MCCB Adjustable trip setting - cable rating

RobHol · Mar 2, 2023

Hi all,

In general do you size the cable to the MCCB full trip setting rather than the adjustable setting for the load being supplied. In some cases upsizing the cable can be costly even from 320/400. One of the site engineers is adamant that it should be sized for full trip setting.

I'm not sure I agree and have rated the cable for the adjustable setting many times previously. What are the views on this.

Thanks

R

westward10 · Mar 2, 2023

I would size it to what it is set as and record this on the Schedule of Test Results as necessary.

davesparks · Mar 2, 2023

Size the cable according to the required trip settings.

pc1966 · Mar 2, 2023

The reason for using an adjustable MCCB is often that you need a non-standard protection requirement. Turning down the thermal trip point is the most common option, but you also have short-time trip settings on some and possibly EL trip settings as well. All of those impact on what cable(s) are acceptable.