On Jan 21, 9:17 am, "Tube Audio" wrote:
Hello

I have an Industrial Installation of a string of about 20 SPST Emergency
Stop Switches in series, They are wired Normally Closed. 24VDC is connected
to the string and the switches will interrupt the 24V when pressed in and
Emergency.

The wire is 18 GA stranded and the total length of the string is about 800
feet.

The wire runs in conduit.

I believe I have an intermittent short to the conduit, usually the short
occurs just momentarily so troubleshooting is difficult.

I was thinking of Hi Potting the Switch String. I was going to disconnect
each end of the string and Hi Pot the cable run along with the installed E
Stop Switches. To verify if some part of the conductor is very close to the
conduit.

I believe the wire is rated at around 600V.

The question is what Voltage should I set the Hi Pot tester to and why. The
other end of the Hi Pot tester will connect to the conduit.

Thanks

Before i would start chasing down a possible short, I would verify
that my coil is getting enough current to stay in, and that my 24VDC
supply is not overloaded. Do you have other loads on the DC supply?
If you have other loads on this supply, especially intermittent ones,
that could be enough to cause the coil to drop out.
1. I would force all other loads on the DC supply to be on, and then
see how the coil in question behaves.
2. If the supply is ruled out, then I would pull the cable off of the
coil and measure the resistance of the cable, including all switches
(bypass the supply). If the supply voltage divided by the system
resistance is marginal, that would be a good place for a problem.
3. If this isn't the problem... 800 feet of conduit will expand in the
sun. And if you have a problem which shows up or goes away with
temperature, the expanding conduit might be pulling on a loose
connection.
4. Then I would check for the short.

Good luck,
Andy