Motor HP and FLA

[fifty60]

I have equipment that contains refrigeration compressors. Generally, I will always use the rated HP and RLA (rated load amps) to list on the fuse label.

The equipment I am looking at now has a CPR valve that will limit the compressor capacity. The compressor manufacturer publishes data on the Running Load Amps for the this capacity, as well as the kilo-watt data at this capacity. There is not a published HP rating at this capacity.

Is it permissible to use the amps that the compressor manufacturer publishes for the controlled capacity, or do I have to use the Rated Load Amps?

Would I then be able to turn the KW data into HP and use that on my fuse label?

The manufacturer does not list the RLA on the nameplate of the compressor. They only list the LRA.

 

[Besoeker]

I have equipment that contains refrigeration compressors. Generally, I will always use the rated HP and RLA (rated load amps) to list on the fuse label.

The equipment I am looking at now has a CPR valve that will limit the compressor capacity. The compressor manufacturer publishes data on the Running Load Amps for the this capacity, as well as the kilo-watt data at this capacity. There is not a published HP rating at this capacity.

Is it permissible to use the amps that the compressor manufacturer publishes for the controlled capacity, or do I have to use the Rated Load Amps?

Would I then be able to turn the KW data into HP and use that on my fuse label?

The manufacturer does not list the RLA on the nameplate of the compressor. They only list the LRA.

Ignorant Brit strikes again...........
But if you already have kW why would you want to convert it to HP?
A little background. We, in UK and the rest of the EU land use just kW, not HP for motor ratings. So, for example, a 55kW motor is rated at 55kW shaft output.

 

[fifty60]

That is a good point. What is confusing me is since the manufacturer produces the amp tables based of of capacity, is it sufficient to use those amps on my equipment fuse label? Or, do I have use the RLA. The NEC says that I have to use the RLA on the nameplate. There is no RLA on the nameplate. The manufacturer publishes the RLA in a data sheet, but this would be at rated HP.

They also publish the Amps for the compressor at other capacities, as well as the KW information. How do I convert the KW to HP? For example, at a certain point I have 836W. Do I need to know the efficiency and power factor to make the HP conversion?

And after the conversion, is it permissible to use that to size my equipment service and put that HP and amp value on the equipment fuse label?

 

[Jraef]

I have equipment that contains refrigeration compressors. Generally, I will always use the rated HP and RLA (rated load amps) to list on the fuse label.

The equipment I am looking at now has a CPR valve that will limit the compressor capacity. The compressor manufacturer publishes data on the Running Load Amps for the this capacity, as well as the kilo-watt data at this capacity. There is not a published HP rating at this capacity.

Is it permissible to use the amps that the compressor manufacturer publishes for the controlled capacity, or do I have to use the Rated Load Amps?

Would I then be able to turn the KW data into HP and use that on my fuse label?

The manufacturer does not list the RLA on the nameplate of the compressor. They only list the LRA.

That's very common with ref compressors. What you usually see listed is the MOCP, Maximum Over Current Protection, for the compressor, along with the MCA, Minimum Conductor (or Circuit) Ampacity, which is what you would list. The OEM of the equipment using the compressor is usually who determines that. If you are using an assembly (such as an air conditioner) that has the compressor inside, that info should be on the unit nameplate of that assembly. But if you are assembling something from scratch using that compressor, YOU are taking on that responsibility and it is up to you to determine the proper equation to use that relates to your unit and the approvals it requires.

 

[Besoeker]

That is a good point. What is confusing me is since the manufacturer produces the amp tables based of of capacity, is it sufficient to use those amps on my equipment fuse label? Or, do I have use the RLA. The NEC says that I have to use the RLA on the nameplate. There is no RLA on the nameplate. The manufacturer publishes the RLA in a data sheet, but this would be at rated HP.

They also publish the Amps for the compressor at other capacities, as well as the KW information. How do I convert the KW to HP? For example, at a certain point I have 836W. Do I need to know the efficiency and power factor to make the HP conversion?

And after the conversion, is it permissible to use that to size my equipment service and put that HP and amp value on the equipment fuse label?

The conversion is 1 HP is 0.746 kW. Bear in mid that this will give you output kW and you would need the efficiency to get input kW. PF gives you kVA.

 

[fifty60]

Is it correct to take the KW and convert it to HP? I know that this will be based of the true power and not the apparent power. Are HP rating generally converted from the true power?

 

[Smart $]

Is it correct to take the KW and convert it to HP? I know that this will be based of the true power and not the apparent power. Are HP rating generally converted from the true power?

A motor HP rating is output power (i.e. mechanical) and can be directly converted to output kW and vice-versa.

 

[Besoeker]

Is it correct to take the KW and convert it to HP? I know that this will be based of the true power and not the apparent power. Are HP rating generally converted from the true power?

HP and kW are both units of power. Real power if you like.

 

[Smart $]

HP and kW are both units of power. Real power if you like.

True, but input kW includes losses (the complement of efficiency) not realized at the mechanical output.

 

[Besoeker]

True, but input kW includes losses (the complement of efficiency) not realized at the mechanical output.

Yes. I made that point in post #5.
But we don't rate motors based on input power. As I said, what we call a 55kW motor means 55kW output.
For input, you would be more concerned with kVA or full load current for sizing supply conductors and overcurrent protection. You can't get that from input kW.

 

[Sahib]

I have equipment that contains refrigeration compressors. Generally, I will always use the rated HP and RLA (rated load amps) to list on the fuse label.

The equipment I am looking at now has a CPR valve that will limit the compressor capacity. The compressor manufacturer publishes data on the Running Load Amps for the this capacity, as well as the kilo-watt data at this capacity. There is not a published HP rating at this capacity.

Is it permissible to use the amps that the compressor manufacturer publishes for the controlled capacity, or do I have to use the Rated Load Amps?

Would I then be able to turn the KW data into HP and use that on my fuse label?o

The manufacturer does not list the RLA on the nameplate of the compressor. They only list the LRA.

My stand:
RLA-for sizing circuit conductor
LRA-OCPD sizing.

 

[fifty60]

If the compressor manufacturer is giving me the amps the compressor draws at a given capacity, then that amps will be the input amps right? To get the output amps, I would need the PF and efficiency, but to size my disconnect I only need input amps at capacity multiplied by the voltage to get the kilowatt rating and then divide that by 746?

So if the RLA is 10.9, and the input voltage is 230V, then my HP rating would be 3.5HP?

 

[fifty60]

That is, the HP rating for my disconnect..

 

[Sahib]

My suggestion is to take LRA and not RLA top calculate JP rating of disconnect.

 

[fifty60]

Yes, understood. What I need to put on the Fuse label is the HP rating and the RLA. There is not an RLA on the compressor. I have the amps the compressor will draw with the CPR valve limiting the capacity. I want to take that information to provide the HP of the largest motor and largest motor amps for my fuse label...

 

[Sahib]

But AFAIK HP rating is assigned by disconnect manufacturer and not in the field and so my last post is cancelled.

 

[Besoeker]

If the compressor manufacturer is giving me the amps the compressor draws at a given capacity, then that amps will be the input amps right? To get the output amps, I would need the PF and efficiency, but to size my disconnect I only need input amps at capacity multiplied by the voltage to get the kilowatt rating and then divide that by 746?

So if the RLA is 10.9, and the input voltage is 230V, then my HP rating would be 3.5HP?

That would give you kVA, not power.

 

[fifty60]

OK, and from the KVA with the PF and EFF I would get the output HP. Here are the Amps and corresponding Watts the manufacturer is giving me. The first row (4.2A and 346W) are for a 115V rated compressor. The remaining two (5.05A and 832W, and 3.6A and 830W) are for a 230V compressor. I should be able to take these watts and devide by 746 to give me my HP rating at that capacity?

4.2 amps	346 Watts
5.05 amps	832 Watts
3.6 amps	830 Watts

 

[Besoeker]

OK, and from the KVA with the PF and EFF I would get the output HP. Here are the Amps and corresponding Watts the manufacturer is giving me. The first row (4.2A and 346W) are for a 115V rated compressor. The remaining two (5.05A and 832W, and 3.6A and 830W) are for a 230V compressor. I should be able to take these watts and devide by 746 to give me my HP rating at that capacity?

4.2 amps	346 Watts
5.05 amps	832 Watts
3.6 amps	830 Watts

If these figures are for input power, you need to multiply by efficiency to get output power.
I'm not sure about the numbers though.
5.05A for 833W
3.6A for 830W

A 40% increase in current (3.6A to 5.05A) for just a 3W power increase?

 

[Smart $]

OK, and from the KVA with the PF and EFF I would get the output HP. Here are the Amps and corresponding Watts the manufacturer is giving me. The first row (4.2A and 346W) are for a 115V rated compressor. The remaining two (5.05A and 832W, and 3.6A and 830W) are for a 230V compressor. I should be able to take these watts and devide by 746 to give me my HP rating at that capacity?

4.2 amps	346 Watts
5.05 amps	832 Watts
3.6 amps	830 Watts

I would convert the watts to HP then use the ampere values in Article 430 Tables, e.g. 346W = 0.46HP round up to 1/2HP, Table value 9.8A for MOCP/MCA ratings.