Control Xformer secondary Grounds

[sundowner]

Have been noticing several control transformers lately, (installed years ago in existing motor starters) most without a secondary bonding wire from the X2 terminal to ground, the new equipment which comes in all have secondary grounding wires installed from X2 to case. ( 480 Volt pri/ 120 volt sec) Am I thinking of this correctly in that there is a KVA level at which it is required to ground the secondary, or is it anytime there is a XO terminal or a X2 terminal. What I'm looking at is some new HVAC motor starters which land on our 3 phase, 3 wire 480 volt busduct.

My real question is when do I need to ground/bond my secondary of the control xformer--is it only when I see an X0 terminal or X2... confused.

Thanks guys

 

[infinity]

Look at 250.30(A)(3)Exception 3.

 

[sundowner]

Thanks Trevor,
I sure could'nt find that page in the code book the other day.

Steve

 

[weressl]

Have been noticing several control transformers lately, (installed years ago in existing motor starters) most without a secondary bonding wire from the X2 terminal to ground, the new equipment which comes in all have secondary grounding wires installed from X2 to case. ( 480 Volt pri/ 120 volt sec) Am I thinking of this correctly in that there is a KVA level at which it is required to ground the secondary, or is it anytime there is a XO terminal or a X2 terminal. What I'm looking at is some new HVAC motor starters which land on our 3 phase, 3 wire 480 volt busduct.

My real question is when do I need to ground/bond my secondary of the control xformer--is it only when I see an X0 terminal or X2... confused.

Thanks guys

Absolutely, otherwise a three wire controller could start on its own upon ground fault.