Wiring Up 7 Emergency Stops on a Conveyor


Thread Starter


We have conveyors and racks with up to 9 estops along the line, but only two actually work. The others do not work. I am trying to find a diagram on how to wire them all up together so anyone of them can shut down the line. But I haven't been able to find one. Can someone point me in the right direction they are low voltage E.STOPS connected to a Mitsubishi PLC.
How are the e-stops wired? You need to make sure that all of the estops are wired in series with one another and that when each e-stop is pressed the contacts are opening on that e-stop, breaking the circuit.

How is the PLC wired? Is each e-stop wired back to its own PLC terminal point, or are the E-stops wired together and only 1 wire coming back to land on the PLC? Sounds like to me you may have multiple groups of e-stops coming back to the PLC.

Let us know what you find, and if you can give more details in what you have found in the field ex. how the switches are wired back to the plc. Also, is the plc receiving the signal when an e-stop is pressed. That could give us a better idea of what's going on.

Does all of this make sense? If not what parts, so that it can be further explained.
Having e-stops on a conveyor that don't work is pretty risky, what if someone gets hurt?

I have never seen e-stops wired through a PLC, not to say they can't be. I'm guessing the PLC has 24 VDC inputs. With a long conveyor, I'm guessing 1000 yards, I don't think AC inputs would work.

It might be possible to get AC inputs to work by loading them down with a resistor effectively making it a current loop rather than Voltage.
If each stop is wired back to it's own dedicated input then you would be able to point to the one that's pulled however in my experience they are usually in series.

Can you give us some more information like how many inputs, Voltage, AC or DC?

I haven't worked on conveyors for quite a while, but I seem to recall there are special relays available for the switch/control system interface.
Really depends on your system, most e-stop systems are wired in series and very basic. However there are network type systems which I have no experience with. The prints are supposed to be in electrical control cabinet. I do believe your system is in serious violation. if you're inspected or someone gets injured, your company will be fined big time. call the OME for diagrams if none available.


I've recently followed a course about machine-safety (European standards). I don't know which standard (NFPA) you have to comply too. But I was told that hooking up a E-stop directly on to a non-safety PLC is a dead sin.

Use a safety-PLC (module) or Safety relays I was told.

Bob Peterson

without knowing more about what you actually have it is very hard to give you any advice. most such circuits are just contacts wired in series. it is a little disconcerting that such a simple circuit is not something you are familiar with. You probably should not be working on this kind of thing if you don't understand it. It is probably best if you find someone more knowledgeable to deal with the problem rather than trying to get random people on the Internet to help you. This is the kind of thing that might lead to someone getting injured or killed if not done correctly and it seems unlikely that you are the guy to get it done correctly.

As others have said, if it's an "e-stop" in the legal sense, what you have is probably not sufficient.

To be sure, you must do a proper risk assessment that identifies each hazard and its severity (measured multiple ways like frequency of exposure, level of potential injury, etc.). That will let you figure out the protection level you need, which will determine if your current circuit is adequate. If your conveyor doesn't have any exposed nip/pinch points and whatever is transported on the conveyor doesn't have much (if any) potential to hurt someone, you may be fine as-is. Otherwise, you're most likely in violation.

The above is NOT legal or safety advice. If you don't have the training/expertise to perform a proper risk assessment, hire someone who does. This is a big deal if OSHA ever comes to call.
I don't think we need a risk assessment study. We all know when you push or pull an emergency stop, the conveyor is supposed to stop. There's no question about that.
It is a matter of what is meant by e-Stop.

A simple PLC (non-redundant) shut-off does not qualify for man-safe stop. This particularly true with boilers, emergence stop or shutdowns in the petrochemical industry, or conveyor belts in manufacturing facilities.

In some cases double redundancy hardwired is insufficient, in other cases quintuple plc processor redundancy with hardwired over-rides is required.

Automation can be far more than simply trusting the plc to register when e-stops are pushed.
"I don't think we need a risk assessment study. We all know when you push or pull an emergency stop, the conveyor is supposed to stop. There's no question about that.*"*

What happens if there is a failure of of some sort such as the estop relay contacts welding closed? The risk assessment helps you decide how far to go in mitigating that kind of risk. You may do the risk assessment and decide that if you push the estop and the conveyor continues to move that is OK. Or you may decide it is not OK.
>I don't think we need a risk assessment study. We all know
>when you push or pull an emergency stop, the conveyor is
>supposed to stop. There's no question about that.

The risk assessment is to identify the hazards and how redundant/reliable your circuit has to be. Without that, anything we say here is pure speculation. Does it need to be category 3? Category 4? If either of those applies, the OP's circuit is NOT ok. If the risk is minuscule, he may be ok.
I don't believe you guys

The poster has a conveyor with 7 of the e-stop pulls not working and you think we should sit down and study it.

Fix the thing.

Presumably this is an old conveyor, and it worked once, are we going to go back now and study everything ever built in case it might not work?
I know how the big chemical companies do it, but they are only a part if industry worried because of some of the monumental screw-ups they made in the past.
Sorry for taking so long, they are wired up in a series. the end to end is connected to N24 that's the 24V. the other end that connects to each E.STOP is connected to the PLC. 3 of them are on PX022 and 3 of them are on PX024, but none of them work. Can we upload pictures here. if so I can get a snap of the diagram if it would help.
Well they have never worked since the lines were installed two-three years ago. A team came in from china to wire and program it. I don't know much about this stuff was just a mechanic here for the past 10 years now I have to try and figure this out. That's Y I am here to get some help is all. I had followed this diagram but it still seems to not shut the conveyor down.

We have 3 on the rack that stops the robot/module down but once you release the stop the robot starts moving again don't think it is supposed to do that. But at the moment I need to get the stops on the conveyor working can it be a programing issue since they are connected to the PLC

Here is the diagram:
I only see six stop switches, two sets of 3. Could be the input is not properly programmed for the set not working. Check your voltage and try a stop button to see if it opens the circuit, check LED for that input to see if it changes. The machine should not restart after release of stop button, you should have have a start button with time delay and warning buzzer.
The buttons are in two series groups.

I am used to emergency stops that are maintained. The operator has to reset them individually before the conveyor can be re-started. It looks as though these must be maintained by the logic.

If you can't look at the logic, at least for a start you can make sure each button kills the input PX022 or PX033. You should see the input light go out.

I wonder if someone has accidentally wired the stops in parallel instead of series.

Another test you can do is drop the wire off the PLC input killing it. That should stop the conveyor for sure. If it doesn't, there has to be something wrong with the programming. no?

We must have some Mitsubishi PLC guys on here who can comment on the configuration.

Can you take a close look at a stop switch and describe how it trips and how it is reset? Most conveyor switches I'm familiar with trip a mechanical latch when you pull the switch and need to be rotated to click back into the closed position.
Yeah I don't think it should work either. These are new additions to the old lines. The old lines when you push a stop, the robot stops and you have to restart it again, but the new ones are wired up and programed different. Will check the led on the PLC tomorrow when I get back to work to see if it is on or goes out.