tranceformer ques

[wireman1]

a 480 transformer single phase is being steped down to 120 volts for control voltage . does the x2 side of the transformer have to be bonded to the case of the transformer or is it bonded by the building steel which it is mounted to.in case the transformer would happen to short out would it clear the fault without bonding x2 of the secondery side. the circuit is being fed by mc cable.

 

[Smart $]

In many cases of 120V-secondary control transformers, they are actually a separately derived systems and one of the secondary conductors is required to be grounded by a GEC... same requirements as a large separately derived system... but that is if it is under the purview of the NEC (many are not)... but under the NEC, IIRC, there are some exceptions in the "Class" powered circuits.

 

[augie47]

As Smart$ states, IF if falls under the NEC (as part of a piece of equipment it might be wired to a different Code) there are some exceptions.
Take a look at 250.30(A)(1) Exception 3

 

[infinity]

As mentioned 250.30(A)(1)Ex#3 would cover the requirement for the system bonding jumper. The GEC requirement is similar and can be found in 250.30(A)(5)Ex#3.