Circuit for Replacement HVAC System

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MyCleveland said:
What HEATER current ? FLA = 131.5
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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."
 
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 ?
 
MyCleveland said:
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 ?
Click to expand...

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
 
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
 
MyCleveland said:
I am sorry, still not following you logic here
Your kVA number converts back to my ampacity that was stated as incorrect
Click to expand...

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
Distributing the 3, single-phase fans on the 3 phases will balance the loading.
"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 motors
MOP = 2.25 X 59.32 + (59.32+7.0+16.7) = 216 or 200A​
 
So some equipment lists a Minimum Circuit Ampacity and other equipment has a Maximum Continuous Amperes?
Same abbreviation, different quantity?

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MyCleveland said:
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
Click to expand...

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.
 
topgone said:
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."
Click to expand...

Some manufacturers use 1.44.
 
If the MCA info. is from a cutsheet, I'd also verify with the equipment nameplate. With a little luck, maybe the nameplate will say 175 amps.
 
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.
 
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.
 
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