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Electrical Troubleshooting Quiz

Oct 13, 2009 2:13 PM

Several areas of the facility suddenly go dark. A quick investigation reveals the power loss originated at the service supplying those areas. None of the breakers on that service has tripped.

Another service feeds from the same electric utility lines, so you don't think the problem is at the utility. Should you call the utility anyhow? What else should you do?

Obviously, a circuit is open somewhere. Because the breakers are closed and the electric utility is supplying power, it's likely that your cable limiters opened due to a short circuit fault.

Yes, call the electric utility. Explain what happened and what you know so far. Suggest that a short circuit fault probably occurred, and ask if they will locate it for you (this may incur a fee that usually is worth paying). Then, see if your service cables have cable limiters. If so, quickly obtain replacements/spares.

Caution: Those cable limiters are probably still energized on the cable end. While you "could" work this hot, there's no reason to do so. Wait for the electric utility to open their switches and confirm lockout/tagout. Put your own lock on those switches before working on the supply side (e.g., replacing cable limiters).

While waiting for the utility:

• Initiate PMs that require an outage.
• Open the breakers in the service panels.
• Test for load-side faults.

Before power can be restored, the fault (or faults) must be identified and repaired. This means cable testing and ground fault testing between the utility switches and your service, plus the same of your service equipment (including power factor correction capacitors).

While all of this is taking place, you have a PM window. If practical, do the PMs that require power interruption but won’t interfere with troubleshooting this problem or put too many people into too little space.

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