Bus Plugs Blog – Expert Safety and Usage Information

We are a maintenance and engineering service company and sometimes we find some rather strange things when we peek on the inside of a bus plug during an outage or Infared scan.  There are the times a three phase, 100 amp bus plug is fitted with two, 80 amp fuses and one 90 or 95 amp fuse.

This begs the question did the other 80 amp fuse blow and all that was lying around was a 95 amp fuse or was the bus plug moved to that location recently from somewhere else and really there should have been  three, 60 amp fuses in it?   Bus plugs come in many voltage and ampere ratings the common ones are 30 amp, 60 amp, 100 amp, 200 amp, 400 amp, 600 amp and even the monster 800 amp bus plugs.  These amp ratings sizes relate to the amp rating of the live parts.  Fuses come in all physical sizes, voltage ratings and ampere ratings.  Just because a fuse will fit in a fuse holder does not necessarily mean it is correct to use.  It is important to ensure that the voltage rating of the fuse meets or exceeds the voltage rating of the bus plug.  A 600 Volt or 480 Volt fuse in a 480 Volt bus plug is OK.  A set of 240 Volt fuses in a 480 Volt bus plug is not OK.  The next consideration is the amperage of the bus plug.  The live parts, the fuseholder and switch, are sized for the amp rating of the plug.  You can always put in smaller fuses, ideally three of the same size, but don’t exceed the rating of the bus plug and install higher amperage ones.  The fuses may just sit there and the poor fuseholder or switch can become the fused element instead.   Reusing your available bus plugs is acceptable if you pay attention to the voltage and current ratings.