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#150203 - 11/12/04 11:09 AM AFTERMATH
rad74ss Offline
Member

Registered: 04/19/04
Posts: 154
Loc: Pryor, OK USA
This was not one of my units, but I saw the aftermath.

Here is the short list.

248V between the metal wall and ground. Which was first noticed by the guy leaning against the wall. Then he touched it again "just to be sure it was live."

This also destroyed the PLC, the VFD, exothermically welded the power block to all of the wires connected to it, and welded the portable heater to the deck.

The fan runs CW through remaining VFD and CCW in bypass?

Tops of main fuses melted, but fuses did not blow? Maybe the arc flash from adjacent power block melted them?

Odd thing was that when they tested the questionable leads to ground there was no continuity. This was before it blew.

Maybe a split in the insulation waiting for enough potential to jump to the conduit? Maybe said insulation was stretched thin, then melted through when energized.

Lab guy was almost in tears. I told him he should take the burned out parts to his boss then ask for a couple of days off.

This was a huge unit and will probably take a week to comb through for any more problems and fix the current problems.

As a side note on my unit the guy doing the cannon plug managed to get almost every pin in the wrong spot. I repaired it myself and told him to ohm out every wire on the entire unit before he proceeds. Then I would do it again myself when he was done, before testing. I guess he didn't understand when I told him one wrong pin could blow up around ten thousand dollars worth of the governments equipment. I hate hawkeyeing people but this stuff has to be perfect the first time around.

So, how was your day?

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#150204 - 11/29/04 04:10 AM Re: AFTERMATH
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Robert,
 Quote:
248V between the metal wall and ground. Which was first noticed by the guy leaning against the wall. Then he touched it again "just to be sure it was live."

I'd just like to ask why that wall or the whole building wasn't bonded to Ground, if it was metallic?.
That's the first thing that is checked by Electrical Inspectors here when a new building is connected to the Grid.
By the sounds of things, there wasn't enough Fault Current to blow the fuses.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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#150205 - 11/29/04 06:35 AM Re: AFTERMATH
rad74ss Offline
Member

Registered: 04/19/04
Posts: 154
Loc: Pryor, OK USA
Trumpy,

They were testing the unit outdoors. Someone had either tripped over or kicked the grounding lead that was connected to the unit and did not re-connect it. That was just another in a series of unfortunate events on that unit.

There was a safety stand-down for everyone in the plant, and a review of quality of work practices. Hopefully it will make everyone pay more attention to what they are doing.

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#150206 - 11/29/04 12:31 PM Re: AFTERMATH
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Any pictures to post?

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#150207 - 12/02/04 03:37 AM Re: AFTERMATH
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Robert,
It seems that this got way out of hand in the testing process.
 Quote:
They were testing the unit outdoors. Someone had either tripped over or kicked the grounding lead that was connected to the unit and did not re-connect it.

I don't think I'd like to be that guy somehow.
The fan on a VFD runs the same way (AFAIK) in both modes, it sucks air out, at least all then units I've seen do.
Hopefully this has been a learning experience for all concerned.
I still can't understand the lack of Equi-potential Bonding.
_________________________
Let's face it, these days if you're not young, you're old - Red Green grin

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