Emergency stop polarity?

Tom Shaughnessy

New User
Location
Detroit, Michigan
Occupation
Engineer
I am looking for information on switching in a 24V emergency stop circuit. is there a code requirement for switching the 0V side or 24 volt side? I am reviewing a piece of equipment and find the estop button is wired on the 0 Volt side of the circuit. In this case the 0 volt or neutral side of the circuit is grounded. in this case a short circuit would be like jumping the circuit out, where if controlled on the +24volt side the shorted condition would cause a breaker to trip and shut down. Before pushing for a change, i wanted to be certain it is not a requirement for some other reason. Any recommendations?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Failsafe design would always dictate having the E-stop in the ungrounded conductor of the circuit for the reasons you mention.
I'm inclined to agree with you for the most part however I don't think it makes a whole lot of difference if it's a shunt trip type breaker that's being tripped by the estop pb.

If loss of power to the main coil is what trips the circuit probably a good idea. I guess it kind of depends on what kind of emergency stop it is. I wouldn't get too excited about some things but some things I might.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
If this is a motor control circuit, see 430.74. Even if it is not a motor control circuit, it is not a good idea to wire the circuit in a manner that would permit a ground fault to disable the E-Stop.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
Could it be that this is a redundant contact style E-stop, with contacts in both hot and grounded conductors. I think this is common with safety relays.
 
Top