Remote disconnect via contactor
Remote disconnect via contactor
(OP)
I am installing a new piece of equipment in a manufacturing plant. Our usual disconnecting means on our electrical devices is to put a locking disconnect on our electrical panel. The disconnect is a 250Amp non fusible disconnect. When there is work to be done they activate the disconnect and lock it out. With our new system the panel will still be in line of site, but hard to get to. I was considering placing a normally closed key switch in the operator panel that would be connected to a 3 pole contactor ahead of the panel. When the operator removes the key the contactor would open and they could safely enter the machine area. We would also place a 3 phase power indicator to show that power was off. Can anyone tell me if this in an acceptable means to lockout the panel.






RE: Remote disconnect via contactor
They just need to update their procedure for that machine and retrain any employees on the changes if necessary.
A tagout procedure can also be used in lieu of lockout if necessary. Thought lockout is highly prefered.
RE: Remote disconnect via contactor
In any event, a control circuit lockout is not acceptable.
Bill
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"Why not the best?"
Jimmy Carter
RE: Remote disconnect via contactor
I would check nfpa 79 too.
i believe if the procedure for a normal disconnect is remote then this has to be posted on the enclosure as a procedure on how to disconnect power.
RE: Remote disconnect via contactor
There must be a positive disconnect of the main power conductors somewhere, at least before I would accept it. You might be able to combine this with a set of fuses or manual disconnect that is more accessible.
RE: Remote disconnect via contactor
My electrical supplier is recommending I use a safety rated contractor and key switch to further reduce the risk of a failure putting someone in harms way.
RE: Remote disconnect via contactor
RE: Remote disconnect via contactor
Pardon my ignorance, but I have no idea what "visible open" means. Can you elaborate.
RE: Remote disconnect via contactor
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RE: Remote disconnect via contactor
In typical applications, key switches open secondary control power circuits. While this is good enough (usually) for shutting down processes, it is NOT good enough for safety of people working on equipment where they must be protected from moving parts,process flows and voltage.
You might want to consider a safety disconnect switch at an easily accessible area just outside the restricted access area.
old field guy
RE: Remote disconnect via contactor
I think we understand what you are proposing, it just that energizing (or de-energizing a contactor that cannot be seen does not guarantee that the circuit is dead. It's pretty easy to come up with situations where the contactor would not function properly.
If you just want to turn something off, the contactor is fine, but if you are trying to create an "electrically safe working condition", then it doesn't cut it.
RE: Remote disconnect via contactor
The answer is no, not safe, not allowed.
Example from the days when it was allowed:
A machine had a problem. The electrician blocked out the control circuit and started troubleshooting. Someone reported the machine out of order. Another electrician got the work order and approached the control room from the other direction. The second electrician manually pushed in the contactor. The first electrician died.
The accident report on this event was part of my safety training module, many years ago. It has been illegal for so long that the younger folk may not know why.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Remote disconnect via contactor
From OSHA 1919.147:
Energy isolating device. A mechanical device that physically prevents the transmission or release of energy, including but not limited to the following: A manually operated electrical circuit breaker; a disconnect switch; a manually operated switch by which the conductors of a circuit can be disconnected from all ungrounded supply conductors, and, in addition, no pole can be operated independently; a line valve; a block; and any similar device used to block or isolate energy. Push buttons, selector switches and other control circuit type devices are not energy isolating devices.
Looks like USA and Canada have a similar take on this.
RE: Remote disconnect via contactor
RE: Remote disconnect via contactor
The code seems very clear to me on this, but you can always ask for an interpretation if you find something unclear. Code and interpretations can all be found at osha.gov.
Between the fines and litigation costs, I am sure the economic benefit of doing it right can be explained to those presuring you.
RE: Remote disconnect via contactor