Auto transformer

[hhsting]

Please see attached sketch i have auto transformer.

Based on the sketch it is non separately derived system.

1. Is there anything in NEC 2017 regarding autotransformer grounding? 450.5(A)(B)(C)?

2. Is their anything regarding primary and secondary breaker sizes and conductors protection?

3. Would this be zizag or T connected transformer?

 

[EC Dan]

450.4/450.5 should have all your answers.

 

[hhsting]

450.4/450.5 should have all your answers.

Ues but I am confused is the one pictured zigzag or T connected? Also input is 208V single phase output is 240V single phase does 450.5 apply? If not then what about grounding which section?

 

[jim dungar]

You have a two winding single phase transformer. There is no true primary or secondary. The HV1/LV1 terminal is referenced to ground at the source.

 

[hhsting]

You have a two winding single phase transformer. There is no true primary or secondary. The HV1/LV1 terminal is referenced to ground at the source.

So then just bring equipment grounding conductor and thats it?

Provide primary breaker per 450.4 and no secondary breaker?

 

[don_resqcapt19]

So then just bring equipment grounding conductor and thats it?

Provide primary breaker per 450.4 and no secondary breaker?

Exactly.

 

[hhsting]

Exactly.

What about secondary conductor size same size as primary conductors?

 

[kwired]

What about secondary conductor size same size as primary conductors?

Technically isn't really a "secondary" but if output current is higher than input current and that crosses over ampacity of the input conductor then probably yes. But will still be at a fixed ratio and input overcurrent device is still protecting the output conductor from overcurrent.

This is not a zig zag or a T either, just a coil in series with another coil in a configuration where it adds or subtracts voltage to what was input, how much current can be utilized is limited by the capacity of the "added" coil.

 

[infinity]

What about secondary conductor size same size as primary conductors?

Are you asking if the primary conductors are too small?

 

[kwired]

Technically isn't really a "secondary" but if output current is higher than input current and that crosses over ampacity of the input conductor then probably yes. But will still be at a fixed ratio and input overcurrent device is still protecting the output conductor from overcurrent.

This is not a zig zag or a T either, just a coil in series with another coil in a configuration where it adds or subtracts voltage to what was input, how much current can be utilized is limited by the capacity of the "added" coil.

I should have paid more attention, in what you posted the load side current will be less then the supply side current. Had you been bucking instead of boosting voltage it would be other way around.

so in your case if you keep same size conductor on load side there is no conductor overcurrent protection violations nor is there any undersized conductors for the load.

 

[hhsting]

Are you asking if the primary conductors are too small?

Secondary conductors on side of 240V in this case

 

[hhsting]

I should have paid more attention, in what you posted the load side current will be less then the supply side current. Had you been bucking instead of boosting voltage it would be other way around.

so in your case if you keep same size conductor on load side there is no conductor overcurrent protection violations nor is there any undersized conductors for the load.

Thanks


Sent from my iPhone using Tapatalk

 

[infinity]

Secondary conductors on side of 240V in this case

The voltage is stepping up so the 240 volt conductors will see less current than the 208 volt conductors.