hi friends

I saw some power circuits that used both MCCB and thermal relay ,i know MCCB can protect as thermal relay and cut off circuits when it is overloaded,so why they used two protection?

Basically MCCB - Short circuit protection

Thermal relay - Overload/overcurrent protection.

HTH.

Hello hamed;

The information in the following article agrees with your last statement.

http://www.ecmweb.com/content/basics-molded-case-circuit-breakers

Which make and model of MCCB do you plan to use?

It would be easy enough to tell whether this particular circuit protects overload as well as short-circuit.

Hope this helps,

Daniel Chartier