Machine EMERGENCY STOP With Power/Air Remaining?!?!? 1

[v57]

We design and build packaging machinery and have an odd request from a customer. They wish to run a compressed air line and 120VAC power through our machine to power a secondary piece of equipment at the discharge of our machine. The twist is they want power and air to remain ON even if our machine is put into emergency stop mode. The power source for this would come from our main electrical cabinet upstream of our e-stop circuit and the air supply would come from upstream of our main air dump valve that opens during e-stop. They would not connect to any devices on our machinery, only to the downstream piece of equipment which resides outside our interlocked guard package.

Our question is, does this violate an emergency stop requirement such as NFPA 79 "Electrical Standards for Industrial Machinery" which contains statements such as :

9.2.5.4.2.2 Emergency switching off shall be accomplished by
disconnecting the incoming supply circuit of the machine effecting
a Category 0 stop. Where the machine cannot tolerate
the Category 0 stop, it shall be necessary to provide other protection
(e.g., against direct contact), so that emergency switching
off is not necessary.

Any help on this would be greatly appreciated.

 

[racookpe1978]

An Emergency Stop MUST "stop" the machine in question from operating.

Sounds basic, but I think you are assuming the Emergency Stop is going to cut off power and compressed air to the unit as if for maintenance or replacement and removal. It doesn't have to do that at all.

Complete energy isolation (lock out/tagout) and complete energy removal (bleeding off air pressure, hydraulic pressure, electric power, potential energy of raised lids and presses, etc.) for maintennace on machine_1 or machine_2 is very different. Your LOTO for EITHER machine_1 OR machine_2 needs to isolate everything or that conductor is still live and could be cut or touched or broken accidently.

But running a cable through a conduit (or an air pipe) through an operating machine_1 to get to machine_2 does not affect the Emergency Stop function of Machine_1.

Unless machine_2 does need to also be stopped at exactly the same time.

 

[v57]

Ahhh, I think we were getting the EPO and LO/TO functions crossed up. LO/TO has resolved it. We tapped into the air system between the dump valve and the LO/TO valve, and the power is supplied by the main but downstream of the LO/TO circuit. LO/TO dumps everything, EPO just stops machine. Customer can choose to shut downstream stuff down via a signal from us if they want.

Thanks!