Discuss Another video on fuses versus MCCB in the UK Electrical Forum area at ElectriciansForums.net
Although a lover of fuses, both for the great current limiting effect, but also ease of use, I do have some suspicions about that video.Thankfully I have never had to work on anything that big, nor deal with the human results of that sort of failure, but I was rather disturbed by the results of testing at what was stated to be the manufacturer's ratings.
I see a lot about arc-flash risk mentioned in relation to USA wiring but not nearly as much over here. I had wondered if that came down to the UK commonly using HRC fuses as the fault protection for many big motors and DBs, instead of MCCB and the like?
Yeah, I think the expectation is a bit too much tbh.There was another comparison video where they had a MCCB tested at 50% of its rating repeatedly and only lasted something like 8 faults, which makes some sense.
One might like to think high PFC faults like that are very rare, so several resets is a lifetime for the system, but I guess there will be some applications when that is not the case.
It's a generator with a large flywheel, you run the machine up to speed, then set the sequence switch in operation. It starts the recording systems, disconnects the motor supply, then closes the generator output through reactors and resistors (to get the correct fault level and x/r ratio etc) , if needed it then sends the trip signal to the switch under test (for opening tests only), then after the required time, opens the circuit again (assuming the breaker under test didn't clear the fault), then stops recording etc.As you say, the MCB/MCCB is seen as modern and fuses as old, but without a great deal of thought or reasoned arguments one way or another.
For domestic CU fuses are not good, more so the rewirable sort, due to the unskilled nature of most folk needing to reset them. But once you get in to industrial situations that becomes less of an argument and certainly if there is any danger of them being closed on to a high energy fault I would be very unhappy about that being done by anyone not skilled and PPE'd-up to deal with it going wrong.
Sadly there seems not to be an option for small fuse/switch units compatible with the MCBs/MCCBs for DB in those cases when you would be better off with the protection let-through, selectivity when cascaded, etc., of a fuse.
As an aside, and since you have actually been involved in the testing, how do those tests generate the PFC? I can't imagine the grid would be happy with a 5MW or whatever sub-station being shorted out for testing, so do they have flywheels and motor/generator sets or something to dump the fault energy as needed?
Reply to Another video on fuses versus MCCB in the UK Electrical Forum area at ElectriciansForums.net
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