Emergency Stop (E-STOP) wiring practice

[Barrnich]

Hello,
I'm based in the US but design machines for US and EU market. Can someone tell me what the codes are for wiring an Emergency stop push button. We have some machines in the field, here and in EU that have primary voltage 3ph 240AC wired to the e-stop that act as the main estop for the machine. I thought that it is common practice to run low voltage 24V etc to the e-stop and have that as a control to a relay contactor that would shut off the primary voltage. Is this a rule or can you run primary current to the estop.

Some additional questions.

1. Are you allowed to run more than 120V AC to an operator control? What code / section would not allow this? I have seen OSHA code 1910.217 for power presses that this is not allowed. This machine is not a power press though and doesn't fall under OSHA specific machines. Does NFPA 79 cover this? Any NEC code?
2. The machine is rated for 20A on the mains label. Each leg is pulling 9A under max load though and the contactors on the back of the estop is rated for 10A continuous (Ith) 690V. Is this a violation of any code?

Modifications were made to current machines for CE compliance that has low voltage running through the E-stop but I am concerned about ones in the field in the US and EU.

Thanks


Thanks for your help.

-Bar

 

[VinceS]

Yes, NFPA 79 defines the various types of STOP conditions (9.2.5.3) and E-STOP (9.2.5.4). If you don't own the 79 you can view it at NFPA's site free..

http://www.nfpa.org/aboutthecodes/list_of_codes_and_standards.asp?cookie_test=1

Not a sales pitch but OMRON's site has outstanding information on machine safety and monitoring..

http://www.sti.com/index.htm

I think running the 24V for control is getting more common with the seriousness of NFPA 70E finally being a consideration. 120V control is not prohibited by the NEC (70) or 70E.

The E-STOP you describe:
"2. The machine is rated for 20A on the mains label. Each leg is pulling 9A under max load though and the contactors on the back of the estop is rated for 10A continuous (Ith) 690V. Is this a violation of any code?"
Makes me think the E-Stop you describe has a contactor not E-STOP switch contacts. I can make one comment: if this is just control power, limit it to 10A with supplementary fused protection.

I have normally used a master control relay tied to a monitored safety relay tied into E-STOPS.

 

[petersonra]

I don't see anything wrong with what you are doing. the estop is there to stop the machine. As long as it does that, exactly how you accomplish that is up to you.

There may be some issues with the pushbutton contactors being rated for the load it is trying to open, but thats is a separate issue.

There is no general rule that describes how e-stops are to be designed into a machine other than where they are to be located. depending on the hazards involved, and personal preferences of everyone involved, you can justify a whole lot of different scenarios for the same machine.

The EU has a different set of rules.

 

[pfalcon]

Disclaimer: NFPA79 is a legal requirement only if (1) your area government has adopted it which is not commonly done or (2) your company has published that it shall comply which is fairly common. Publishing corporate compliance to NFPA79 permits OSHA to legally bind your company to the standard including both civil and criminal liability.

Short Answer: VIOLATION - But see disclaimer.

See NFPA79:2007 9.1 Control Circuits.
Especially NFPA79:2007 9.1.2 Control Circuit Voltages.
"... shall not exceed 120 volts, ac single phase." Exceptions are listed in the standard.

As per VinceS many in the industry are moving toward 24VDC for easier compliance with NFPA70E issues. Safety rated relays and safety rated contactors are used to break the higher voltages but the operator controls must comply with 9.1.2 at 120VAC 1ph or less.

petersonra: Since NFPA79 was noted in the OP I would tend to presume that it is a part of his company's policies and therefore legally binding on him. Section 9.2.5.3 and other sections go extensively into the proper wiring and operation of the Estop circuit. This is far from "is there to stop the machine." or "that is up to you."

 

[petersonra]

petersonra: Since NFPA79 was noted in the OP I would tend to presume that it is a part of his company's policies and therefore legally binding on him. Section 9.2.5.3 and other sections go extensively into the proper wiring and operation of the Estop circuit. This is far from "is there to stop the machine." or "that is up to you."

Have you actually read those sections? There are a lot of ways to accomplish what NFPA79 says you have to do. And if you read closely, a fair amount of it requires that you decide upfront just what is required for your specific situation, and it is quite possible for two completely reasonable people to come up with quite different solutions to the problem.

using the estop to directly shut off the mains does not violate the maximum 120V control circuit voltage requirement, as it is not a control circuit.

 

[Strahan]

Allen Bradley offers a wide range of safety packages that we use in our industry. We use guard master monitoring safety relays for all our apps. MSR210P with modular MSR220P modules that we use to energize a 100S-C60 3phase safety contactor. What these devices do in general is monitor a dual channel input one N.O and the other N.C it has to see operation of both channels and also monitors each channel for shorts. In turn we use the safety rated auxiliary's to energize the 3phase safety contactor which energizes all of our 3phase loads. Within these packages the safety relay itself can operate on 120VAC or 24VDC but the contacts from door safety's and or e-stops are simply contact closure's. These packages when installed correctly meets the requirements of category 4 per EN594-1. We actually had an outside firm come in and provide risk assesments for all our equiptment in order to provide the proper guard packages.

 

[petersonra]

The price of safety relays has come down to the point where it is probably a good idea to just put one on any new or rebuilt machine. The kind of time it will take you a year from now to defend not putting one on makes it worth doing on its own merits.

 

[dbuckley]

Certainly in the UK (and thus probably Europe) there is no problem running 240V to the estop buttons, however, the estop must interrupt the primary power in a fail-safe manner (ie if the estop circuit fails, the machine must not run) so shunt trips are out. Also once the estop is pressed there must be an action to reset the supply. This often means mechanically latching estop button(s) with a key to release them.

I'd also agree with the other poseters that if your needs are complex then use safety relays from any of the big manufacturers, and follow their directions to the letter.

 

[pfalcon]

Have you actually read those sections? There are a lot of ways to accomplish what NFPA79 says you have to do. And if you read closely, a fair amount of it requires that you decide upfront just what is required for your specific situation, and it is quite possible for two completely reasonable people to come up with quite different solutions to the problem.

using the estop to directly shut off the mains does not violate the maximum 120V control circuit voltage requirement, as it is not a control circuit.

petersonra,
The OP is talking about taking the mains power to the operator. The Estop operator is definitely a control circuit component - its function is defined under Chapter 9 Control Circuits and Control Functions for pity's sake. Two completely reasonable people may come up with quite different solutions but they both better be 120VAC or less at the Estop operator or it directly violates NFPA79:2007 9.1.2 Control Circuit Voltages. which sets the limit for the circuits expressed in NPFA:2007 9.2.5.4.1 Emergency Stop.

He is required to use a device comparable to what Strahan suggested that operates the coil side off of "120VAC or less" or "250VDC or less". The other side can be 10GW or more to power the DeLorean if sized correctly.