?? What Happened ??

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Existing switchboard energized at 480Y/277 volts, with 1200 Amp Class L fuses; 200,000 Amps A.C.

Switchboard feeds a lighting panel with 100 Amp switch, with 100 Class RK5 fuses; 200,000 Amps A.C.

When lighting panel was de-energized for some building renovation, the electrician meggered and checked the feeder for continuity.

All branch circuit breakers in the lighting panel were in the off position.

When lighting panel was re-energized, all three 100 Amp fuses failed and destroyed the 100 Amp switch, and also took out the 1200 Amp fuses.

Why did this occur??
 

zog

Senior Member
Location
Charlotte, NC
Ole'sBuddie said:
Existing switchboard energized at 480Y/277 volts, with 1200 Amp Class L fuses; 200,000 Amps A.C.

Switchboard feeds a lighting panel with 100 Amp switch, with 100 Class RK5 fuses; 200,000 Amps A.C.

When lighting panel was de-energized for some building renovation, the electrician meggered and checked the feeder for continuity.

All branch circuit breakers in the lighting panel were in the off position.

When lighting panel was re-energized, all three 100 Amp fuses failed and destroyed the 100 Amp switch, and also took out the 1200 Amp fuses.

Why did this occur??

Sounds like either the insulation was damaged by improper meggering methods or the installation wasnt done right and they didnt actually test it, or didnt test it right.
 

jghrist

Senior Member
ptonsparky said:
You may not be hearing the complete story, just what they want you to know.
Like maybe that they connected phase conductors together to megger them all at once and then didn't take the jumpers off.
 
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