Conveyor Pull Wire

[bs123]

Good Morning,
Under the NEC are pull wires required to be hardwired directly to the conveyor safety circuit.
The installation we have here has each pull wire going to the PLC and the logic stops the conveyor.

In the past under IEC the safety circuit has been a requirement.

Also is there an NEC article focused on Conveyors. I would assume there would be rules like the pull wire must activate in both directions, must activate it the wire is cut etc.

Thanks in advance.

 

[petersonra]

Good Morning,
Under the NEC are pull wires required to be hardwired directly to the conveyor safety circuit.
The installation we have here has each pull wire going to the PLC and the logic stops the conveyor.

In the past under IEC the safety circuit has been a requirement.

Also is there an NEC article focused on Conveyors. I would assume there would be rules like the pull wire must activate in both directions, must activate it the wire is cut etc.

Thanks in advance.

could be it is a safety PLC.

could also be they did a risk assessment and determined there was no need for a safety relay.

the NEC does not deal with machine safety.

the closest thing you might find to getting some guidance would be in NFPA79 but it will not tell you that you must have a safety relay.

 

[kwired]

Good Morning,
Under the NEC are pull wires required to be hardwired directly to the conveyor safety circuit.
The installation we have here has each pull wire going to the PLC and the logic stops the conveyor.

In the past under IEC the safety circuit has been a requirement.

Also is there an NEC article focused on Conveyors. I would assume there would be rules like the pull wire must activate in both directions, must activate it the wire is cut etc.

Thanks in advance.

Closest things in NEC that apply is either art 430 which would primarily be for the motor and control circuits, or if it is a listed appliance then it is a 422 application.

The requirement for the safety cable is not something covered by NEC, certain aspects of the safety circuit when present however are covered by NEC, things like minimum conductor ampacity, overcurrent protection...

 

[The Smashing Electrons]

Manufactuers instructions are by extention part of the code 110.3(B)

Manufactuers instructions are by extention part of the code 110.3(B)

The manufacture's of e-stop devices have extensive instructions that accompany any product that has anything to do with safety.

If they say there device must be tested annually or sooner then that becomes code .

I have never seem any device (rope switch, e-stop button, light curtain, safety interlocks and gate switches) that did not have extensive instructions and requirements.

If the manufacture says a risk assessment must be done and that the installation must comply with NFPA 79 then that becomes code.

It may be that if you get a copy of the instructions for the device in question it may clear up a lot.:happyyes:

Also PLC's that are for safety are normally red.

 

[a.bisnath]

code and other considerations

code and other considerations

The manufacture's of e-stop devices have extensive instructions that accompany any product that has anything to do with safety.

If they say there device must be tested annually or sooner then that becomes code .

I have never seem any device (rope switch, e-stop button, light curtain, safety interlocks and gate switches) that did not have extensive instructions and requirements.

If the manufacture says a risk assessment must be done and that the installation must comply with NFPA 79 then that becomes code.

It may be that if you get a copy of the instructions for the device in question it may clear up a lot.:happyyes:

Also PLC's that are for safety are normally red.

20 years ago certain insurance companies would not accept any thing but hard wire installations with electromagnetic relays rather than PLC for safety circuits and wiring ,also what must be considered is the area classification and the suitability of the enclosures used especially if it is hazardous (class 1 div1 and 2).I have now seen this changed over the years with the use of intrinsically safe barrier relays and modules ,proper and tested grounding systems and strict adherence to NEC codes. Area and application are determining factors. I will always choose to follow the safest way within the codes. I have seen crazy things happen when compromises are made in conveyer belt systems

 

[petersonra]

The manufacture's of e-stop devices have extensive instructions that accompany any product that has anything to do with safety.

If they say there device must be tested annually or sooner then that becomes code .

I have never seem any device (rope switch, e-stop button, light curtain, safety interlocks and gate switches) that did not have extensive instructions and requirements.

If the manufacture says a risk assessment must be done and that the installation must comply with NFPA 79 then that becomes code.

It may be that if you get a copy of the instructions for the device in question it may clear up a lot.:happyyes:

Also PLC's that are for safety are normally red.

I have never seen one that requires you to wire it to a safety relay or a safety PLC. if you want certain performance levels it is required, but not in general.