Thermal overload relay vs MPCB

[ghostdog]

Sometimes I see that a thermal overload relay (combined with a protection against short circuits) is used instead of a MPCB (motor protection circuit breaker.



When do you prefer to use a thermal overload relay vs a MPCB.

 

[BryanG]

I think this is a European versus North America standards thing, which I realise may not apply in Okinawa . MPCB (motor protection circuit breaker) also called 'Combination motor controllers' are common in systems built to EU standards. Their use allows for more compact panels, and though Thermal Overloads are generally cheaper than MPCBs, by the time you add in protection against Over Current, MPCB are cheaper. Even better I can use one make of MPCB with another make of Contactor, and because they are made to the same standard, it is acceptable. This was very useful during the recent supply chain problems.

From the reading and research I have done MPCBs are far less common in the US, though they are starting to gain acceptance. But if you do use them they have to be in combinations that have passed NFPA testing, which limits your choices. Plus MPCBs often need additions to their incoming terminals to get to the required 'Over Air' and 'Over Surface' creapage distances.

For me, working mostly in the EU market and with small motors, MPCBs are a no-brainer. For systems going to regions using UL standards it requires more consideration.

 

[lfe]

It depends on the machine.

If, for example, it has a lot of inertia, like a high-pressure centrifugal fan, then you have to use a thermal protection relay with a higher "Overload tripping class" and that is not usually found integrated into an MPCB and therefore you have to use a separate thermal protection relay.