In article ,
Ned Simmons wrote:

On Thu, 27 Nov 2008 22:18:30 -0500, Joseph Gwinn
wrote:

In article ,
Ned Simmons wrote:

On Tue, 25 Nov 2008 20:31:18 -0500, Joseph Gwinn
wrote:


I didn't qualify it enough. I'm not talking about substation switches.
I heard this from an electrician in Rhode Island.

Perhaps he was talking about some requirement other than the NEC. For
example, I built equipment for GE's steam turbine division and they
had some in-house rules that were considerably stricter than the NEC.
The one that comes to mind was a limit of 240V in flexible cords.

The electrician probably had local industrial practice and/or code in
mind. He was very definite on the subject, but didn't mention where the
rule came from. The conversation was in an old mill building in
Pawtucket, RI, that houses a number of small manufacturers.

In that environment they could have been following JIC/NFPA79
guidelines for machinery, which specify that control voltage should be
115VAC. The intent is that switches on control panels, limit switches,
contactor coils, etc., operate at 115V. This does not preclude higher
voltage at disconnects and manual power switches. These are voluntary
standards and are not intended to be applied to premises wiring. If I
have a choice, I use 24VDC controls on the equipment I build.

This sounds reasonable. As I recall, we were talking about a big
480-volt Clausing four-spindle gang drill press.


Another poster mentioned arcs blowing the cover off so one should stand
off to one side. Sounds like a job for a contactor in a steel box.

I've seen it happen on a 480V motor starter. Pretty exciting.

Hope the cover was screwed down tightly.

It was before the bang, it was across the room after. g

Sounds like a stronger box was needed. And/or bigger, to dilute the
overpressure. Until the main breaker pops.


Joe Gwinn