Water Source Heat-Pump Breaker Sizing

[Jackbenimble7]

Hi all,

I have 4 water source heat pumps that I'm trying to size protection for and I'm given the following electrical specs:

ELECTRICAL	-	-	-	-
EVAPORATOR FAN	-	-	COMPRESSOR	-
V/PH/HZ	FLA	HP	RLA	LRA
480/3/60	2.6	1/3	2.9	30
480/3/60	5.5	3/4	6.3	55
480/3/60	5.5	1/2	6.1	41
480/3/60	2.6	1/3	2.9	30

So I'm a little confused on what this chart is trying to tell me. It appears that there are two devices drawing power, the compressor and electrical fan. My first instinct is to add the FLA of the evaporator fan to the RLA of the compressor and size the breaker/wire for that summation. For example, my first water-source heat-pump would have (2.6A + 2.9A) * 125% = 7A = 15A breaker/#12 wire. But the LRA is confusing me. To be honest, this whole schedule confuses me and I'm not sure how to size the OCPDs in this situation.

Can anyone shed some light on what they think I need to do here?

Thank you.

Jack

 

[texie]

Are these units listed? They should have MCA and Max OCPD listed on the labels.

 

[Jraef]

Are you wanting to size the protection for each individual unit, a branch circuit with multiple motors, or a feeder for multiple stand-alone starters for each of the units?

Each individual unit, your rules are laid out in Article 430.52.

Multiple motors on one branch circuit, 450.53

Multiple stand-alone starters for units on the same feeder, 430.61.

 

[Ingenieur]

model/pn/mfg are invaluable

LRA = locked rotor amps, not really pertinent to sizing other than CB should be smaller

 

[Jackbenimble7]

Thanks for responses everyone.

Waiting on cutsheets, but the mechanical engineer has been less than responsive...

JRaef - my confusion is more due to the fact that the schedule lists two separate loads - one for the compressor and one for the evaporator fan. All devices shall be on their own circuit, so that's not as big of a deal, but I wanted to see if that's typical for these pumps to have a compressor and an evaporator fan on the same circuit. And if that's the case, do you just add those two amperages together to determine your OCP sizes.

 

[david luchini]

And if that's the case, do you just add those two amperages together to determine your OCP sizes.

See 440.22(A)(1).

 

[kwired]

Hi all,

I have 4 water source heat pumps that I'm trying to size protection for and I'm given the following electrical specs:

ELECTRICAL	-	-	-	-
EVAPORATOR FAN	-	-	COMPRESSOR	-
V/PH/HZ	FLA	HP	RLA	LRA
480/3/60	2.6	1/3	2.9	30
480/3/60	5.5	3/4	6.3	55
480/3/60	5.5	1/2	6.1	41
480/3/60	2.6	1/3	2.9	30

So I'm a little confused on what this chart is trying to tell me. It appears that there are two devices drawing power, the compressor and electrical fan. My first instinct is to add the FLA of the evaporator fan to the RLA of the compressor and size the breaker/wire for that summation. For example, my first water-source heat-pump would have (2.6A + 2.9A) * 125% = 7A = 15A breaker/#12 wire. But the LRA is confusing me. To be honest, this whole schedule confuses me and I'm not sure how to size the OCPDs in this situation.

Can anyone shed some light on what they think I need to do here?

Thank you.

Jack

Got me confused on what you have there as well. 1/2 hp 3 phase 480 volt motor should only draw about an amp, which makes it even more confusing, 5.5 amps is a little more then you would see from a 3 HP motor.

 

[kingpb]

Until you can get better data, you can add the FLA (Fan) to the RLA (compressor comes in Rated Load Amps) to get the total unit FLA. These are 1 fan/1 compressor units. Add about 20% above that for your estimate MCA.

This should get you by until you can get the actual MCA.

 

[JoeStillman]

With a water source heat pump, the compressor and evaporator fan are going to be on the same circuit. For bidding purposes (not for construction!) I would calculate the WSA and MOCP like this;

MOCP = Comp RLA x 2.25 + fan FLA
WSA = Comp RLA x 1.25 + fan FLA

When it's time for construction, throw these calculations in the trash and size wire and OCP per the equipment nameplate.