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Old 02-23-2016, 09:24 AM   #1
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Help!! Advice for electrical issue. Not sure what we did.

Just purchased a 06 class A DP. The unit was plugged into 50a SP and owner fired up the gen before unplugging the SP. Thus, we were pushing power from 2 sources at the same time. I am not sure this is a good idea.

Owner turned on the rear air and in a minute or so we started smelling burning. It was definitely electrical fire! We shut everything down to find the source. We fried the Convection / Microwave!

Owner had never used a protection device so my first investment was purchased one at CW for the SP/50a. Ok, this should take care of that and the other appliances appear to still be working fine. Here are a few questions.

1. What do you think caused this? I am told it is safe to be plugged in and run the gen.

2. The fwd TV/entertainment system is plugged into a standard surge protector which was turned off at the time. Should I just continue to use that device for those electronics?

3. The bedroom set is plugged into standard 110 coach outlet. Should I put a surge protector on that?

4. This new convection/microwave is costly and the previous one we fried was plugged directly into the overhead cabinet 110 outlet with no powerstrip/protector. Is that the SOP? Should I find a protector of some kind and if so give me your recommendations.

Thanks!! James
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Old 02-23-2016, 09:40 AM   #2
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FWIW If everything was working correctly it should not make a difference. When the generator is started it runs for roughly a half minute while the engine settles down then turns on the AC. The presence of AC from the generator causes the transfer switch to trip changing the coach internal AC power from the line cord to the generator. That can introduce a very short term power spike that your protection circuit will not catch if it is in the power line from the pedestal to the transfer switch.

If the microwave was on during the transfer then the power spike might have been a problem for the microwave power supply. That might be what the problem was. OTOH that is somewhat of an aberration as there is no good reason to run the generator when AC is available from shore. If one wants to go to generator power under those conditions a wise person would not be running either the A/C, the microwave, or any other high current loads. That is asking for trouble from the switchover spike. It is also detrimental to the transfer switch.
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Old 02-23-2016, 09:54 AM   #3
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I've fired up my gen set many times with the coach on shore power; although probably not a great idea, I haven't found anything in the ATS booklet that warns against it ; I would assume the first item to be effected would be the Auto Transfer Switch, then the A/C units if they were turned on with the two sources.

If the Con/Mic fried without being turned on , I would think ; maybe ; some kind of cleaner or fluid from cleaning got in somewhere it shouldn't have been.

A previous owner had installed a single circuit surge guard at the C/M outlet in my coach, and I've continued to use it, and have installed a hardwired 50 amp protector in the shore power for the coach.
If your entertainment systems are powered from an inverter as well as shore power then an additional surge bar would be a good idea.
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Old 02-23-2016, 10:04 AM   #4
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Like others had said, the transfer switch will not let 2 power sources go past it, so that shouldn't be a factor.

If the oven or an AC or 2 were running when it switched, then a drop then surge in power could fry stuff.

One other thing to check would be the output voltage on the generator. If it is running too fast, the volts go up.
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Old 02-23-2016, 10:27 AM   #5
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If your coach has a MSW inverter, there's a good chance that it's what fried your microwave. Things with timers and MSW frequently don't play well.
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Old 02-23-2016, 10:36 AM   #6
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The transfer switch may be bad. I always unplug from SP before cranking the genie or kill the genie before plugging into SP. Old habit from switching Industrial type generators (had to wait for everything to equalize before switching).
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Old 02-23-2016, 10:43 AM   #7
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Find out what transfer switch you have. There was a recall on certain models. Caused several fires.
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Old 02-23-2016, 10:52 AM   #8
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Originally Posted by ernieh View Post
If your coach has a MSW inverter, there's a good chance that it's what fried your microwave. Things with timers and MSW frequently don't play well.
The microwave should not be running off the inverter if switching between shore and generator power.
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Old 02-23-2016, 03:47 PM   #9
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It really doesn't matter if the microwave was "on" when the generator was fired up. The controller in the microwave is always powered up (the buttons turn on displays and operate the heating elements (microwave or convection) but it is always alive when power is applied. I never run both shore power and the generator at the same time.

The transfer switch is only supposed to connect one at a time, but when it decides to switch the two sources aren't synchronized so you can go from the positive peak of one source to the negative peak of the other. That is an instantaneous swing of about 300 volts into everything connected to the AC lines. It's no different than the normal swing as far as voltage is concerned, but it happens in microseconds instead of milliseconds.

I suspect that is what fried the microwave. It's also the reason I avoid running both shore power and the generator at the same time and letting the transfer switch decide to swap inputs. It's a high stress change over if both are running. Your mileage may vary.
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Old 02-23-2016, 05:06 PM   #10
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Transfer switch fried !!

Transfer switch fried! Model ATS 5070

Progressive Dynamics Inteli-Power 9200 Series Converter/Charger seems to be ok.

Lesson here... I think never chance firing up the gen-set while hooked to SP even though it is supposed to not hurt anything. We are talking electricity and components and in my mind that push from both ends can and I believe in this case caused some very expensive repairs.

Just glad it did not fry anything else.

lastly, should I put some kind of protection device on the convectionwave oven where it plugs into 110 outlet?

Thanks for all the advice!! James
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Old 02-23-2016, 10:25 PM   #11
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I make it a habit to remove heavy loads when switching between the two systems.

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Old 02-24-2016, 06:09 AM   #12
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Switching heavy loads is the problem, not just switching. The current spike when the out of phase power is applied causes the damage.

If the ATS still works then there is no reason to replace it. It is a dumb relay that does not monitor phase angle or worry about matching phases. Neither does the generator controller. It is not an issue for normal operation of starting and using the generator when there is no shore power available. The only reason to protect against it would be if someone was making a habit of being stupid as opposed to making a mistake.
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Old 02-24-2016, 06:14 AM   #13
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The Shore ground should be removed when running the generator. The coach chassis becomes ground when running the genny. We always unplug and make sure the ground pin is not touching the ground or any water on the ground.
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Old 02-24-2016, 07:23 AM   #14
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In all areas of the U.S. Isolation of the generator and the shore cable is required by code to protect the electrical distribution system from back feeds. Your transfer switch serves this purpose and when properly installed and working will cause no harm under these conditions. Many RV manuals actually call for this when doing monthly generator exercises.

The fault or potential problem is starting the generator or connecting the shore cable under load. In all cases, the breakers should be off until connections are made, transfer has happened and so on. If not, all sorts of spikes, noise, transients, and potential problem situation can cause subsequent problems.

While many will say this is not a good practice, the system is designed to be foolproof and not cause any problem that were operator injected, assuming everything is working correctly.

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