Help Me Troubleshoot 120VAC Please !

[BC Bus]

this is a new problem.

When I plug in my RV shore power cord it trips the breaker in breaker box in the campground,(or my house)  instantly like a direct short. This has been working fine for  many months and I just can't figure out where to even start troubleshooting.

Here is the set up :

I have a 30 AMP RV plug going into a tarnsfer switch, with a generator also going into the same switch.  the main power supply box then feeds to all of the circuits including with one going to the Trace dr 2424 inverter with a pass through circuit going into a sub panel and out to a few items.

Like I said this has worked fine until two days ago and now it started tripping the source power breaker.

I turned all of the breakers off, including the breaker that provides power to the inverter, in the bus in both the main panel and the sub panel and it still trips the breaker at the source instantly if I plug in the shore power cord.

I have turned off all AC power, and checked continuity between the white and black wires in the power supply box and I dont get any continuity between blacks and the white.   Does this mean there are no direct shorts in the circuits?  

There is continuity between whites and green, this should be the case, correct?

I suspect that the shore power cord may be bad so I will check it for a direct short this afternnoon.

I am interested in your ideas and possile troubleshooting methods,

Thanks,
Bill

[Sean]

I have turned off all AC power, and checked continuity between the white and black wires in the power supply box and I dont get any continuity between blacks and the white.   Does this mean there are no direct shorts in the circuits? 

Not necessarily.  Your transfer relay can be causing a short only when energized, which would not show up on a test with a low-voltage meter.

There is continuity between whites and green, this should be the case, correct?

No.  Ground (green) and neutral (white) should also read open between each other.  If they do not, you have a ground fault in the coach, which is dangerous.  That won't trip a shore breaker, though, unless it is the GFCI type, in which case it will trip immediately.

I suspect that the shore power cord may be bad so I will check it for a direct short this afternnoon.

That's definitely the right place to start.

I am interested in your ideas and possile troubleshooting methods,

There is really no substitute for disconnecting the main circuit at each junction point until the problem goes away.  That said, if all the branch circuits, including inverter/charger, are off, and there is no continuity showing between hot and neutral at the input, I suspect a problem in the transfer switch.

-Sean
http://OurOdyssey.BlogSpot.com

[papatony]

You are O K on your read outs . I would double check the relay box for a bleed thru to the generator . I f it is throwing  the breakers you have a dead short ,check for loose wire or bad connections.

[robertglines1]

 Caution       would not try until problem fixed: A loose wire in shore cord just cost me a tv,1 air conditioner,microwave,surround sound and satlite box.  Mine was a loose common wire in the male end of the 50 amp shore cord.   

[BC Bus]

Sean and Guys,

Thanks so far !  I meant to say transfer switch not relay.

The transfer swithch swithches all 3 wires.  I am going to disconnect all whites and start hooking then up until I find the direct short.  Somehwere the Green and whites are probably tied together or shorted.

It makes sense that testing the blacks to white will not help

[gcyeaw]

I a new to this forum, but not new to motorhome electrical circuits.

The electrical code requires the neutral and ground (white and green) to be bonded at the source. If the coach generator is the source, they will be bonded at the generator (prior to the transfer switch) , if an inverter is the source then they will be bonded at the inverter (an internal relay) , if shore power is the source then they will be bonded at the shore power source (the campground main power panel). If you are checking for a ground to neutral short (which won't trip a breaker other than a GFI) then you need to have the transfer switch set to shore power, the inverter shut off, and the shore line disconnected.

  I believe you are correct in suspecting the shore power cord, or a problem in the transfer switch or transfer switch wiring.

[BC Bus]

Got it fixed guys.

I unhooked all of the whites in the power supply braker box in the bus and this caused no breakers in the garage to trip.  With the shore power stil plug in i started to connect the white wires until I popped the breaker in the garage (shore power). 

I turned out to be the neutral wire going to the block heater had rubbed through the insulation near the block heater input. 

Thanks for all of your help ! 

Great board

[eagle19952]

Question ?
Does this mean that the block heater was also being energized,were you using the heater ?

[Sean]

Does this mean that the block heater was also being energized,were you using the heater ?

A ground fault will trip the GFI breaker even if the circuit is not energized.

The neutral having rubbed through to the ground means that some of the return current from other circuits in the coach finds its way onto the ground through this single neutral-ground fault.

Since it was the neutral that rubbed through and not the hot, the branch circuit protection for that circuit would not trip.

-Sean
http://OurOdyssey.BlogSpot.com

[napamikey]

There is continuity between whites and green, this should be the case, correct?

I had exactly the same problem!  I was having a weird shorting problem as well when the breakers were all off.  Turns out that a white/green(ground) wire was touching in one of the kitchen outlet boxes.  I cleaned it up and all is good again.

Hope this helps.

Mike