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Joined: Jan 2003
Posts: 4,391
I
iwire Offline OP
Moderator
The following pictures show the result of a simple line to ground fault on a 277 volt lighting circuit.

You can see the plastic switch housing melted from the heat.

Luckily the cover plate was in place when this flashed, all that happened to the person that turned the switch on was a good scare.

[Linked Image]

[Linked Image]

[Linked Image]


[This message has been edited by iwire (edited 04-06-2004).]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Feb 2002
Posts: 840
C
Member
Wow! Since I primarily do residential work, I've never encountered a 277/480 volt circuit.

However, this forum and pictures like these have made me well aware of the added danger.

Bob, was this caused by a wiring error (skinned wire, etc) or a fault with the motion sensor itself?


Peter
Joined: Jan 2003
Posts: 4,391
I
iwire Offline OP
Moderator
This was a wiring problem.

I do not know if the wire was damaged by the roto zip of the dry wall guy or if the wire was pinched when stuffing the MS into the box.

It was the wire on the load side of the switch, the MS was installed and the circuit turned on, then when someone pushed the button on the MS it "lit up".

Remember this is just a 277 volt fault not a 480 fault and the 20 amp breaker never tripped, the wire was blown apart clearing the fault.

Just something to think about before sticking your fingers into a live 277 volt (or any voltage) box.

On the same job a sprinkler contractor thought he would help me out and move a live 277 volt 2' x 4' troffer, well the wiring plate came off when it was jammed against duct work and the 12 AWG was cut into by the troffer.

Again the breaker did not trip, the wire just blew apart, this guy did not even know how lucky he was not to have gotten blasted.

My guess is the wooded ladder kept him from being a conductor, as the light fixture enclosure was 'hot' for a short period of time.


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Dec 2003
Posts: 59
B
Member
I use 4x21/8 box on all dimmers GFCI and other biger switches that takes more
space than a general snap switch. That is why i do it big guy

Joined: Jan 2003
Posts: 4,391
I
iwire Offline OP
Moderator
Big Guy That describes every box on this job. [Linked Image]

All the boxes I purchase (the Company purchases [Linked Image]) are 4" Sq deeps and this has a 3/4" raised ring on it.

Only 3 - 12/2s in this box, out of about 100 of these MS, only one blew up. [Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
Joined: Dec 2003
Posts: 59
B
Member
ok it looked like a 4x1.5 anyway thing like this happen's Hay maybe no anti-short
LOL just joking

Joined: Feb 2002
Posts: 840
C
Member
Bob, just curious, do you also use the color coded MC cable? like the brown/gray for 277 etc. Not a code requirement, I realize, but makes the job easier. [Linked Image]

Also, when you say the wire "blew apart," I assume you mean the copper vaporized and splattered everywhere?
Peter

[This message has been edited by CTwireman (edited 04-06-2004).]


Peter
Joined: Aug 2001
Posts: 599
N
Member
CT,
Technically it is a code requirement, though rarely followed. Not the colors necessarily but differentiating systems. Take a look at 210.4(D)

Joined: Dec 2000
Posts: 4,287
Member
"The Watt Stops Here"...well, almost [Linked Image]
Where did you find cable with all black conductors?

Seriously, this could very easily happen to a finger or hand, and they can't be replaced like boxes and wire.

Joined: Oct 2003
Posts: 289
:
Member
can anyone get me some info. i still don't look through these things, like breaker reset arc-flash ect.
never heard of things like these here.
If you short 230V to N/ground here, you will trip the breaker, and thats it.
and breakers usually trip before you fire up a milimeter of wire.

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