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#97980 04/29/06 08:07 PM
Joined: Jul 2004
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There was a picture floating around a while ago showing a piece of RMC with the side blown out by a fault in a service conductor so that is not foolproof.
(IAEI Magazine maybe?)


Greg Fretwell
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#97981 04/29/06 10:31 PM
Joined: May 2003
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e57 Offline
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Nothing ever is... Foolproof that is.


Mark Heller
"Well - I oughta....." -Jackie Gleason
#97982 04/29/06 10:37 PM
Joined: Jan 2003
Posts: 4,391
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Quote
There was a picture floating around a while ago showing a piece of RMC with the side blown out by a fault in a service conductor

Was this it?

[Linked Image]

This is one of mine and I thought of posting it this thread but to be fair the available fault current here greatly exceeds that of a typical home service.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#97983 04/30/06 05:05 AM
Joined: May 2003
Posts: 2,876
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e57 Offline
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Was this the 4-4" on the side of a supermarket? 'Cause of that one ever figured out?

Also to be fair, I have seen some bad demo accidents where they send in gorillas to demo a building and go too far too fast.

Diamond blade through encased conduit, wall supporting panels removed leaving panels in mid-air until they gave under thier own wieght. And a feeder with a 3/8 drill through it, and the MOCP failed to trip. I have also had one go off right in my hand. I was closing a cover and a kearny broke loose and popped through the tape against the cover I was holding in my hand. A little pinch against the split side of a split bolt through the tape blew a 2" hole in the cover. Went off like a grenade! Accually lucky to see this screen right now. But I can appreciate the hazards, but the risk is low, as in rare, for a fault to happen on its own, all by itself. Outside of over-load/fault by circuit use and failure of MCOP, in which it would happen anyway for simular results, inside, or outside.

[This message has been edited by e57 (edited 04-30-2006).]


Mark Heller
"Well - I oughta....." -Jackie Gleason
#97984 04/30/06 12:11 PM
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Bob That is not the one I was thinking about but I remember that one too. Yours is probably better [Linked Image]

All you really have to do is think of an arc welder. Even a fairly small one will easily blow a hole in an eighth to 3/16 inch of steel. A bolted fault would eventually open the primary fuse but an arcing fault could go on, virtually forever. I was in the Keys a while ago watching a service drop boiling and jumping around in a puddle for more than an hour. It was amusing for a bar full of patrons who were smart enough to watch from a safe distance. It was still burning when the PoCo finally got there to pull the disconnect. By then all the water in the puddle had boiled away and the asphalt was smoking.


Greg Fretwell
#97985 04/30/06 12:43 PM
Joined: Mar 2005
Posts: 399
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After the fire in the building caused the insulation to fail, the service conductors started cutting a hole in the rigid conduit while the firemen were pouring water on the blaze. Twenty feet of pipe split open before it was done.
This was on a downtown grid that the utility counldn't disconnect because the fire was too close to the cut outs. Transformer fuses finally opened.
In the after fire report the fire department was trying to make it an electrical fire because they saw the arcing.
The utility company and I clarified that the fire caused the arcing not the other way around.
Further investigation showed suspicious origin, possible arson.
They didn't blame that one on the electricians.
Alan--


Alan--
If it was easy, anyone could do it.
#97986 04/30/06 02:24 PM
Joined: Jun 2003
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The cable installers always seem to find these types of "hidden" service entrance conductors.


Pierre Belarge
#97987 04/30/06 03:25 PM
Joined: Feb 2002
Posts: 840
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One of the amazing things about Bob's pic is the molten metal splattered all over the wall. [Linked Image]

The cause of this one? I think the terrorists are to blame. [Linked Image]


Peter
#97988 05/02/06 02:16 PM
Joined: Apr 2005
Posts: 73
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In Bob's picture, I would guess faulty insulation possibly damaged pulling it. All it takes is one bad piece of RMC with a burr of some sort.

I recently pulled new wire for some parking lot lights. I was amazed at the bad wire in that it looked to me like there was about 4" of copper gone and the insulation still intact. Maybe the water in the conduit kept insulation cool enough not to melt. I don't know. Any thoughts from you people?

#97989 05/23/06 09:07 PM
Joined: Feb 2002
Posts: 2,233
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Hey Greg,

The Sheriff is an AHJ is Norristown which I think is right outside of Philly. Also I remember reading somewhere that 1 or 2 states do this kind of service all the time. They install a service pipe right down in between the block and brick leaving only the meter pan and the service head exposed. I don't remember which state it was.

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