Thermal overload

[Jako13!]

Got a 7.5kw pump that’s blocked. Overload set to full load current of 13amp and fuses are BS88-2 20M25 but it keeps blowing the main fuses every time it’s blocked why would this be. The motor electrical is fine tested insulation resistance and resistance of winding. Thanks for your help in advance.

 

[James]

faulty overload, overload not removing power from main contactor, fuses are blowing before overload has heated up enough to trip contactor.
it is likely one of the above.

 

[pc1966]

It is not really my area of expertise, but to me a 20M25 fuse is quite low for selectivity with a 7.5kW motor overload trip.

Usually the BS88 fuses are there for fault protection (i.e. to limit short-circuit I2t energy) and would be significantly larger than the overload trip than the factor of just under 2.5 here.

Hopefully someone else can comment?

 

[Pete999]

Got a 7.5kw pump that’s blocked. Overload set to full load current of 13amp and fuses are BS88-2 20M25 but it keeps blowing the main fuses every time it’s blocked why would this be. The motor electrical is fine tested insulation resistance and resistance of winding. Thanks for your help in advance.

Locked Rotor when pump is jammed causing overcurrent hence fuse rupturing.

 

[pc1966]

Locked Rotor when pump is jammed causing overcurrent hence fuse rupturing.

I thought afterwards what exactly was meant by "blocked pump" and as you say if has locked the motor then the current will shoot up and take out the fault protection in most cases.