EGC for 120V Control Circuits

[Smart $]

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.

What it is saying is if the system powering the circuit is required to be grounded, then an EGC must be run with circuit conductors.

Don't forget 250.110 is a separate section to be complied with, regardless 250.112.

 

[jtinge]

What it is saying is if the system powering the circuit is required to be grounded, then an EGC must be run with circuit conductors.

Don't forget 250.110 is a separate section to be complied with, regardless 250.112.

That's what I needed. For some reason that section just wasn't popping out to me. Thanks again.

 

[jtinge]

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?

Still curious how anyone would size or select EGC as described above.

 

[petersonra]

What it is saying is if the system powering the circuit is required to be grounded, then an EGC must be run with circuit conductors.

Don't forget 250.110 is a separate section to be complied with, regardless 250.112.

i agree the sections stand alone.

However your first assertion is not quite there. neither section exempts you from running an EGC with the other conductors which is found in another section. It only refers to grounding of the non-current carrying conductive parts of the equipment.

 

[Smart $]

i agree the sections stand alone.

However your first assertion is not quite there. neither section exempts you from running an EGC with the other conductors which is found in another section. It only refers to grounding of the non-current carrying conductive parts of the equipment.

Let's look at this as a...

What if the equipment (let's say essentially all metallic) at the load end of a circuit is already bonded by means of an EGC under both 250.110 and 250.112 (let's say a power circuit EGC), and you are now running a control circuit which does not require an EGC specifically per 250.112, does 250.136(A) permit you to not run an EGC?

 

[tom baker]

Yes.

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

Control conductors may be an Art 725 Class 1 control circuit, which still requires an EGC. With out a EGC, if there was a failed or shorted solenoid, how would the fault current get back to open the OCPD?

 

[jap]

Control conductors may be an Art 725 Class 1 control circuit, which still requires an EGC. With out a EGC, if there was a failed or shorted solenoid, how would the fault current get back to open the OCPD?

There would be no need for an EGC the way the example is worded above.

If the solenoid failed it would simply stop working.
If it was shorted, the high current would return through the grounded conductor.

Only if the overcurrent protection didn't trip and the solenoid heated up and proceeded to short to ground would an EGC be of any use.

JAP>

 

[iwire]

There would be no need for an EGC the way the example is worded above.

If the solenoid failed it would simply stop working.
If it was shorted, the high current would return through the grounded conductor.

Only if the overcurrent protection didn't trip and the solenoid heated up and proceeded to short to ground would an EGC be of any use.

JAP>

You lost me, why don't you think an EGC is needed for the solenoid? Class 1 circuits can be 120 volts.

 

[jap]

Cause a solenoid doesn't require an EGC to operate.

If a solenoid "Fails" that generally is a description of an open coil winding.
If a solenoid "Shorts" that generally is a description of a winding that has failed and created a short with less resistance and high current that trips the OCPD through the neutral return path.

It's only when the solenoid "Shorts to ground" or normally non current carrying parts that an EGC is needed for a return path.


JAP>

 

[Smart $]

Control conductors may be an Art 725 Class 1 control circuit, which still requires an EGC. With out a EGC, if there was a failed or shorted solenoid, how would the fault current get back to open the OCPD?

I said an EGC is required, so why are you asking me?

 

[iwire]

Cause a solenoid doesn't require an EGC to operate.

If a solenoid "Fails" that generally is a description of an open coil winding.
If a solenoid "Shorts" that generally is a description of a winding that has failed and created a short with less resistance and high current that trips the OCPD through the neutral return path.

It's only when the solenoid "Shorts to ground" or normally non current carrying parts that an EGC is needed for a return path.


JAP>

And this is different from say your household refrigerator how?

 

[jap]

Not saying it isn't needed.
just putting more clarification as to when and why.

JAP>

 

[jap]

And this is different from say your household refrigerator how?

There is no difference.
As I said in earlier posts the EGC is needed whether that be the raceway or of the wire type.

But if you tell me your refrigerator "Failed" id consider that it simply failed to cool anymore and you came home and there was water all over the floor.
If you told me that your compressor motor was "Shorted" it may be shorted between the motor leads and not the case of the fridge.

Its only when the refrigerator shorts to the "Case" or ground that the EGC comes into play.

I was just having fun with the wording.

JAP>

 

[jtinge]

I thought we had established that a conduit that contained only 120 volt control wires needed an EGC. But let me give a more specific example:

Control cabinet "A", fed by circuit 1 and associated EGC, contains a PLC, where the cabinet and PLC are connected to the EGC.
Control cabinet "B", fed by circuit 2 and associated EGC, contains a power supply and relays, and the cabinet and power supply are connected to the EGC.
A conduit routed between the two cabinets contains 10-#14 AWG, 120 volt control wires from the 120 volt output module of the PLC and are connected directly to the relays.

If the conduit is RMC, would you use this as the EGC for the control wires? Would you run a wire-type EGC with the control wires? Why or why not. NPFA 79 does not permit you to use the conduit as an EGC. Would you apply the same logic to this case?

If the conduit is non-metallic conduit, would you run a wire-type EGC with the control wires? What code section would you use to size the EGC since the control wires are not fed by an OCPD?

 

[jap]

I always pull a wire type EGC so there's no need for me to put that much thought into it.


JAP>

 

[Smart $]

I thought we had established that a conduit that contained only 120 volt control wires needed an EGC. But let me give a more specific example:

Control cabinet "A", fed by circuit 1 and associated EGC, contains a PLC, where the cabinet and PLC are connected to the EGC.
Control cabinet "B", fed by circuit 2 and associated EGC, contains a power supply and relays, and the cabinet and power supply are connected to the EGC.
A conduit routed between the two cabinets contains 10-#14 AWG, 120 volt control wires from the 120 volt output module of the PLC and are connected directly to the relays.

If the conduit is RMC, would you use this as the EGC for the control wires? Would you run a wire-type EGC with the control wires? Why or why not. NPFA 79 does not permit you to use the conduit as an EGC. Would you apply the same logic to this case?

If the conduit is non-metallic conduit, would you run a wire-type EGC with the control wires? What code section would you use to size the EGC since the control wires are not fed by an OCPD?

Pulling #14 AWG control conductors, I'd pull a #14 EGC.

If I were pulling one or more cables, I would not pull any additional EGC. If there was an EGC it would be in the cable.

I believe #14 is the smallest EGC permitted by Code.

 

[petersonra]

I believe #14 is the smallest EGC permitted by Code.

take a look at 250.122 (A).

 

[Smart $]

take a look at 250.122 (A).

:?

 

[petersonra]

:?

What does it tell you about minimum size here?

Sent from my SM-G900R4 using Tapatalk

 

[Smart $]

What does it tell you about minimum size here?

"equipment grounding conductors of the wire type shall not
be smaller than shown in Table 250.122, but in no case
shall they be required to be larger than the circuit conductors
supplying the equipment"

So you just want to point out that smaller is conditionally permitted?