I have a customer who does not want any local control or disconnecting means for their motors. It is a chemical plant. Sometimes this is because a local stop could affect the process up and down the line that a local operator would not be aware of. Given that this is often true, is not at least an e-stop or a "system e-stop" required locally? In the latest instance, we are looking at a cooling tower. I typically use at least a general (or system) e-stop even if they don't want local start/stop or local disconnects. This customer is resistant to even that and I would like to show them a code reference where we can say it has to go in whether they like it or not.
local control or disconnect required
- Thread starter trallio
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PaulMmn
Senior Member
- Location
- Union, KY, USA
- Occupation
- EIT - Engineer in Training, Lafayette College
When a motor goes >SpitZ#< >Sp@rkL3< >Poomph!< with a cloud of Magic Smoke, the process will come to a screeching halt (or backup everything in the processing upstream) whether they like it or not!
It sounds as if they need a redundant motor (or '2-of-3') to guarantee that a single motor failure won't interrupt their processing. Then, an e-stop that clearly identifies which motor it controls should be acceptable.
It sounds as if they need a redundant motor (or '2-of-3') to guarantee that a single motor failure won't interrupt their processing. Then, an e-stop that clearly identifies which motor it controls should be acceptable.
- Location
- Illinois
- Occupation
- retired electrician
I tend to agree with the customer...I would not want general e-stops in a chemical process. Maybe a complete process shutdown, but the ones like that that I have seen have been in the control rooms and not local to the equipment. Typically the company has a written lockout system in place and the exception to 430.102 permits the local motor disconnects to be omitted.
Typically in a chemical plant or gas plant or similar, the e-stops are not the hard wired e-stops you see elsewhere. They go through a safety DCS and the DCS shuts down or opens or closes motors or valves upstream and down that will make the e-stop safe.
In this case, we are talking about a cooling tower. Shutting it down will eventually cause the rest of the process to shutdown, but normal overtemp controls should do that. Alternatively, you could have a motor on fire and the only way to shut it down is to go to the MCC and open the disconnect if you know where it is. No controlled interlock there...
OK. I was hoping someone could point me to a code reference that I couldn't find myself.
Thanks for the input.
In this case, we are talking about a cooling tower. Shutting it down will eventually cause the rest of the process to shutdown, but normal overtemp controls should do that. Alternatively, you could have a motor on fire and the only way to shut it down is to go to the MCC and open the disconnect if you know where it is. No controlled interlock there...
OK. I was hoping someone could point me to a code reference that I couldn't find myself.
Thanks for the input.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
not covered by the NEC.
The customer needs to do a risk assessment and determine what measures are needed to eliminate or mitigate whatever hazards are uncovered. It is unusual that an estop out in the field on these kind of systems would actually contribute to the safety of a system.
As for a disconnect, it is not there as anything other than a means of opening the power to the motor. It is not there so you can shut off the motor. In fact, it is perfectly legal to lock it in the closed position.
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