Air conditioner OCPD

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benmin

benmin

Senior Member
Location
Maine
Occupation
Master Electrician
Little rusty with Air conditioner calcs.

What size OCPD for a unit with the following nameplate

Comp 1 480 Volts/3 PH/ 7.8 RLA/ 52 LRA
Comp 2 480 Volts/3 PH/7.8 RLA/52 LRA
Indoor Blower 480 Volts/3 PH/ 3.9 FLA/2 HP
Outdoor Blower 480 Volts/1 PH/o.85 FLA/2.2 LRA
 
augie47

augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Ingenieur said:
what is?
mfg
model number/pn
btu/tonnage
Click to expand...

Historically I don't look for any of that as none of it does me a bit of good as an inspector.
As mentioned in Post #2, give me the min circuit amps and max overcurrent protection and I'm good to go.
If its a large unit and I have a a high SCA I might also want the withstand rating.
 
R

Russs57

Senior Member
Location
Miami, Florida, USA
Occupation
Maintenance Engineer
You are in Maine, no heat strips?

Based on what little info there is you are in the 30 tp 40 amp range. But you have to get info from manufacturer on maximum/minimum OCP. Brand and model number should suffice along with internet search.
 
I

Ingenieur

Senior Member
Location
Earth
augie47 said:
Historically I don't look for any of that as none of it does me a bit of good as an inspector.
As mentioned in Post #2, give me the min circuit amps and max overcurrent protection and I'm good to go.
If its a large unit and I have a a high SCA I might also want the withstand rating.
Click to expand...

it helps me as an engineer, guess that is why they provide it
the manual has that info
can't find the manual without mfg/pn/etc

ref page 45 for an example
looks like outdoor = 1.25 x fla comp 1 + fla comp 2 + fla fan
indoor is simply 1.25 x fla fan and smallest cb a 15
http://www.trane.com/download/equipmentpdfs/ssprc002en_r2.pdf
some units have similar specs as the op's
 
augie47

augie47

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Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
as Russs57 mentioned, be careful with that "indoor" number. The basic nameplate often does not taken into account any heat strips.
That info is normally provided by a multi-choice nameplate or an added nameplate that comes with the heat (if any)
 
david luchini

david luchini

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Staff member
Location
Connecticut
Occupation
Engineer
benmin said:
Little rusty with Air conditioner calcs.

What size OCPD for a unit with the following nameplate

Comp 1 480 Volts/3 PH/ 7.8 RLA/ 52 LRA
Comp 2 480 Volts/3 PH/7.8 RLA/52 LRA
Indoor Blower 480 Volts/3 PH/ 3.9 FLA/2 HP
Outdoor Blower 480 Volts/1 PH/o.85 FLA/2.2 LRA
Click to expand...

MCA=22.3
MOCP=25
 
kwired

kwired

Electron manager
Location
NE Nebraska
If all four motors are on a single nameplate, which OP sort of seems to be saying they are, then it is likely a rooftop unit or similar with all four motors within one housing.

Still should be MCA and MOCP on that plate, if the unit complies with listing standards.
 
I

Ingenieur

Senior Member
Location
Earth
kwired said:
If all four motors are on a single nameplate, which OP sort of seems to be saying they are, then it is likely a rooftop unit or similar with all four motors within one housing.

Still should be MCA and MOCP on that plate, if the unit complies with listing standards.
Click to expand...

makes sense
mfg/pn would clear things up
 
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