500 VAC coursing through chasse

[Timnvt]

Out of nowhere I've got 500 volts going through the bus chasse. Dog got fried first.  I got fried twice before I could get a read on my voltmeter.
The bus is (was) plugged into 240 VAC shore power.  HOW in the world did I get 500 volts from chasse to ground (terra firma).

I do have a house bank of batteries and 120 vac inverter. But the inverter system is on a three position tripple throw manual switch disconnect so only the shore line or the inverter bank can feed power. Position one - shore power, position 2 - all off, position three - inverter power. I probably have the neutral bonding thing wrong. However, if I disconnect the shore line I have problem with voltage traveling through the chasse.

The inverter system seems to be working fine. But how can I be generating 500 volts?

Tim.

[Sean]

Was your bus parked under a power line?  Read here:
http://ourodyssey.blogspot.com/2009/07/shocking-experience-at-dump-station.html

-Sean
http://OurOdyssey.BlogSpot.com

[Timnvt]

No. Not under any power lines. I'm parked in my driveway packing to head out on a weekend trip in the morning! I checked my incoming power and all is fine feeding into the bus.  Funny.  We were working on the bus all day and no problems.  All of a sudden we've sprung a major voltage leak.

Tim.

[Nusa]

Start with the obvious. Use your meter to determine what the voltages on the shore line are. It's probably 240ish between the two hots. And probably 120ish between either hot and the neutral. But check that to be sure. Now check each line against ground and see what you get. And if all that looks kosher, find/make an actual earth ground and check against that....the "ground" on the shore line may not actually be ground.

edit...oh, wait...you're saying this is when you're NOT on shore power? If so, never mind.

[Timnvt]

Problem is only when connected to shore power.  I did check the curcuit breaker feeding the power from the garage to the bus and I had 120 on each leg to ground and 240 common.

[Sean]

You may have ground and neutral connected internally inside the coach.  That would have the effect of putting at least 120vac on the chassis, which is enough to give you a buzz.

500 volts is a different matter, though, and so I am wondering if your meter is set on the correct range?  I would expect to see a reading in the range of 20-100 volts, possibly 120 if there is both a ground fault in the coach, and an open neutral or ground on the shore connection.

Certain devices can create this kind of voltage, and, if there is a wiring fault, possibly put it on the chassis.  Examples are fluorescent and HID ballasts and electroluminescent displays.

-Sean
http://OurOdyssey.BlogSpot.com

[HighTechRedneck]

Certain devices can create this kind of voltage, and, if there is a wiring fault, possibly put it on the chassis.  Examples are fluorescent and HID ballasts and electroluminescent displays.

If the meter is reading correctly, then this would make the most sense to me because if it was 500V and had the high current potentials of line power, Tim's dog would be dead and Tim would be in the hospital or worse.

[Timnvt]

Well, The dog ( big german shepard) laid on the ground for a couple minutes crying like he'd been run over by the bus. He couldn't hardly walk for a long time.  The meter is reading corrrectly! It hurts. The second hammer I took hurt my chest for a while. I have no doubt it's 500 volts.  Amps are what kills you isn't it?  I'm checking with the meter at the shoreline or gen/inverter switch at my bus electrivcal distribution panel.  All is fine going into the switch so long as the switch is in neutral (off) position.  As soon as the switch is activated the chasse is live.
I'm wondering if I have a bad transfer switch or is there some electrical device on board that might be malfuntioning that could cause a back feed while increasing the voltage.  Yet, I know I don't have any backfeed problem when running on inverter power which feeds the electrical devices through the same distribution panel so that would seem to rule out a malfuntioning appliance.

I think there is a problem with that transfer switch.  120 + 120 + short in switch to neutral. Does that equal 500 volts some how?

[Sean]

I think there is a problem with that transfer switch.  120 + 120 + short in switch to neutral. Does that equal 500 volts some how?

No.  If your house is wired normally, the most potential you can have between anything and the ground would be 120 volts.

A transformer would be required to step the 240 volts of house power up to the 500-volt range, and then the secondary would have to have one leg connected to (shore) ground, and the other leg connected to the chassis.  That should result in an immediate trip, because chassis and shore ground should be bonded (shorted together).

Before you go any further, I would connect the shore cord (with power to the receptacle OFF) and then check that the coach chassis and ground in the shore panel are connected.  Using an ohmmeter you should read less than 5 ohms.

I'm betting, for starters, that you are going to find this connection "open," and that's the first problem you need to correct.  This, ultimately, is what keeps you safe and ensures that any wiring problem aboard the coach can not create a hazardous voltage to ground.

Once you've corrected this problem, we can start to diagnose where the voltage is coming from.

-Sean
http://OurOdyssey.BlogSpot.com

[HighTechRedneck]

Yup, it is the amps that kill (actually 50-100 milliamps, iirc). But the higher the voltage, the more ability it has to drive a deadly amount of current through the body.

... or is there some electrical device on board that might be malfuntioning ...

That is what Sean was eluding to.  For example a wire leading to the bulb in a flourescent fixture that is somehow getting grounded.

The reason that makes sense relates back to the point about amps (milliamps) being the killer.  If the 500V had all the amps of the shore power at it's disposal, your dog almost certainly would not have made it and there is a strong chance that you wouldn't have either.  But if it only has a few milliamps of current (like is possible in flourescent lights, electroluminscent panels, plasma screens, etc.), then it bites you, but not lethally unless it hits just the right path to cross your heart.

[Timnvt]

You guys hit it right on. The fault is in the circuit feeding the fluorescent light fixtures.  With that circuit breaker off all is OK.  With that circuit on, 500 VAC!  Now to find where the short is.

Sean,  I will check the grounding that you described. Something must be wrong for no breaker to have tripped!

[bevans6]

My understanding, feeble as it is, would be that if you are getting the 500 volts from the fluorescent lamps you are getting it from the lamp side of the ballast, which may have some built in current limiting.  The high voltage is used to start the lamps.  So there would be no abnormal draw on the supply side of the ballast, hence no breaker would be expected to trip.  Look for a chafed wire on the run from the ballast to the lamp sockets inside the fixture.

Do you get the voltage when power to the lamps is on at the breaker, but the lamps are  turned off?  That would imply a wiring issue as well.

Brian

[robertglines1]

 breakers are tripped by to high of amperage....In this case you had high volt and not amperage..good post!! reminds us all of hard to find problems...I had a friend die in a electrical duct by 1/2 amp to back of neck..Steve was a journeyman electician and it was a locked out work area.the feed was from a contol monitor that wasn't isolated...be careful  Bob

[john9861]

Tim,
      Please keep this thread going as it shows exactly how dangerous electricity can be. This is an area too easily taken for granted, usually due to lack of understanding. The prevention, isolation of, & handling of this type of problem will be invaluable information. Thanks to those who are providing the diagnostic help that will hopefully educate the rest of us busnuts.

[desi arnaz]

i got to this thread way too late.  my first thought before reading anything was the ballast of  the tube lights. i hope the poor dog has not suffered any ill effects? did you find the exact place of the fault yet?