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Randall, RVIA Certification
Category: RV
Satisfied Customers: 11633
Experience:  RVDA/RVIA Master Certified Technician with many years experience.
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When we plug into shore power it trips the circuit breaker

Customer Question

When we plug into shore power it trips the circuit breaker on the post (we're at a campground) it was running fine, then just tripped and will not let us plug in again. All electrical systems run normal on generator power.
Submitted: 6 years ago.
Category: RV
Expert:  Randall replied 6 years ago.
Hi: Thank you for coming to Just Answer with your question. My name is XXXXX XXXXX perhaps I can assist you with this issue.

Were you using any kind of adapter? This is a 50 amp shore cord? If everything works fine on the generator in your coach there is a good chance this is either a problem with the breaker on the pedestal OR a bad automatic transfer switch on your coach. This is what controls the power from one source to another. They can work on one source and not the other from a solenoid grounding out. It might also be a polarity issue on the pedestal if someone worked on it recently and got it backwards. Those are the most likely causes.

We can run some tests if you have a multimeter. Those can be found at most automotive or hardware stores for about $15 to $35 for a digital readout version. These are easy to use and come with instructions. Please get back to me if you need more help with this as follow ups are included in our fee. R.J.
Customer: replied 6 years ago.
We were using an 50/30 amp adapter, could the adapter have gone bad? Nothing had changed recently with the shore power hook-up. It just happened, nothing else had been turned on or off inside the coach when the breaker on the post went.
Expert:  Randall replied 6 years ago.
It can be the adapter...............and I suspect you know that you do lose half your service when you use an adapter so some of your systems or plugs won't function. You still may have had too much load for a 30 amp service to handle........especially if you had the A/C on. On a hot day the A/C an pull about 20 amps by itself. If you have the water heater on AC mode and the fridge on AC mode you can be over that 30 amps quickly. So there may not actually been anything wrong.......except just too much load. R.J.
Customer: replied 6 years ago.

We turned absolutely everything off, the AC, the Fridge, the water heater etc. so it would have the least amount of draw, but it was still tripping the breaker. We hooked the 110 adapter in to try that circuit, and it tripped that too with nothing on, he actually saw a blue spark. We tried a different 30 amp hook up, same issue. So I'm having my husband go buy another 50/30 amp adapter and hopefully it's that simple.


I've had the coach since it was new, and put 130k on it. I've experienced the fuse going in the inverter, replacing the automatic transfer switch cylinoid, having to reset the inverter by unplugging and plugging it back in. So I knew those symptoms, this is new.

Expert:  Randall replied 6 years ago.
It could be the automatic transfer switch that is going bad and has a short in the shore cord side. Using an adapter tends to be harder on them as a rule over having both sides feed equally. That is where I would start if the adapter proves to be fine. A loose wire in the hookup of the ATS might do this as well. Road vibration loosens up those wires sometimes. R.J.
Randall and 3 other RV Specialists are ready to help you
Customer: replied 6 years ago.
can you call me. two zero eight three six zero one two four nine.
Expert:  Randall replied 6 years ago.
We won't have a call option for about a week for now, this is the only format.
They have had so many calls for this they are adding that feature. If you want to test out the ATS let me know and I can guide you in that. R.J.
Customer: replied 6 years ago.
I do want to test it out. I read the IOTA information at the web site. I dont have a multi-meter with me. If I need it I can run to the hardware store...
Expert:  Randall replied 6 years ago.
That would help.............and you can track this down in a hurry. I will be out for a while and then back later this evening. R.J.
Customer: replied 6 years ago.

OK. Got the multi meter. Funny thing is I have one at home too...never around when you need them...


I will keep checking the web to see if oyu are back.

Expert:  Randall replied 6 years ago.
Sorry for the delay in getting home.............see the diagram in the lid off the ATS. You want to take a reading on the incoming leads from the shore cord. With the power OFF see if the hot lead (black) on the shore cord is showing an ohm reading between the lead and ground. If so you can see the problem. This is with it still connnected to the terminal on the ATS. Then take the lead loose and take it again...........first on the black lead. Should be none. Then take the terminal on the ATS where this was connected............and ground and it should be none, but I susepet it shows it is grounded out. Let me know what you find. R.J.
Customer: replied 6 years ago.

OK...Got the multi meter.


Installed new ATS.


I am at a different campground with 50 a shore power.


Turn break on pedestal off.


Schematic says shorepower far left three slots - black hot / red hot / white neutral and we all know green is ground.


Next three slots are Generator Black Red White


Next three slots are load Black Red White.


Black multi meter lead to ground.


Touch black (hot shore power) no reading

Touch red (hot shore power) 176 on the multi meter.

Touch White shore power - no reading


Touch black generator no reading

touch red generator no reading

touch white generator no reading


Touch load side black no reading

Touch load side red 178 on meter

touch load side white no reading.


I think what this is leading to is a short on the red hot wire leading to inverter or from the power cord.


I think I need to remove power cord and see what the readings are...If I loose the reading when the red courd is unhooked it means I have a short in the red lead in the shore power cord. If the reading is still there, it is between the ATS and the inverter.


Is this correct?

Expert:  Randall replied 6 years ago.
Check the reading on your meter...........sounds like you might have been on the wrong scale. There is no way you can get that high a reading on an AC circuit. Make sure you were on the AC Volts scale or some have just a curvy line for that scale and a straight line with some dots under it for the DC scale. And are these on the new or the old ATS? That part isn't clear to me. You may have a problem in the should be reading about 120 VAC between the BLACK and WHITE and then the same between the RED and WHITE leads on the cord. Black lead to the white wire. Red lead to the postive feeds. Be sure they are plugged into the meter in the correct places........on the Volts or Ohms pin and not on the "A" or "mA" pin. Those are for reading amps. Get back to me with what you find. I will be out all day and returning this evening. I will check back in then. R.J.
Customer: replied 6 years ago.
OK...I was using the ohms side. I can change to voltage and retry...
Customer: replied 6 years ago.



Shore power side red 122, the balck is 124


load side red is 122 and black is 124



Expert:  Randall replied 6 years ago.
That is a good reading...........does everything work now? The minor difference is just due to the variance in the loads hooked up.........perhaps the charging of the inverter. Get back to me if there are remaining issues to be resolved. R.J.
Customer: replied 6 years ago.
Still can't run 50 amp stuff. Namely A/C. I still have to beleive it is between the pole and ATS.
Expert:  Randall replied 6 years ago.
Those voltages you showed were good..............what about the voltage at the OUTPUT screw of the breakers that control the A/C? What do you have there? R.j.
Customer: replied 6 years ago.
Expert:  Randall replied 6 years ago.
All good..........What about the voltage OUT of the actual service breakers that go to the A/C units? Do you have any kind of EMS system on this? (Energy Management System) If so, what is the make and model? R.J.
Customer: replied 6 years ago.

The ATS switch disconnects shore power for generator and vice versa.


It appears to me they use the same feed into the house coming out of the ATS.


If it doesn't then I am baffled. Yes we ahve an energy management system. It is a Xantrex Freedom 458. I read a little at the company web side...but there could be other stuff wrong with it...

Expert:  Randall replied 6 years ago.
I am not getting this to you...............the main breaker panel. Where the breakers are for the various circuits. What do the ones that control the air conditioners read at the outgoing wire? The Xantrex Freedom 458 is an inverter charger..........but has no affect on the air conditioner circuits. The air conditioners do have a 12 VDC control board and so if those fuses are bad OR the thermostat is bad then the air conditioners won't work. R.J.
Randall and 3 other RV Specialists are ready to help you
Customer: replied 6 years ago.
when on shore power 123 v front and 126 v rear
Expert:  Randall replied 6 years ago.
Then this A/C problem is more likely not a result of not getting the proper power to the unit.
More likely the thermostat or a DC voltage problem. What is the make and model of the thermostat? Digital or analog? We can try to track down the source here of the problem. And do you have just one thermostat or two?
Customer: replied 6 years ago.

OK. Power is about the same when we tested with the generator.


So, I am with you...thermostat or there is a circuit board in the breaker box once I took the cover off. I know nothing of the circuit board diagnosis.


There is just one thermostat. That is a fairly common part. I will take it to the shop on Wednesday and let them deal with the rest of the problem.


I feel you have helped me through more than the origonal issue was...There actually were three shorts in the ATS. We got that back on the right track. Now the thermostat or the voltage to the thermostat is a different issue.


You fulfilled your part of the technician part.


THanks for your help patients and advice.

Expert:  Randall replied 6 years ago.
Glad to assist...............get back to me if you want to do some checking on the other. Some thermostats have a fuse..............pull the cover off and check that. Some feed the AC power in from a furnace and the 12 VDC breaker in the furnace can trip and then you have no power to the thermostat. Also check the fuses or resettable breakers in the service center to see if that is the problem. I suspect it is one of these.

Thank you for the generous bonus............much appreciated! Please tell your friends about our service here at Just Answer. Most of the time we can get you an immediate answer and save you a bunch of $$$ as well. Please come back again if you have another issue "down the road" and be safe! R.J.