size breaker

[smileonmoon]

I met a problem of sizing a three phase breaker. the current in each wire is measured around 50A, and it is well balanced in three phases. The breaker using now is 225A. Is it too large for the current load? how can I choose the breaker according to the current in wiring? Can I just use 50A or do I need multiply a factor?

 

[jbartos]

Suggestion: There are many factors involved in sizing breakers. More information is needed, namely:
1. Is there any motor load?
2. What is the largest motor in HP?
3. What is the starting arrangement of the motor?
4. Expected load growth?
5. Ambient temperature derating?
6. Altitude derating?
7. Sizes of conductor?
8. The largest rated circuit breaker or fuse downstream?
9. Does the breaker have a sensor?
10. What type of 225A circuit breaker is it?
11. Etc.

 

[DanDel]

The C/B rating is based on the cable, and the cable size is based on the load. If the system is already installed, there is usually no problem with leaving it alone if the only problem is 50A on a 225A circuit.
To size a new circuit, the NEC specifies several procedures, but mostly that the circuit is sized for at least 125% of the calculated load.

 

[pablo02]

Breakers for motor loads are usually sized differently from other loads -- you need to know what load the breaker is serving....

As DanDel poins out the NEC specifies several procedures... take the time to review these...

 

[advidana]

a better question is Why do you want to reduce the breaker size?

 

[jbartos]

Suggestion: Except for some fire protection equipment such as fire pumps, the circuit breaker should be protecting conductors, load, etc. downstream.