Bonding Transformer

[jasonmorgan]

hey guys,

I have a 277 to 120 volt transformer 750 VA, just wondering do i need to bond the neautral on the 120 side of the secondary side to ground ?

Thanks
Jason

 

[RUWired]

hey guys,

I have a 277 to 120 volt transformer 750 VA, just wondering do i need to bond the neautral on the 120 side of the secondary side to ground ?

Thanks
Jason

Yes per article 250.30(A)1 and exception #3. If you didn't, there would'nt be an effective ground fault path on the secondaty side of the transformer. The primary side of the transformer would see it as a load and may or may not trip the OCPD.

 

[augie47]

be sure to look at the exception he mentioned..might make your life a bit easier.

 

[Rich Elec.]

I need a little help understanding how 250.30 (A) (1) Ex. 3 applies. I read it as applying to Class 1,2,3 type circuits. When "jasonmorgan" says that his xfmr is 277 to 120 750VA, I think that his numbers are greater than a Class 3 circuit.

 

[cadpoint]

... Class 1,2,3 type circuits. When "jasonmorgan" says that his xfmr is 277 to 120 750VA, I think that ...

... they forgot to put the K in there like 7.5 K or 75.K VA

Besides it could all be sitting outside a structure that it serves.

Maybe the OP can rephrase ...

 

[RUWired]

Class one motor control circuits operate at 120 volts for an example. The exception 3 max rating is 1000VA.

 

[ArcNSpark]

Yes, you do, my friend. I learned the hard way. I wasted almost a whole day of troubleshooting this exact problem. I got a nice, even, 120V reading with nothing under load, but as soon as things (computers) got plugged in, the voltages went all over the place.

Trust me...and spare everyone my explanation. Bond the neutral.