Fans

[hhsting]

I four fans in one circuit which are also fed from emergency generator in bio lab. Each fan draws full load amps of 3A. Manufacturer has not provided MOCP so engineer shows it calculated as follows:

(1.25x3) + 3 + 3 + 3 = 12.75A.


The breaker size he provided is 20A with #12awg conductors.


However i think the engineer above calculated MCA not MOCP.

According to me calculation should be for MOCP

(2.25x3) + 3 + 3+3 = 15.75A

But above 15.75A is MOCP (maximum overcurrent protection)

So the question I have is should not the breaker be sized 15A and not 20A?

 

[augie47]

120v ?? Thermally Protected ??

 

[hhsting]

120v ?? Thermally Protected ??

They are 120V.

Thermally protected as in thermal breaker or thermal overload protection? Which one?

I am not sure if it has thermal overload protection.

 

[GoldDigger]

They are 120V.

Thermally protected as in thermal breaker or thermal overload protection? Which one?

I am not sure if it has thermal overload protection.

Posssibly impedance protected, as is common for small fan motors?

 

[hhsting]

Posssibly impedance protected, as is common for small fan motors?

I am not sure. What does all that have to do with post #1 questions?


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[GoldDigger]

I am not sure. What does all that have to do with post #1 questions?


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Well, it might have an impact on the need for Overload protection on the multiple fan circuit.

 

[david luchini]

So the question I have is should not the breaker be sized 15A and not 20A?

20A circuit breaker is fine, assuming each fan is properly protected against overload.

 

[don_resqcapt19]

No calculations required...see 430.53(A).

 

[Rock86]

I four fans in one circuit which are also fed from emergency generator in bio lab. Each fan draws full load amps of 3A. Manufacturer has not provided MOCP so engineer shows it calculated as follows:

(1.25x3) + 3 + 3 + 3 = 12.75A.


The breaker size he provided is 20A with #12awg conductors.


However i think the engineer above calculated MCA not MOCP.

According to me calculation should be for MOCP

(2.25x3) + 3 + 3+3 = 15.75A

But above 15.75A is MOCP (maximum overcurrent protection)

So the question I have is should not the breaker be sized 15A and not 20A?

If it is a design engineer, they are not designing MOCP, they are calculating circuit ampacity. Manufacturer assigns MOCP.
Refer to don_resqcapt19's post for a valuable reference.