EGC for multiple circuits in DIFFERENT raceways

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LPS

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Let's say I have a large piece of industrial equipment with ten 50A 480V three phase heating circuits. The heaters are are mounted on large flange like pieces of steel and bolted into a very heavy steel piece of metal equipment. There are more than one heater circuit per flange. All the flanges and heater connections are enclosed in a sheet metal cover. The OCP and contactors are in a separate enclosure connected with ten 8ft lengths of flexible metal conduit. The question is, does the code require me to:

a. run a seperate 10AWG copper EGC in each of the conduit?
b. run a single 10AWG copper EGC in one of the 10 conduits?
c. run a single 10AWG copper EGC by itself in its own conduit?
 
(a) is the default. (b) is a possible option if the FMC is non-ferrous (e.g. aluminum) and the requirements of 300.3(B)(3) are complied with.

Cheers, Wayne
 
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I'm looking at 250.142 (2)
"By connecting to an equipment grounding conductor of the wire type that is contained within the same raceway, contained within the same cable, or otherwise run with the circuit conductors"

I assume that because exceptions 1 and 2 which give two instances when the EGC can be run separately from the circuit conductors, the "or otherwise run with the circuit conductors" is more about cable tray, wireway, etc..
 
LPS said:
Let's say I have a large piece of industrial equipment with ten 50A 480V three phase heating circuits. The heaters are are mounted on large flange like pieces of steel and bolted into a very heavy steel piece of metal equipment. There are more than one heater circuit per flange. All the flanges and heater connections are enclosed in a sheet metal cover. The OCP and contactors are in a separate enclosure connected with ten 8ft lengths of flexible metal conduit. The question is, does the code require me to:

a. run a seperate 10AWG copper EGC in each of the conduit?
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If the conduit qualifies as an EGC no separate wire is needed at all.

LPS said:
b. run a single 10AWG copper EGC in one of the 10 conduits?
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If the conduit does not qualify as an EGC you need a wire type EGC in each conduit.

LPS said:
c. run a single 10AWG copper EGC by itself in its own conduit?
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If the conduit qualifies as an EGC this is allowed but serves no real purpose. If the conduit does not qualify as an EGC, you cannot use this means as your sole EGC. Each conduit having power circuits must either be an EGC itself or have a wire style EGC inside of it.
 
petersonra said:
If the conduit qualifies as an EGC no separate wire is needed at all.


If the conduit does not qualify as an EGC you need a wire type EGC in each conduit.


If the conduit qualifies as an EGC this is allowed but serves no real purpose. If the conduit does not qualify as an EGC, you cannot use this means as your sole EGC. Each conduit having power circuits must either be an EGC itself or have a wire style EGC inside of it.
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Per 250.118 FMC as an EGC is limited to 20A circuits, 6ft max, and 1-1/4" max, among other things. So it definitely doesn't qualify. When asked, it's hard to explain to someone why we have to have 10 EGCs... I suppose this is an unusual application. Thanks for your reply.
 
LPS said:
I'm looking at 250.142 (2)
"By connecting to an equipment grounding conductor of the wire type that is contained within the same raceway, contained within the same cable, or otherwise run with the circuit conductors"
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I believe you mean 2020 NEC 250.134(2).

For the non-ferrous case 300.3(B)(3), I believe if you route the FMC runs together, that would count as "otherwise run with the circuit conductors". I'm assuming from "All the flanges and heater connections are enclosed in a sheet metal cover" that the 10 runs all terminate in the same compartment, i.e. if derating weren't an issue, you could have run one large piece of FMC instead of 10 pieces of FMC. If you have multiple compartments at the equipment end, you could argue that you would need one EGC per compartment even in the non-ferrous case.

Cheers, Wayne
 
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LPS said:
Per 250.118 FMC as an EGC is limited to 20A circuits, 6ft max, and 1-1/4" max, among other things. So it definitely doesn't qualify. When asked, it's hard to explain to someone why we have to have 10 EGCs... I suppose this is an unusual application. Thanks for your reply.
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Given how cheap #10 green wire is I can't imagine why it is even being brought up.
 
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wwhitney said:
I believe you mean 2020 NEC 250.134(2).

For the non-ferrous case 300.3(B)(3), I believe if you route the FMC runs together, that would count as "otherwise run with the circuit conductors". I'm assuming from "All the flanges and heater connections are enclosed in a sheet metal cover" that the 10 runs all terminate in the same compartment, i.e. if derating weren't an issue, you could have run one large piece of FMC instead of 10 pieces of FMC. If you have multiple compartments at the equipment end, you could argue that you would need one EGC per compartment even in the non-ferrous case.

Cheers, Wayne
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D'OH! I don't know why I typed 240.134... lol
They are run together, and yes, derating is an issue. I think the issue is that this thing is one giant hunk of steel, so the idea of running multiple EGCs from the control panel a short distance to the machine doesn't really make a whole lot of sense to non-electrical types. I've been asked to look into the issue, so I'm trying to come up with a reasonable answer, hopefully something better than "sometimes the NEC makes us do things that really can't be explained". lol
 
infinity said:
If this is one piece of equipment the NEC may not even apply.
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Yeah, that's always bugged me. I have a copy of 508A, but not NFPA 79. I'm not even sure if this falls within the scope of NFPA 79 because the examples they give in the first couple of pages I was able to view seems to be more for things like...
• CNC Machines: These are classic examples as they require operator interaction for setup, loading, and frequent maintenance.
• Packaging Lines: These typically involve conveyors, wrapping machines, and multiple control elements.
• Injection Molding Machines: Similar to CNC machines, these involve significant electrical and mechanical components and are used in a process environment.

I need to get my hands on a copy of NFPA 79, but I hate to plunk down the money only to find it doesn't really address my concerns.
 
Ok. My 2017 Handbook has commentary for 250.134 that reads:

"The EGC run in the same raceway or cable as the circuit conductor(s) allows the magnetic field developed by the circuit conductor and the EGC to cancel, reducing their impedance.
Magnetic flux strength is inversely proportional to the square of the distance between the two conductors. By placing the EGC away from the conductor delivering the fault current, the magnetic flux cancellation decreases. This increase in impedance of the fault path delays operation of the protective device contrary to the performance requirements specified in 250.4(A)(5) and (B)(4) for ground-fault-current path."

Although I don't know how much of an increase in impedance we would have in such a short run, this is good explanation of why running the ECG inside the conduit is important.
 
LPS said:
Although I don't know how much of an increase in impedance we would have in such a short run, this is good explanation of why running the ECG inside the conduit is important.
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The increase is quite a bit bigger if there's a piece of steel between the two conductors, which is why 300.3(B) only requires an EGC in the same conduit for ferrous conduits.

Cheers, Wayne
 
LPS said:
I need to get my hands on a copy of NFPA 79, but I hate to plunk down the money only to find it doesn't really address my concerns.
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If you make a free account at nfpa.org, which requires providing contact info and might get you on a physical mailing list from them, you can get free online access to (all? most of?) the standards including NFPA 79. The interface is a bit clunky, which I expect is intentional, but adequate if you just need to check it occasionally.

Cheers, Wayne
 
wwhitney said:
The increase is quite a bit bigger if there's a piece of steel between the two conductors, which is why 300.3(B) only requires an EGC in the same conduit for ferrous conduits.

Cheers, Wayne
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Aha! I get it now. 300.3(B) !! You've only mentioned this like three or four times.... I get it now. Thanks for your patience.
 
wwhitney said:
If you make a free account at nfpa.org, which requires providing contact info and might get you on a physical mailing list from them, you can get free online access to (all? most of?) the standards including NFPA 79. The interface is a bit clunky, which I expect is intentional, but adequate if you just need to check it occasionally.

Cheers, Wayne
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Yes, I went back and noticed I already had created a link to the free access version a while back. Chapter 8 of NFPA 79 is only one page... It's clunky, but it works.. Thanks
 
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