Isolated conduit.

[itsmoked]

Yesterday a guy at a re-tasked cannery asked me some disturbing questions about an outlet he was trying to plug a TIG welder into. It was in a 208V setting. Seems he was getting at the outlet 120 from L1 to N and 208V from L2 to N AND 208 from L2 to the conduit! About then I told him to stay the %$#@ away from it all until I got there. I get there and the 'good Samaritan' non-electrical guy showed me the problem outlet and the subpanel where he'd just moved the white N wire to the neutral bus from the ground bus.

Turned out he'd color coded the wires starting in the outlet box according to the screws they landed on on the receptacle. I informed them that there was no ground visible and that the outlet should be L1, L2, GND not L1, L2, N. I realized they had the GND in the recep L1 and L1 in the recep GND! I re-marked the N whites to green on both ends and re-landed it on the GND bus and the recep GND. Moved the red L1 back to the recep L1 and recognizing that the recep had a big brass bar that lead down to the recep mounting screw wondered why there hadn't been an immediate breaker tripping ground-fault.

On closer inspection it was found that a rubber insulator was installed at the receptacle box AND the subpanel completely isolating the EMT from both ends thru two interposing businesses.

I removed both isolators.

Can anybody posit a rational about why this had been done decades ago "by an electrician" and then all nicely painted over?



Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Easy.
1. It wasn't done by an electrician.
2. That brass bar or something like it is a standard feature on receptacles. It's been there since the days when the conduit was used as the grounding conductor to connect the receptacle ground terminal to the junction box and through that to the hopefully grounded conduit. or EMT. The insulators/isolaters were the non-electricians solution to the breaker tripping.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dpc]

Doesn't seem to apply here, but years ago, conduits containing instrumentation circuits were sometimes isolated completely from the plant grounding system and instrument grounds tied to the infamous "quiet" ground system that was "isolated" from the normal ground. It was abandoned a long time ago since it was an NEC violation and potential safety hazard.