Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 6 replies
  • Subscribers 34 subscribers
  • Views 562 views
  • Users 0 members are here
Options
You may also be interested in
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

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?!

  • 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.)

     

  • 0

    Thanks Mike - I may take a look at the surge limiters for the workshop supply.

    He might have fitted an 80A if the meter tails had been big enough.  Meter operator only fitted 16mm tails I think, when fitting the smart meter, even though my CU tails are 25mm.

    He did say that if I upgraded the tails then they would fit a larger fuse.

  • 0

    Interesting one! Usually, the start-up current is about 6 times the motor rating, so if the saw has a 3 hp motor, it could easily be close to 60 A. I wouldn't expect even a B20 to trip instantly.

  • 0

    Indeed so - but I wouldn't expect a 60A fuse to blow that quickly at a current of 60A either - certainly not faster than a 20A MCB with the same current!

  • 0

    I think the fuse was probably just a bit tired as someone said almost certainly been thermally stressed  probably multiple times it could be the originall fuse put in when the house was first wired  in which case it will of seen its share of overloads. Anyway dont talk to me about luck if Jordan (Katie Price)had triplets ide be the one who was bottle fed

  • 0

    if you do need/want to look at inrush limiting, come back, as there is quite a bit of dark arts to selecting the right one for inductive loads, happy to advise. (https://www.ametherm.com/blog/inrush-current/ac-motor-inrush/)

    mike.

Community Rules & Guidelines