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Old 05-18-2022, 11:44 AM   #1
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Weird 120 VAC problem

I have a 2001 Itasca Sundancer 27P
I am having a electrical issue with my front AC circuit.

I know the circuit line. I have disconnected it.

If its hooked up to the circuit breaker it shorts out the AC line and sparks fly when I try to plug it in. If I measure the resistance on the line it reads open. If I read the resistance to ground and across the AC lines on the 30Amp plug I get a high resistance ( open ). When I connect the black wire from the bad leg I get a high résistance also so I'm not seeing any shorts.
Yet when I plug it in with that leg connected sparks fly, but doesn't trip the breaker.
I am really stumped because in my mind, if the resistance is in the 100's of kilohms I shoud not be seeing sparks fly.
Any idea what I'm missing here?
Thanks

Kip
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Old 05-18-2022, 12:52 PM   #2
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I'm thinking that your resistance measurements are giving the reading for an idle state. When you apply the 120VAC something kicks on and your short is back. Consider when you measure a relay coil you will see the high resistance of the coil. When the coil gets energized, the contacts close and bang.

I think there is a motor start capacitor in there somewhere.
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Old 05-18-2022, 01:21 PM   #3
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Did you "zero" the ohmmeter first? A good battery in the multimeter is required for resistance readings.
But as mentioned, if the A/C thermostat is calling for 'cool', then the relay/fan motor will energize once AC is applied. This could be upwards of 8 amps inrush starting current.
Turn the thermostat "off" or up to a high temp.
Open the breaker and then plug in the cord. Use the breaker to energize the line, not the cord end, then turn the thermostat on to call for coolness.

You did mention the breaker does not trip, so I assume the A/C is working.


Good luck
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Old 05-18-2022, 01:33 PM   #4
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I'm a little confused as the OP appears to be referring to one of his Alternating Current lines, not Air Conditioning. And where exactly are the sparks flying from and what are you plugging in when they fly? Are you plugging in your main power cord and that's where it sparks but the breaker holds? What things are on the circuit you have isolated? If it's the air conditioner it could very well be what Jos said, there will be no compressor delay if the 12 volts is not interrupted because the compressor delay is built into the thermostat meaning an inrush of 5 to 6 times the running load (70-80 amps) that you won't see with the relay open. Try killing the 12 volts for a bit, then plug in.
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Old 05-19-2022, 06:21 AM   #5
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Update:
Let me clarify
I have some kind of electrical issue that I have isolated on one line.
This line appears to be feeding 2 outlets in the passenger side ( overhead bunk and TV outlet ) and 2 outlets in my bedroom slide.

With this line disconnected everything in my rig works ( all appliances and AC ) No sparks when I plug in.

This line reads open ( no resistance ) when I check it.

When I connect it back up to the 15 AMP breaker ( that it shares with the converter ) I will get sparks when I plug in the shore power . The breaker does not blow.

Yet, when I test the line I read opens line to line and line to grounds.
With this leg disconnect all of the other outlets and appliances work as normal.

These outlets worked a few weeks ago.
Its acting like there is a short somewhere, and yet, my ohm meter is not showing one on the actual line. Nothing is plugged into these outlets. This leg seems to only feed these 4 outlets.

After reading the replies I did check the rooftop air. It was off, and I did turn it on and it started normally.
I can't find any other appliance that might be hidden that I'm not aware of that might be connected to this leg.
All my usual appliances work with this leg disconnected : AC,fridge,micro, converter ( electric water heater is off, have not tested that )

I'm very perplexed. Is there some electrical device under the rig that might need power that I'm not aware of?

Thanks
Kip
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Old 05-19-2022, 09:43 AM   #6
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Here are the Body, 110 Volt Wiring Diagram and Body, 110 Volt Wiring Installation diagram for your coach. Inspecting them may help you identify where the problem might be.

You might also find the Wiring Diagram Help and Wiring Identification Guide useful as well.
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Old 05-19-2022, 09:58 AM   #7
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High resistance on the VOM meter designates continuity. A Zero reading is necessary for an "Open" circuit.
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Old 05-19-2022, 01:34 PM   #8
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So sorry, my bad.

I interpreted this "I am having a electrical issue with my front AC circuit." as the A/C (air conditioner)... should not ass-u-me I guess.
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Old 05-19-2022, 03:58 PM   #9
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Quote:
Originally Posted by TandW View Post
High resistance on the VOM meter designates continuity. A Zero reading is necessary for an "Open" circuit.
WUT?
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Old 05-19-2022, 04:59 PM   #10
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Quote:
Originally Posted by kwftlaud View Post
Update:
Let me clarify
I have some kind of electrical issue that I have isolated on one line.
This line appears to be feeding 2 outlets in the passenger side ( overhead bunk and TV outlet ) and 2 outlets in my bedroom slide.

With this line disconnected everything in my rig works ( all appliances and AC ) No sparks when I plug in.

This line reads open ( no resistance ) when I check it.

When I connect it back up to the 15 AMP breaker ( that it shares with the converter ) I will get sparks when I plug in the shore power . The breaker does not blow.

Yet, when I test the line I read opens line to line and line to grounds.
With this leg disconnect all of the other outlets and appliances work as normal.

These outlets worked a few weeks ago.
Its acting like there is a short somewhere, and yet, my ohm meter is not showing one on the actual line. Nothing is plugged into these outlets. This leg seems to only feed these 4 outlets.

After reading the replies I did check the rooftop air. It was off, and I did turn it on and it started normally.
I can't find any other appliance that might be hidden that I'm not aware of that might be connected to this leg.
All my usual appliances work with this leg disconnected : AC,fridge,micro, converter ( electric water heater is off, have not tested that )

I'm very perplexed. Is there some electrical device under the rig that might need power that I'm not aware of?

Thanks
Kip
Hello and sorry for your issues but it sounds like there is grounding problem. If something has rubbed thru the insulation and it is grounding out this is exactly what will happen. Sounds like there is a ground wire somewhere in the system that is grounded out.
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Old 05-19-2022, 05:11 PM   #11
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So the converter is on that breaker. So have you never ever plugged in a vacuum or a lamp or anything similar that happened to be switched on, and seen some arcing as the prongs entered the receptacle? That is what your converter is doing and what you are seeing. If this doesn't answer your question I am at a loss for what you are trying to explain.
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Old 05-19-2022, 07:39 PM   #12
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If you plug a shore power plug into an electrical supply and the other end of that shore power cord is attached to a converter (ie Battery Charger) that battery charger will instantaneously begin to supply a couple of hundred amps (DC) to the battery. Than translates to an AC power draw of 15-20 amps. Some sparking is inevitable as the plug first makes contact with the live AC receptacle
My suggestion is that, for starters, you stop plugging in your shore power without turning off the shore power breaker. The fact that no breakers ever trip indicates that you do not have any sort of short circuit or over current fault.
So turn off the pedestal breaker, plug your shore cord in and then turn on the pedestal breaker. No more sparks, all good.
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Old 05-19-2022, 07:50 PM   #13
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Quote:
Originally Posted by TandW View Post
So the converter is on that breaker. So have you never ever plugged in a vacuum or a lamp or anything similar that happened to be switched on, and seen some arcing as the prongs entered the receptacle? That is what your converter is doing and what you are seeing. If this doesn't answer your question I am at a loss for what you are trying to explain.
I don't think the converter is the issue because he says the circuit in question "shares the breaker with the converter" so the converter is connected when he plugs in and gets no sparks. From what he is telling us so far there is no load that he can account for.
I would like to know more about the sparks, a load spark/arc is not exactly the same as "shooting sparks". I have seen a short that causes shooting sparks but clears itself before the breaker trips caused by a single strand shorting out and melting, but not numerous times.
I'll be standing by waiting for more info.
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Old 05-19-2022, 08:01 PM   #14
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@Bigb56 I guessed that the OP was saying that the sparks flew when plugging the shore power cord into the power pedestal. Nothing else that I could think of made any sense. Of course checking the circuit with an ohmmeter doesn’t show any problem because the Converter doesn’t start drawing a load until it sees 120VAC at its input but when the 120VAC shows up then it’s “Katy bar the door!”
Also, @TandW I think you meant to say just the opposite of your description of how to interpret a multimeter when measuring resistance.
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