Remote disconnect via contactor

[moosetracks555]

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.

 

[mcgyvr]

A keyed (removable key) switch is a lockout device per OSHA.
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.

 

[waross]

That would not be acceptable under Canadian codes. Time was when a control circuit lock-out was accepted but too many people died. A local disconnect switch adjacent to the machine is the best but budgets now often go for second best. With lockout at the panel there are mistakes made. Locks inadvertently get placed on the wrong switch. I have seen this happen too many times. A local disconnect switch costs more but removes most of the opportunity for mistakes.
In any event, a control circuit lockout is not acceptable.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[controlsdude]

if usa nec article 409 enclosures refers to 430 part IX disconnecting means

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.

 

[dpc]

I'm not familiar with use OSHA acceptance of a pilot device such as a selector switch as a lockout device. As waross says, many years ago, we used lockable pushbuttons as "lockout stop" devices, but I don't know of any situations where anyone would allow this today as a lockout device used to permit maintenance work.

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.

 

[moosetracks555]

Just so everyone is clear the key switch will activate a 3 pole contactor that *will* completely remove power from the panel and equipment. It is not just an key switch to remove control power, or an input into a PLC.

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.

 

[davidbeach]

Can you say "Visible Open"?

 

[moosetracks555]

davidbeach,
Pardon my ignorance, but I have no idea what “visible open” means. Can you elaborate.

 

[jraef]

NFPA 79 covers machine safety and requires that machine electrical power systems must have visible indication that the power is disconnected before access to an electrical panel or motor terminal box is allowed. A pilot light is not considered reliable because there are so many possibilities of false indication. I don't have my copy with me here, but I believe it is stated(?) that you be able to look at the blades or contacts of the disconnect device, implying that they must be open for viewing or have clear covers.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[oldfieldguy]

If your key switch does not mechanically open the contactor, then it does not meet the intent of safety codes.

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

 

[dpc]

moosetracks,

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.

 

[waross]

moosetracks555 (Electrical)
1 Oct 08 16:43
Just so everyone is clear the key switch will activate a 3 pole contactor that *will* completely remove power from the panel and equipment. It is not just an key switch to remove control power, or an input into a PLC.

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.

I'm clear, dpc is clear davidbeach is clear, jraef is clear and oldfieldguy is clear.
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

 

[stevenal]

Seems to be some miscommunication here. If the key switch interrupts current to the contactor coil, this removes control power. The contactor then becomes the intended isolation device that removes power from the equipment. This might be acceptable if the contacts could then be inspected and locked in the open position. Might as well save a step, and use a disconnect.

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.

 

[moosetracks555]

I am not in disagreement with your opinions. My preference was to run the power over to the operator and then back to the panel and not have the remote contactor. I am being pressured to save the money / time to use the remote contactor. We are in the US, so Canadian codes don’t apply. For each of you saying it is not safe I have others saying it is OK. One persuasive argument is “I have been to several theme parks where the operator removes a key switch before going into harm’s way” so I assume there are no regulations against using this type of disconnect. If there is I would like to have specific regulations or something to provide a definitive answer weather we can or can’t do this. Ultimately it is my decision and I plan to use the mechanical disconnect I just wanted something concrete to back my decision.

 

[stevenal]

The citation above from OSHA is not my opinion, and is also not from Canadian code. I fail to see why annectodal evidence is any more persuasive. Your observers may have been looking at mechanically keyed lockout devices on those rides.

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.

 

[moosetracks555]

Stevenal, I was posting that message in responce to the message before yours.