Close Call at Fire Station

[tom baker]

From a friend of mine comes the following question:
We had a close call at a fire station with possible electrocution.
> The ground was a piece of emt on the outside of a building with cast
> LBs that fed a second panel. A CADET overhead heater shorted out and
> cooked a LB fitting never tripping the breaker.
>
> A fireman came to me, since I'm the Safety Officer and told me he was
> getting a shock from a truck plugged into an outlet.
>
> I tested the outlet with a TrippLite tester to find all 3 lights on!
>
> I turned off the breaker and found 2 lights still on indicating the
> ground and power as reversed.
>
> 242VAC was on the surface mount conduit and truck chassis.
>
> QUESTION:
>
> If the outlet had been a GFI, would it have tripped and protected us?
>

 

[david]

Re: Close Call at Fire Station

Tom I assume the third light indicated an open ground. I also do not believe the equipment ground is run through the donut to trip the GFCI.

It sounds like the equipment ground was open on the line side of the LB and the fault was taken to the truck via the equipment ground load side of the LB.

IF I am right I do not see how this fault would establish an unbalance to trip the GFCI rec.

 

[BAHTAH]

Re: Close Call at Fire Station

I am not totally sure I have the system layout correct in your post but here goes. I assume there is a feeder conduit with LB's from the service to a second panel and then two conduits leaving the sub-panel, one going to the electric heater and one going to an outlet in the firehouse for the trucks. If the heater shorted out, it did so on the heating element leaving enough resistance so that the breaker did not trip, while destroying the LB fittting or the conduit fittings were not tight enough to provide a solid ground path, energizing the conduit and not tripping the breaker because of the resistance of the heating element or fittings still being apart of the circuit. The fireman felt a shock when touching the conduit to the outlet in the firehouse as he provided a return to ground. If my assumptions are correct I do not see a GFCI at the receptacle providing any protection since the current would be from the faulted heater and not the load side of the receptacle. This is just my opinion based on what may not be the correct layout of the system.