[RE-wrenches] Supply Side Connections: Grounding

Sun Sep 8 10:11:02 EDT 2019

I researched some articles on this before replying but they are too out 
of date to be of much help.

This is my two cents worth.

The pv system EGC needs to be connected to the grounding busbar system.

The pv system EGC also needs to be irreversibly connected to the GEC.

The system neutral and the ECG need to be bonded, usually that is at the 
Supply Side Disconnect.

If you have a ac combiner upstream, it should just be grounded, not 
bonded. If a production meter is involved, that too, should be grounded, 
not bonded. Below is a graphic from Mike Holt with some edits.  Chris

On 9/7/2019 11:55 AM, Ray wrote:
>
> I've seen all 3 options.   This question actually comes up in the 
> wiring of sub panels, and out buildings as well.  I find improperly 
> bonded wiring all the time that allows current to flow on the ground, 
> because Neutral was bonded at both ends, with an EGC also run in 
> parallel(option 2 done incorrectly). This is a big No No, and can 
> cause voltages on exposed metal. Next, my understanding is that option 
> 1 is no longer allowed on a single service, although that is how all 
> grid connected houses are wired to the grid and each other with 
> separate meters. (sorry I'm out of the office, so I don't have a code 
> reference)
>
> As far as different opinions from different AHJs, I've had inspectors 
> switch mid project, with the first inspector saying option 2 was ok, 
> then the 2nd inspector required us to later run a GEC back to the GE 
> after.   On option 3,  you would always want an EGC running with the 
> conductors.  I have occasionally then not connected that EGC at one 
> end, if we also had the separate GEC running back to the GE, to avoid 
> a "lightning loop".  Having 2 ground conductors running to the same 
> point along different paths allows lightning to induce a current in 
> the wiring through the loop that is created.
>
> It really does get more complicated, when you also consider the 
> grounding system's secondary purpose of providing lightning 
> protection.   I have a great book from Polyphasor on grounding for 
> lightning protection that is a whole nother world beyond NEC.  They 
> had grounding systems with dozens of GEs (for communications towers) 
> but everything was attached in a star pattern to avoid any lightning 
> loops.  Its actually possible to meet both NEC and lightning 
> protection requirements, but it takes more consideration, and hence 
> the varied opinions.  Not having current running on the ground system 
> however is a serious safety issue.
>
> Ray Walters
> Remote Solar
> 303 505-8760
> On 9/7/19 7:05 AM, Jason Szumlanski wrote:
>> There doesn't seem to be a definitive and detailed consensus 
>> article/resource out there that addresses this topic. There are 
>> articles that dance around the subject, but little in terms of 
>> practical ways to accomplish grounding/binding with a supply side 
>> interconnection. AHJ's and engineers have all kinds of differing 
>> opinions. As an industry, it seems like we should have a definitive 
>> guide on the subject.
>>
>> Let's take a simple/common ungrounded inverter (or microinverter) 
>> system that is interconnected using supply side taps inside an 
>> existing load center with main disconnect. From the roof to the PV AC 
>> Combiner you have an appropriately sized EGC, and no GEC because a 
>> GEC is not required in this ungrounded system other than the existing 
>> premises GEC (and GE system). Let's assume the AHJ agrees that no GEC 
>> is required from the roof, which is a whole other subject that drive 
>> me nuts). Coming from the PV AC Combiner panel (if present) or 
>> Inverter you have two current carrying conductors L1 and L2 that are 
>> tapped on the service conductors. The neutral from the PV AC Combiner 
>> or inverter is landed on the existing neutral bus of the same main 
>> load center where the tap is made.
>>
>> Now what happens with the EGC that comes from the roof to the PV AC 
>> Combiner (or inverter)?
>>
>> What I have run into, and there may be other opinions, are the 
>> following assertions by AHJs:
>>
>>   * Land the EGC on the PV AC Combiner and stop there. Bond neutral
>>     to ground. The neutral carries the fault current to the system
>>     bonding point in the main service panel.
>>   * Land the EGC in the PV AC Combiner and continue the EGC to the
>>     ground bar in the main service panel. Do not bond neutral to
>>     ground in the PC AC Combiner.
>>   * From the PV AC Combiner, install a GEC directly to the existing
>>     grounding electrode, and do not run an EGC to the main service panel.
>>   * Some combination of the above.
>>
>>
>> Can anyone point to a clear and concise 3-line diagram that explains 
>> the acceptable options? Hopefully something that and AHJ will 
>> consider, like an IAEI article or NEC Handbook graphic.
>>
>>
>> Jason Szumlanski
>> Florida Solar Desing Group
>>
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