electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
How to size branch circuit OCPD and conductors for this
- Thread starter electrofelon
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I would use the KW÷480×1.25. Which would be a 60 amp breaker with #6's. I'll be interested to see what someone else says. It's a good question. Not sure my answer is right........
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- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Yes. 22kW /.746 = 29.46HP. Use the NEC tables for FLA to size conductors based on 30HP. Use the 45FLA only for sizing the OL heaters if you are supplying them, and for sizing the fuses or CB.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Thanks. I haven't looked at the actual motor, the thing is still crated up, but I assume the motor will be rated in kw, is that because it is European?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Yes. We still like our horsies here. The Europeans ate theirs...
- Location
- New Jersey
- Occupation
- Journeyman Electrician
According to T430.250 a 30 HP @ 460 volts has an FLC of 40 amps so minimum conductor size is 40*125% = 50 amps. Could be #8 THHN with 75° terminals.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I realize we should use the table for conductor sizwe but if the unit requires a 45 amp fla then I would use that and not 40 amps.
The overcurrent protective device usually, depending on a few factors, can be sized 250% of the fla. 430.52
The overcurrent protective device usually, depending on a few factors, can be sized 250% of the fla. 430.52
JFletcher
Senior Member
- Location
- Williamsburg, VA
I'm thinking a 60A breaker will not hold on startup, I'd probably use a 90 or 100. I would go with #6 or larger wire depending on how far the motor is from the panel.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Yeah its odd the fla is higher than the table
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
A little more sleuthing shows that this is a Gardner - Denver Variable Speed oil free compressor and it likely has a cooling fan and/or lube pump that runs constant speed in addition to the main compressor motor, explaining why the nameplate says 45A. If so, you need to get hold of the installation manual and find the "MCA" and / or "MOCP" values for the entire SYSTEM.
MCA = Minimum Circuit Ampacity; i.e. conductor size
MOCP = Maximum Over Current Protection; i.e. circuit breaker or fuse.
Gardner Denver doesn't provide manuals on-line, you will need to call their local distributor most likely.
MCA = Minimum Circuit Ampacity; i.e. conductor size
MOCP = Maximum Over Current Protection; i.e. circuit breaker or fuse.
Gardner Denver doesn't provide manuals on-line, you will need to call their local distributor most likely.
Unfortunately, this particular unit is made in Germany.
You can get manuals for G-D US manufactured products here:
https://sgdsap1.gardnerdenver.com:1443/sap/bc/gui/sap/its/ZDOC/!
kwired
Electron manager
- Location
- NE Nebraska
I'd base everything off the nameplate load of 45 amps. That should have power factor and efficiency built into it.
The 22kW might be motor output, might be compressor output.
Add: I guess it says motor capacity, but is likely output rating not input rating.
The 22kW might be motor output, might be compressor output.
Add: I guess it says motor capacity, but is likely output rating not input rating.
I agree
if nameplate (45) > (30 HP, 40 A) table I would use np to size conductors, #6
ol's obviously nameplate
cb i/t < 250%, so not a big deal, 100 vs 112 (110 or 125), use the 100
perhaps the 45 A is not only motor?
the 22 kw is 'installed motor capacity'
kwired
Electron manager
- Location
- NE Nebraska
I figured that out after initial reply. But I bet that is rating of output shaft, once you figure out power factor and efficiency the rated input KVA is higher, and ultimately is the 45 amps @ 460 volts.
JFletcher
Senior Member
- Location
- Williamsburg, VA
Jraef brought up good points re: cooling and lube oil pumps. How would these small motors typically be protected? Internal fuses? I'd presume they are pretty small and even a dead short would fry either before tripping the unit's main breaker/fuses. Or would they be mechanically driven from the main motor?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
That's something Ive never been clear on. When do I need to provide NEC overload protection for something that has a motor in it? Does the manufacturer take care of that? Am I supossed to dive into and dissect the whole thing and see if it supplied to meet the NEC? It would be nice if everything was supplied with the data like HVAC equipment, as Jraef mentioned. I often don't see that provided.
How to size branch circuit OCPD and conductors for this
If I recall correctly, “VS” in the model number indicates variable speed as in VFD. If air-cooled, it will have an additional fan motor. This fan motor should have its own IEC starter with overloads and fuses. The amps on the nameplate should include everything at full load.
If I recall correctly, “VS” in the model number indicates variable speed as in VFD. If air-cooled, it will have an additional fan motor. This fan motor should have its own IEC starter with overloads and fuses. The amps on the nameplate should include everything at full load.
drktmplr12
Senior Member
- Location
- South Florida
- Occupation
- Electrical Engineer
did it come with a UL listed panel? if so, take a look at the schematics and see what, if anything is provided.
430.32 covers which overload protections are suitable for continuous duty motors over and under 1 HP.
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