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%
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.
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.
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.
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.
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.
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)
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?