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.
Buy PQ3206 Square D Bus Plug
MIDWEST was asked if the reliable life expectancy of bus plugs followed the classic bathtub curve. In other words, the rate of failure of bus plugs would be high when they are first put into service, ie new bus plugs. Then the failure rate would remain very low until the bus plug was very old, near the end of its reliable life. At that time the failure rate would rise again, similar to the rate when new. If one plotted the curve of the failure rate, it would have the shape of a bathtub. MIDWEST had two answers to the question. The first answer was “We don’t know, ask the manufacturer.” Our second answer was more important, “The failure rate is related to environment and not age.” We know the causes of old or new bus plug failures. New, old, and very old, obsolete bus plugs fail if they are overloaded, overheated. Bus plugs fail if they are in an area with a lot of vibration or physical movement. All bus plugs fail early in wet areas. The enclosure eventually just rusts away. New bus plugs fail if they are not properly installed. This is much more common than one might think. Old and new bus plugs fail if they get very dirty and vibrate and overheat. There isn’t much to a bus plug. So, if you install them properly and keep them dry, clean, no vibration, and under loaded, they will last for decades and you do not need to worry about the bathtub phenomenon. Sounds like a good idea for all electrical equipment.
Buy Square D PQ3640 Bus Plugs
All too often our little friend the bus plug ends up making the ultimate sacrifice resulting in a catastrophic failure in the line of duty.
Not long ago we got a call from a customer asking for a bus plug replacement for one of theirs which failed in service. The circumstances surrounding the bus plug failure cannot be discerned.
The bus plug involved was a Square D PQ3640 (3 phase, fusible, 600 volts, 400 amps), the older version of the Square D PBQ style bus plug. One can only speculate as to what happened exactly, but the evidence told of a frightening scenario. A hole the size of an orange was burned completely through the bus plug cover. The inside guts burned beyond recognition, copper splattering along with carbon residue scattered throughout the inside of the bus plug.
Oddly enough the extent of the damage was confined to the bus plug itself and did not affect the bus duct proper. As mentioned many times before, bus plugs often operate under highly stressed conditions seriously compromising their life in service.
Our Switchgear Shop claims nothing surprises them anymore. Well they got a surprise last week. We received a 400 amp, old bus plug for reconditioning. It looked in great condition, almost like a new bus plug. The receiving inspection read something like, Good, Good, Good, on and on, and at the end, Junk. It seems the reason the customer sent in this bus plug was because it looked like the Titanic. It had an 18 inch slice along one side of the enclosure. Very clean, very deep and perfectly straight. We have no clue how they did this. But we suspect a fork truck was involved. MIDWEST gets a few old bus plugs that have lost a battle with a fork truck. So our guys took a picture and added this one to our “Wall of Horror.”