Trailer house frame energized

[tschepers]

I got a call from a guy that was working under a trailer house and was getting shocked from the metal frame of the trailer home.

What could cause this?

 

[infinity]

How was he getting shocked, from the trailer to the ground? Could be many things, one the trailer isn't grounded and there is a fault in the wiring somewhere energizing all of the metal parts.

 

[ptonsparky]

Neutral bonded at the trailer.
Neutral compromised anywhere from POCO transformer to trailer service disconnect.
Similar condition anywhere in mobile home park.

 

[erickench]

Take a look at NEC 552.56(A). All exposed metal parts including frames have to be bonded to the grounding terminals or enclosure of the distribution panelboard. If a hot wire is touching that frame then the OCPD should've tripped.

 

[IamJonscranium]

How was he getting shocked, from the trailer to the ground? Could be many things, one the trailer isn't grounded and there is a fault in the wiring somewhere energizing all of the metal parts.

Take a look at NEC 552.56(A). All exposed metal parts including frames have to be bonded to the grounding terminals or enclosure of the distribution panelboard. If a hot wire is touching that frame then the OCPD should've tripped.

Can these two comments be reconciled? Would lack of ground cause the OCPD to not function?

 

[jumper]

Can these two comments be reconciled? Would lack of ground cause the OCPD to not function?

If the trailer frame is not grounded/bonded and becomes energized, how would the OCPD trip? There would not be any current flow.

 

[IamJonscranium]

If the trailer frame is not grounded/bonded and becomes energized, how would the OCPD trip? There would not be any current flow.

I agree with you.

From another thread, which is why I asked the question:

Hard to interpret your questions using only the word "ground" to mean several aspects of a properly wired system, but...

Neutral is typically bonded the grounding system at or near the power source. The grounding system has equipment grounding, non-current-carrying metallic parts grounding, and also earth grounding (the grounding electrode system, GES). Losing any part of this grounding system will still allow over current devices to trip as long as the remaining paths provide sufficiently low enough impedance for the fault current to return to the source.

I'm probably missing something...

I IM'd Smart with a link to this thread. Hopefully he or one of you can clear it up for me.

 

[infinity]

If the trailer frame is not grounded/bonded and becomes energized, how would the OCPD trip? There would not be any current flow.

Exactly. I've seen something similar happen to a radio antenna hut on the top of a building. The big structure about 10'X30' was made of metal prefab sections and sat on a steel I-beam frame. Between the frame and the hut were rubber insulators. The EC temped out the panel in the hut with a 3?, 4-wire feeder in free air and failed to bond the neutral in the panel. A short to ground in a light fixture energized the entire metal structure for days before it was found.

 

[Smart $]

Can these two comments be reconciled? Would lack of ground cause the OCPD to not function?

Yes... but it may not be a grounding issue.

There is a fault somewhere, without a doubt. Even if the frame is grounded, the fault may be resistive, thus not allowing enough current to trip the breaker.

The bonding jumper connection to the frame, if present (usually installed by the manufacturer, though), may be corroded and resistive rather than solidly connected.

If the person getting shocked is touching the frame at a point remote to where it is grounded and much closer to where the fault is occuring, he is completing one path back to the source. It does not take much current to get shocked.

 

[hillbilly1]

As with many trailers the "electrician" ran only three wires to the panel, instead of four. The missing wire is the equipment ground. Now to complicate things, there is a fault to ground, either from the wiring, or an appliance or fixture. If you turn off the power to the trailer, install a jumper between the nuetral bar and the ground bar in the trailer panel, you will very likely have one of the breakers in that panel now trip. You now have narrowed down where the fault is coming from. Keep dividing that circuit until you find the problem. By the way, to correctly fix the other problem, you need to get that fourth wire from the service disconnect to the panel and correctly ground the trailer, do not just drive a couple of ground rods and think your grounding the trailer.

 

[IamJonscranium]

Yes... but it may not be a grounding issue.

There is a fault somewhere, without a doubt. Even if the frame is grounded, the fault may be resistive, thus not allowing enough current to trip the breaker.

The bonding jumper connection to the frame, if present (usually installed by the manufacturer, though), may be corroded and resistive rather than solidly connected.

If the person getting shocked is touching the frame at a point remote to where it is grounded and much closer to where the fault is occuring, he is completing one path back to the source. It does not take much current to get shocked.

Thanks.