Bus Plug Fits, But It’s Not Connected
Buy Square D Bus Plug
Maintenance mechanics and maintenance electricians are very self reliant people. They have the ability to get things done, often with limited resources, and they have a lot of common sense in the maintenance world, the real world. When it comes to installing replacement electrical bus plugs, their common sense may tell them, if it fits, it’s connected right. This is not always true. The problem, when installing replacement or new bus plugs is that it is very hard to see the actual disconnect finger connections when sliding the bus plug into place on the bus duct. Installing an old bus plug from a platform lift, much less from ladders, can be a real challenge. One can’t always get the lift right under the bus duct. It’s hard and sometimes impossible to see well enough to make sure the replacement bus plug disconnect fingers line up properly with the bus duct bus bar. And some bus plugs are very heavy. They may take two people to install. It can be a challenge. Using Thermographic Scanning, Infrared Scanning, MIDWEST sometimes finds overheating at the disconnect fingers that connect the bus plug to the bus duct. When we check it out, we find that one or more of the fingers has slid under the bus bar inside the bus duct. The actual contact surface may be only 25% of what it should be and the contact pressure may be very little if the disconnect finger assembly breaks and the only real connection occurs because it is jammed between the bus bar and the bus plug phase assembly. The big worry is for a short circuit between the bus bar of the bus duct. So, for old or new replacement bus plugs, just because the bus plug enclosure fits on to the bus duct, does not mean the bus plug is properly connected to the bus duct. It can be a challenge, but care must be taken when installing bus plugs. One can not rely on alignment alone to assure the proper connection is made.
For arc flash safety reasons, MIDWEST recommends turning off the bus duct before replacing a bus plug or installing a new bus plug.