Switch the 0VDC in a PNP Panel

So I have a solenoid manifold with 9 solenoids Coils. I have 2 options for the E-Stop to kill them.

I can have the 24VDC going to the PLC Output switched by the E-Stop or I can have Switch the 0VDC from the Solenoid Coils


I'd kind of prefer to switch the 0VDC as it would give me more granular control on future panels about what is being killed by the E-Stop.


Is switching the 0VDC ok in a PNP Panel?



Thoughts?

theColonel26,

this is a very dangerous way of doing and e-stop and is not allowed, see NFPA79 - electrical standard for industrial machinery. you must kill the power to the I/o.

killing the power side of the circuit when you press the e-stop will kill the power and free someone who is touching the power wire and becoming a path to ground from obtaining further damage. someone can then provide first aid.

killing the 0 volt or neutral of a 120 volt circuit will do nothing for that person who has become the path from power wiring to ground. the power to the I/o still remain hot and anyone who touches that individual will also be a path to ground.

again, refer to NFPA 79 for their rules regarding e-stops.

james

I suggest you keep to switching the + supply, it is possible that if a solenoid coil common leaks to earth i.e. some solenoids have an earth lead on casing) and the - lead shorts to ground removing the -ve via e-stop may cause the solenoid to operate, this would be true if the -ve was tied to ground as is often the case. I know it's only 24v but would you open the neutral instead of the live ? convention helps engineers to fault find if they are unfamiliar with the panel, also if you break the common -ve then putting a meter on the supply or output card terminal will show a voltage, confusing to any engineer.
I have had an instance where the solenoid shorted to earth somewhere in the middle to ov end of the coil, this would blow the fuse only on odd occasions, presumably when that solenoid operated at the same time as others. It took some time to find this fault because operating the solenoid in isolation of the others on the card would not blow the fuse and it operated correctly.
Remember sourcing & sinking NPN/PNP outputs you normally disconnect the +

Think of somebody coming in behind you.
Id be shaking my head!

Thanks Guys, I'll stick with switching the +Power