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Rotary phase converter question

C

collinkonow

Connecticut E-1 Electrical Contractor
Location
Franklin, CT
Occupation
Electrician
I am wiring a rotary phase converter. Its a Kay Industries unit model MA-4-A-VS-PA3-20-S. The RPC supplies power to 3 rooftop HVAC units. I have a few questions. The unit nameplate lists ONLY the following information:

input single phase voltage-230v
output 3 phase voltage- 230v
HP-20
Largest motor-20
Unit does NOT list single phase FLA, but there is a spot for it on the nameplate. However, it is blank.


1- I am guessing that because the FLA is not listed on the RPC, I need to size the conductors to 250% of FLA of the 3 rooftop units. They only have a max rated amps on the nameplate. I am assuming this would be used as FLA. Would this be correct? I am planning on contacting Kay Industries regarding the FLA but I'm guessing there was a reason it was left blank in that area on the nameplate. I would rather size based on 125% FLA as it should upsize the conductors.

2- The RPC load side feeds a main lug panel adjacent to the RPC. This MLO panel in turn feeds the three units. Is any OCP required between the RPC and the MLO panel? It seems that the OCP provided on the single phase line side of the unit should protect the load side of the RPC based on the total KVA. Am I correct in assuming this?

I appreciate any feedback/advice.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
455.4(4) requires the phase converter to show the input full load current.

The minimum circuit ampacity on the nameplate of the AC equipment is the sum of 125% of the compressor load plus the full load of all of the other motors in the unit. Typically you can also find the actual full loads of the compressors and the other motors. The sum of those currents is what I would use for the 250% in 455.6(A)(2).
 
C

collinkonow

Connecticut E-1 Electrical Contractor
Location
Franklin, CT
Occupation
Electrician
don_resqcapt19 said:
455.4(4) requires the phase converter to show the input full load current.

The minimum circuit ampacity on the nameplate of the AC equipment is the sum of 125% of the compressor load plus the full load of all of the other motors in the unit. Typically you can also find the actual full loads of the compressors and the other motors. The sum of those currents is what I would use for the 250% in 455.6(A)(2).
Click to expand...
Yes I found those individual loads as well on the rooftop unit nameplates. That'll be what I'll use for the 250%. Thanks for that advice.

Any idea regarding my question about OCPD load side of the RPC?

Thanks
 
E

Eddie702

Licensed Electrician
Location
Western Massachusetts
Occupation
Electrician
I looked on their web site and not a lot of info there.

For an MA-4 they call for a 100amp disconnect on the single-phase input with 80-amp fuses in it and 1/0 for the feeder.

On the load side they call for #4 wire.

I couldn't find any information on input or output amps

Their phone # is 574-780-7464

I would call them you don't want to install it and have it not be large enough. Give them all the load information
 
kwired

kwired

Electron manager
Location
NE Nebraska
Occupation
EC
hillbilly1 said:
Good, I don’t know why they rate them in hp, that they will not even run. Usually you have to at least double the size of the converter.
Click to expand...
Last one I did not so long ago was a Phase-A-Matic. They had a maximum single motor load that was less than the combined motor load. Seems the maximum single motor was about half the total motor rating. From recollection one I used was a 7.5 HP max but max single motor was 3 HP.

Depending on load characteristics you may get away with starting a larger motor in some instances though, it's really mostly all about the starting torque needed to accelerate the load.
 
don_resqcapt19

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
collinkonow said:
Yes I found those individual loads as well on the rooftop unit nameplates. That'll be what I'll use for the 250%. Thanks for that advice.

Any idea regarding my question about OCPD load side of the RPC?

Thanks
Click to expand...
I don't see anything in Article 455 requiring any protection on the load side of the phase converter.
 
C

collinkonow

Connecticut E-1 Electrical Contractor
Location
Franklin, CT
Occupation
Electrician
Eddie702 said:
I looked on their web site and not a lot of info there.

For an MA-4 they call for a 100amp disconnect on the single-phase input with 80-amp fuses in it and 1/0 for the feeder.

On the load side they call for #4 wire.

I couldn't find any information on input or output amps

Their phone # is 574-780-7464

I would call them you don't want to install it and have it not be large enough. Give them all the load information
Click to expand...
Thanks! I saw that info too.
Still makes me wonder where they get these wire and OCPD/Fuse sizes without disclosing FLA. Ultimately the NEC overrules their stated sizes and they should really disclose FLA as Don stated earlier
 
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