Hope this is the correct area to post this. Would someone be able to steer me in a clear direction in the code book as to the proper method of fusing shunt trip control wiring in general. One application is an x-ray unit 480 volt, 3 phase with an 80 amp shunt trip circuit breaker. I am trying to clarify the required way to wire the shunt trip with respect to fusing the control conductors. I seem to be getting two differences of opinions.
First idea is that it is required to come off the equipment breaker so that there is little to no chance that the circuit will be interrupted, loss of power and subsequently will not be able to operate the shunt unit in an emergency via the emergency switch. Is it permissible to connect the control wiring to the load side of the 80 amp circuit breaker and then wire through the emergency shutdown switch and back to the shunt unit? Wouldn?t there be a potential issue with multiple wire terminations on the circuit breaker lug? I checked the manufacturer?s instructions and it doesn?t appear that there are provisions for this but nor does it indicate it is not permissible. Also I did not see any tabs/stabs to connect cable terminals (crimp on) to the load lugs as some times motor starters provide them. If this arrangement was done, would the conductors need to be fused to their normal current ratings, #12-20amp or #10-3 amp?
The second idea is that an independent control voltage source be used and then ultimately wired to the shunt unit. The concern is, if the breaker was turned off (or install lock on handle), or tripped without knowledge, the emergency shutdown would not work.
Would someone please clarify this for me as to the NEC code requirements? I have resolved the state?s requirements but am having a hard time with the NEC requirements, rather than the ?it would be nice? scenario. Thank you
First idea is that it is required to come off the equipment breaker so that there is little to no chance that the circuit will be interrupted, loss of power and subsequently will not be able to operate the shunt unit in an emergency via the emergency switch. Is it permissible to connect the control wiring to the load side of the 80 amp circuit breaker and then wire through the emergency shutdown switch and back to the shunt unit? Wouldn?t there be a potential issue with multiple wire terminations on the circuit breaker lug? I checked the manufacturer?s instructions and it doesn?t appear that there are provisions for this but nor does it indicate it is not permissible. Also I did not see any tabs/stabs to connect cable terminals (crimp on) to the load lugs as some times motor starters provide them. If this arrangement was done, would the conductors need to be fused to their normal current ratings, #12-20amp or #10-3 amp?
The second idea is that an independent control voltage source be used and then ultimately wired to the shunt unit. The concern is, if the breaker was turned off (or install lock on handle), or tripped without knowledge, the emergency shutdown would not work.
Would someone please clarify this for me as to the NEC code requirements? I have resolved the state?s requirements but am having a hard time with the NEC requirements, rather than the ?it would be nice? scenario. Thank you