Breaker Selection for Roof Top units

[kitha]

MOCP=50
FLA=47

Can somebody tell me the procedure to select the breaker for above Roof Top AC unit. I am doing a project in Canada and bit confused with their code. The code is same as NEC but they do it differently.

If I did it accori8dng to NEC I would go with the 110A breaker with 50A trip setting and feeder for 50A. But my Canadian counter parts select the 50A breaker and feeder for 50A. Can this be right?

 

[davidbeach]

What part of MAXIMUM OverCurrent Protection do you have problems understanding?

I have no idea what so ever what you could mean by 110A breaker with 50A trip. I've never seen a 110A breaker that could have a 50A trip.

 

[kitha]

MOCP is usually for fuses. i.e if a fuse is selected it should be 50A. But if a breaker is selected shouldnt it be different to take care of starting requirements?

 

[waross]

Are you sure you have read the nameplate correctly? MOCP=50 seems a little low for FLA=47, for fuses or breakers.
50 seems low even for Maximum Over Load Protection.
Possibly the MOCP=50 should be MOCP=150 or 250.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[rbulsara]

Assuming the MOCP value is correct, you can use either a breaker or fuse rated the MOCP value, that 50A in this case. If there is an error in the nameplate itself, it is a different matter.

On the face value, your Canadian counterpart is correct.

If you really want to calculate you need to list the components and their rating in the unit, such as motors, heaters, fans, etc and need to know what components are likely to run simultaneously.


Rafiq Bulsara

http://www.srengineersct.com

 

[Pikoplatt]

Check the Manual on the Roof-Top unit (I assume an HVAC unit). It usually tells you the maximum rating of the Overcurrent Protective Device(OCPD) required for the unit. It also indicates that the OCPD should be UL listed as Type HACR (Heating, Air-Conditioning and Refrigeration).