AC Pump/Motor E-Stops in Hazardous Locations

[Mr. BNA]

Question - The existing facilities have whole bunch of pump/motors and MCCs as well as E-stops used for hazardous locations (Class 1, Div. 1 or 2). The idea is that to install additional E-stops closer to egress for the operation personnel to stop the pump/motors in case of emergency and leave the hazardous areas faster. So the question is "Isn't true that we can simply install additional E-stops by parallel wiring them to existing E-stops including new conduit and conductors matching the existing assuming the existing installation is correct? if yes, what parameters should we look for? For example, is distance a factor (How far from existing E-stop, we can install the new one)? Should we look for the voltage rating of auxillary contactor used in conjunction with the existing e-stops? What conductor sizes should we use, No. 16, No. 18 AWG, etc? Assuming the conduit and housing of E-stops meet the requirements of Class I, Div.1 or 2.

Thank you,

 

[benaround]

Mr BNA,

If e-stops are n.o. then I say you have it right, if e-stops are n.c. then they need to be wired in series

frank

 

[justdavemamm]

E-Stops are never wired in parallel. NEVER. They are always N.C. contacts wired in series. This way a broken wire can be detected. If you ever see any E-Stops wired in parallel, then it's time to rip out that circuit and do it correctly.

The series wires of a field mounted E-Stop Pb are not normally daisy chained from one push button to the next but rather brought back to a central source (typ. the control panel) and connected in series there on the terminal strip. This aids in trouble shooting and in the case of multiple zones, connecting all Pb's in each zone together.

Most modern day E-Stops have two N.C. sets of contacts and a light to indicate. The double set of contacts are typically wired in the circuit of a 'Safety Relay", not the old style MCR (Master Control Relay).

The size and type of wire will depend on the length and voltage of the circuit along with the location of the circuit. Typically, and I say this in very most of general terms, 14 gauge 600V THHN stranded wire is used for discrete field devices. However, other circumstances, local laws and company rules may require other considerations. Along with other factors.

You should really have a Controls Engineer review and determine the wiring of all that I have commented on. A Controls Engineer does this type of stuff for a living and should be well versed in this area.