One of the guys was unscrewing a blank cover on a different box about 100' away when he heard the pop inside the box he was working on. The screw had apparently rubbed a conductor raw inside.

The simultaneous sound of this one kind of made it hard to hear, though.

Just a guess that one of the switches was not happy with the available fault current.

That is really ugly.

Scott,
What make/brand switches are those?.

i am sure it look like Hubbel 2 pole switch but the Pass & Syemour look very simuir too but i am not too sure about Levetion they look little diffrent

i can tell this was wired up on 277/480 volt circuit

if running more than 300 volts it should have " divider " on there and i dont see any of it in the switch box at all.

the other thing i can see that the switch is allready wired on 480 volts so that get more spooky there

Merci, Marc

Were these 4ways or 2pole switches? If they're 2 pole, and there was 480V being run through these, the fault downstream (I'm assuming) probably found its weakest link being the switch contacts not being rated for the fault voltage.. But you say a faceplate screw caused the fault which would be at 277V if all was grounded properly, or did more than one wire get damaged?

The switches are Hubbell, you can make out their oval insignia above the toggles on the yokes...

Yup, Marc's right. (I told the answer on the chat, which may have helped )
2 Poles, Hubbell, with a label on the side "2 Pole for single circuit only".

The installer chose to disregard the label, and ran 480V through them. The fault was 277V, caused by 8-32 in the corner of a 4-S box. The switch on the left took the fault, and its failure sent this "Jack and the Beanstalk" effect into high gear.

There were 18 of these switches installed (that's 36 circuits). The customer had me remove all of them
They will be replaced with contactors.
(BTW, None of the 20 Amp breakers tripped)



[This message has been edited by electure (edited 11-18-2005).]

Here's what I found instead of contactors when I happened by the place again.





Now what ??

[This message has been edited by electure (edited 02-02-2007).]

Where's that rolleyes smiley, wait, here it is!

Whaddaya expect? Someone to spend money replacing the old switches with new contactors?

(BTW Scott, no cursing. )

Ian A.

[This message has been edited by Theelectrikid (edited 02-02-2007).]

To quote a character from an old British movie about a couple fixing up an old house (including wiring):

"They never learn!"

I wonder if this is why the code wants dividers for >300V.. to block the shrapnel from the other switches.

I have an old GE 3P toggle switch rated 20A 600V if they're really against the contactors, they might want to look into them. I'm sure they're not cheap though. Here are the ones from P&S..

edited to fix link

[This message has been edited by Lostazhell (edited 02-03-2007).]

Minimum distance between live components increases with voltage- after a certain voltage, you wouldn't legally be able to fit components into boxes like this without dividers.

Are you sure that the new switches are not controlling contactors, perhaps in the cabinet they are mounted in?

In all fairness,



they did double the number of switches. Now the switches control single 277 Volt circuits each.
They are still in 4-gang boxes, mounted to the side of an old (GE, I think) panelboard.
There are no contactors.

The issue of >300 volts between adjacent devices still remains. 404.8(B). It still isn't right.

It would be a simple matter to fix it, but it won't happen unless this thing blows up again.

How could it be fixed?

If all the switches in the same box are run off the same phase of 277V, then that shouldn't be an issue. But the fact that there are 4 boxes means that either one phase has extra loading (unless some of the switches control smaller than the average load), or the above rule is violated in at least one of the boxes.

3 phase breaker panel with every other numbered circuit on the same phase? I don't think so.

Perhaps someone is using a single phase panel with two legs of a three phase system. That still sounds unlikely.

Larry C