A
JBD wrote:
I think 'maintenance switches' are one of the most misapplied mitigation techniques. Many people do not understand that a breaker mounted switch does nothing for mitigating the incident energy at that breaker. Rarely are these switches located near the equipment that they do impact.
Agree, the switch should affect the CB feeding that equipment, usually a remote device.
A properly implement maintenance switch (goes by various names in the market [RELT, alternate setting group, etc]) should; 1) Incorporate visual indication of the status of the trip's/relay's protection - is it or is it not in the protective mode or standard mode? This should be driving by the device itself, not the condition of the input or signal to the device requesting the safe mode. 2) The switch should be locakable and be able to be incorporated into a safety procedure as if it was LOTO...which it is not. 3) The indication could be mounted where the protected equipment is... that is probably a good idea and if you are operating off a contact closure it could be done.
Sophisticated switch systems are able to send emails if the safe mode remains on too long (did somebody forget it?) and can use one input to operate or change multiple settings is appropriate should the equipment haved multiple sources, or be powere via an ATO that would re-energize it upon a power loss... may not be a good idea to repower 10 seconds after an AF incident!
So there are lots of considerations. Use of a maintenance switch does not preclude other hazard mitigation solutions. Improving protection as muc as you can 7x24 may mitigate hazard somewhat, as well as minimize equipment damange for any fault thereby improving MTTR and consequently improving reliability... many AF solutions can improve reliability and provide double value for the buck!
