Understanding that mysterious GEC. Purpose and construction strategy.

[carultch]

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?


2. Where should the GEC connect to the GE?

If everything is on one building, I'd find the premises wiring electrode and run my irreversible wire back there. Likely, my inverters are already the the immediate viscinity to that electrode.

What if my array/inverters are on a separate building?
What if my array/inverters are in a distant ground-mount field, and interconnected at the building?
What if the inverters are scattered throughout an array field?

I understand that minimizing the number of electrodes is desirable, to avoid the consequence of ground potential rises.
I also understand that the GEC should avoid distance and bends as much as practical, due to the nature of high frequency currents.
Obviously, it is hard to meet these goals on a project of a scattered layout.

[sensij]

I think you have the general idea, and the specific answers to your questions are beyond my knowledge of code. Fortunately, inverters are moving full speed to transformerless / non-isolated designs, which leave the array ungrounded and eliminate the need for a GEC. In the scattered layout that you suggest, I would use inverters of that type instead of worrying about how many electrodes would be required, and how to bond them together.

[carultch]

I think you have the general idea, and the specific answers to your questions are beyond my knowledge of code. Fortunately, inverters are moving full speed to transformerless / non-isolated designs, which leave the array ungrounded and eliminate the need for a GEC. In the scattered layout that you suggest, I would use inverters of that type instead of worrying about how many electrodes would be required, and how to bond them together.

I'm aware of that. Sounds like a good strategy.

Do away with the whole damn thing, and use the EGC alone, whose function and design requirements make a lot more sense.
I haven't found anything in the NEC that specifically allows us to omit the GEC for TL ungrounded type inverters.
I was challenged on one particular project to add it back in, and I couldn't find anything in the NEC to cite to show that it wasn't needed. Hopefully NEC2017 will clarify this issue. I'll submit a proposal.


Other times, I already got an inverter selected from initial design work (that's hard to change), and now it is time to come up with means and methods.
Do I pull 500 ft of irreversible #6 in the pipe with the main wiring to get from the field to the building's rod?
Or do I just drive my own rod nearby the inverters?

[sensij]

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.

[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.

[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.

[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.

[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]

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]

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.

[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?

[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]

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.

[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.

[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