Why the HVAC vendors do not provide name plate details of the Motor, Instead they provide only MCA (Minimum Circuit Amperes), MOCP (Maximum Over current protection), RLA ( Running Load Amperes), LRA (Locked Rotor Amperes). Suppose if the ACCU has " 2 compressors + 6 condenser fan's + some auxiliaries" we just have the MCA and MOCP. How do we calculate the voltage drop from these data as we do not have the starting PF and starting amperes?. I suppose I have to ask for RLA and LRA in this case but why don't they just provide the name plate details of the motor or datasheet of Motor?
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HVAC Motors - Name Plate Details 2
- Thread starter charz
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My solution. There may be other suggestions.
The fans generally do not start immediately, however the fan load is typically very low compared to the compressor load.
I would ignore the fans.
Assumption #1
Starting Amps = LRA
Full load Amps = RLA
FLA is mostly real current.
LRA is mostly reactive current and the real component will be at 90 degrees to the reactive component and have minimum effect.
I would use these values to calculate starting PF.
Assumption #2
The calculated PF will be lower than the actual starting PF. This will compensate for the fan load being ignored.
I would use the LRA to calculate the voltage drop three ways:
1 Using the calculated value for PF.
2 Using a starting PF or 5%.
3 Using a stating PF of 10%
Compare the voltage drop results and pick the result that feels good.
The installer may not have the technical training to use the information that you lack.
In the majority of installation, voltage drop calculations are not needed or performed.
Often only when there is a voltage drop issue after installation and then only if an engineer is engaged to solve the problem will detailed voltage drop calculations be performed. But at that point the actual current and voltage drop measurements should be available and the detailed calculations may never be done.
Bill
--------------------
"Why not the best?"
Jimmy Carter
The fans generally do not start immediately, however the fan load is typically very low compared to the compressor load.
I would ignore the fans.
Assumption #1
Starting Amps = LRA
Full load Amps = RLA
FLA is mostly real current.
LRA is mostly reactive current and the real component will be at 90 degrees to the reactive component and have minimum effect.
I would use these values to calculate starting PF.
Assumption #2
The calculated PF will be lower than the actual starting PF. This will compensate for the fan load being ignored.
I would use the LRA to calculate the voltage drop three ways:
1 Using the calculated value for PF.
2 Using a starting PF or 5%.
3 Using a stating PF of 10%
Compare the voltage drop results and pick the result that feels good.
In many jurisdictions the HVAC installer will be working on a restricted license that allows him to add a circuit to an existing panel.OP said:
The installer may not have the technical training to use the information that you lack.
In the majority of installation, voltage drop calculations are not needed or performed.
Often only when there is a voltage drop issue after installation and then only if an engineer is engaged to solve the problem will detailed voltage drop calculations be performed. But at that point the actual current and voltage drop measurements should be available and the detailed calculations may never be done.
Bill
--------------------
"Why not the best?"
Jimmy Carter
- Moderator
- #4
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