Dangerous Sagging Bus Plug
A maintenance electrician asked MIDWEST what he should do about a 200 amp Square D Bus Plug that was sagging several inches down from the overhead bus duct. He said the conduit from the bus plug was poorly supported and was pulling it down. His supervisor wanted him to try and fix it on the fly. That made him really uncomfortable and he wanted MIDWEST’s recommendations.
This problem has nothing to do with the manufacturer. It could have been a General Electric or Westinghouse bus plug just as easy. The problem is the installation, not the equipment. We have seen this all too often when doing Infrared Scans of overhead bus duct and bus plugs.
First of all we recommended in the strongest terms that no one try to fix this problem without shutting the power off. We mean shut off the power to the bus duct, not just shut off the bus plug. The connection of the disconnect fingers on the back of the bus plug to the bus duct is the most vulnerable to failure and will do the most damage if it faults while the system is on. Besides possibly getting someone seriously injured or killed, you could lose a section of bus duct and have a protracted power outage. The danger to the maintenance electrician is too great to even consider adjusting the bus plug energized.
As far as just leaving well enough alone, we don’t buy that either. This is what MIDWEST calls an incipient failure, a failure that will happen sometime in the future. When, we are not sure. But it will certainly happen. Our experience is these things happen on July 4th or Thanksgiving Day. That’s just the way things seem to go sometimes.
The danger of catastrophic damage to equipment and, more important, the danger to a maintenance electrician trying to adjust the bus plug while it is hot, is just too great. We would categorize the idea of doing this hot as “Crazy.” Besides, you are not allowed to do something that has the danger of serious injury or death.
Turn all the power off and properly plumb and support the bus plug. We also recommend removing the bus plug and checking it for damage, before reinstalling it correctly. Do it right and no one gets hurt, always a good idea.