Understanding that mysterious GEC. Purpose and construction strategy.

[inetdog]

What does "choke" mean?

An inductor is commonly called a choke. Comes from the early days of electricity and radio. When put in series with a wire in a circuit it chokes off the high frequency current or just supplies a known inductance for other circuit purposes.

An isolated run of wire, without the return current wire nearby, will have a calculable inductance. This will vary with the size and length of the wire.
If you curve the wire into one or more loops the inductance increases.
If you wind the wire around an iron (or magnetic steel alloy) core, the inductance goes up a whole lot.

Now for the tricky part. If you run a piece of wire through a ferrous metal conduit, that is for practical purposes the same as winding a partial turn of wire through an iron core. That means that at the range of frequencies present in a lightning even (including a near strike), the presence of the raceway will greatly increase the impedance of the GEC.

To avoid this, we let the high frequency currents flow in the conduit itself (via the bonding jumpers at both ends), so the magnetic field is outside the "core" and does cause a large inductance in the length of conduit.

[carultch]

I still have the feeling you are not clear on the differences between GEC and EGC.

I'm trying, but it is tricky.

It doesn't help that they are anagrams of one another.

A GEC is a single conductor that connects to the ground electrode system at any point. It is a Single Conductor, and as such you cannot CHOKE IT. So if you run it in a ferrous metal, it has to be bonded at each end to make the raceway a part of the conductor. Otherwise it can be ran in plastic or aluminum raceway, or no raceway at all providing it is protected from damage.

What does "choke" mean?

Does it need a dedicated raceway, if it will be in one that is plastic?

Does it need a dedicated raceway/routing path, if it will be in one that is ferrous metal?

Can it be routed in the same raceway as phases ABC/Neutral/EGC, if the raceway is plastic?

Can it be routed in the same raceway phases ABC/Neutral/EGC, if the raceway is metal, and I correctly bond both sides of the raceway to the GEC with bonding bushings? Above and beyond the ordinary conduit grounding requirements.

I'd treat non-ferrous aluminum conduit by the same standards as ferrous conduit, for this purpose. Using metal conduit that isn't steel is very rare in my scope of work.

An EGC is always ran with its associated phase conductors.

Got it! I always put in an EGC.

For 200A and less (local), I'd combine with the GEC. Normally my GEC is sized as "#6...done". And that is what 100A to 200A feeders need for the EGC.

I know NEC 690.47, especially 690.47(D) has caused a fire storm in cycle 2014. It will be repelled. Unless you are using 2014 cycle ignore it. If you are using 2014 cycle conform to get inspected, then correct after inspection. Here are two videos from Mike Holt. They are are long and very specific.

Hahaha! Put in the superfluous electrode just to make a picky and ignorant inspector leave you alone, and then rip it out to make the system safe.

I've seen that video, and what I gather from it is this:
1. bond anything and everything that you want to bond, above ground. Any metal that doesn't intentionally carry current, including non-metals that are conductive. More BONDING is always better. When in doubt, add more bonding.
2. bond everything below ground together.
3. make exclusively one connection between that which is above ground, and that which is below ground.
4. bond the neutral and ground at exclusively one point, and close to the same point as that which is above ground is bonded to that which is below.

One thing I'm not understanding, is what to do about the GEC when the inverters aren't immediately adjacent to the service equipment and premises grounding electrode. Maybe they are on a different building. Maybe they are out in the middle of a field, not even part of a building (but still connected to one electrically). Maybe they are on the roof, on a building that is 200 ft tall. The GEC is going to contain excessive length, and it is going to contain bends. Both of these hinder its performance substantially, and there's nothing anyone can do to compensate for it.

Another thing I do not get, as part of #3 and #4, is that obviously we don't do this at exclusively one point on the entire national electrical distribution system. It is usually a straight forward case of doing it at one point per "service". And this is easy when there is only one service disconnect, one service transformer, one service meter, and one building, on that service. However, it is not so easy if one "service" contains multiple, of any of the above. or if multiple services are at a single building. What is the correct definition of where we should do our system grounding and our driven ground?

Fill in the blanks:
1. We should connect our EGC system to our GE via a GEC at exclusively one point PER ___________.
2. We should connect our EGC system to our neutral at exclusively one point PER ___________.

And before the word "service" is the answer, that word doesn't mean anything to the electrons, or anything in physical reality. Therefore, what piece of equipment defines where the grounding of the neutral, and grounding the EGC system to the earth should take place?

[Sunking]

A long time ago, I stumbled on a post of yours that said "you can't use trays in a residential application"

Not entirely accurate interpretation. You can run cable in trays if it is TC rated (Tray Cable) Remember when I mentioned closely couple cables in raceways? That is where the EGC is ran with phase conductors. TC cable like NM NM-B cable for 240/120 will have the phase conductors and EGC all in a single sheathed cable which keeps them closely magnetically coupled eliminating choke effect on the EGC. TC insulation is tougher and more durable than say NM or NM-B.

[Sunking]

Obviously I don't want to construct more raceways than necessary, therefore if I do properly bond both sides, then can I run it with the rest of the wires?

I still have the feeling you are not clear on the differences between GEC and EGC.

A GEC is a single conductor that connects to the ground electrode system at any point. It is a Single Conductor, and as such you cannot CHOKE IT. So if you run it in a ferrous metal, it has to be bonded at each end to make the raceway a part of the conductor. Otherwise it can be ran in plastic or aluminum raceway, or no raceway at all providing it is protected from damage.

An EGC is always ran with its associated phase conductors.

I know NEC 690.47, especially 690.47(D) has caused a fire storm in cycle 2014. It will be repelled. Unless you are using 2014 cycle ignore it. If you are using 2014 cycle conform to get inspected, then correct after inspection. Here are two videos from Mike Holt. They are are long and very specific.

690.47 (D)
690.47 (D)

The 690.47 (D) video Mike has done something he has never done. He point blank comes out and says it is Deadly and the dumbest thing ever to come out of the NEC. John Wiley is taking a lot of heat and lost a lot of respect. If you only watch one of the videos, watch the first one 690.47 (D) It will open your eyes.

[bcroe]

The NEC makes a distinction between residential uses where the wiring may stay unchanged and uninspected for many years and commercial/industrial applications where there is an expectation of higher level of surveillance and maintenance.
Use of cable tray is most suitable to situations where the wiring will be altered/added to/changed on a relatively frequent basis. To use that in a residential environment would expose wiring to tampering of damage by other than an electrician.

PS: AFAIK you can use trays in a residence for limited power wiring and communication wiring, you just cannot use it in residential in a situation where Chapter 3 wiring methods are required, as for power wiring.

I found some plastic rack with snap on cover, was a good way to organize some 20 cables
under my solar panels. Hundreds of feet from any building. Before they were just flapping
in the breeze, waiting for the deer to start chewing on them. Bruce Roe

[inetdog]

Sunking, on an unrelated note:

A long time ago, I stumbled on a post of yours that said "you can't use trays in a residential application", even thought the guy was asking about something that was for a school.

Any idea what you meant by that? Code reference perhaps?

I don't see how trays would work any differently, just because they are in a house.

The NEC makes a distinction between residential uses where the wiring may stay unchanged and uninspected for many years and commercial/industrial applications where there is an expectation of higher level of surveillance and maintenance.
Use of cable tray is most suitable to situations where the wiring will be altered/added to/changed on a relatively frequent basis. To use that in a residential environment would expose wiring to tampering of damage by other than an electrician.

PS: AFAIK you can use trays in a residence for limited power wiring and communication wiring, you just cannot use it in residential in a situation where Chapter 3 wiring methods are required, as for power wiring.

[carultch]

Sunking, on an unrelated note:

A long time ago, I stumbled on a post of yours that said "you can't use trays in a residential application", even thought the guy was asking about something that was for a school.

Any idea what you meant by that? Code reference perhaps?

I don't see how trays would work any differently, just because they are in a house.

[carultch]

In the 2014 NEC you are specifically required (with limited exceptions) to install a separate DC grounding electrode and run a separate DC GEC up to the frame and racking of the panels, whether you have a grounded or an ungrounded system. This is called an auxiliary (short for useless) electrode and is not required to be interconnected to the rest of your ground electrode system (GES).
Many people argue that this is worse than useless and is actually a specific hazard in the event of a nearby lightning strike.

Can you say...690.47(D)anger?

[carultch]

GEC and EGC are two completely different animals and different purposes.

[...]

Here is what it boils down to the EGC conductors are ran with their associated phase conductor, thus magnetically and closely coupled. When ran inside metallic raceways this magnetic coupling cancels out CHOKING effect. GEC are not ran with any phase conductos, and thus any fault current are easily choke dout preventing them from carrying fault current effectively. GEC takes care of crap outside, and EGC takes care of crap inside.

Sunking! I'm glad you found my question. You seem to have a good understanding of the mysterious GEC, better than I do, so maybe you can clear up a few things for me.

I like your summary of "GEC's take care of the crap outside, EGC's take care of the crap inside".

You say that if I run it in any metal raceway with the rest of the metal circuit, that I have to bond it to both ends. I'd imagine that this implies bonding bushings, even for those situations that are <250V and don't use ring KOs on the boxes. I never even thought about that before.

Obviously I don't want to construct more raceways than necessary, therefore if I do properly bond both sides, then can I run it with the rest of the wires?

What if I use a plastic raceway? Can I route it with the rest of the circuit in that case?

Likely, if I use plastic conduit, it's outside underground anyway. In the case where the array and inverters could be several hundred feet away from the building where I interconnect, does this mean that the GEC should NOT go back with the interconnect wiring to the premises wiring electrode? But rather to a dedicated ground rod nearby the inverters/array?

[sensij]

There is only one conductor allowed to be called GEC, the one that runs form the AC service entrance equipment to the GES ground electrode system. Having said that you can attach as many Bonding Conductors to the GES or GEC as you need or want like those for Lightning Protection Systems or a separate service like a Solar system. But they all have to use a common GES.

FWIW my cut and paste was from 2011 cycle. You need to go to Mike Holt Forum for code references rather than a Trade Magazine. Mike has a lot of instructional material and videos covering this very topic. I use to teach some of the classes and a moderator there. Mike's forum is where many of the code writers hang out like John Wiles who wrote 690. You have to be in the industry to join and it sounds like you qualify. There is a Forum for solar there.

Perhaps a mistake in Dave's post was in calling the conductor between the array and the auxilliary electrode a DC GEC. I think, however, his point regarding the requirement of the auxilliary electrode is correct, as is the optionality in connecting it to the GES. Which is, I think we all agree, kind of dumb.

Yes, I use a lot of sources to try to get my interpretations correct, with the Mike Holt forums being at the top of the list. Sometimes trade magazines are easier to link for a single explanation, and I try to be choosy about the quality of those links. Those forums, like these, sometimes drift a bit throughout the threads.

[Sunking]

What you are saying was true for the 2008 version of code, but not 2014. 690.47(D) calls the required electrode an auxillary grounding electrode in 2014, and because of that designation it follows 250.54. 250.54 creates an exception to 250.50, which would have required the electrodes be bonded together into a single GES. It is discussed extensively here. I think Dave's interpretation is the consensus at this time, and I hope that CA chooses not to keep this language when they roll 2014 NEC into the next CEC cycle.

In the post previous to that, I appreciate your explanation of the difference between EGC and GEC. That is the clearest I have seen it described.

There is only one conductor allowed to be called GEC, the one that runs form the AC service entrance equipment to the GES ground electrode system. Having said that you can attach as many Bonding Conductors to the GES or GEC as you need or want like those for Lightning Protection Systems or a separate service like a Solar system. But they all have to use a common GES.

FWIW my cut and paste was from 2011 cycle. You need to go to Mike Holt Forum for code references rather than a Trade Magazine. Mike has a lot of instructional material and videos covering this very topic. I use to teach some of the classes and a moderator there. Mike's forum is where many of the code writers hang out like John Wiles who wrote 690. You have to be in the industry to join and it sounds like you qualify. There is a Forum for solar there.

[sensij]

What you are saying was true for the 2008 version of code, but not 2014. 690.47(D) calls the required electrode an auxillary grounding electrode in 2014, and because of that designation it follows 250.54. 250.54 creates an exception to 250.50, which would have required the electrodes be bonded together into a single GES. It is discussed extensively here. I think Dave's interpretation is the consensus at this time, and I hope that CA chooses not to keep this language when they roll 2014 NEC into the next CEC cycle.

In the post previous to that, I appreciate your explanation of the difference between EGC and GEC. That is the clearest I have seen it described.

[Sunking]

In the 2014 NEC you are specifically required (with limited exceptions) to install a separate DC grounding electrode and run a separate DC GEC up to the frame and racking of the panels, whether you have a grounded or an ungrounded system. This is called an auxiliary (short for useless) electrode and is not required to be interconnected to the rest of your ground electrode system (GES).
Many people argue that this is worse than useless and is actually a specific hazard in the event of a nearby lightning strike.

Sorry Dave that is not correct and forbidden. 250.58 forbids that and for good reason as you eluded to. Many telephone, CATV, SATV, Electricians, and Sola rInstallers have been sued to hell and back over this issue from damages incurred to life and property.

1. NEC Article 250.58 instructs us to use "the same electrode for grounding conductor enclosures and equipment in or on that same building." The concept of "separate ground" is nonsense. Two good sources for more information on this are Soares Book on Grounding and IEEE-142.

250.58 Common Grounding Electrode
Where an ac system is connected to a grounding electrode in
or at a building or structure, the same electrode shall be used
to ground conductor enclosures and equipment in or on that
building or structure. Where separate services, feeders, or
branch circuits supply a building and are required to be connected
to a grounding electrode(s), the same grounding
electrode(s) shall be used.
Two or more grounding electrodes that are bonded together
shall be considered as a single grounding electrode
system in this sense.

[Sunking]

1. What purpose does the GEC serve for a grid-tied system, that the EGC does not do?
They both are ultimately connected to the same point, and would each carry their share of unintentional current when it flows.
Could I interpret the GEC as a "backup ground", so that the DC side gets bonded to the Earth independently of the AC side?

GEC and EGC are two completely different animals and different purposes.

GEC or Ground Electrode conductor has a few different functions:

• To Establish a Zero potential difference between earth and the electrical equipment so to stabilize electrical voltages and minimize stress on cable insulations formed by the capacitance of the electrical distribution. It shorts out all cable capacitance to earth. Otherwise system voltage could go extremely high and if you get between the system and earth you get fried.
• But here is the biggie. It is used to limit voltage potential during line fault outside your home like lighting, line surges, primary to secondary contact from storms or transformer faults, and a planned path to discharge static electricity.

Here is the jest of a GEC it cannot be ran with any other conductors like in a ferromagnetic race way unless the GEC is bonded to both ends to cancel out choking effect. High intensity surges would be choked out when it arrives at a ferromagnetic race way greatly increasing the impedance thus effecting the ability of the GEC to dissipate the energy to earth as quickly as possible. The whole purpose of the and provide a reference point. GEC is to keep crap from entering the facility.

EGC or equipment grounding conductor now called EBC equipment bonding conductor only has two functions.

• Provide a planned fault path of sufficient capacity to operate an OCPD over current protection devices. There to blow a fuse or breaker.
• Minimize touch potential during normal operation and under fault conditions to safe acceptable levels.

The EGC has no other purpose and in fact is not needed under normal conditions.

Here is what it boils down to the EGC conductors are ran with their associated phase conductor, thus magnetically and closely coupled. When ran inside metallic raceways this magnetic coupling cancels out CHOKING effect. GEC are not ran with any phase conductos, and thus any fault current are easily choke dout preventing them from carrying fault current effectively. GEC takes care of crap outside, and EGC takes care of crap inside.

[inetdog]

If 2014 is your code, I would try making the case for no GEC for an ungrounded inverter with 690.35, 690.41(1), and 690.47(B), which says that the AC equipment ground can be used as the GFDI reference in the ungrounded inverter.

If you sink supplemental electrodes, my understanding is that they would need to be bonded to the primary electrode anyway, so it doesn't really buy you anything except a lower impedance ground, perhaps helpful for lightning.

In the 2014 NEC you are specifically required (with limited exceptions) to install a separate DC grounding electrode and run a separate DC GEC up to the frame and racking of the panels, whether you have a grounded or an ungrounded system. This is called an auxiliary (short for useless) electrode and is not required to be interconnected to the rest of your ground electrode system (GES).
Many people argue that this is worse than useless and is actually a specific hazard in the event of a nearby lightning strike.