Buck Boost Transformer

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Little Bill

Little Bill

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If you have a piece of equipment that is rated at 48A and you have to adjust for a motor by 125%, making it need 60A. Then you need a buck/boost transformer to boost the voltage from 208V to 240V, would the transformer need to be 48A or 60A?
 
I would say the 60a number. Remember, you only need to size the transformer for 60 x (240-208) = 60 x 32 = 1920 = 2 kVa.
 
Little Bill said:
If you have a piece of equipment that is rated at 48A and you have to adjust for a motor by 125%, making it need 60A. Then you need a buck/boost transformer to boost the voltage from 208V to 240V, would the transformer need to be 48A or 60A?
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The equipment is a single motor? What size is the OCPD?
 
The nec doesn't provide much guidance in sizing transformers. I think it just comes down to 110.3, but even then it's not clear exactly what figure to use for your load. I wouldn't hesitate to use less than the required conductor ampacity in many situations
 
david luchini said:
The equipment is a single motor? What size is the OCPD?
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iceworm said:
LB -
The motor is 240V, 3ph?
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The equipment is a Hot Tub. It has two, maybe three motors, and heaters. The tub is capable of 40A, 50A, or 60A. The 60A is if you want the heaters to work while the jets are running.
I have another thread that explains the reason for this but I didn't want to add to that thread. https://forums.mikeholt.com/showthread.php?t=195825

The dwelling has a 1200A 3Ø service 208/120. The tub is single phase 240V. To cover myself, I called the Spa manager and he checked with the mfg. The mfg said I would need a buck/boost transformer to bring the voltage to 240V. He said something about the control board not liking the 208V and would try and reset everytime another pump or heater would come on.
The nameplate on the tub says 48V but I know from experience they don't include the 125% for the motor(s). So 48A x 125% = 60A

I just needed to know if I should size the transformer for 48A or 60A.
 
Little Bill said:
I just needed to know if I should size the transformer for 48A or 60A.
Click to expand...

If you get the 60A it will cost more and the markup will be more but I wouldn't let that influence me.:happysad:

Schneider Electric has a transformer calculator and I think they use the 48A but you can check.

The bad thing is that you have motors and heaters.
 
Does this hot tub require straight 240 or 120/240? If it requires 120/240 the Buck Boost transformer will not work since it will also change the voltage from hot to neutral.
 
Little Bill said:
... The tub is single phase 240V.
... The mfg said I would need a buck/boost transformer to bring the voltage to 240V. He said something about the control board not liking the 208V and would try and reset everytime another pump or heater would come on. ....
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Okay, 1ph, 240V. So you don't need an auto transformer or three buck-boost.

(Slow poster: As curt S said, )
Next question:
Does the equipment need a balanced neutral from the 240V? If so, one BB won't work.

I know that this is not what you are asking, however, how the equipment is configured may well limit your options
 
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iceworm said:
Okay, 1ph, 240V. So you don't need an auto transformer or three buck-boost.

(Slow poster: As curt S said, )
Next question:
Does the equipment need a balanced neutral from the 240V? If so, one BB won't work.

I know that this is not what you are asking, however, how the equipment is configured may well limit your options
Click to expand...

No neutral required on the tub.
 
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