Hermetically sealed compressors have internal heaters
I would think that was in the rating
the few extra amps may be controls
Circuit for Replacement HVAC System
- Thread starter Npstewart
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Hermetically sealed compressors have internal heaters
I would think that was in the rating
the few extra amps may be controls
Please read the original post. None was posted about a heater in the OP's case, let's assume there's none in his equipment. The equipment FLA is posted as 142 A, not your figure.
Besides, HVAC manufacturers use do not put FLA of their compressors. They are using "rated load amperes" instead. RLA is a computed figure that manufacturers do to get UL listing; "the compressor manufacturer must run a series of tests to determine the Maximum Continuous Amps (MCA) before the overload trips. Once that has been determined, UL says to divide the MCA by 1.56 to determine the RLA."
peter d
Senior Member
- Location
- New England
I would leave the existing 2/0 there in a heartbeat. 
MyCleveland
Senior Member
- Location
- Cleveland, Ohio
topgone
MCA is Minimum cct amps ? no
RLA is Running load amps ? no
UL reference, you are stating the 177 (MCA) value /1.56 = normal operating amps ~ 114amp ?
Do you have a UL reference I can look this up ?
MCA is Minimum cct amps ? no
RLA is Running load amps ? no
UL reference, you are stating the 177 (MCA) value /1.56 = normal operating amps ~ 114amp ?
Do you have a UL reference I can look this up ?
it has nothing to do with the NEC (other than being used for determining the mfgs mca)
it's the UL method to get the nameplate amps for the compressor
Force the compressor into overload
say it draws 200 A to trip the thermal OL
rated rla = 100 / 1.56 = 64 A
MyCleveland
Senior Member
- Location
- Cleveland, Ohio
afaik you must use the 177 A
based on the numbers the actual kva is ~47.4
but afaik the mfgs 177 must be use
MyCleveland
Senior Member
- Location
- Cleveland, Ohio
I am sorry, still not following you logic here
Your kVA number converts back to my ampacity that was stated as incorrect
Your kVA number converts back to my ampacity that was stated as incorrect
Please have a copy of UL 1995. or download it here.
Please read Clause 36.12 Determination of Rating. Hope that helps.
- Location
- Massachusetts
I would leave the existing 2/0 there in a heartbeat.
At the very least I would speak with the inspector about doing that.
MyCleveland
Senior Member
- Location
- Cleveland, Ohio
Thanks topgone
My comments were all based on 36.14 of your referenced doc
Taking us back to the fla value on the nameplate is wrong and therefore the MCA is wrong which would end up making the 2/0 wire OK
My comments were all based on 36.14 of your referenced doc
Taking us back to the fla value on the nameplate is wrong and therefore the MCA is wrong which would end up making the 2/0 wire OK
Let me help you.
"MCA" here refers to "maximum continuous amperes".
"RLA" here refers to "rated load amperes".
RLA = 64% of MCA or: MCA = RLA/0.64
FLA = 74% x MCA (of the compressor motor) or: FLA = MCA x 0.74
Given the RLA, we get the MCA:
MCA = RLA/64% = 51.3A/0.64 = 80.16A
With MCA = 80.16A, we can compute for the full-load amps (FLA) of the compressor motor:
FLA = MCA x 74% = 80.16 x0.74 = 59.32A!
PHP:
COMPRESSOR 1 59.32
COMPRESSOR 2 59.32
CONDENSER FAN1 7.0
CONDENSER FAN2 7.0
CONDENSER FAN3 7.0
SUPPLY FAN 16.7"Equipment FLA" = 59.32x2 +7.0 + 16.7
"Equipment FLA"= 142.3A
The Minimum Circuit Amperes = 1.25 * 142.3A = 177.8A!
The Maximum Overcurrent Protection = 2.25 X largest motor plus sum of the rest of the motorsMOP = 2.25 X 59.32 + (59.32+7.0+16.7) = 216 or 200A
- Location
- Massachusetts
Perhaps theoretically but when the MCA is provided that is what we have to go by.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
So some equipment lists a Minimum Circuit Ampacity and other equipment has a Maximum Continuous Amperes?
Same abbreviation, different quantity?
Sent from my XT1585 using Tapatalk
Same abbreviation, different quantity?
Sent from my XT1585 using Tapatalk
Mgraw
Senior Member
- Location
- Opelousas, Louisiana
- Occupation
- Electrician
Unfortunately the name plate is correct. Compressor manufacturers are required to use "rated load amps" to determine mca and mocp. As stated before rla is determined by test involving overload trip current and gradual voltage drop. RLA has no other purpose but determining mca and mocp.
Mgraw
Senior Member
- Location
- Opelousas, Louisiana
- Occupation
- Electrician
Some manufacturers use 1.44.
- Location
- Connecticut
- Occupation
- Engineer
Nothing in 36.12 says that the RLA is maximum continuous amps divided by 1.56:?
kwired
Electron manager
- Location
- NE Nebraska
Based on data in OP I don't see why MCA should be any more then 153 amps - and that is with all the single phase blower motors connected to same two lines. Balance them across all three lines and it shouldn't be more then about 144.
curt swartz
Electrical Contractor - San Jose, CA
- Location
- San Jose, CA
- Occupation
- Electrical Contractor
Then nameplate on most of the A/C equipment I have connected shows the MCA as the largest motor (compressor) X 1.25% + plus 100% of the other motors.
In this situation I would talk to the manufacture to confirm the nameplate data is correct. The data in the OP is from a cut sheet, not the actual unit. It would not be the first time a cut sheet and actual nameplate data don't match.
In this situation I would talk to the manufacture to confirm the nameplate data is correct. The data in the OP is from a cut sheet, not the actual unit. It would not be the first time a cut sheet and actual nameplate data don't match.
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