EGC for 120V Control Circuits

[Smart $]

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?

Quite likely, but it's not a certainty without further investigation. One or the other terminal enclosure must be bonded to the 120V source with a jumper or EGC not smaller than #12.

 

[petersonra]

Quite likely, but it's not a certainty without further investigation. One or the other terminal enclosure must be bonded to the 120V source with a jumper or EGC not smaller than #12.

What exactly do you mean by this? This is a fairly ambiguous statement.

 

[Smart $]

What exactly do you mean by this? This is a fairly ambiguous statement.

The 120V circuit originates somewhere. Under the NEC, with few exemptions, this 120V source is required to be a grounded system. The referenced 1" RMC must be bonded to the grounding system in a manner consistent with Article 250. If you wish, you can go directly to 250.110 to evaluate whether it must be grounded or not. If you believe Article 725 supersedes 250.110 grounding requirement, please cite the section which states such.

 

[Smart $]

Quite likely, but it's not a certainty without further investigation. One or the other terminal enclosure must be bonded to the 120V source with a jumper or EGC not smaller than #12.

What exactly do you mean by this? This is a fairly ambiguous statement.

PS: I assumed there was no bonding jumper installed directly to the 1" RMC at either end of the run. As such bonding would appear to rely on the connection to a bonded, grounded enclosure... at least one of them, then both through the 1" RMC if not previously.

 

[jtinge]

EGC for 120V Control Circuits

PS: I assumed there was no bonding jumper installed directly to the 1" RMC at either end of the run. As such bonding would appear to rely on the connection to a bonded, grounded enclosure... at least one of them, then both through the 1" RMC if not previously.

Assume at least one of the cabinets is bonded to ground and the RMC is bonded using lock nuts.

It's common practice for us to require a wire type EGC be routed with all branch and feeder circuits. Conduit is not relied on as the EGC. It is always considered supplemental to the wire type EGC. But for the control conduit described in my previous post, I'm still trying to determine if an EGC is required to be routed with the control wires.

If this is a NEC scope installation, RMC could satisfy the required EGC. If it is an NFPA 79 scope installation, conduit can't serve as an EGC, if required, and a wire type EGC would need to be installed.

I'm just trying to determine if the conduit containing only 120V control wires needs an EGC?

The fact that we're on several pages of responses already without a clear cite tells nm the requirement is nested in the code and is not obvious, or its nit there.

 

[petersonra]

Assume at least one of the cabinets is bonded to ground and the RMC is bonded using lock nuts.

It's common practice for us to require a wire type EGC be routed with all branch and feeder circuits. Conduit is not relied on as the EGC. It is always considered supplemental to the wire type EGC. But for the control conduit described in my previous post, I'm still trying to determine if an EGC is required to be routed with the control wires.

If this is a NEC scope installation, RMC could satisfy the required EGC. If it is an NFPA 79 scope installation, conduit can't serve as an EGC, if required, and a wire type EGC would need to be installed.

I'm just trying to determine if the conduit containing only 120V control wires needs an EGC?

The fact that we're on several pages of responses already without a clear cite tells nm the requirement is nested in the code and is not obvious, or its nit there.

the NEC has no requirement to run wire type egc with control circuits (or feeder circuits or branch circuits, with a few exceptions). it likely requires an egc, but it does not have to be a wire.

just because it may be common practice where you work to do so does not mean it is actually required.

In any case, NFPA79 is not a legally required standard and only applies within the scope of an industrial machine. Essentially it only applies if someone in charge says it does. Like the P.O. for the work being done or your boss.

It will not hurt anything to run a wire type EGC with the conductors even if it is not necessary.

 

[petersonra]

The 120V circuit originates somewhere. Under the NEC, with few exemptions, this 120V source is required to be a grounded system. The referenced 1" RMC must be bonded to the grounding system in a manner consistent with Article 250. If you wish, you can go directly to 250.110 to evaluate whether it must be grounded or not. If you believe Article 725 supersedes 250.110 grounding requirement, please cite the section which states such.

even if it is an ungrounded system the EGC is still required.

 

[Smart $]

even if it is an ungrounded system the EGC is still required.

Yep.

 

[jtinge]

Thanks everyone for the feedback.

 

[petersonra]

The 120V circuit originates somewhere. Under the NEC, with few exemptions, this 120V source is required to be a grounded system. The referenced 1" RMC must be bonded to the grounding system in a manner consistent with Article 250. If you wish, you can go directly to 250.110 to evaluate whether it must be grounded or not. If you believe Article 725 supersedes 250.110 grounding requirement, please cite the section which states such.

suppose you have a typical 2 wire 4-20mA transmitter. it could be arranged to be part of a class 2 circuit, and often is, even though people might not realize it, however it is also common that it is not a class 2 circuit.

that would appear to make it a class 1 power limited circuit in most cases.

does the signal cable have to have an EGC? have you ever actually seen one wired this way?

 

[Smart $]

suppose you have a typical 2 wire 4-20mA transmitter. it could be arranged to be part of a class 2 circuit, and often is, even though people might not realize it, however it is also common that it is not a class 2 circuit.

that would appear to make it a class 1 power limited circuit in most cases.

does the signal cable have to have an EGC? have you ever actually seen one wired this way?

I can't answer your first question. Depends on whether the equipment at the other end needs grounded.

I've not seen any with an EGC in the signal cable as far as I can recall because all the control equipment I have dealt with has been inherently grounded through mechanical connection and/or jumper or power-circuit EGC bonding.

I've seen plenty of shielded cable with shield landed both ends, and I've seen plenty with one end lifted (the preferred, oft required method). When in these situations, I hardly ever give thought to equipment grounding. :angel:

 

[petersonra]

I can't answer your first question. Depends on whether the equipment at the other end needs grounded.

I've not seen any with an EGC in the signal cable as far as I can recall because all the control equipment I have dealt with has been inherently grounded through mechanical connection and/or jumper or power-circuit EGC bonding.

I've seen plenty of shielded cable with shield landed both ends, and I've seen plenty with one end lifted (the preferred, oft required method). When in these situations, I hardly ever give thought to equipment grounding. :angel:

There is nothing in the code that allows you to skip running the EGC with circuit conductors just because there is nothing at the other end that needs to be grounded, or because there is metal connecting the piece being supplied to the source (unless it is some kind of metal raceway).

 

[Smart $]

There is nothing in the code that allows you to skip running the EGC with circuit conductors just because there is nothing at the other end that needs to be grounded, or because there is metal connecting the piece being supplied to the source (unless it is some kind of metal raceway).

250.136(A)... but you are essentially correct.

 

[jtinge]

These are the only two sections I can find that address the need for an EGC when the conductors are not power supply wires or when there is not an OCPD supplying the conductors. One could infer that control conductors routed in RMC without any power supply wires or not having an upstream OCPD could have a similar requirement, but I haven't found it.

640.7 Grounding
(A) General. Wireways and auxiliary gutters shall be connected
to an equipment grounding conductor(s), to an equipment bonding
jumper, or to the grounded conductor where permitted or
required by 250.92(B)(1) or 250.142. Where the wireway or
auxiliary gutter does not contain power-supply wires, the equipment
grounding conductor shall not be required to be larger than
14 AWG copper or its equivalent. Where the wireway or auxiliary
gutter contains power-supply wires, the equipment grounding
conductor shall not be smaller than specified in 250.122.

690.45 Size of Equipment Grounding Conductors
Equipment grounding conductors for PV source and PV output
circuits shall be sized in accordance with 250.122. Where no
overcurrent protective device is used in the circuit, an assumed
overcurrent device rated at the PV maximum circuit current shall
be used when applying Table 250.122. Increases in equipment
grounding conductor size to address voltage drop considerations
shall not be required. An equipment grounding conductor shall
not be smaller than 14 AWG.

 

[iwire]

These are the only two sections I can find that address the need for an EGC when the conductors are not power supply wires or when there is not an OCPD supplying the conductors.

An EGC or a wire type of EGC?

This thread is all over the place.

 

[jtinge]

An EGC or a wire type of EGC?

This thread is all over the place.

My original post was to ask if an EGC is needed for 120V control wires. My last post was to highlight what requirements I found that specifically stated "an EGC is required when". If an EGC is required, then one can decided if the raceway satisfies the requirement for an EGC or if a wire type would be required. This was the reason for highlighting the difference between routing the 120V control wires in RMC or PVC.

If we were discussing a branch circuit, an EGC is required. One that requirement is understood, you can decide if the raceway satisfies the EGC requirement or if a wire type is required, as would be the case if it was routed in PVC or non-metallic conduit.

I'm just trying to establish if there are similar requirements that apply to the case described in the OP.

 

[Smart $]

...
I'm just trying to establish if there are similar requirements that apply to the case described in the OP.

As far as I can tell, here's the requirement you have to figure out first...

250.112 Specific Equipment Fastened in Place (Fixed)
or Connected by Permanent Wiring Methods. Except as
permitted in 250.112(F) and (I), exposed, normally non–
current-carrying metal parts of equipment described in
250.112(A) through (K), and normally non–current-carrying
metal parts of equipment and enclosures described in
250.112(L) and (M), shall be connected to an equipment
grounding conductor, regardless of voltage.
(A) Switchgear and Switchboard Frames and Structures.
Switchgear or switchboard frames and structures
supporting switching equipment, except frames of 2-wire
dc switchgear or switchboards where effectively insulated
from ground.
(B) Pipe Organs. Generator and motor frames in an electrically
operated pipe organ, unless effectively insulated
from ground and the motor driving it.
(C) Motor Frames. Motor frames, as provided by
430.242.
(D) Enclosures for Motor Controllers. Enclosures for
motor controllers unless attached to ungrounded portable
equipment.
(E) Elevators and Cranes. Electrical equipment for elevators
and cranes.
(F) Garages, Theaters, and Motion Picture Studios.
Electrical equipment in commercial garages, theaters, and
motion picture studios, except pendant lampholders supplied
by circuits not over 150 volts to ground.
(G) Electric Signs. Electric signs, outline lighting, and associated
equipment as provided in 600.7.
(H) Motion Picture Projection Equipment. Motion picture
projection equipment.
(I) Remote-Control, Signaling, and Fire Alarm Circuits.
Equipment supplied by Class 1 circuits shall be grounded
unless operating at less than 50 volts. Equipment supplied
by Class 1 power-limited circuits, by Class 2 and Class 3
remote-control and signaling circuits, and by fire alarm circuits
shall be grounded where system grounding is required
by Part II or Part VIII of this article.
(J) Luminaires. Luminaires as provided in Part V of Article
410.
(K) Skid-Mounted Equipment. Permanently mounted electrical
equipment and skids shall be connected to the equipment
grounding conductor sized as required by 250.122.
(L) Motor-Operated Water Pumps. Motor-operated water
pumps, including the submersible type.
(M) Metal Well Casings. Where a submersible pump is
used in a metal well casing, the well casing shall be connected
to the pump circuit equipment grounding conductor.

 

[iwire]

I'm just trying to establish if there are similar requirements that apply to the case described in the OP.

Yes, 120 volt class 1 circuits require an EGC. I think that has clearly be established in this thread.

 

[jtinge]

Yes, 120 volt class 1 circuits require an EGC. I think that has clearly be established in this thread.

Since 120 volt class 1 circuits require an EGC, what type and size EGC would you use for #14 AWG, 120 volt class 1 control conductors, routed in RMC? Would you use the RMC as the EGC?

If on a large industrial system, installed under NEC, but similar in configuration to a system under the NFPA 79 scope, would you require a wire type EGC be installed with the control conductors in the RMC, using the same rationale that raceways are not permitted to be used as EGC's under NFPA 79?

 

[petersonra]

As far as I can tell, here's the requirement you have to figure out first...

(I) Remote-Control, Signaling, and Fire Alarm Circuits.
Equipment supplied by Class 1 circuits shall be grounded
unless operating at less than 50 volts. Equipment supplied
by Class 1 power-limited circuits, by Class 2 and Class 3
remote-control and signaling circuits, and by fire alarm circuits
shall be grounded where system grounding is required
by Part II or Part VIII of this article.

IMO, the system grounding here refers to connecting the electrical system to earth (i.e.-creating a grounded conductor), not whether you have to route an EGC with the circuit conductors.