Moving Estop Wiring

N

Thread Starter

Nate B

In a controls cabinet that we are retrofitting with new equipment, all switches and signals are 24VDC or less EXCEPT for an Estop running 120VAC. This triggers a severe headache for troubleshooting due to the company's arc flash policy that requires the "hazmat" suit to even open the panel to check if an output is firing correctly. Therein lies the question.

Is it against any code to run 24VDC through the Estop to a relay in an remote cabinet that interrupts the 120VAC? Does it have to be a certain type or a certified relay of some sort? I already have this in mind: N/C Estop contact (pulled out) fires remote relay that closes N/O contacts to make 120VAC connection.
 
I don't think your approach violates any code in the United Sates, but adding the 120 VAC relay is adding 1 more device which could fail. However, in your case, if the 120 VAC relay fails, the 120 VAC relay contacts will most likely open.

Check to see how ANSI standard B11.19-1990 applies to your situation. It defines control reliability as “…the device, system or interface shall be designed, constructed and installed such that a single component failure within the device, interface or system shall not prevent normal stopping action from taking place but shall prevent a successive machine cycle...” So make sure your machine cannot start again unless the E-Stop is reset. Normally this ANSI standard is referenced for owners and manufacturers of machine tool equipment, but the words quoted above are something you should work into your design even if this is not a machine tool application.

You may need a safety relay which complies with ANSI standard B11.19-1990.
 
S
"This triggers a severe headache for troubleshooting due to the company's arc flash policy that requires the "hazmat" suit to even open the panel to check if an output is firing correctly."

[eyeroll] Safety is good, except when managed by idiots.
 
Just what does your e-stop control?

Most e-stops are contacts in series with other conditions, such as manual disconnects, etc. so you can usually add another condition that being you 24v control circuit as long as it is designed foR fail safe.

Whatever changes you make, be sure to document them and have someone familiar with your process go over it.

 
G

Gerald Beaudoin

Depending on the process/risk, it may even be prudent to have it certified by an qualified third party.
 
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