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Unlucky and lucky?

jbrameld

I used the table saw in my 'workshop' at the bottom of the garden on Saturday for the first time in a while. I pressed the ‘start’ button and within about a second everything went dark and quiet.

Local 20A MCB feeding the ring final in the workshop was not tripped, and neither was the RCD in the workshop board.

So I head back to the house to be greeted by House Management declaring that the power has gone off.  Nothing tripped on the CU in the house either, and the Smart meter was dead, so a call to UKPN followed.  All neighbours still had power.

The lucky part was that UKPN were working 15 doors down the road on a more serious cable fault affecting a property and they sent a nice chap round to replace the 60A fuse in the service head - all fixed inside 40 minutes from going off.

The load in the rest of the house at the time was minimal - no ovens, kettles, toasters, washing machines or tumble driers etc. running - just the fridges, routers etc. and House Management's TV.

I know the table saw has a bit of a surge current on switch on, but I'm guessing I just got unlucky that discrimination didn't really work out for me this time and the service fuse went pop.

Further operations of the saw caused no further problems.

Any thoughts on any other causes - other than bad luck?!

Parents
  • 0

    Pity that the chap didn't fit an 80…

    still, a chance to write  the rating on the wall next  to it.

    Probably nothing sinister at all, fuses do age and can do so in a way that in effect reduces the rating , especially if they have been over run in the past and the internal element has been warm enough to sag/stretch a bit. ( if you have a full household then a shower ,cooker tumble drier running, can take a 60 A fuse for a short flight over its nominal rating, and you'd not notice any change immediately)

    Also I suppose the saw may have been stiffer than normal after a period of dis-use, or the brakes assuming it is that sort, may not have released as promptly as they should.

    If it ever does it again, think about an inrush limiter - I have a lathe motor that would reliably fire a B32 on start up, that has been as good as gold on a 16A breaker since it had a small box added in series with a couple of “surge gards” inside to limit the inrush to something more respectable. 

    Mike.

     

    Edit if you feel the urge to test the 20A breaker that didn't, then do so with a lower voltage such as a car battery or a stick welder transformer, not by shorting the mains (I'm sure you would not, but we never know who is reading these threads later.)

     

Reply
  • 0

    Pity that the chap didn't fit an 80…

    still, a chance to write  the rating on the wall next  to it.

    Probably nothing sinister at all, fuses do age and can do so in a way that in effect reduces the rating , especially if they have been over run in the past and the internal element has been warm enough to sag/stretch a bit. ( if you have a full household then a shower ,cooker tumble drier running, can take a 60 A fuse for a short flight over its nominal rating, and you'd not notice any change immediately)

    Also I suppose the saw may have been stiffer than normal after a period of dis-use, or the brakes assuming it is that sort, may not have released as promptly as they should.

    If it ever does it again, think about an inrush limiter - I have a lathe motor that would reliably fire a B32 on start up, that has been as good as gold on a 16A breaker since it had a small box added in series with a couple of “surge gards” inside to limit the inrush to something more respectable. 

    Mike.

     

    Edit if you feel the urge to test the 20A breaker that didn't, then do so with a lower voltage such as a car battery or a stick welder transformer, not by shorting the mains (I'm sure you would not, but we never know who is reading these threads later.)

     

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