Theory behind pulling a ground wire with every circuit in one conduit

[Eddy Current]

The word "ground" has no meaning when discussing the rules of the NEC. Are we talking about the grounded conductor or are we talking about the Equipment Grounding Conductor?

EGC.

 

[hurk27]

If conduit is installed in a code compliant installation then adding additional EGCs are a waste of money and are not doing anything to increase the safety of an installation, improperly installed raceways are the biggest reason for this requirement.

There are also many myths that have propagated over the years that also have added to the reason for the extra GEC requirements, like the one that is said that the EGC in a buried conduit will eliminate corrosion which is totally false, because this EGC in the event of a fault will see very little of the fault current, or any current that might be on the conduit if there is a problem with stray current on the system grounding because of voltage drop on the service neutral, electrically isolating the conduit from the grounding is the only thing that would work, but I don't think it would be code compliant, for this last reason I do not like running any metallic conduits in Earth as PVC will last much longer in this case.

I hear of what if set screws don't get tighten, well if your the boss then do your job, get after the installers if they are not tightening the screws.

Corrosion is another reason I hear all the time and can be a good one, and I agree underground installations it is not a bad idea to run an GEC, but for above ground where EMT is installed on masonry, concrete or block walls it is important to always leave a space between the wall and conduit, 300.6(D) even requires this for indoor wet locations as dust or dirt can collect in this space and keep moisture against the conduit and cause it to corrode, seal any air flow that can occur in a conduit that runs from an inside point to an outside box, I even do this for all my outside lights and receptacles because it stops moisture from condensing in the box's and conduit.

As for the requiring of an EGC for each circuit in the OP, I have no idea why someone would require this unless they want isolated EGCs for these circuits, as the NEC only requires one EGC sized for the largest circuit in the conduit if an EGC is required such as when using PVC conduit, if these are run for isolation grounding then they need to be run all the way back to the point of the main bonding jumper at the service disconnect or they would not be considered a IG.

My view on IG's are a band-aid to stop other problems that wouldn't exist on a code compliant install, and running extra EGC's also fall into this category as they serve no purpose for added safety if the conduit is installed in a code compliant method, and corrosion was addressed above what is required by the NEC as like where I work we have allot of corrosive areas and we address it by using a conduit that will hold up, some places we use Rob Roy that also has PVC coating both inside and out , or stainless steel.

Running all these extra EGC's can cause not only the extra expense of the extra copper, but also cause the use of larger conduits because of fill limits and or the requirement of extra runs of conduits that can make the price of a job go through the roof if it is properly bid, if these requirements were not put in the bidding requirement I will be sending RFI's and change orders to cover them or they will be getting some other company to do their work as I won't be doing it for free, I have had requirements like this stuck into the job specs after the bid, and they will try to tell me I should have known as it is the normal way to wire, I just tell them not by my book, as I bid by what the NEC requires unless it was in the bidding specs it is an up charge.

 

[mivey]

I know a good conduit makes a better return path but I have seen to many connection failures. I might allow a conduit ground on rigid or even EMT for very specific cases or controlled environments (even those are not so "controlled" over time). Otherwise an EGC inside the conduit will be specified. Just the way it is.

P.S.: I would not specify one per circuit in the conduit as I think that is over-kill.

 

[hurk27]

130208-2345 EST

A likely reason, and it might be good if the EGC was insulated, is:

Consider an EGC that is the same material of wire and the same diameter as the Hot wire. At the end of the run short Hot to EGC. The resulting voltage at the shorted point relative to the EGC bus at the main panel is about 1/2 of the Hot voltage.

If you have only a single EGC, then some of that 1/2 voltage appears at other points along the EGC.

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This does not make any sense?

Any conduit that is enclosing the circuit conductors would almost always have a lower impedance then the size of the circuit conductors that would be allowed in the conduit, larger circuit conductor larger conduit in most cases.

A fault to the conduit would in most cases result in a voltage drop in the faulted conductor that would be much higher then the voltage drop across the conduit run.

If your description was a problem then we would have a problem with any NM feeds as it would only have one EGC, and remember once you get above a 30 amp circuit the EGC is smaller then the circuit conductors, but the available fault current in a bolted fault will still be high enough to open the protection device before any damage is likely, if not you have a severe voltage drop problem that needs to be address.

 

[jumper]

The word "ground" has no meaning when discussing the rules of the NEC. Are we talking about the grounded conductor or are we talking about the Equipment Grounding Conductor?

Agreed. The word "ground" also gets used for the GEC also.

 

[jumper]

In secondary circuits, a ground wire is a common term for the EGC. I doubt it would be confused with the grounded conductor except among those that wouldn't normally be allowed to post here anyway. YMMV.

Yes, but I see the word "ground" often used for GEC also and sometimes it is hard to tell what somebody is asking.

For example, not an untypical post/question:

I am installing a 400A service with two 200A panels. One panel will feed a 100A sub panel. What size ground do I need?

 

[mivey]

Agreed. The word "ground" also gets used for the GEC also.

Really? You think there is some chance the OP or the ones making the industrial standard or someone here is confusing a circuit's "ground wire" with the "grounded conductor"? Come on now.

Yes, but I see the word "ground" often used for GEC also and sometimes it is hard to tell what somebody is asking.

For example, not an untypical post/question:

I am installing a 400A service with two 200A panels. One panel will feed a 100A sub panel. What size ground do I need?

Well a GEC would not not get pulled in alongside each circuit so could hardly be confused with the "ground wire" being discussed by the OP could it?

 

[jumper]

Really? You think there is some chance the OP or the ones making the industrial standard or someone here is confusing a circuit's "ground wire" with the "grounded conductor"? Come on now.

Well a GEC would not not get pulled in alongside each circuit so could hardly be confused with the "ground wire" being discussed by the OP could it?

Mivey, I was not referencing the OP. I was merely making a comment that the use of the term "ground" is often used for both a EGC and a GEC.

Like in my fictional example:

I am installing a 400A service with two 200A panels. One panel will feed a 100A sub panel. What size ground do I need?

What "ground" would this person be referring to? This was just to point this out, not to disagree with you.

 

[mivey]

I was merely making a comment that the use of the term "ground" is often used for both a EGC and a GEC.

Like in my fictional example:

What "ground" would this person be referring to?

OK. Got it. Surrounding context sure helps to clarify the use of the term and without supporting info our loose use of the term "ground" does leave one having to guess.

 

[gar]

130210-0852 EST

hurk:

There was very little information in the original post. The general question of the post was what theory exists for the requirement. There are many different assumptions that can be made. In trying to provide an answer to the question that might have some technical reason, other than redundancy, I made assumptions and some were not specified.

In my description of what happens when there is a short from hot to the EGC I made the assumption that there was only the single EGC wire that was part of the EGC path. Quite typical of hundreds of machines in one plant in which I had equipment. These machines were being moved often, and were not hard piped. A flexible cable was dropped to the machine from an overhead 440 bus. The only EGC to the machine was from the EGC in the cable.

If the EGC is smaller or has higher resistance than the Hot wire, then the fault voltage at the shorting point is even greater than my example.

There is no electro-mechanical circuit breaker fast enough to prevent destruction of a small semiconductor device in the example I described. Probably can not even protect a large semiconductor. That is why there are ultra-fast fuses.

Reasonable protection of an RS232 port can be provided by a clamping transient limiter across the 232 input and fed by a 100 ohm 1/4 W resistor. A 15 V Transorb could be the clamping device. A Transorb is essentially a bidirectional Zener diode with enough thermal mass that when combined with a suitable current limiter will not have its maximum junction temperature exceeded.. The resistor serves as a fuse, it explodes when 120 V is applied. Also can use a low current pico fuse.


petersonra:

RS232 is not dead, and there are a very large number of machines in the field using RS232 every day. Every HAAS CNC made has had two RS232 ports. Probably more than 100,000 HAAS machines have been built. One port is for local purposes such as control of an accessory. The other port is for program and data transfer over a few feet to hundreds of feet.

With RS422 or 485 you can probably work to 4000 ft at 115.2 kbaud, and longer at a lower baud rate. Wired Ethernet or USB can not do this without amplifiers and/or repeaters.

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[Ponchik]

I doubt this since some of higher ups are actually on the board that wrote the NEC code book.

If they are part of the CMP then they should know that only one EGC is required. I would still question them. Maybe we can all learn as to why "one EGC per circuit"

 

[kwired]

Ok i think im seeing why they might want this now but in a commercial building inside the plant why would they need this?

I was also thinking about tray cable that is used through out the plant and it does not have a ground per circuit, if it is say something like 12-3 tray cable there is only one ground in the cable.


Im not sure when the plant started making a ground per circuit required but it might have started when an employee was killed about 10 years ago from a fan casing becoming energized.

Maybe they should have determined why the fan casing became energized. Running a separate EGC with every circuit even though they are in same raceway may not have helped out with that incident at all, assuming code was met otherwise. Next they will want bonding jumpers for bonding jumpers to assure that bonding jumpers are effective.

 

[mivey]

Maybe they should have determined why the fan casing became energized. Running a separate EGC with every circuit even though they are in same raceway may not have helped out with that incident at all, assuming code was met otherwise. Next they will want bonding jumpers for bonding jumpers to assure that bonding jumpers are effective.

Hydraulic fans would do it.

 

[kwired]

250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes.

Where circuit conductors are spliced within a box, or terminated on equipment within or supported by a box, any equipment grounding conductor(s) associated with those circuit conductors shall be connected within the box or to the box with devices suitable for the use in accordance with 250.148(A)through (E).

Exception: The equipment grounding conductor permitted in 250.146(D) shall not be required to be connected to the other equipment grounding conductors or to the box.

Exception covers the isolated ground installations, otherwise if you ran multiple EGC's in a raceway and they all pass through a metallic receptacle box, by this code section they must all be tied together as well as to the box if it is a metallic box. This effectively makes them about as useful as one conductor, and is questionable if you could call it non compliant paralleling of conductors unless they are 1/0 or larger, I would need to look into that some more as it may not apply to EGC's.

 

[Eddy Current]

Maybe they should have determined why the fan casing became energized. Running a separate EGC with every circuit even though they are in same raceway may not have helped out with that incident at all, assuming code was met otherwise. Next they will want bonding jumpers for bonding jumpers to assure that bonding jumpers are effective.

I believe it was a ground issue, back to my tray cable wire comment that i was wondering about maybe that's why out in the industrial part of the plant everything is required to have a bonding jumper to the conduit.

 

[renosteinke]

I would double-check the exact wording of their specification.

I've seen that done at my current job site, but that was the result of a 'weak' contractor with unqualified help having trouble understanding instructions.