Wild Leg Theory for 480 3 Phase Involving A Fire

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cyado1607

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just recently had a 480v 3 phase 400 A pole mounted service catch fire. Here is what happened:

after the fire it was determined that the wild leg had welded iteself together with another phase at the weatherhead. The power had initially gone out for a little while and then kicked back on and stayed on until then the whole thing went up in smoke. Anybody have any ideas of why this might have occured this way? Or give me some more input on the wild leg?
 
cyado1607 said:
just recently had a 480v 3 phase 400 A pole mounted service catch fire. ...after the fire it was determined that the wild leg had welded iteself together with another phase at the weatherhead. ... Or give me some more input on the wild leg?
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If the system was in fact a "wild leg 480V, 3ph", it likely is the only one in existence. Never seen one, never heard of one. It is physically possible to build one, however, there is no use for one.

With a high degree of confidence, I'd say there is no wild leg on 480V, 3ph.

carl
 
cyado1607 said:
... Anybody have any ideas of why this might have occured this way? ...
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Just the obvious one. The OCPD was not set to protect the transformer.

If the transformers were utility owned, then the NESC governs the installation and it's okay and quite reasonable for the transformers to burn up.

If the transformers were customer owned, then the installation is subject to the NEC, and the burn up is now terrible and disgusting.

carl
 
coulter said:
With a high degree of confidence, I'd say there is no wild leg on 480V, 3ph.

carl
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I recall hearing of 480V 'high leg delta' systems being used to avoid the requirements of 230.95. I have no direct experience with this, so consider it a rumor until substantiated. It wouldn't apply in this case anyway, since 230.95 applies to 1000 amp services and above.

-Jon
 
cyado1607 said:
after the fire it was determined that the wild leg had welded iteself together with another phase at the weatherhead.
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Out of curriosity, who made this determination?

Roger
 
coulter said:
If the system was in fact a "wild leg 480V, 3ph", it likely is the only one in existence. Never seen one, never heard of one. It is physically possible to build one, however, there is no use for one.

With a high degree of confidence, I'd say there is no wild leg on 480V, 3ph.

carl
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Must have been some use at one time. Look under the 'MAINTENANCE ONLY' on page 2

http://www.jocarroll.com/uploads/approvedsockets(2).pdf
 
winnie said:
I recall hearing of 480V 'high leg delta' systems being used to avoid the requirements of 230.95. I have no direct experience with this, so consider it a rumor until substantiated. It wouldn't apply in this case anyway, since 230.95 applies to 1000 amp services and above.

-Jon
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Don't know why anyone would do that, 230.95 says 150V to ground - it wouldn't apply no matter what the current level.

carl
 
What about an open delta bank where X2 is grounded? This would give them a high-leg.
 
Whether there is a high leg or not, on a Delta system, the line-to-line voltage is the same all around. If one phase welded itself to another, the voltage to ground is not a factor.
 
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