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# Single Phase Exhaust Fan Motor Circuit Breaker

## Single Phase Exhaust Fan Motor Circuit Breaker

(OP)
Hi, How to calculate the Rating of the Motor Circuit Breaker of the Control panel if I have .18Kw 240V/1phase/50Hz Exhaust Fan? Shall I consider starting current for the sizing of Motor Circuit Breaker?

### RE: Single Phase Exhaust Fan Motor Circuit Breaker

In Canada that is governed by the Electrical Code.
The code requires two types of protection for a conductor.
1. Overload protection, often provided by an inverse time function that is set at the breaker rating.
2. Overcurrent or short circuit protection, typically provided by an instantaneous function set at from 5 times to 10 times the rating of the breaker.
BUT, MOTORS are a Special Case.
The code recognizes that overload protection may be provided by the motor starter.
The code recognizes the starting current of motors and allows motor circuit conductors to be protected by a circuit breaker rated at 250% of the full load current of the motor.
An exception is that the breaker need not be less than 15 Amps rating.
In Canada, the motor circuit conductors will have a minimum ampacity of 15 Amps and will be protected by a 20 Amp or 25 Amp breaker depending on the actual Full Load Current rating of the motor.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

### RE: Single Phase Exhaust Fan Motor Circuit Breaker

KikoRamos06 (Electrical)(OP)1 Nov 23 12:32
[color #3465A4]" How to calculate the Rating of the Motor Circuit Breaker of the Control panel if I have .18Kw 240V/1phase/50Hz Exhaust Fan? Shall I consider starting current for the sizing of Motor Circuit Breaker? "[/color]
Your motor is rated 0.18kW 240V 1-ph 50Hz should be in a location where IEC or BS prevail. Refer to your local regulation or IEC or BS 7671 . Canadian Code or NEC are NOT applicable.

Che Kuan Yau (Singapore)

### RE: Single Phase Exhaust Fan Motor Circuit Breaker

A correction.
I misplaced the decimal place as 1.8 kW rather than .18 kW.
A thermal-magnetic breaker of 2.5 Amps or more should start that motor.
That is based on the instantaneous trip being 10 times the thermal trip.
If the instantaneous trip is a lessor multiple of the thermal trip, you may need a higher rating.
Depending on local practice, the maximum allowable protection for the motor circuit conductors will probably be adequate to start the motor.
While the Canadian Code may not apply, motor starting currents and minimum breaker sizes to start the motors is about the same world wide.
The Canadian Code gives values that reliably start motors.

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

### RE: Single Phase Exhaust Fan Motor Circuit Breaker

Let’s not “bury the lead” here folks. 0.18kW is 1/4 HP, this is a very small blower motor, most likely Shaded Pole or at best, PSC type. In 99% of single phase motors that small, they are going to be made as “Thermally Protected”, meaning the motor itself has a built-in thermal protective device to protect against overload. It should say so right in the nameplate of the motor, or at the very least in the manufactures data sheets. Sometimes it is a simple thermal switch in the motor housing, sometimes in the case of Shaded Pole type motors it is the form of the motor itself being designed to be able to withstand locked rotor current indefinitely (called “Impedance Protected”).

In either case, you only need Feeder protection sized for the conductors going to it. Before adding superfluous devices to the circuit, I suggest that you investigate that motor a little more.

If you DO determine that it needs external protection, a Motor Protection Circuit Breaker is always sized to the motor nameplate Full Load Amps. Starting current is factored into the trip curve of the thermal protection in that breaker.

" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

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