Breakers not tripping, when direct short to ground.

[OK Sparky 93]

Went on a call to a mobile home. The customer states that the furnace just shut off through the night. I get there and discovered in fact that’s the furnace had a direct line. No splice.
I observed the furnace appear to be operating normally. The Cust. Turned on another breaker which caused the fan speed to drop way down. The furnace indicated that it had reverse polarity. Indeed it did.
also at the panel observed that it appeared that I lost a phase. And the ground bus and the frame of the trailer were energized.
I went through each breaker until it went away. Front porch light. Line side connection at the light. Clear the light connection things are working. But are they?

Why didn’t the breaker trip?

 

[GoldDigger]

Two strong possiblities:
1. The breaker is defective. Like some Federal Pacific breakers, and simply will not trip anywhere near the design amperage.
2. There is enough resistance in the circuit and the "dead short" that it does not draw enough current to trip the breaker.
The second possiblity is less likely given that the current drawn is enough that the voltage drop in the service conductor is approximately the line voltage.
I suspect, based on your other findings, that there is also a compromised neutral and an incorrectly bonded ground system. The fault current is trying to return through the ground electrode system instead of through the neutral.

 

[marmathsen]

also at the panel observed that it appeared that I lost a phase. And the ground bus and the frame of the trailer were energized.

What sort of tool did you use to determine the ground bar was energized?

Rob G

 

[LarryFine]

I suspect, based on your other findings, that there is also a compromised neutral and an incorrectly bonded ground system. The fault current is trying to return through the ground electrode system instead of through the neutral.

Agree and thought as much as I was reading it.

There is likely a weak or missing bond between the trailer chassis/skin and the service neutral.

A trailer is always supposed to be wired as a 4-wire load, but depends on an intact EGC and service bond to function.

 

[OK Sparky 93]

What sort of tool did you use to determine the ground bar was energized?

Rob G

The volt / continuity tester I have detects which line is hot. The customer was also getting shocked messing around under trailer.
240v phase to ground

 

[mopowr steve]

Sounds like a bad neutral connection somewhere