I have a problem that I must please explain to an irate engineer ( must be a mechanical ) why he must pay for 8 new 6 pole 2.2kw extractor fans. What caused them to burnout, the Gent.wants to know if the correctly rated fuses were used. Now let me explain the circuits in question , the fans, 16 in all ,are part of a heat pump producing hot water for a hospital, they are exposed to the elements and are about 7years old. I do not know the I.P. rating but I suspect the I.P. protection is diminishing as for protection there are two fans in parallel and supplied through a C H G G 10 ( info on circuit diagram ) in addition there is also circuit protection via thermistor.Now my argument is that the fuses ( slow blow or delay blow I do not know ) are not there to protect the motors and should one blow as in this case, the motor will continue to run untill the thermistor detects an increased temp in the windings and cuts the circuit out,not very efficient as the motor has a constant draught passing over the housing so it won`t overheat instantly ( being an extractor fan and extracting cold air ) so what we have is not a very effective protective system, What is required is a 3 Phase D Curve m.c.b. and or a motor protection circuit breaker like a telemecanique G V M 2 or whatever make, there are plenty on the market, Now what I would like to know, What is coarse current and fine current protection.Does anyone have any more info on fuses types and action.