Bus Plugs Blog – Expert Safety and Usage Information

PQ3620G Square D Bus Plug For Sale

Sometimes you couldn’t write the script for the strange things that happen in the real world.  At least in our world of reconditioning old used bus plugs and selling them to folks that tell us they couldn’t tell the difference from new.  The technical world seems so boring to outsiders, but MIDWEST has its share of action. For example, a large food processing facility called at 6:15 PM on a Monday night, in a screaming panic, because they needed a replacement 200 amp bus plug and they needed it right away. They couldn’t get a new one immediately and the electrical suppliers for most of the US were already closed for the day.  The cracking in his voice changed to audible relief when we told him we had a fully reconditioned Square D PQ3620G bus plug, boxed and ready for shipping pickup. It was set to go to another customer, but it was part of an order for over 100 bus plugs and there was no urgency for it to ship. It was a shipping scramble but the food processing plant had their like new Square D bus plug the next morning. What’s the chance MIDWEST would have a Square D PQ3620G bus plug sitting at the shipping dock, ready to go, and someone calls and needs it “right now.”  The answer to that question is that it’s much more common than one would ever guess. It seems improbable, but it happens fairly often. The odds may be higher because of the number of bus plugs, transformers and circuit breakers we ship.  But it’s always a nice thrill for MIDWEST to defy the odds. And it gives the Engineers something to argue about, the odds versus reality.

General Electric AC323R Bus Plug Available from MIDWEST

Sometimes you just can not safely perform an electrical maintenance service per the written specification. For example, in today’s world of real concern for arc flash hazards, safely opening the cover of an energized bus plug, to perform an Infrared Scan, may not be possible. It may not be safely justified because of the high risk. So one argument is whether or not one can actually tell if a bus plug is hot because of overloading or because of a poor connection that is overheating. Is it a load problem or a connection problem?  Is there a problem at all?

Because our Thermographers are all required to work on bus plugs in our switchgear shop, they are very familiar with the interior of most bus plugs. They may have totally reconditioned a specific Square D or Bull Dog 100 amp bus plug. Or they may have repaired many ITE, GE General Electric or Cutler Hammer 60 amp bus plugs. Therefore they know where the interior switch or breaker is located. They may know exactly where the conductors connect to the bus plug feeder terminals.  This knowledge and experience is a big advantage, but the Infrared task is still difficult. The indications of overheating, whether load or connection related, may be very subtle because the interior heat must be re-emitted by the bus plug enclosure, greatly dampening the heat pattern.

Again, knowledge of the bus plug allows the Thermographer to turn art into science, at least to some degree. The thermographer may compare a suspect old bus plug to an identical bus plug nearby. Comparing the feeder conduit helps identify the possible ampacity of an old bus plug.  Comparing the heat pattern of the different plane surfaces of a suspect old or new Cutler Hammer or Square D bus plug may give additional information to help determine the existence and cause of heating.

Our thermographers have special safe ammeters to measure the load on a bus plug feeder, where practical and safe. Knowing the actual load, say on a feeder from an old Federal Pacific bus plug, is extremely helpful in determining if the suspected heating is load related or connection related. It is extremely difficult, if even possible, to determine the presence of overheating, much less the cause, by just looking at one plane of the energized bus plug with even a very sensitive Infrared Scanner.

It is the combination of the Thermographer’s experience and equipment knowledge that makes scanning energized bus plugs still very useful.  This same experience and knowledge aid in determining the possible cause of a suspected problem manifested by heat.