Estop relay question

I am wanting to use an estop relay for the first time

http://www.automationdirect.com/adc...Relays_-z-_Gate_Safety_Relays/LG5925-48-61-24

The two channel would mean that the button (estop button)has two contacts and both are wired to the safety relay correct? I am planning on having probably 3 estop buttons, would I just wire the buttons in series (still two sets per button wired in parallel) or would I use 3 seperate safety relays? If I wanted my system to also be able to kill the estop bus, would you suggest having the system enable/disable power to the safety relay, or should I use a normal control relay and wire through its NO contacts to act as another estop button? I want the buttons or system to be able to initate an e-stop.

Thanks

g.mccormick said:

I am wanting to use an estop relay for the first time...

Click to expand...

Then you'll want to be doing a Risk Assessment for the first time?
An emergency stop safety circuit, whether protecting "man or machine", should always be designed based on an RA.

g.mccormick said:

...The two channel would mean that the button (estop button)has two contacts and both are wired to the safety relay correct?

Click to expand...

That's correct, but do note, dual contacts are not compulsory for all cases. The RA again will decide this, but I would advise anyone to make it their default minimum.

g.mccormick said:

...would I use 3 separate safety relays?...

Click to expand...

A proper RA will determine the level of safety you require for this "system".
Only then can you decide if one e-stop per safety relay is required or not. For most standard machines, if there is such a thing, multiple e-stops on one safety relay is often permitted, up to a maximum resistance value for the safety channel circuits.

g.mccormick said:

...Would I just wire the buttons in series (still two sets per button wired in parallel)...

Click to expand...

The dual channel circuits are series wiring only, and completely separate to each other, except in cases where the first wire is a looped common at the first device. You do not parallel wire both contacts on a dual contact e-stop. Unless, by parallel, you're referring to their physical orientation towards each other?

g.mccormick said:

...If I wanted my system to also be able to kill the estop bus, would you suggest having the system enable/disable power to the safety relay, or should I use a normal control relay and wire through its NO contacts to act as another estop button? I want the buttons or system to be able to initate an e-stop.

Click to expand...

Removing power to a safety relay will trip its safety contacts by default, but it's not normally the done thing. If, for example, a safety relay has a delayed de-energise circuit, this would prematurely activate the safety function.

If by "system" you are referring to PLC control, then the PLC must be of a suitable safety category, as per the RA, before it can be considered as part of the safety function.
i.e. A safety PLC.

If, for instance, a certain logical condition should initiate the safety function, a standard PLC would not be deemed fit as it has no built-in redundancy and self-checking measures. Likewise, a standard relay should not be used as an emergency stop device as it is not activated by a single human action. To implement an auxiliary circuit into a safety relay's dual channel circuit, you should use another safety relay, activated by a safety rated device, such as a safety PLC. You wire the channels of the e-stop safety relay through the safety output contacts of the auxiliary safety relay.

Risk Assess, Risk Assess, Risk Assess!

G.

This is not for a machine. It is for an engine test cell. Always before, a MCR estop has been used. With all estop contacts and other contacts (flame detector, dyno water flow switch, etc) wired in series to trip the estop circuit. The estop circuit is usually powered by a digital output, so that either software or hardware (button, flow switch, etc) can trip the estop circuit.

I was thinking that by adding the safety relay, it would be a more correct implementation. I'm not planning on doing a risk assesment for this.

Basically I'm going on the assumption that mcr being replaced by safety relay is >= safety of the mcr.

g.mccormick said:

I am wanting to use an estop relay for the first time

http://www.automationdirect.com/adc...Relays_-z-_Gate_Safety_Relays/LG5925-48-61-24

The two channel would mean that the button (estop button)has two contacts and both are wired to the safety relay correct? I am planning on having probably 3 estop buttons, would I just wire the buttons in series (still two sets per button wired in parallel) or would I use 3 seperate safety relays? If I wanted my system to also be able to kill the estop bus, would you suggest having the system enable/disable power to the safety relay, or should I use a normal control relay and wire through its NO contacts to act as another estop button? I want the buttons or system to be able to initate an e-stop.

Thanks

Click to expand...

You wire the buttons in series, with the power supplied from the safety relay and the returns back to the safety relay. The SR has two "output" terminals and two "input" terminals that monitor the EStop PBs, or the door contacts, or what have you. There are various flavors of safety relay that use various types of contacts. The one you've selected is designed to monitor a pair of NO contacts that open and close together, like a pair of NO contacts on an EStop PB.

You generally set them up something like this...

The SR in this diagram is an Allen-Bradley, but the AD you've referenced is wired exactly the same way. That's why AD sells so many of them, LOL.

As above, In todays age os Safety paperwork & liability you should do a Risk Assessment and determine the Safety catagory required, you may also ned to isolate Air/Hydraulics/Water etc too.

Also a little explanation on the reseting of the safety system after a trip is important to know, generally you set your Safety Relay's reset button or the reset link to go through series connected normally closed Auxillary contacts on dual main power contactors so that if one of the contactors "welds in" the system can not reset, depending on the safety rating required the contactors may have to be safety rated contactors.

I also use the NO contacts on the main power contacts in series to isolate the supply to the PLC Outputs and any other Output Solenoids etc.And then I also make Input 0 always a monitoring input of the status from the Safety Relay so the PLC knows what's going on.

Of course also make sure the feed for your Safety system doesn't come through those safety contactors

OzRoo said:

As above, In todays age os Safety paperwork & liability you should do a Risk Assessment and determine the Safety catagory required, you may also ned to isolate Air/Hydraulics/Water etc too.

Also a little explanation on the reseting of the safety system after a trip is important to know, generally you set your Safety Relay's reset button or the reset link to go through series connected normally closed Auxillary contacts on dual main power contactors so that if one of the contactors "welds in" the system can not reset, depending on the safety rating required the contactors may have to be safety rated contactors.

I also use the NO contacts on the main power contacts in series to isolate the supply to the PLC Outputs and any other Output Solenoids etc.And then I also make Input 0 always a monitoring input of the status from the Safety Relay so the PLC knows what's going on.

Of course also make sure the feed for your Safety system doesn't come through those safety contactors

Click to expand...

Yup, that is the best way to do it. The schematic I showed is for a system that doesn't have big main contactors to trip everything off - we didn't need them on this panel. So, the reset is just wired through the PB. However, a pair of main contactors in series is typical and is usually the way to go.

Thanks guys. I was pretty sure thats how it went.