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Circuit breakers flashing over or exploding

Johno12345

choosing my words carefully here.

 

Resetting MCBs in a DB or in a machine control panel.  

We have people who are trained in MCB resetting, contactor trips etc inside control panels, and the Schneider MCBs in a dis board are rated for operation by ordinary persons. 

 

I recently lectured someone on the danger of resetting something with the power energised in a control panel, and reminded him that it must be isolated before opening the door (even interlocked isolators can be turned on with the door open. 

 

Well, low and behold, a breaker tripped, panel was isolated correctly, breaker reset, panel turned back on and the MCB and contactor blew up

 

At least it illustrated my point but does this happen much? I have seen it a few times in my years and never in a dis board. Reading the thread about arc flashes has made me think, and if he had his hand on it as it blew up, there would have been an injury of some sort.

 

I'm just thinking about things really, id be interested in your experience of this

  • 0

    Well, one of the nice things about fuses is that unlike a  breaker there is nothing to rust up and stop working, or grease to go hard and sticky- the most credible failure modes are fail to safe - a disconnection of some sort is pretty much assured.

     It is telling that there are expulsion fuses on the HV network that have been up poles in the rain for many decades, but come the moment they still operate correctly. stored properly  fuses more or less last for ever, at least if you can keep the innards free of water, and even that tends to make them open sooner, though not as safely.

    Mike.

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