EGC for 120V Control Circuits

[jtinge]

For an industrial installation, conduit containing only 120V control conductors is routed between enclosures and from enclosures to field devices.

Is there a requirement that 120V control conductors have an EGC routed with them? I know that metallic conduit can serve as the EGC, but is there a requirement that an EGC is required. If the control conduit was PVC would an EGC be required to be routed with the control conductors? Just looking for the NEC code cite.

 

[jap]

For an industrial installation, conduit containing only 120V control conductors is routed between enclosures and from enclosures to field devices.

Is there a requirement that 120V control conductors have an EGC routed with them? I know that metallic conduit can serve as the EGC, but is there a requirement that an EGC is required. If the control conduit was PVC would an EGC be required to be routed with the control conductors? Just looking for the NEC code cite.

Not too far into 250.4 will reveal a lot of answers.

JAP>

 

[jtinge]

Not too far into 250.4 will reveal a lot of answers.

JAP>

From NFPA 79, I see these requirements that infer that an EGC needs to be routed with the control circuit conductors, but I don't see similar language in 250.4 or elsewhere. Maybe I've been looking to hard and have tunnel vision.

8.2.1.2 Equipment Grounding. The machine and all exposed, non-current-carrying conductive parts, material, and equipment likely to be energized shall be effectively grounded. Where electrical devices are mounted on metal mounting panels that are located within nonmetallic enclosures, the metal mounting panels shall be effectively grounded. Where specified by the manufacturer, components and subassemblies shall be bonded to the equipment grounding (protective bonding) circuit in accordance with the manufacturer’s instructions.

8.2.3 Continuity of the Equipment Grounding (Protective Bonding) Circuit.
8.2.3.1 The continuity of the equipment grounding (protective bonding) circuit shall be ensured by effective connections through conductors.
8.2.3.2 Removing a device shall not interrupt the continuity of the equipment grounding (protective) circuit.
8.2.3.3 Bonding of equipment with bolts or other identified means shall be permitted if paint and dirt are removed from the joint surfaces or the bonded members are effectively penetrated.
8.2.3.4 Raceways, wireways, and cable trays shall not be used as equipment grounding or bonding conductors.

 

[don_resqcapt19]

In general, the NEC never requires an EGC of the wire type, in a non-flexible metallic raceway.

 

[petersonra]

From NFPA 79,
8.2.3.4 Raceways, wireways, and cable trays shall not be used as equipment grounding or bonding conductors.

It appears that NFPA79 does not allow raceways, wire ways, or cable trays to serve as an EGC. So if the wiring in question is subject to NFPA79, then it needs to have an EGC of the wire type pulled with any conductors in raceways, wire ways, or cable trays.

Having said that, just because some conductors are associated with something covered by NFPA79 does not mean those conductors are subject to NFPA79. For instance, the feeder coming into the control cabinet is just a normal feeder. NFPA79 starts inside the box so the feeder conductors would not require a wire type EGC.

 

[jap]

The OP mentioned control conductors installed in a nonconductive raceway such as PVC. If these conductors end up in an enclosure or the like that would require bonding, by, definition of of an EGC I would think an EGC of the wire type would need to be installed to connect all of the non-current carrying metal parts of the equipment to provide a path back to the system grounded conductor.

No?

JAP>

 

[Smart $]

The OP mentioned control conductors installed in a nonconductive raceway such as PVC. If these conductors end up in an enclosure or the like that would require bonding, by, definition of of an EGC I would think an EGC of the wire type would need to be installed to connect all of the non-current carrying metal parts of the equipment to provide a path back to the system grounded conductor.

No?

JAP>

Yes.

120V control conductors are still branch circuit conductors and EGC requirements apply UON.

 

[jap]

Yes.

120V control conductors are still branch circuit conductors and EGC requirements apply UON.

That's good to hear.
Was starting to get concerned there a little bit.

JAP>

 

[petersonra]

Yes.

120V control conductors are still branch circuit conductors and EGC requirements apply UON.

are class 1 circuits also branch circuits?

 

[Smart $]

are class 1 circuits also branch circuits?

AFAICT, yes. Just not your typical power branch circuit.

Article 725 circuits are not excluded from any grounding requirement. However, in many if not most cases, the equipment these circuit conductors run to are already grounded by way of the power conductors, and running an EGC becomes moot...



...but not always. :happyno:

 

[petersonra]

AFAICT, yes. Just not your typical power branch circuit.

Article 725 circuits are not excluded from any grounding requirement. However, in many if not most cases, the equipment these circuit conductors run to are already grounded by way of the power conductors, and running an EGC becomes moot...



...but not always. :happyno:

Typical door bell wiring does not include an EGC. Class 2 circuit.

 

[jtinge]

Yes.

120V control conductors are still branch circuit conductors and EGC requirements apply UON.

How do control conductors that go between terminal blocks, relays, or control devices meet the definition of branch circuit conductors?

Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

If they aren't branch circuits, are they Article 725 conductors and what is the requirement then for EGC's to be routed with them, if any?

 

[Smart $]

Typical door bell wiring does not include an EGC. Class 2 circuit.

How do control conductors that go between terminal blocks, relays, or control devices meet the definition of branch circuit conductors?

Branch Circuit. The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

If they aren't branch circuits, are they Article 725 conductors and what is the requirement then for EGC's to be routed with them, if any?

See 210.2, more specifically a listing in Table 210.2.

Then see 725.3.

With that said, let's take the door bell circuit as an example. So we run a 120V circuit to a 4sq box to which is installed a KO mount 24V Class 2 doorbell transformer. We run a 24V circuit to bell and switch. The switch is installed in a metal bell box. Where is there an exception that says this bell box does not have to be grounded?

 

[jtinge]

See 210.2, more specifically a listing in Table 210.2.

Then see 725.3.

With that said, let's take the door bell circuit as an example. So we run a 120V circuit to a 4sq box to which is installed a KO mount 24V Class 2 doorbell transformer. We run a 24V circuit to bell and switch. The switch is installed in a metal bell box. Where is there an exception that says this bell box does not have to be grounded?

I'm not seeing where any of those specific purpose branch circuit articles amend or supplement article 210 to require an EGC be routed with 120V control conductors.

My experience on industrial control systems has been that individual 120V control wires are routed in RMC or EMT without a separate EGC. The conduit is bonded to the interconnected equipment enclosures, but is the bonded conduit a required EGC or just a non-current carrying exposed metal raceway that needs to be bonded similar to other non-current carrying exposed metal parts that could become energized?

 

[jap]

I'm not seeing where any of those specific purpose branch circuit articles amend or supplement article 210 to require an EGC be routed with 120V control conductors.

My experience on industrial control systems has been that individual 120V control wires are routed in RMC or EMT without a separate EGC. The conduit is bonded to the interconnected equipment enclosures, but is the bonded conduit a required EGC or just a non-current carrying exposed metal raceway that needs to be bonded similar to other non-current carrying exposed metal parts that could become energized?

Without a wire type EGC pulled in the raceway, it is both.

JAP>

 

[jtinge]

For an industrial control system, fixed control cabinets interconnected with permanenent wiring methods (control wiring routed in RMC), 250.110 seems to be the requirement for connection to an EGC.

250.110 Equipment Fastened in Place (Fixed) or Connected by Permanent Wiring Methods
Exposed, normally non–current-carrying metal parts of fixed
equipment supplied by or enclosing conductors or components
that are likely to become energized shall be connected to an
equipment grounding conductor und er any of the following
conditions:
(1) Where within 2.5 m (8 ft) vertically or 1.5 m (5 ft) horizontally
of ground or grounded metal objects and subject
to contact by persons
(2) Where located in a wet or damp location and not isolated
(3) Where in electrical contact with metal
(4) Where in a hazardous (classified) location as covered by
Articles 500 through 517
(5) Where supplied by a wiring method that provides an
equipment grounding conductor, except as permitted
by 250.86 Exception No. 2 for short sections of metal
enclosures
(6) Where equipment operates with any terminal at over
150 volts to ground

250.118 lists RMC as an EGC; however, NFPA 79, 8.2.3.4 says raceways shall not be used as equipment grounding or bonding conductors. Seems like this is driving the need to install an EGC with the control conductors in a conduit.

 

[Smart $]

For an industrial control system, fixed control cabinets interconnected with permanenent wiring methods (control wiring routed in RMC), 250.110 seems to be the requirement for connection to an EGC.
...

I see you got there without my help...

250.118 lists RMC as an EGC; however, NFPA 79, 8.2.3.4 says raceways shall not be used as equipment grounding or bonding conductors. Seems like this is driving the need to install an EGC with the control conductors in a conduit.

NFPA 79 does not apply to field wiring (last time I checked). It is covered by the NEC.

NFPA 79 will apply to machine-integral raceways, so a wire type EGC would be required... but you are not manufacturing machines, are you?

 

[jtinge]

Not manufacturing. The type of installations I'm involved with are large compressor systems, large motor drive systems, large heater power supplies, etc. that would have multiple control cabinets that are field installed and interconnected. MCCs, PLC cabinets, marshaling boxes, etc. The control conduits are part of the system but are used to interconnect factory supplied control cabinets and equipment.

 

[Smart $]

Not manufacturing. The type of installations I'm involved with are large compressor systems, large motor drive systems, large heater power supplies, etc. that would have multiple control cabinets that are field installed and interconnected. MCCs, PLC cabinets, marshaling boxes, etc. The control conduits are part of the system but are used to interconnect factory supplied control cabinets and equipment.

If the control conduits and wiring therein are furnished by the manufacturer as part of the system, even though it is field installed, it still falls under NFPA 79. Otherwise, the NEC applies.

 

[jtinge]

If the control conduits and wiring therein are furnished by the manufacturer as part of the system, even though it is field installed, it still falls under NFPA 79. Otherwise, the NEC applies.

So would a 1" RMC,routed between a field marshalling box and a PLC cabinet and containing 12-#12 AWG, 120V control wires, and no wire-type EGC be compliant with NEC?