Calculation of circuit breaker size

How to Calculate circuit breaker for all HVAC equipments system (AHU,FCU,CHILLER,FANS,HEATER,HUMIDIFIER) as per IEC and NEC?


asked 8/29/2012

1 Answer

Your best bet is to refer to manufacturers catalogues as they provide a wealth of information.

For distribution supplies I would look at the anticipated current, select the next larger frame size and an appropriate protection module. Other things you need to consider include selecting frame sizes to ensure you get discrimination, catering for expansion, being a little practical and allowing for expansion (particularly on incoming circuit breakers of any DBs you have). Depending, you may also want to consider the fault current limiting capabilities if you want to use lower rated breakers downstream.

Some of your loads are motors, in which case while the above still applies, you do have to deal with motor inrush and starting currents. Most catalogues from the good manufacturers do provide a lot of guidance in selecting the correct breaker for these conditions. I tend to follow these and have not had any problems so far.

On the ''Steven's Technical Links" page unto the Tools menu, I have a link to the Schneider Circuit Breaker Application Guide which gives good understanding of circuit breakers. If you can also get a copy of the Schneider Compact NSX catalogue, it will help you a lot in selecting the correct device.
answered 8/29/2012 Steven McFadyen 240
Steven McFadyen

Your Answer

In order to provide an answer to this question, you must Login

I am flagging this question because...

10 inform moderator flags remaining

I am deleting this question because...

I am flagging this answer because...

10 inform moderator flags remaining

Flagging a Post

You have already flagged this post. Clicking "Remove Flag" below will remove your flag, thus reducing the count by one as well.

I am deleting this answer because...

Our website uses cookies so that we can provide a better experience.
To learn more about what cookies are and how to manage them visit