Using a contactor with emergency stop button
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holmslaw
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An emergency stop system can be complex or very simple and the first question must be why do you require an emergency stop.
If there is no danger to personnel and it is to protect the plant then the method is pure balance cost of install v cost if it fails v likelihood of failure. There are not rules that need following.
If however it is to protect personnel then again a risk assessment will it cause reversible injury, non reversible injury, or death v how likely is it that it will happen. With this there is a very well laid out procedure and requirements.
So if the emergency stop was to stop the discharge of Halon gas then very strict rules must be followed but if it is to switch of to just stop it destroying, it’s self then it is completely different.
As to diagram it is labelled stop / start rather than stop / reset and although it may be similar not quite the same. The circuit shown will work but there is no testing of switch contact break / make times and if this was life dependent would not be allowed. The safety relay has two sets of contacts on the stop button and they must be open to start with and close within so many micro seconds of each other then the reset pressed to work so if the cable or switches are damaged it can’t be reset.
I can’t understand why you would want an emergency stop on a server maybe you can explain why there is an emergency stop? Is it anything to do with automatic fire prevention?
If there is no danger to personnel and it is to protect the plant then the method is pure balance cost of install v cost if it fails v likelihood of failure. There are not rules that need following.
If however it is to protect personnel then again a risk assessment will it cause reversible injury, non reversible injury, or death v how likely is it that it will happen. With this there is a very well laid out procedure and requirements.
So if the emergency stop was to stop the discharge of Halon gas then very strict rules must be followed but if it is to switch of to just stop it destroying, it’s self then it is completely different.
As to diagram it is labelled stop / start rather than stop / reset and although it may be similar not quite the same. The circuit shown will work but there is no testing of switch contact break / make times and if this was life dependent would not be allowed. The safety relay has two sets of contacts on the stop button and they must be open to start with and close within so many micro seconds of each other then the reset pressed to work so if the cable or switches are damaged it can’t be reset.
I can’t understand why you would want an emergency stop on a server maybe you can explain why there is an emergency stop? Is it anything to do with automatic fire prevention?
me again, this has got popular.
Basically we have a stop button because our rules say we have to have one also we tend to work on equipment with the power still on.
The system I have has UPS anyway so if the coil failed the system would not shut down. Also also the areas we have the equipment in is 24hr manned so any failure would be apparent as the UPS would beep.
Our rules (not BS or 17th regs) only say we need single action shut down and this is in an area the public do not have access to.
Basically I think I am ok as I can shut power off with one hit.
Thinking about it the UPS has a start button which needs pressing in order to make power go back on and sounds exactly like the afore mentioned 'start button' so I am more than sure I am ok.
Thanks all and enjoy
Basically we have a stop button because our rules say we have to have one also we tend to work on equipment with the power still on.
The system I have has UPS anyway so if the coil failed the system would not shut down. Also also the areas we have the equipment in is 24hr manned so any failure would be apparent as the UPS would beep.
Our rules (not BS or 17th regs) only say we need single action shut down and this is in an area the public do not have access to.
Basically I think I am ok as I can shut power off with one hit.
Thinking about it the UPS has a start button which needs pressing in order to make power go back on and sounds exactly like the afore mentioned 'start button' so I am more than sure I am ok.
Thanks all and enjoy
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As I understand it (and I am not an electrician) the power is supplied through the contactor which is basically a switch, open and closed, off and on.
The switch is controlled by a coil, if the coil is energised by applying power to a1/a1 then the switch closes and is 'on'. If you hit the stop button the coil circuit is broken and the contactor opens (off).
The coil itself takes power from the same supply as the system input, the question is should this power be on permanently (as I have it) or should it be through a start button so as to require a positive action to restart.
All this means is the restart needs 2 actions (reset stop button and push start button) to restart the equipment, instead of my way (just reset the stop button)
Either way you can control several supplies with one stop button by switching not the individual supplies but the contactor as a whole.
The switch is controlled by a coil, if the coil is energised by applying power to a1/a1 then the switch closes and is 'on'. If you hit the stop button the coil circuit is broken and the contactor opens (off).
The coil itself takes power from the same supply as the system input, the question is should this power be on permanently (as I have it) or should it be through a start button so as to require a positive action to restart.
All this means is the restart needs 2 actions (reset stop button and push start button) to restart the equipment, instead of my way (just reset the stop button)
Either way you can control several supplies with one stop button by switching not the individual supplies but the contactor as a whole.
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With the diagram if non latched emergency stop button is used one action to reset.
With no reset button i.e. direct switch to contactor using mechanical latch again one action to reset.
With new information with no legal requirement for emergency stop either could be used.
The XB4 telemecanique harmony range are rated at 10A or to quote direct from PDF:-
Standard blocks (single or double) with screw clamp terminals:
A600: Ue = 600 Vac and le = 1.2 A or Ue = 240 Vac and le = 3 A
or Ue = 120 Vac and le = 6 A
Continuous Thermal Current = 10 A
Blocks for plug-in connector:
A300: Ue = 120 Vac and le = 6 A or Ue = 240 Vac and le = 3 A
Standard blocks for printed circuit board connection:
B300: Ue = 120 Vac and le = 3 A or Ue = 240 Vac and le = 1.5 A
Just in case it's not a thermal load and yes took a lot of finding. As to other makes you can DIY.
With no reset button i.e. direct switch to contactor using mechanical latch again one action to reset.
With new information with no legal requirement for emergency stop either could be used.
The XB4 telemecanique harmony range are rated at 10A or to quote direct from PDF:-
Standard blocks (single or double) with screw clamp terminals:
A600: Ue = 600 Vac and le = 1.2 A or Ue = 240 Vac and le = 3 A
or Ue = 120 Vac and le = 6 A
Continuous Thermal Current = 10 A
Blocks for plug-in connector:
A300: Ue = 120 Vac and le = 6 A or Ue = 240 Vac and le = 3 A
Standard blocks for printed circuit board connection:
B300: Ue = 120 Vac and le = 3 A or Ue = 240 Vac and le = 1.5 A
Just in case it's not a thermal load and yes took a lot of finding. As to other makes you can DIY.
I would question how your EPO system worked if it switches the UPS input and not the output?
The stop button has 2 contacts in it
1. A normally open contact which connects to the UPS and switches it off completely when closed.
2. A normally closed contact which connects to the coil and energises the coil until opened.
So if you hit the button both things happen while if the coil fails it only stops the UPS input, the UPS will still run on its battery (for a while).
1. A normally open contact which connects to the UPS and switches it off completely when closed.
2. A normally closed contact which connects to the coil and energises the coil until opened.
So if you hit the button both things happen while if the coil fails it only stops the UPS input, the UPS will still run on its battery (for a while).
An EPO system which relies on a normally open contact....it's getting worse so I wont dig any deeper.
You'll find thats how all UPS are switched off. The idea being that if things fail (like normally closed contacts opening) then the UPS will carry on.
You can set the UPS to switch off using a normally closed contact but then a fault will switch the equipment off. Its a question of how important your equipment functioning is to you, risk assesment etc.
You can set the UPS to switch off using a normally closed contact but then a fault will switch the equipment off. Its a question of how important your equipment functioning is to you, risk assesment etc.
I don't want to draw the post out but regardless of risk assessments EPO circuits are always made up of normally closed contacts.
You can never rely on a contact making in an emergency situation. If someone has decided, for whatever reason to fit an EPO circuit to IT equipment the most important thing is when you hit the button it works. With normally open contacts that can never be guaranteed.
This is why there are so many regulations covering EPO and other safety circuits.
In a past life I worked in the UPS industry and I can assure you that the EPO contacts are always normally closed. The main function of the UPS EPO circuit is to shut it down in the event of fire. It’s normally linked to the second knock of the gas flood system or the house fire alarm.
EPO circuits that are designed to isolate the power are normally done with contactors switching the UPS output either at the distribution board or somewhere similar.
You can never rely on a contact making in an emergency situation. If someone has decided, for whatever reason to fit an EPO circuit to IT equipment the most important thing is when you hit the button it works. With normally open contacts that can never be guaranteed.
This is why there are so many regulations covering EPO and other safety circuits.
In a past life I worked in the UPS industry and I can assure you that the EPO contacts are always normally closed. The main function of the UPS EPO circuit is to shut it down in the event of fire. It’s normally linked to the second knock of the gas flood system or the house fire alarm.
EPO circuits that are designed to isolate the power are normally done with contactors switching the UPS output either at the distribution board or somewhere similar.
Interesting, as you worked in the industry you would probably know more than me, so why do they have normally open contacts for use in stop buttons and normally open connections on the UPS.
This also doesn't change the fact that the system is critical and as someone advised me above there is no legal requirement for a stop button at all, we only have one in an effort to be ultra safe.
This also doesn't change the fact that the system is critical and as someone advised me above there is no legal requirement for a stop button at all, we only have one in an effort to be ultra safe.
Stop and emergency stop are two completely different things. UPS have all sorts of remote connections and you may find the normally open stop connects you are using are for remote telemetry.
As for the regs I don't disagree but to cover yourself, I would label the stop button "Power Shutdown" as opposed to emergency stop.
As for the regs I don't disagree but to cover yourself, I would label the stop button "Power Shutdown" as opposed to emergency stop.
H
holmslaw
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