Electrical standards

[thinker]

Please help to resolve a critical situation.We supplied to
the customer Variable Speed Drive system. The input main
circuit breaker is equipped with the standard shunt trip
device (120VAC) which opens circuit breaker when its coil
is energized. The customer does not accept this device
stating that the usage of shunt trip is a violation of NEC,
NFPA since this is not a fail safe solution. The customer
suggests that only de-energizing should be used (probably,
using undervoltage trip device).Please advise whether the
customer is right. Otherwise, why standard shunt trips exist? Our understanding was that shunt trip should be powered by independent reliable feeder, but this still does
not seem to be a fail safe system (in terms of broken wire
situation). I would appreciate if anyone with a proper
knowledge of electrical standards brings clarity in this issue.

 

[busbar]

Request specifics on the Code ‘violation’—ask the originator to cite section and paragraph.

There are two settings where shunt trips work acceptably in equipment/facility protection. In some regions, fire marshals mandate a break-glass-initiated shunt trip that will remotely open the building’s main service-disconnecting means for use by emergency responders. Most AC-powered shunt-trip accessories are suitable for NEC §230-95 equipment ground-fault protection. The only “extra” requirement for operation of a shunt trip with ground-fault protection is that it must function at 57% of line voltage for phase-failure conditions; per UL Standard 1053, "Ground-Fault Sensing and Relaying Equipment." In both cases the shunt-trip device is intended to be powered from the incoming AC-line voltage.

 

[REDDOG]

Right on Busbar.
The customer may be refering to The Machinery Directive.
Allen-Bradley Publication S114-CA001A-EN-P November 2000,
refers to IEC application of safety devices.
The main circuit breaker may also disconnect other circuits
that are safety related.
For E-Stop application normally a contactor would disconnect power from the drive to the motor. Reseting the E-Stop circuit would allow the contactor to be closed electrically. Using the shunt trip CB would require the operator to manually reset the CB. The CB is not switching duty rated.

 

[electricuwe]

I hope the others could help you with the standards, but a few month ago I thought abou the same question as you:

If shunt trip is not considered fail safe, why do shunt trip devices exist ?

The answer is quite simple: Imagine a utility trying to reenergize their grid after a fault with all the breakers using undervoltage trip devices.

 

[thinker]

Thank you very much, gentlemen. Your responses helped me
to resolve the problem.