Dirt, Metal siding, and metal frame shock

[resistance]

I'm on my way to a service call, and would like some input before I get there. Here's what I know [had someone else go out before me]: 1. Voltage reading--using a digital meter--shows 120v when touching one probe to mobile home, and sticking the other probe in the dirt. 2. I had him turn off one breaker at a time, and he immediately found the circuit that's causing the problem. 3. I was told they had a person (non-electrician) over at the mobile home doing some wiring. 4.My guy says a number of wiring violations noticed at a few electrical boxes, he also noticed that one metal box shows a small spark when the EGC touches the metal box.

The good news: We know which circuit.
The bad news: It's a mobile home.

any thought?

 

[ceb58]

The good news: We know which circuit.
The bad news: It's a mobile home.

That's about it. Just a matter of tracing it out until you find the problem.
Do the people that live in the MH own it or are they renting? If they are renting has the owner give the OK to do the work? Who is going to pay?

 

[resistance]

Renting, and we are well aware of the business portion of the deal.
Thanks for the input!


Can anyone offer up any science in the matter?

 

[Jim W in Tampa]

Would start by checking everything the handy man was into. You have it down to 1 circuit so should not be hard. Find the middle of this circuit and see what half has the problem. Keep dividing till found. Chances are high someone reversed a hot and neutral. Might take half a day or more, so warn them about cost upfront.

 

[hurk27]

I'm on my way to a service call, and would like some input before I get there. Here's what I know [had someone else go out before me]: 1. Voltage reading--using a digital meter--shows 120v when touching one probe to mobile home, and sticking the other probe in the dirt. 2. I had him turn off one breaker at a time, and he immediately found the circuit that's causing the problem. 3. I was told they had a person (non-electrician) over at the mobile home doing some wiring. 4.My guy says a number of wiring violations noticed at a few electrical boxes, he also noticed that one metal box shows a small spark when the EGC touches the metal box.

The good news: We know which circuit.
The bad news: It's a mobile home.

any thought?

The above in red tells me this home is not properly bonded, I would more then bet there is no insulated EGC ran with the feeder cables to the home, there is no current path for a fault, and some where a load has return current being placed on the grounding, two very common things that I find is electric water heater element gone to ground, or an electric cloths dryer that the element has gone to ground, now with an inexperienced person who has tried to fix something that he doesn't understand anything goes, grounded neutral, miss wiring, who knows.

One of the first things I would do is make the bonding right, as right now you have a whole trailer sitting there with 120 volts that anyone could walk up and touch, including a child!

 

[G._S._Ohm]

Load it with an incand. bulb to check if it's a phantom voltage although a shock almost certainly means more than 1 mA flowed.

 

[Jim W in Tampa]

There should be a bonding wire from panel ground to frame. If trailer is old that connection might be damager or making poor connection. If it was working the breaker would be tripping. Do suggest it gets fixed fast

 

[resistance]

The above in red tells me this home is not properly bonded, I would more then bet there is no insulated EGC ran with the feeder cables to the home, there is no current path for a fault, and some where a load has return current being placed on the grounding, two very common things that I find is electric water heater element gone to ground, or an electric cloths dryer that the element has gone to ground, now with an inexperienced person who has tried to fix something that he doesn't understand anything goes, grounded neutral, miss wiring, who knows.

One of the first things I would do is make the bonding right, as right now you have a whole trailer sitting there with 120 volts that anyone could walk up and touch, including a child!

Actually the home did have a properly sized EGC. The home's non-service rated panel did not have the white conductor's isolated. We also found the hot and white conductors reversed--on the circuit causing the problem. Not to mention the same circuit did not have the EGC's "made" continuous. I was able to get rid of the problem by simply reversing the the hot and white conductor. We plan to return to do a full check of each electrical box in the home.
--It was at 3mA.

 

[hurk27]

Actually the home did have a properly sized EGC. The home's non-service rated panel did not have the white conductor's isolated. We also found the hot and white conductors reversed--on the circuit causing the problem. Not to mention the same circuit did not have the EGC's "made" continuous. I was able to get rid of the problem by simply reversing the the hot and white conductor. We plan to return to do a full check of each electrical box in the home.
--It was at 3mA.

So how was there 120 volts to the frame or siding of the trailer if it had an EGC with the feeders?

There should be a EGC that most of the time runs from the grounding bar in the trailer panel down to a place on the frame just under this panel, if that connection is there, there is no way a branch circuit can energize the frame or siding of this trailer, touching a hot from a branch circuit to the siding would open the breaker for that branch circuit, also since 1993 all feeder EGC's have to be green insulated.

We had a contractor from Michigan who was wiring trailers in parks around here that would put a ground rod at the trailer and run a green #6 in with the feeders to the panel, with the neutral bar isolated from the ground bar there was no fault path back to source, and inspectors didn't catch it as they thought that the #6 was ran with the feeders all the way from the service, well one day an elderly friend of mine who lived in one of these parks came home on a rainy day, and grabbed the door handle holding on to a metal stair handrail and was electrocuted, luckily she she made it but was in a coma for about 2 months, We call in the state HUD inspector as well as our state AHJ, and we found that the water heater element had gone to ground, so with just a ground rod for fault current path, instead of the breaker tripping it caused the trailer siding to heat up to 120 volts to earth.

This is why I bring this up as it is very easy to miss if you don't verify the other end of that EGC, and the fact you said the siding went to 120 volts to earth.

 

[G._S._Ohm]

--It was at 3mA.

More than 10 mA is supposed to be painful and 20 mA or so is the let-go threshold.

"inspectors didn't catch it as they thought that the #6 was ran with the feeders all the way from the service"
There must be some simple, safe way to test for this.

 

[LarryFine]

Can anyone offer up any science in the matter?

Something is obviously energizing the chassis, which should be easy to find knowing the circuit.

The questions are 1) what, 2) is there a neutral or neutral/EGC bonding issue, and 3) why no OCPD is opening.

 

[resistance]

We had a contractor from Michigan who was wiring trailers in parks around here that would put a ground rod at the trailer and run a green #6 in with the feeders to the panel, with the neutral bar isolated from the ground bar there was no fault path back to source, and inspectors didn't catch it as they thought that the #6 was ran with the feeders all the way from the service, well one day an elderly friend of mine who lived in one of these parks came home on a rainy day, and grabbed the door handle holding on to a metal stair handrail and was electrocuted, luckily she she made it but was in a coma for about 2 months, We call in the state HUD inspector as well as our state AHJ, and we found that the water heater element had gone to ground, so with just a ground rod for fault current path, instead of the breaker tripping it caused the trailer siding to heat up to 120 volts to earth.

Wow!! In this case the EGC (From the main to the home) is ran properly. But, the ground bar (Inside the home) was energized--from the one neutral (white) conductor associate with the circuit that killed the problem immediately after we turned the one 15A breaker off. We isolated the grounding from the grounded conductors, and corrected the wiring, and that fix the problem. Yet, I will be going back, for a more in depth look at everything. I dont see a bad element as the problem---seeing that the H2O is not associated with the "15A" circuit. I should mention that the breaker did trip, if we tried to splice the black, and white conductors correctly. My only conclusion: The Neutral conductor energized the ground bars---leading to the problem of the chassis, and frame being energized. Note: The Grounding, and grounded conductors where not isolated in the beginning.

 

[resistance]

I should add the ground bar layout before we isolated the conductors. The white conductor from the bad circuit was on the same ground bar as the Main EGC. The EGC from the main was isolated from all other egc's and including the cabinet (Basically, it was operating as a neutral in a sub-panel ), but was connected to all the white conductors--via bonding jumper. The branch circuit egc's where bonded to the cabinet (only)--having no connection to the main EGC. The white condutors where as mentioned above--connected to the main EGC.

 

[resistance]

Update:
We did a check of every electrical box in the home. The trailer had all the proper EGC's grounds in place, and working as designed (with the correction of the improper termiation at the panel--as mentioned in an earlier post). We found a few problems and corrected them--mainly reversed wiring. After all work was done, we re-energized the house, and the 15 amp breaker that was causing the problem decided to trip immediately after turning it on. [Note: All boxes are up to code at this point, and all grounding looks good]. Well, I decided the process of elimination [on the 15a circuit], and found the problem. [Note: All power sorces begin at a light fixture box first. Switch loops for each switch leg]-->A cable at a light fixture box would cause the breaker to trip, if the black conductor (Which was reversed before we corrected everything) was connected to the source of power at the box. Well, we decided to eliminate the cable, and do a plug check--making sure everything worked without it. Well, everything worked fine, and the breaker held as designed. *** Where this cable goes specifically is unknown, but what we do know, is that when the cable (14-2 with ground) is reversed, the breaker will not trip, but would energize the frame--and other metal parts--of the trailer. We did take pictures of some live wires they buried behind the walls of the trailer. I'll try to post them if I can.

 

[G._S._Ohm]

when the cable (14-2 with ground) is reversed, the breaker will not trip, but would energize the frame--and other metal parts--of the trailer.

Therefore the hot side goes to the frame which does not have a return to ground or neutral?

This contradictory chain of events means that you are assuming something that is not true. I'd recommend getting fresh eyes to look at this.