Nec article 610.53(a) taps to control transformer calculation questions

[javiersalas52d]

I have a question regarding taps to control transformer calculations, NEC ARTICLE 610.53(A) TAPS TO CONTROL TRANSFORMER
1. I have a 100 VA 460/120 motor control transformer.
2. The rated secondary current is 100/120 = 0.83.
3. As I read the article rated secondary current 0.83 x 200% , 0.83 X 2 = 1.67. 1.67 should be my max size of secondary protective device.
4. The last part of the article is where I believe I am confused, not more than 200% of the ampacity of the control circut conductors. As I read it, if the control circuit ampacity is 10 then multiply it by 200% and 10 x 2 = 20. The maximum amperage of the tap conductors can be no larger than 20? Any help you may provide will be be greatly appreciated.

Javier

 

[mbeatty]

I have a question regarding taps to control transformer calculations, NEC ARTICLE 610.53(A) TAPS TO CONTROL TRANSFORMER
1. I have a 100 VA 460/120 motor control transformer.
2. The rated secondary current is 100/120 = 0.83.
3. As I read the article rated secondary current 0.83 x 200% , 0.83 X 2 = 1.67. 1.67 should be my max size of secondary protective device.
4. The last part of the article is where I believe I am confused, not more than 200% of the ampacity of the control circut conductors. As I read it, if the control circuit ampacity is 10 then multiply it by 200% and 10 x 2 = 20. The maximum amperage of the tap conductors can be no larger than 20? Any help you may provide will be be greatly appreciated.

Javier

Javier, you are correct in that your secondary protective device cannot exceed 1.67 amps (200% of secondary current). For the control circuit conductors, the control circuit ampacity cannot be higher than 200% of the control circuit conductor ampacity (corrected for temperature, etc.). The conductor ampacity can always be higher than 200% of the control circuit ampacity. It just cannot be lower. Hope this helps.
Mark

 

[mbeatty]

Javier, you are correct in that your secondary protective device cannot exceed 1.67 amps (200% of secondary current). For the control circuit conductors, the control circuit ampacity cannot be higher than 200% of the control circuit conductor ampacity (corrected for temperature, etc.). The conductor ampacity can always be higher than 200% of the control circuit ampacity. It just cannot be lower. Hope this helps.
Mark

I meant to say that the control circuit protective device must be sized to not exceed 200% of the control circuit conductor ampacity, after corrections.
Mark