MCCB Ith & Ir Acronym Meaning

I_th is the thermal current rating of the breaker. The more the motor current exceeds this, the quicker the breaker will trip. I'm unsure of the other abbreviations, but they may represent the magnetic trip rating, which is nominally instantaneous.

If the motor requires 911 A, it is likely to trip this breaker either 1) right away if the starting current exceeds 6300 A, or 2) in a short time if the running current exceeds 800 A. So I don't think this combination will work.

Thanks, but how about the Iu (1250 Amps) which i believed is the nominal current rating. Our MCCB rating Iu = 1250 Amps & Ue is 660 volts. then their is anothr rating which is Ith = 800 max @ 45 Deg C. any idea on this Sir?

My idea on that is exactly as before. If the thermal rating I_th of 800 A is exceeded by the 911 A motor, the breaker will trip (sooner or later).

However, if the ambient temperature at the breaker is less than 45°C, the I_th will be somewhat higher. This may get you by, but it looks really borderline. Reduced-voltage and unloaded starting will also help.

ASK ABB for their catalogue on MCCBs select yourself you will find all inputs required you could download the catalogue from ABB web site.

good luck

murali

Ex power user

thanks. this an old model MCCB from ABB. SACE SN1250 model. Installed last 1986 by the German Contractors here in KSA.

All I want to know is if could still use this MCCB. But i think the best solution now is to buy a new MCCB.

Rgards to all.

• Start with the instruction manual that came with it, and a mk.1 eyeball with which to read it.
• If that fails, get on the 'phone to <...Schneider...> and ask.