power per phase

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kiki12

Member
Location
Canada
i'm trying to calculate the power per phase for my panel schedule. few things are confusing me. I have a 120/208 panel. I am using a 50 amp breaker 2 pole for a condenser . Although the condensing unit spec is 230/1/60, i believe that is 230 volts single phase 60 hz.
Would the power per phase be
(208*50)/2 ?:?
or (230*50)/2
 

Smart $

Esteemed Member
Location
Ohio
i'm trying to calculate the power per phase for my panel schedule. few things are confusing me. I have a 120/208 panel. I am using a 50 amp breaker 2 pole for a condenser . Although the condensing unit spec is 230/1/60, i believe that is 230 volts single phase 60 hz.
Would the power per phase be
(208*50)/2 ?:?
or (230*50)/2
Well first of all, it should be verified the unit spec'd will operate on 208V. The cut sheet should have the 208V operation data necessary, as should the nameplate.

But should's and do's don't always align. :lol:

Anyway, the motor will attempt to achieve rated power... so the kVA will be approximately same.

Assuming the unit is rated 50A at 230V (which for calculation purposes is 240V)...

240V ? 50A = 208V ? ?

240V ? 50A ? 208V = ?
 

kiki12

Member
Location
Canada
i'm sorry i couldn't understand after "Assuming the unit is rated 50A at 230V (which for calculation purposes is 240V)...".
which of the calculations would i be using
 

Smart $

Esteemed Member
Location
Ohio
i'm sorry i couldn't understand after "Assuming the unit is rated 50A at 230V (which for calculation purposes is 240V)...".
which of the calculations would i be using
You didn't state the equipment kVA or current rating. As I said the kVA rating will be approximately the same at either 240V or 208V for motor operated equipment. Both equations arer the same, except in the latter 208V has been transposed to the left side... used to determine the amperes at 208V... just in case your panel schedule is using amperes instead of kVA (kVA yields reasonably accurate result; amperes do not).

Anyway, kVA is just nominal voltage times rated current... FOR EXAMPLE:

240V ? 50A = 208V ? 57.7 = 12,000VA = 12kVA

You'd enter 6kVA in each ? column the load is connected to.
 

kwired

Electron manager
Location
NE Nebraska
All calculations done so far seem to be based on 50 amps which was the breaker size for this unit. Actual rated load of this unit is probably in the 20-25 amp range if 50 amps is recommended breaker size.
 

kiki12

Member
Location
Canada
thats actually right. the rated ampacity is 21 amp. after calculation the maximum over current protection size was 50amp
 

Smart $

Esteemed Member
Location
Ohio
thats actually right. the rated ampacity is 21 amp. after calculation the maximum over current protection size was 50amp
The you'd use the 21A value for your kVA. Also, condensing units typically show minimum circuit ampacity (MCA) on the nameplate... and it includes 125% factoring for the motor. Also, maximum overcurrent protection (MOCP) is typically shown on the nameplate, so calcuation of ocpd is not necessary.

Getting back to your OP, you said this is for a condensor spec'd 230V 1?. As noted in post #2, you need to verify this condensor will operate on 208V... and the 208V MCA/MOCP should be provided on the nameplate (or documentation if the nameplate is not available for reference).
 
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