OCPD on a Water Source Heat Pump

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dpenbert

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I have technical data on a water source heat pump that gives me MCA, Maximum Fuse Size, and total unit Full Load Amps. The MCA is 26.8(A), the Max. Fuse Size is 60(A) and the total Full Load Amps is 27.2(A). Based on this information, what is the appropriate panel breaker size(branch-circuit protection) that needs to be used and the conductor size? I am not for sure if I can take this FLA and multiply it by my required 175% (Dual Element Time-Delay Fuse) max rating. It doesn't provide me with the hp.

Thanks,

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David - St. Louis, MO
 
Re: OCPD on a Water Source Heat Pump

my first thought is that IF the instructions only mention a fuse size, then you need a fuse somewhere.
 
Re: OCPD on a Water Source Heat Pump

Then you will have to find some heat pumps that list "Max. fuse or breaker size". If it says maximum fuse size, fuses are required.

Steve
 
Re: OCPD on a Water Source Heat Pump

How do you end up with a full load amp rating higher than the minimum circuit ampacity rating?
 
Re: OCPD on a Water Source Heat Pump

I checked the actual unit in the building and it says min ckt brk amps = 35. Based on this information, what size conductors and ckt brk size would one use?


Thanks,

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David
 
Re: OCPD on a Water Source Heat Pump

Lets start over.. I have was looking at another size when I gave the information..

The MCA = 26.8(A) , FLA = 22(A) , MOCP = 45(A)


Sorry, thanks for catching that.


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David
 
Re: OCPD on a Water Source Heat Pump

Originally posted by dpenbert:
Lets start over.. I have was looking at another size when I gave the information..

The MCA = 26.8(A) , FLA = 22(A) , MOCP = 45(A)


Sorry, thanks for catching that.


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David
Click to expand...
David if that is now correct and it says that MOCP can be a breaker this is what is allowed.

45 Amp breaker

10 AWG copper

You can forget about the FLA.

BUT, as the others have pointed out if it says max fuse size you will have to put in a fusible disconnect and some fuses.
 
Re: OCPD on a Water Source Heat Pump

The thing that has been hard for me to understand is what size of circuit breaker to use at the panel. If you use the MCA to size the wire, you should be able to use #10 conductors. For the OCP I was told to generally use 175% multiplied by the FLA to find the maximum rating of OCP. In this case if you take 175% x 22(the nameplate rating FLA)you get 38.5(A) and per 430.52 you can use a 40(A) breaker. At the Water Source Heat Pump side we are installing a non-fusable disconnect. If you use a 40(A) breaker, that doesn't really protect the #10 conductors. I have been told that the motor side protects the conductors, but what part? I've seen similar threads to this, but I still don't understand it. Any explanations would be greatly appreciated.


Thanks,
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David
 
Re: OCPD on a Water Source Heat Pump

David,
In this type of circuit the panel breaker provides short circuit and ground fault protection for the conductors. The 45 amp breaker will provide this protection for the #10 conductors. The only way that the circuit conductors could be overloaded is if the equipment itself has some type of malfunction. In that case the internal unit overload will open and protect both the equipment and the conductor. Short circuit and ground fault protection can only be provided at the source of the circuit, but overload protection can be provided at either the source end or the load end.
Don
 
Re: OCPD on a Water Source Heat Pump

So when given the nameplate MOCP, FLA, MCA, how would I find the "minimum" panel circuit breaker that can be used? Also, if the equipment's internal function protects the equipment and conductors, a 30(A) or 60(A) non-fusable disconnect will suffice for safety means on the load side?

Thanks,

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David
 
Re: OCPD on a Water Source Heat Pump

David for an HVAC unit that is labeled with the MCA and the MOCP you must use those figures.

Forget the FLA, forget about 175%.

Also, if the equipment's internal function protects the equipment and conductors, a 30(A) or 60(A) non-fusable disconnect will suffice for safety means on the load side?
Click to expand...
No, you must use a breaker or fuse no larger than the MOCP, remember MOCP is Maximum Overcurrent projection. You may use a breaker as small as the MCA but it may trip sometimes.

You may also use wire larger than the MCA, depending on the circuit length it may make good sense to use 8 or 6 AWG but you may use 10 AWG with the 45 breaker or fuse.

It's all about how it was tested by UL or whoever, that is why if the unit only lists fuses you must use fuses.

You may not think it makes a difference and you could be right, except you would have a NEC violation. 110.3(B)
 
Re: OCPD on a Water Source Heat Pump

Don't you have to have disconnecting means on or near the equipment for service, or a "lockout" breaker?

Thanks for the responses,

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David
 
Re: OCPD on a Water Source Heat Pump

Originally posted by dpenbert:
Don't you have to have disconnecting means on or near the equipment for service, or a "lockout" breaker?
Click to expand...
That is another issue all together and IMO a lockout breaker will not be compliant most times.


ARTICLE 440 Air-Conditioning and Refrigerating Equipment

440.1 Scope.
The provisions of this article apply to electric motor-driven air-conditioning and refrigerating equipment and to the branch circuits and controllers for such equipment. It provides for the special considerations necessary for circuits supplying hermetic refrigerant motor-compressors and for any air-conditioning or refrigerating equipment that is supplied from a branch circuit that supplies a hermetic refrigerant motor-compressor.

440.14 Location.
Disconnecting means shall be located within sight from and readily accessible from the air-conditioning or refrigerating equipment. The disconnecting means shall be permitted to be installed on or within the air-conditioning or refrigerating equipment.

The disconnecting means shall not be located on panels that are designed to allow access to the air-conditioning or refrigeration equipment.

Exception No. 1: Where the disconnecting means provided in accordance with 430.102(A) is capable of being locked in the open position, and the refrigerating or air-conditioning equipment is essential to an industrial process in a facility where the conditions of maintenance and the supervision ensure that only qualified persons service the equipment, a disconnecting means within sight from the equipment shall not be required.

Exception No. 2: Where an attachment plug and receptacle serve as the disconnecting means in accordance with 440.13, their location shall be accessible but shall not be required to be readily accessible.
Click to expand...
This heat pump must have a disconnecting means within sight.

[ September 29, 2005, 05:48 AM: Message edited by: iwire ]
 
Re: OCPD on a Water Source Heat Pump

This makes much more sense to me now, thanks iwire for the reference on the disconnect. My last question involves fuse vs breaker. The technical data sheet says maximum fuse size and the actual unit says maximum ckt brk size. Can I assume it is ok to use a 45(A) circuit breaker based on the nameplate of the equipment?
Also, since I am dealing with the disconnect as well, should I go with a 60(A) disconnect?

Thanks a bunch,


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David
 
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