Heater control on a machine

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wireman

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Short version of my question: On a machine, does a contactor that controls a 208VAC single phase heater need to disconnect both hot legs or just one? Right now the contactor only breaks one leg of the heater.

This is a heating pad for that lays on a platform under a bag of fluid for a lab process. There is a 2-pole 10 amp CB that protects it, so that part is OK.

We have been asked to modify the existing controls and install a PLC to control it. A PLC output would control the relay, but do I need to install a 2nd relay for the other leg of the heater to make it code compliant?
 
wireman said:
Short version of my question: On a machine, does a contactor that controls a 208VAC single phase heater need to disconnect both hot legs or just one? Right now the contactor only breaks one leg of the heater.

This is a heating pad for that lays on a platform under a bag of fluid for a lab process. There is a 2-pole 10 amp CB that protects it, so that part is OK.

We have been asked to modify the existing controls and install a PLC to control it. A PLC output would control the relay, but do I need to install a 2nd relay for the other leg of the heater to make it code compliant?
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If the heater is integral with the machine, the NEC does not apply. If the heater is field wired (i.e. not integral with machine), the NEC applies to the field wiring, its overcurrent protection and disconnecting means. A disconnecting means would have to break both legs. However, control can be a single pole switch or relay contacts.
 
Thanks for the info. Can you cite a code section on that.

The heater is located on a stand-alone platform about 10 ft. from & within sight of the control panel so I'd call it "field wiring" between the two. I would call the 2-pole circuit breaker that protects the heater the disconnecting means. The control panel is actually a portable console on wheels that is cord connected.

Thanks again.
 
wireman said:
Thanks for the info. Can you cite a code section on that.

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Click to expand...

Unfortunately, I cannot. I do not believe there is/are any regarding control. If others can think of any (for this particular application), I invite them to jump in and correct me...???
 
UL508a says this

33.3 Location
33.3.1 A load controller marked with the words "break all lines" or having a diagram illustrating a break
all lines configuration shall have contacts in each conductor to the load. Other controllers, not marked
"break all lines" shall be configured with contacts in one conductor to a single-phase load and in two
conductors to a three-phase load.
 
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