Scarifier blows fuses

[Topaz]

This question is prompted by a discussion in the Buying Advice / Tool Reviews section.
https://www.ukworkshop.co.uk/forums/view ... c&start=15

I have a 12-blade lawn scarifier driven by 1800W electric motor.

Unfortunately I have a rather uneven "lawn" and thus the effective depth of scarifing varies from place to place. In the extreme, when two or more wheels are in a low place, the blades try to cut very deep and the motor stalls.
Also, if I start the motor with the scarifier in the lowered position the same thing can happen so I always tip the machine back on its rear wheels when starting the motor and let it get up to speed.
In both cases, when the motor stalls the fuse can blow (16A) or, more often, the differential switch (earth leakage?) trips out.

I think the machine has an induction motor (when running freely it make a nice hum).
Is this behaviour typical of an induction motor or would the same thing happen with a universal one?
Isn't this a very bad design for a piece of equipment that, by definiton, is operating on an uneven surface?
Surely the machine should be protected against the high current caused by stalling?

Should I try and slacken off the belt drive so that it slips before the motor stalls?

 

[davy_owen_88]

If the RCD is tripping, you have an earth fault. This is probably due to a damaged cable or possibly a loose connection within the scarifier, but one thing is for certain, you shouldn't use it until the problem has been identified and then rectified. If the scarifier has any exposed metal parts, don't touch them while the machine is plugged in either.

 

[Anonymous]

Hi Topaz

If the motor is stalled, it should really trip an overload of some sort which is usually a small push button on the equipment itself rather than blowing the main fuse.

The 16A fuse (large for an 1800W motor) is actually in place to protect the cable (and user), not the motor and I am surprised that you are actually blowing it during stall conditions
You could try to source a motor rated fuse for the appliance but I would suggest simply switching off as soon as it stalls and then freeing it before carrying on withe the scarifying. If the motor staling is taking out the fuse, then it should take a short while before it blows under stall conditons.

Could you modify the machine slightly so that it doesn't dig in?

 

[Topaz]

Hi, thanks for the replies.
Is it likely this is an live-to earth problem ? I have never felt anything approaching a shock . . .

I have set the machine so it is scarifying above the normal "zero" position.

How can I get it tested? Do such labs exist? The supplier (a better class garden/park equipment supplier) does not have the specialized gear for testing this.
An overload button is just what I would expect but do not have.

BTW, this is in Belgium. We have continental wiring: no fuses in plugs, no switches at the wall sockets, spur wiring (not ring), sockets daisy-chained on spur, and one fuse at the "consumer unit" per spur.
Not much scope for individual fusing.

 

[davy_owen_88]

RCD's test for an imbalance between the phase (live) and neutral conductors. If there is an imbalance it means some 'electricity' is going through the live but isn't coming back through the neutral.

Under no circumstances will an overload cause an RCD to trip, but an earth fault can cause a fuse to blow, so you either have a L-E or N-E fault. Like I mentioned previously, this is most likely to be in the cable, so check that for any damage and replace if necessary.

 

[Losos]

Hi Topaz.
Continental wiring, yes know all about that In my workshop I've installed UK 13A sockets alongside all the continental ones.

I have long held the belief that a fuse on each appliance is useful. The wiring may be perfectly OK but if a motor draws more current than planned for in the design then you do wan the fuse to blow.

RCD's and the other earth leakage thingys are good but a fuse still has uses.

BTW don't increase your fuse, as others have said it seems to high a value for an 1800 watt motor anyway.