wire may or may not be a problem. Depends on type of wire, environment, and length of run.

 

[kakampers]

What we're trying to poke at is whether the two 50 amp lines are actually different phases. If they are the same phase you will have problems. That's why you need to verify that the voltage reading between L1 and L2 is 240V.

8 gauge wire may or may not be a problem. Depends on type of wire, environment, and length of run.

OK...he will check that at the plug tomorrow...

 

[kakampers]

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.

He's tested everything with a digital volt meter....even determined the EMS needed recalibrating using his voltmeter.

 

[kakampers]

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?

The run from the house panel is maybe 30-35 feet to the 50 amp receptacle...he used 8 gauge wire. It's a solid run of cable, no splices inside a conduit. DH has check all connections from the breaker to the receptacle...all connections are tight. Haven't tried new breakers yet...

 

[cookie]

Kathy, this won't help your voltage loss but if using #8 copper wire you should be protecting it with a 40 amp breaker.

Peace
Dave

 

[TedS]

Ok...DH says it's 8 gauge wire. He checked voltage at the breaker was 125 and at the receptacle was 123, but that was before we plugged the RV up.

Those voltages should be the same, equal with nothing connected. There should be no drop. Something is drawing current for there to be a voltage drop.

 

[kakampers]

Those voltages should be the same, equal with nothing connected. There should be no drop. Something is drawing current for there to be a voltage drop.

we can't figure out what's causing the drop and when we turn on the AC's it's a massive drop...

 

[kakampers]

OMG!! Thank YOU! You guys were dead on...the idiot electrican wired it single phase!!! Ken is out right now trying to find the breakers he needs to seperate the two legs....un-freaking believable!!

Yesterday, when we were trying one AC at a time I kept wondering why it affected both legs...the voltage would drop on each side, even though the amps were showing on just one leg. Ken woke up this morning and said...I think they're right...sure enough.

 

[jayc]

Glad you got it figured out.

 

[kakampers]

Glad you got it figured out.

Us too...we had this installed last summer while we were here and it was a problem then too but we were just here for a few nights and it was way cooler. This time we're staying for a month and realized there was a real problem...hopefully he can find the breaker he needs for this old panel...