heat pump min and max

[sid123456]

Why is there a min and max on heat pumps breaker size. I have a 35 min 50 max pump. If I size the panel to all 35 amps, does that affect the efficiency?

 

[Buck Parrish]

Why is there a min and max on heat pumps breaker size. I have a 35 min 50 max pump. If I size the panel to all 35 amps, does that affect the efficiency?

Minimum 35 amps is the wire size? Maximum 50 is the breaker.
It will draw more current when it turns on.
The disconnect must be 125%

 

[sid123456]

Minimum 35 amps is the wire size? Maximum 50 is the breaker.
It will draw more current when it turns on.
The disconnect must be 125%

If I have 5 heat pumps 36 min and 50 max breaker. And I need to size a panel for just that. Is 185 right. 36*1.25 + 36 +36 +36 +36????? or 50*1.25 +50+ 50+ 50+ 50

 

[Buck Parrish]

Pretty close, Its the total calculated load; see 440.33

 

[infinity]

I don't see how this is directly addressed in the NEC. The MCA will already contain a 125% factor so why would you need to multiply 5 * 35 * 125%?

 

[soleowner]

Min max

Min max

I don't see how this is directly addressed in the NEC. The MCA will already contain a 125% factor so why would you need to multiply 5 * 35 * 125%?

The minimum and maximum over current protection is a good indicator of what heat pump manufacturer wire size they are recommending. Get the make and model and check their installation guide. Most HP manufacturers recommend the wire, fuse and breaker size. The name plate is not the place to do a load calc.

The range is offered because the compressor motor manufacturers do like to be held to an narrow amperage because of the varying installation conditions and codes.

Since a 36 min amp breakers don't exist, go with a 40 AMP as your wire and breaker size. The fuse, disco, wire gage, and breaker should match each other. These sizes are up to 50 feet.

Use a HACR breaker for the inrush amps on compressor start up. Non-HACR breakers tend to fail prematurely.

On the freak day that all the heat pumps start on the same time, I would install a 24v time delay relay "on break" and stagger the delay time. Get with you HVAC contractor on this.

 

[sid123456]

These are five pool heaters - 250 ft from main panel. I am trying to calculate the main breaker size for the subpanel.

I know when calculating motors, you take the largest and multiply by 125%, and then add the others. I assume that it is the same with these heaters, but which one do I use - the 36 or the 50?

Thanks for all your help.

 

[mcclary's electrical]

The minimum and maximum over current protection is a good indicator of what heat pump manufacturer wire size they are recommending. Get the make and model and check their installation guide. Most HP manufacturers recommend the wire, fuse and breaker size. The name plate is not the place to do a load calc.

The range is offered because the compressor motor manufacturers do like to be held to an narrow amperage because of the varying installation conditions and codes.

Since a 36 min amp breakers don't exist, go with a 40 AMP as your wire and breaker size. The fuse, disco, wire gage, and breaker should match each other. These sizes are up to 50 feet.

Use a HACR breaker for the inrush amps on compressor start up. Non-HACR breakers tend to fail prematurely.

On the freak day that all the heat pumps start on the same time, I would install a 24v time delay relay "on break" and stagger the delay time. Get with you HVAC contractor on this.

There are at least six things incorrect in this statement. The nameplate is all the information needed for this calculation. The first number is NOT MIN BREAKER. It's the min circuit ampacity, use it to size the wire. The second number is the maximum ocpd. ALWAYS use this for your breaker. A 40 will not hold under starting load. And a standard breaker is just fine.

 

[augie47]

These are five pool heaters - 250 ft from main panel. I am trying to calculate the main breaker size for the subpanel.

I know when calculating motors, you take the largest and multiply by 125%, and then add the others. I assume that it is the same with these heaters, but which one do I use - the 36 or the 50?

Thanks for all your help.

You would be fine using the 36. The 50 is for short-circuit/ground fault protection.
My initial thoughts are that you would be safe with the 36 x 5 as the 36 amps has the necessary multipliers factored in.
Per 440.33 you could take the actual currents and add 25% of the highest which would probably resulkt in a lower number.

 

[infinity]

There are at least six things incorrect in this statement. The nameplate is all the information needed for this calculation. The first number is NOT MIN BREAKER. It's the min circuit ampacity, use it to size the wire. The second number is the maximum ocpd. ALWAYS use this for your breaker. A 40 will not hold under starting load. And a standard breaker is just fine.

IMO an inverse time CB will allow the unit to start even if it's the same value as the MCA. The OCPD can be any size from the minimum (MCA) to the Max OCPD listed on the nameplate.

You would be fine using the 36. The 50 is for short-circuit/ground fault protection.
My initial thoughts are that you would be safe with the 36 x 5 as the 36 amps has the necessary multipliers factored in.
Per 440.33 you could take the actual currents and add 25% of the highest which would probably result in a lower number.

If this were a test question I believe that this would be the correct answer.

 

[marti smith]

The 35amps is the minumim ampacity that will allow the unit to start, and the 50 amps is the highest that the unit is allowed to reach and sustain a decent lifespan.

 

[sid123456]

Here are the specs, just got them now.
SQ155BRDEBNB

for the compressor: MCA - 32.3, Max breaker - 50, 3-phase, RLA 25, MCC 39, LRA 164

for the fan motor: HP 0.2, FLA 1

So, the consensus is that 5 of these heat pumps can safely be installed using a 200 amp breaker?

(32.3*5=161.5)

 

[augie47]

The 35amps is the minumim ampacity that will allow the unit to start, and the 50 amps is the highest that the unit is allowed to reach and sustain a decent lifespan.

sorry, but that sounds like an ole wives tale to me :grin: Here is what the NEC says:

440.4 Marking on Hermetic Refrigerant Motor-Compressors and Equipment.
(B) Multimotor and Combination-Load Equipment. Multimotor and combination-load equipment shall be provided with a visible nameplate marked with the maker's name, the rating in volts, frequency and number of phases, minimum supply circuit conductor ampacity, the maximum rating of the branch-circuit short-circuit and ground-fault protective device, and the short-circuit current rating of the motor controllers or industrial control panel. The ampacity shall be calculated by using Part IV and counting all the motors and other loads that will be operated at the same time. The branch-circuit short-circuit and ground-fault protective device rating shall not exceed the value calculated by using Part III. Multimotor or combination-load equipment for use on two or more circuits shall be marked with the above information for each circuit.

IV. Branch-Circuit Conductors
440.33 Motor-Compressor(s) With or Without Additional Motor Loads.
Conductors supplying one or more motor-compressor(s) with or without an additional load(s) shall have an ampacity not less than the sum of the rated-load or branch-circuit selection current ratings, whichever is larger, of all the motor-compressors plus the full-load currents of the other motors, plus 25 percent of the highest motor or motor-compressor rating in the group.

III. Branch-Circuit Short-Circuit and Ground-Fault Protection
440.22 Application and Selection.
(A) Rating or Setting for Individual Motor-Compressor. The motor-compressor branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the motor. A protective device having a rating or setting not exceeding 175 percent of the motor-compressor rated-load current or branch-circuit selection current, whichever is greater, shall be permitted, provided that, where the protection specified is not sufficient for the starting current of the motor, the rating or setting shall be permitted to be increased but shall not exceed 225 percent of the motor rated-load current or branch-circuit selection current, whichever is greater.
Exception: The rating of the branch-circuit short-circuit and ground-fault protective device shall not be required to be less than 15 amperes.
(B) Rating or Setting for Equipment. The equipment branch-circuit short-circuit and ground-fault protective device shall be capable of carrying the starting current of the equipment. Where the hermetic refrigerant motor-compressor is the only load on the circuit, the protection shall comply with 440.22(A). Where the equipment incorporates more than one hermetic refrigerant motor-compressor or a hermetic refrigerant motor-compressor and other motors or other loads, the equipment short-circuit and ground-fault protection shall comply with 430.53 and 440.22(B)(1) and (B)(2).

 

[sid123456]

Here are the specs, just got them now.
SQ155BRDEBNB

for the compressor: MCA - 32.3, Max breaker - 50, 3-phase, RLA 25, MCC 39, LRA 164

for the fan motor: HP 0.2, FLA 1

So, the consensus is that 5 of these heat pumps can safely be installed using a 200 amp breaker?

(32.3*5=161.5)

Is this right gentlemen?

 

[Cow]

What happens when the power goes out, then comes back on with all the units trying to start?

Do you think that 200 amp breaker will hold it or are you going to install some time delays like mentioned earlier?

 

[augie47]

Usig 440.33 you would obatin a load of 136.25 amps, using your 36 x 5 = 180, so would certain;y be comfortable with a 200 amp feeder/panel.
Soleowner/Cow's suggestion on a delay module merits some consideration, IMHO.

 

[Ragin Cajun]

The MCA of 32.3 is to size the conductors for one unit - #8. The MOCP is to size the breaker for one unit - 50A

For 5 units, to size the conductors per the NEC is as follows:
25 x 1.25 +1 + 4 x (25+1) = 136A (minimum)

For 5 units, to size the MOCP per the NEC is as follows:
50 + 4 x (25+1) = 154A or the next standard size, 175A

The total load for 5 units is a follows:
5 x (25+1) = 130A at whatever the voltage is. For example, @ 230V:
130A x 230V = 29.9 KVA (NOT KW)

Simply multiplying the MCA x 5 doesn't give you anything useful.

To make sure all 5 units don't start at once after an outage, typically a random start feature is available.

RC

 

[sid123456]

What happens when the power goes out, then comes back on with all the units trying to start?

Do you think that 200 amp breaker will hold it or are you going to install some time delays like mentioned earlier?

manufacturer is going to install delay circuit board....

 

[sid123456]

I would really like to say thanks for everybody's input.. It's a never ending learning experience....

Thank you

 

[LarryFine]

Sid, I'd agree with #8 copper and 50a breakers, and yes, a 200a panel should be just fine. Your calculated load should be ((5 x 25) + (25% of 25, which is 6-1/4)) 131.25a in total.