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Old August 11th, 2017, 01:48 PM   #1
RogerBrunner
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Emergency device

I think it is against NEC/NFPA code to wire a emergency device thru a software relay (PLC), although I unable to locate the code. If the software fails the emergency device will not work. Any suggestions or ideas on this? I seem to recall some sort of code when i was installing fire alarms.
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Old August 11th, 2017, 02:15 PM   #2
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http://www.plctalk.net/qanda/showthread.php?t=35637

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Old August 11th, 2017, 07:01 PM   #3
Timbert
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Short answer is yes PLC devices can be used in emergency stop circuits.

Slightly longer answer is that all devices involved in emergency stop and other functional safety circuits must be rated for such use and installed properly.
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Old August 12th, 2017, 04:00 AM   #4
mk42
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Quote:
Originally Posted by Timbert View Post
Short answer is yes PLC devices can be used in emergency stop circuits.

Slightly longer answer is that all devices involved in emergency stop and other functional safety circuits must be rated for such use and installed properly.
To expand on Timbert's comment:

If you run your Estop through just any old cheap PLC, you're in for trouble. If you use a Safety PLC, and use it as indicated by the manufacturer, then it is probably OK. Siemens has the F (failsafe) PLCs, AB has Guardlogix, I'm sure other brands have them as well, in addition to smaller standalone safety controllers.

To OP: Sorry, I don't have references to specific codes.
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Old August 12th, 2017, 11:10 AM   #5
QvixoteRoux
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Its complete against current NEC/NFPA regulations

all safety input devices (e-stop, interlock, light curtains, two hands, other) must be wired to a certified safety control, they cant be neither used directly to control lets say a motor, directly wiring the motor supply into the e-stop

Rokwell has a nice safety handbook hat you can get for free (even phisical book) from their website
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Old August 15th, 2017, 09:20 AM   #6
RogerBrunner
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Thanks for all your input. I'm not controlling machines. We are controlling access into communities, the 1st responders have a "key" that will open the barrier gates, that key is the emergency device that i believe should be hardwired into the gate controller and not run thru the PLC. I just can't locate a code in NEC/NFPA.
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Old August 15th, 2017, 11:56 AM   #7
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Take a look at Fortress. They have keyed systems that can include safety-rated switches. They should be able to supply keys and locks to accomplish this.
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Old August 15th, 2017, 12:11 PM   #8
George Graziano
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My last job had 2 gates. They both had installed on them a sensor so that a Siren triggered them open. One of the Electricians was a Volunteer Fireman (Chief)so he had a siren on his truck and would test it at intervals. There was also a lockbox used by Emergency Personnel that had a passkey in it.
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Old August 15th, 2017, 02:06 PM   #9
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There is nothing in the NEC (NFPA 70) about that. There might be some other NFPA document on LV emergency / alarm systems, such as NFPA 72. But enforcement of things other than the NEC is generally hit and miss in many places. The first place I would check though would be the local Fire Marshall, since they are generally the First Responders. NFPA 72 article 17.3.2 says that the functionality of any "initiating" system must be acceptable to the AJH (Authority Having jurisdiction). That's for fire / safety alarm systems, but it likely applies to this too, if anything does.
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