Emergency Stop circuit

[Andy-1960]

Yes, an auxiliary contact from each contactor is wired to the safety relay, the relay will not reset if one of the contactors is welded.

 

[netblindpaul]

I admit I have been a bit nieve and not as simple as I first thought (although this is how it appears to be at the college I go to). I can see how a safety relay is really required with possibly a 2 channel emergancy stop circuit, with dual contactor and feedback loop although I don't quite understand how the two contractors are integrated into the feedback loop? Do you have auxiliary contacts from the contractors wired though the reset inputs? How does the relay know if say one contactor has welded closed?

So are you talking about a "work area emergency switching system" under BS4163, or an emergency stop circuit on a piece of machinery.
Either way EN 13850 applies, but, is more often than not totally misunderstood by electrical contractors installing these systems in educational establishments, and that's from experience.
Many don't even know of the existence of the CoP that they should be working to let alone have a copy of it to know how to comply!

 

[Rocboni]

This is a work area Emg stop system, hopefully the OP will make an appearance.

This is for my own benefit I am asking these questions, do all safety relays input a momentary button i.e. Take care of latching themselves or does its input have to be latched via a relay?

 

[Darkwood]

@Rocboni
Safety relays come in a variety of forms with many allowing compliance of the varying safety level of differing systems depending on how you wire them, the usual method to reset a safety relay is a momentary closing of a monitored N/O loop, depending on other criteria that the relay is monitoring it won't reset until certain conditions are satisfied.

 

[netblindpaul]

For a work area switching system, the buttons and control system must comply with EN 13850 as this is required by BS 4163, this means red mushroom head trigger action latching on a yellow background, circuit to PLc, with an analysis & design against EN 13849-1 to ensure that PLc is adequate, then verification to EN 13849-2 to prove that the implementation is correct.
The emergency stop buttons feed straight into the safety relay.
PLc is basically suitable actuators, dual channel with a safety relay monitoring the stop buttons, you also must take into account fault masking, and, then this must operate a suitable actuator, for example a power contactor to disconnect the supply.
This power contactor must be proven as suitable under EN 13849-1, potentially it will require a redundant partner in series, only the analysis can show what is required.

 

[Rocboni]

I see that some relays the start and reset are the same input.

Could you have a key and reset button latching a relay with contacts in series with a start button to take care of the deliberate action?

So if a Emg stop Is pushed to restart you have to twist the key and push reset to acknowledge activation then push start?


I presume all the Emg stops are wired in two loops when it's dual channel, the stop at the key station would be wired like a Emg stop but just a flush red button?

 

[Rocboni]

What would delatch the relay?

 

[netblindpaul]

I see that some relays the start and reset are the same input.
You mean some safety relays? The start/reset commend to them can be the same, they can't re-start a machine on their own, they are not allowed to.
Could you have a key and reset button latching a relay with contacts in series with a start button to take care of the deliberate action?
Not sure what you mean. You would have to have a key to comply with BS4163, this could be reset of the e-stop, or start, and the other action could, be a push button. Probably thinking about this in EN 13849 language the reset should be a blue pb, with the re-energise being the momentary key operation.

So if a Emg stop Is pushed to restart you have to twist the key and push reset to acknowledge activation then push start?
This depends on the design, blue is required as the reset under EN 60204-1 which is also called by BS 4163. So blue to reset, momentary, resets the safety relay, to allow re-energising the supply system, then momentary operation of the key switch to re-energise the supply.

I presume all the Emg stops are wired in two loops when it's dual channel, the stop at the key station would be wired like a Emg stop but just a flush red button?
Allowing for the effects of fault masking then yes. the stops would all be wired in series. However, this depends on the analysis under EN 13849 as to what the requirements for the mitigation of fault masking are. There are basically two channels in series in parallel, yes.
The stop at the single start location could be just a red button, but it could not be flush it must be proud. However, if it has the same action as the emergency stop buttons, then it must be an emergency stop button. If you implement a normal stop action at the start location, then you would also have to provide an emergency stop at the location in the event that the stop did not function, the normal stop could bypass the safety relays, but, if it had any influence on the safety circuit/function then it would fall under the same requirements.

 

[netblindpaul]

What would delatch the relay?

Delatch what relay?

 

[Rocboni]

As far as I can see ther is only one input to reset, when you say you have one button to reset and another button to re energise how do achieve this, is the reenergising circuit not wired as part of the safety relay circuit?

You just output contacts of the safety relay like a stop button in a latching stop/ start circuit?

So if you did have a blue reset, green button and key switch to start (held at same time), red to switch off say at the end of the day? You would need to have a Emg stop at this location

Sorry just trying to learn!

 

[netblindpaul]

Resetting the safety relay (e-stop circuit) must only allow re-start, not implement re-start.
The start function is not a safety function.
The stop/e-stop MUST override the start function.

Not sure what you mean by the way you are looking at the outputs of the safety relay.

Why would you have 3 devices to start?
Blue to reset, yes.
Green to start not acceptable under BS4163, key switch required, key switch can be used as a start under other standards. Both must be momentary.

A conventional stop button would not be part of the safety function, so, if there was an incident requiring e-stop and witnessed at the start location then an e-stop would be required.

These things are not the sort of thing that you can "get" over internet forums, you need to get the standards and study them, then get mentored really.
There are various commercial machinery safety courses, mine was the CMSE validated by TUV Nord.

Please don't "play" with this stuff, because people die in and around machinery and there was a recent case where a machine designer has I think done time, if not certainly been found guilty of manslaughter because his design was negligent.

What makes it worse is the actions of one of the parties involved resulted in the death of a family member, they basically burned to death, or suffered a heart attack due to the temperatures when they were trapped inside an oven.
So just like the guys pictured hugging on top of the burning wind turbine with no means of escape, he knew that he was going to die, and was just sat/stood there waiting to die.
Horrible, so just realise that machinery safety is not something to take lightly.