Irreversible Connection of Photovoltaic EGC to Service Grounding Electrode Conductor

Status
Not open for further replies.

Militantchicken

New member
Location
California
I have a question regarding a problem I have run into in a perticular jurisdiction my company installs Photovoltaic solar systems in. I have a Building and Safety Inspector that is requiring us to put an irreversible crimp on the EGC for the photovoltaic system and the Grouding electrode for the residential Service (GEC to ground rod for the main electrical panel).

Could anyone point in the right direction to the code that references this because I cannot find it any where?

His logic, "IF" some one were to disconnect the EGC for the photovoltaic system from the ground bar connection in the Main electrical panel, the Photovoltaic system would not be grounded anymore. I can spout "what if's" all day doesnt mean it is actually required by code.

I understand that the EGC for the system can have a common ground point for both ac and dc systems which is in the inverter, this is not what I am talking about, I am talking about the EGC from inverter to the common ground bus inside the house main electrical panel.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I have a question regarding a problem I have run into in a perticular jurisdiction my company installs Photovoltaic solar systems in. I have a Building and Safety Inspector that is requiring us to put an irreversible crimp on the EGC for the photovoltaic system and the Grouding electrode for the residential Service (GEC to ground rod for the main electrical panel).

Could anyone point in the right direction to the code that references this because I cannot find it any where?

His logic, "IF" some one were to disconnect the EGC for the photovoltaic system from the ground bar connection in the Main electrical panel, the Photovoltaic system would not be grounded anymore. I can spout "what if's" all day doesnt mean it is actually required by code.

I understand that the EGC for the system can have a common ground point for both ac and dc systems which is in the inverter, this is not what I am talking about, I am talking about the EGC from inverter to the common ground bus inside the house main electrical panel.

Depends on what exactly he is referring to. If it is just an EGC (grounding the PV equipment by connecting it to the ground bar of a panel which in turn has an EGC running back to the main panel) it does not require irreversible splices. If it is a conductor which is bonding a separate Ground Electrode located at/near the PV system to the main Ground Electrode at the main electrical panel, then IMHO it would have to be continuous or irreversibly spliced.
There is no inherent difference in the demarcation between equipment and ground network just because there is PV involved, except to the extent that you are justified in treating it as a separately derived system. (not).
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Could anyone point in the right direction to the code that references this because I cannot find it any where?

To begin with, your inspector's request is far from unusual. Every single jurisdiction I've worked in requires the irreversible splice of the solar GEC to the premises GEC.

If the EGC from the inverter to the breaker panel is only an EGC then the requirement doesn't hold. However this is very unusual in my experience. Usually the grounding conductor is a combined EGC/GEC. (Sometimes it is a combined EGC/bonding jumper.) You don't mention a separate DC GEC or a bonding jumper.

The requirement, if there is one, comes from 250.64 (C)(1). Various parts of 690.47 have referred specifically to this section specifically or to 250.64 generally over the last few code cycles.

In the 2011 code, things were made a bit more ambiguous because 690.47(C)(3) states that the combined EGC/GEC can be "run...to the grounding busbar in the associated equipment." This seems to imply that it can just terminate there without any other splice. However 690.47(A) and (B) still refer generally to 250.64.
 

hurk27

Senior Member
First if this array is or could be considered a separate structure then it is only required to have its own grounding electrode system just like any outbuilding located remote from the main building, there is no requirement for the two grounding electrode systems to be bonded together, all that is required is that an EGC to be run between the two buildings, this is and has been a very big misconception, but the code clearly states "For each building served" see 250.50

In 690.47 (A) and (B) it is requiring a grounded electrode system, it does not say conductor, it refers to 250.64 to remind the installer that like at the main service the first GEC to the first grounding electrode is to remain without splice if not it has to be made with an irreversible splice, other grounding electrodes if available can be bonded between each electrode with a grounding electrode bonding jumper, and there is no requirement for a irreversible splice on these just like at a main service.

Now 690.43 require a EGC to be run with the PV circuit conductors that leave the area of the PV array like running back to the house, this conductor like any EGC lands in the main panel on the grounding or neutral bar like any EGC.

Think of it this way, if you have a non-attached garage that you fed from the main service panel then you would have to establish a grounding electrode system at the garage, and a EGC would be required to be run with the supply conductors back the main service, if you put a subpanel in an attached garage then you are not required to install another GES but you still have to run a EGC back to the main panel.

So if your array is a stand alone it requires a GES at the array and a EGC back to the main service run with the other circuit conductors, if your arrays are on the same building as the main service, now, then you only need an EGC back to the main panel of course if it was my house I would want a GEC to the GES of the house just to try to help in lowering the voltage traveling into the house but I don't see it as a requirement.

Unless I'm missing something that is the way I see it.

Of course you have to know when to pick your battles.

so if this inspector wan't it so no one could disconnect this conductor how do you make an irreversible splice at the array? there will always be some kind of lug connection at one end or both ends of this conductor, just like the main GEC at the main service?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
First if this array is or could be considered a separate structure then it is only required to have its own grounding electrode system just like any outbuilding located remote from the main building, there is no requirement for the two grounding electrode systems to be bonded together,...

Sorry but this is wrong. 690 requires separate AC and DC grounding electrode systems to be bonded together (even if 250 doesn't).

Now 690.43 require a EGC to be run with the PV circuit conductors that leave the area of the PV array like running back to the house, this conductor like any EGC lands in the main panel on the grounding or neutral bar like any EGC.

Sorry this is also wrong. An array EGC should be brought directly to the inverter (or GFDI device, if it is separate). Or at least it should be tied more directly to the DC GES, not the AC GES (even though they are bonded together).
 

c_picard

Senior Member
Location
USA
SREC and Rebate programs

SREC and Rebate programs

To further confuse things, there are State incentive programs that have their own install requirements. Mass CEC guidlines require the DC GEC to be irreversibly spliced outside of the main panel, for example.
 

hurk27

Senior Member
Sorry but this is wrong. 690 requires separate AC and DC grounding electrode systems to be bonded together (even if 250 doesn't).

First lets separate the grounding requirements between Equipment grounding and Grounding electrodes, and AC and DC systems, While 690 leaves much to desire in its wording it still clearly refers to 250 in most of its instructions as to how to ground the equipment and or the structure.

First the requirements in 690 are separated in two parts 690.43 thru 690.46 are the requirements for equipment grounding (EGC's) and 690.47 thru 690.50 are for grounding electrode requirements (GEC or GES) with some requirements for Equipment bonding and EGC's also put in it.

690.43 Equipment Grounding. Exposed non?current carrying metal parts of module frames, equipment, and conductor enclosures shall be grounded in accordance with
250.134 or 250.136(A) regardless of voltage. An equipment grounding conductor between a PV array and other equipment shall be required in accordance with 250.110.
Devices listed and identified for grounding the metallic frames of PV modules shall be permitted to bond the exposed metallic frames of PV modules to grounded mounting
structures. Devices identified and listed for bonding the metallic frames of PV modules shall be permitted to bond the exposed metallic frames of PV modules to the metallic
frames of adjacent PV modules. Equipment grounding conductors for the PV array and structure (where installed) shall be contained within the
same raceway or cable, or otherwise run with the PV array circuit conductors when those circuit conductors leave the vicinity of the PV array.

The above in red is for EGC's and is not repeated for GEC's anywhere in the code, this is the same for separate structures in 250 as each building or structure served is required to have it own GES and there was never a requirement to run a GEC between separate structures and for good reason, doing so does not provide any additional protection from lightning or any other condition that the EGC would already provide as it is meant to only protect the structure it serves.

690.47(D) Additional Electrodes for Array Grounding.
Grounding electrodes shall be installed in accordance with
250.52 at the location of all ground- and pole-mounted
photovoltaic arrays and as close as practicable to the location
of roof-mounted photovoltaic arrays.
The electrodes
shall be connected directly to the array frame(s) or structure.
The dc grounding electrode conductor shall be sized
according to 250.166. Additional electrodes are not permitted
to be used as a substitute for equipment bonding or
equipment grounding conductor requirements.

The above in red further supports the requirement to have a grounding electrode system at the location of the array even when 250 kind of already states this for separate structures, the last statement of the electrodes not being allow to be used in lew of an EGC or bonding is the same as stated in 250 as the Earth can not be used for a fault clearing path as it is too high of resistance to do so.

Sorry this is also wrong. An array EGC should be brought directly to the inverter (or GFDI device, if it is separate). Or at least it should be tied more directly to the DC GES, not the AC GES (even though they are bonded together).

Since there are many methods of design 690.47 gives us many ways to apply the requirements in (1) thru (8) with (1) basically stating that if there is both an AC system and a DC system that the two shall be bonded together (this is a bonding conductor not a grounding electrode conductor, the grounding electrodes were taken care of back at the PV array) it requires the DC system to be bonded to the AC system (yes that is what 690.47(1) states) (2) of 690.47 tells us even to size it per the requirements of 690.45 which is for the EGC not a GEC (3) allows us to use a common conductor for both systems more then likely when the inverter is mounted on the array in which (6) seems to confirm this as it allows a common electrode system where the inverter is mounted out on the array and the output conductors are brought to the house will only require a EGC, (7) is only to remind us that GEC's are to be sized to 250.66 where you have a GES at the array or at the house where a GES is required or as in (8) where we can use the premises
grounding electrode system when utility-interactive inverters are used.

The parts that I had to think about is the requirement of additional grounding electrode systems when a roof top array is installed but then I remember the requirements of 800 for antennas where if the antenna will require over 20' of grounding conductor to reach the service electrodes it is required to install a separate grounding electrode then bond it back to the service electrodes.

The problem with understanding grounding and bonding requirements is we tend to cross the two and apply the wrong term to the wrong requirements, bonding is more part of equipment bonding as in EGC as in this case it even points to use the sizing for EGCs in the requirements.

The other point is to understand that lightning will not travel very far on most conductors sized per 250.66, it is a high frequency event and impedances of our round conductors will be very high which will limit the amount of current on the conductors if over a certain length, most of the NEC doesn't seem to follow this line of thought, except in article 800 on antenna requirements and in 690 where it requires that the GES to be as close as it can to the PV array, I'm very surprised that 690 also doesn't mention the requirement of bonding the two GES where a roof top PV array is used on a house with a GES at the service even when 250 will require it, this has to be done as if lightning were to strike the PV array there will be a difference of potential between the two GES systems, again another reason that there is no requirement for a GEC to be brought to the house from an out building or structure is because the differance of potential is to far apart between the two systems, on the same building this could be more of a problem.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
First lets separate the grounding requirements between Equipment grounding and Grounding electrodes, and AC and DC systems, While 690 leaves much to desire in its wording it still clearly refers to 250 in most of its instructions as to how to ground the equipment and or the structure.

690 still has the additional requirement of bonding the two grounding electrode systems (if they are separate systems).

With regard to equipment grounding, it may not be in the code that one needs to run the array EGC to the inverter/GFDI advice, but it is a matter of following manufacturer's instructions and ensuring the (required) GFDI works as designed. Adding additional conductor length/resistance to the EGC will reduce the chance of the GFDI detecting a fault.

..there was never a requirement to run a GEC between separate structures and for good reason, doing so does not provide any additional protection from lightning or any other condition that the EGC would already provide as it is meant to only protect the structure it serves.

I am not sure what the reasoning is, but the code has required running a bonding jumper for PV systems for several code cycles.

The above in red further supports the requirement to have a grounding electrode system at the location of the array even when 250 kind of already states this for separate structures ...

The other point is to understand that lightning will not travel very far on most conductors sized per 250.66, ... most of the NEC doesn't seem to follow this line of thought, except in article 800 on antenna requirements and in 690 where it requires that the GES to be as close as it can to the PV array, I'm very surprised that 690 also doesn't mention the requirement of bonding the two GES where a roof top PV array is used on a house with a GES at the service even when 250 will require it, this has to be done as if lightning were to strike the PV array there will be a difference of potential between the two GES systems, again another reason that there is no requirement for a GEC to be brought to the house from an out building or structure is because the differance of potential is to far apart between the two systems, on the same building this could be more of a problem.

Note that 690.47(D) exists only in the 2008 code cycle. It was put in for 2008 and taken out in 2011. I have heard Bill Brooks explain that it was taken out because lightning concerns vary across the country and it was felt to be too onerous a requirement for a national code.

Note also that 690.47(D) more or less requires a separate (dc) GE for the array even on the same structure. Which is probably overkill in a lot of cases (albeit not all) and may be why it was felt to be too onerous. In my experience (in low lightning areas) 690.47(D) is often not followed or enforced for rooftop arrays. OTOH, ground mounted arrays are usually given their own grounding electrodes.

...

You said a lot of other stuff but I don't see how it was a response to me even though you quoted me.
 

hurk27

Senior Member
Ok after digging out my 2011 hand book I can now see where you are coming from, as the 2008 seemed to more treat the bonds or jumpers as equipment grounding conductors, 690.47 was totally revised and they now state grounding electrode jumpers or bonding jumpers, I still do not see the need to connect two separate GES from two separate structures as all that is doing is paralleling the EGC at each end since it will be bonded at both points.

This piece of commentary from the 2011 kind of opens the option to use one conductor between the two systems:

Inverters used in PV power systems usually contain a transformer
that isolates the dc grounded circuit conductor from
the ac grounded circuit conductor. Isolation necessitates that
both a dc and an ac grounding system be installed. The two
grounding systems are to be bonded together or have a common
grounding electrode so that all ac and dc grounded circuit
conductors and equipment grounding conductors have
the same near-zero potential to earth.
The combined dc equipment grounding, dc system
grounding, and ac equipment grounding required by this
section establishes only one grounding circuit and connection
for the entire PV system from the PV array to the ac
point of connection. Under PV dc ground-fault conditions,
an interruption of this single circuit may allow exposed metal surfaces to become energized up to the maximum PV system voltage.

While I can understand this under fault conditions, it makes no sense under a lightning strike, again lightning strikes are a very high frequency event and a long run between the two systems will still create a difference of potential, this is the part I was getting at before, it makes no sense to run GEC's between two buildings electrode systems, as it will not decrease the difference of potential in a lightning strike and if anything might increase it and the damage because of the circuit conductor paths also run between the two points.

I think the re-write of the 2011 requirements will have some potential of more damage when the lightning strike reports start coming in.
 

SolarPro

Senior Member
Location
Austin, TX
Right. If you talk to member of CMP 4, I suspect they will agree with that analysis. 690.47 is not intended as a lightning protection measure. Supplemental systems can be added as needed for lightning protection.
 

Werone

Member
Location
El Paso, Tx USA
Lightning protection and anything having to do with solar electric systems are two seperate areas of expertise. I use copper crimp sleeves for my combo GEC/EG #8 wire from the panels to the inverter/inverters for the irreversible splice. It seems that in naming the solar panel grounding system conductor a Grounding Electrode Conductor, it confuses people since normally a GEC is run directly from a busbar to a Grounding Electrode. The PV system has this combo GEC/EG (Grounding Electrode Conductor/Equipment Ground) running to the inverter terminals on the DC side, then from the terminals on the AC side of the inverter I go directly to the ground bus bar with a #8 GEC for conductors up to #2 from the inverter (From table 250.66). For microinverter systems it is the #8 irreversibly spliced to the Solar Only panel (Where you combine the output of the paralled inverters using backfed breakers) then to the main breaker's grounding terminal. I think that the main objective was to follow the rules of the GEC for running the combo GEC/EG.
 

SolarDude

Member
Location
Los Angeles
I have a question regarding a problem I have run into in a perticular jurisdiction my company installs Photovoltaic solar systems in. I have a Building and Safety Inspector that is requiring us to put an irreversible crimp on the EGC for the photovoltaic system and the Grouding electrode for the residential Service (GEC to ground rod for the main electrical panel).

Could anyone point in the right direction to the code that references this because I cannot find it any where?

His logic, "IF" some one were to disconnect the EGC for the photovoltaic system from the ground bar connection in the Main electrical panel, the Photovoltaic system would not be grounded anymore. I can spout "what if's" all day doesnt mean it is actually required by code.

I understand that the EGC for the system can have a common ground point for both ac and dc systems which is in the inverter, this is not what I am talking about, I am talking about the EGC from inverter to the common ground bus inside the house main electrical panel.

You probably work in an area the company I works in . Because we require our installers to do this unless they drive a ground rod for the inverter itself.
 
Status
Not open for further replies.
Top