solar panel AC main disconnect

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hhsting

Senior Member
Location
Glen bunie, md, us
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Junior plan reviewer
Attached sketch shows main service disconnect that has line side tap to main AC solar disconnect. However, main AC solar disco has no main bonding jumper. Is this acceptable by code under 2014?
 

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Attached sketch shows main service disconnect that has line side tap to main AC solar disconnect. However, main AC solar disco has no main bonding jumper. Is this acceptable by code under 2014?
The short answer is yes. The longer answer is yes, subject to interpretation. Most AHJs I deal with say yes, but a couple say no. I just ask the AHJ and do what they say.
 

shortcircuit2

Senior Member
Location
South of Bawstin
The 2020 NEC added new section 250.25 which requires separate supply-side connected system enclosures to comply with 250.24(A)-(D)... which will not only require a Main Bonding Jumper per 250.24(B), you also need a Grounding Electrode Conductor per 250.24(D) and it must be connected in compliance with 250.64(D)

Given that the 2014 NEC gives no direction for installer or AHJ on your supply-side connected PV Disconnect...I agree ask the AHJ...but I would suggest to install the green screw because IMO this will be a safer installation by creating a ground-fault path to the utility source. I do not see how it would create a hazard by installing the main bonding jumper. Doing so is consistent with separate service disconnect enclosures as required by 250.24(B)
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
The 2020 NEC added new section 250.25 which requires separate supply-side connected system enclosures to comply with 250.24(A)-(D)... which will not only require a Main Bonding Jumper per 250.24(B), you also need a Grounding Electrode Conductor per 250.24(D) and it must be connected in compliance with 250.64(D)

Given that the 2014 NEC gives no direction for installer or AHJ on your supply-side connected PV Disconnect...I agree ask the AHJ...but I would suggest to install the green screw because IMO this will be a safer installation by creating a ground-fault path to the utility source. I do not see how it would create a hazard by installing the main bonding jumper. Doing so is consistent with separate service disconnect enclosures as required by 250.24(B)

Post #1 attachment has bonding jumper and neutral from main service disconnect. The main service disconnect has main bonding jumper.

Let’s take a look at EGC fault path post #1 it would from PV AC main disco EGC to EGC of main service disco to main bonding jumper in service disco to neutral. It has main bonding jumper connection only in service disco.

Now if you add main bonding jumper in PV AC disconnect let’s take a look at EGC fault current it would go from EGC PV AC disco to main bonding jumper PV AC disco to neutral in AC PV disco to neutral in main service disco then to utility. It still has to go thru neutral in main service disco.

Between the two scenarios how is one safe the other not safe?

Now l am not sure how it would work if their was lightning strike utility line or tree fell on utility line side line and fault current flow. If anyone here know what exactly happens each of the scenarios and how one is safer than other?



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shortcircuit2

Senior Member
Location
South of Bawstin
Proper sizing of the Main Bonding Jumper per 250.28 is important for each separate service enclosure on services with multiple switches. 250.28 does not have exception for situation of a Main Bonding Jumper installed in another switch. Each separate switch needs its own based on the conductors feeding that switch.

In your diagram, I agree there is a ground-fault path.

But, lets say we have a 800-amp service with 2 sets of 500MCM copper service entrance conductors feeding a trough with 4 separate 200-amp switches with their main bonding jumper sized for the 200-amp conductors feeding the switch. Now a 600-amp solar PV switch is added in its own enclosure connected to the SE conductors in the trough. Would that 600-amp PV switch have an effective ground-fault path through the other 200-amp main bonding jumper? No it will not.

There is no exception to 250.28(2) with regard to separate enclosures.
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
Proper sizing of the Main Bonding Jumper per 250.28 is important for each separate service enclosure on services with multiple switches. 250.28 does not have exception for situation of a Main Bonding Jumper installed in another switch. Each separate switch needs its own based on the conductors feeding that switch.

In your diagram, I agree there is a ground-fault path.

But, lets say we have a 800-amp service with 2 sets of 500MCM copper service entrance conductors feeding a trough with 4 separate 200-amp switches with their main bonding jumper sized for the 200-amp conductors feeding the switch. Now a 600-amp solar PV switch is added in its own enclosure connected to the SE conductors in the trough. Would that 600-amp PV switch have an effective ground-fault path through the other 200-amp main bonding jumper? No it will not.

There is no exception to 250.28(2) with regard to separate enclosures.

Ok in your example so let’s say your PV disconnect SE conductors are now connected not to trough but to one of the 4 disconnects line side lug inside the disconnect and supply side bonding jumper and neutral are brought to PV disconnect separate enclosure from the disconnect then you would have clear ground fault clear path thru EGC to the disconnect main bonding jumper. What would be the problem be with this scenario?
 
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hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
Ok in your example so let’s say you have 3 - 200A separate PV disconnect enclosures (making same as 600A one PV disconnect enclosure) and SE conductors each one are now connected not to trough but to one of the 3 200A disconnects line side lug inside enclosure and supply side bonding jumper and neutral are brought to each PV disconnect separate enclosures from its respective disconnect then you would have clear ground fault clear path thru EGC to the respective disconnect main bonding jumper. What would be the problem be with this scenario?
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
On post #1 let’s say main service disco is 400A and PV AC disconnect is 100A. Let’s assume simultaneous fault occurs on 400A side and 100A side then would the main bonding jumper in 400A main service disco be sufficient size to handle both fault same time? I think not since it’s sized for 400A main disco and so two options:

1. Either provide separate main bonding jumpers in each enclosure 400A and separate in 100A or

2. Re size the main bonding jumper in main service disconnect to handle both the 400A and 100A incoming service entrance conductor sizes.

Not sure. What are your thoughts about two options above and are both per code?


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shortcircuit2

Senior Member
Location
South of Bawstin
Ok in your example so let’s say your PV disconnect SE conductors are now connected not to trough but to one of the 4 disconnects line side lug inside the disconnect and supply side bonding jumper and neutral are brought to PV disconnect separate enclosure from the disconnect then you would have clear ground fault clear path thru EGC to the disconnect main bonding jumper. What would be the problem be with this scenario?
Connecting 600-amp SE conductors to the line side of a 200-amp disconnect just wouldn't work...something would meltdown and burst into flames.
 

shortcircuit2

Senior Member
Location
South of Bawstin
There are many rules in the NEC where you can have an installation that will work and not comply directly with the rule. But given that there is not an exception to the rule, the installation violates the rule. This Main Bonding Jumper rule in discussion here is a good example. The Code requires a MBJ in each separate disconnect per 250.28(2)

Your diagram in post #1 will require a MBJ in 2020. Installing a MBJ in your 2014 installation will not create a hazard, and will provide a properly sized MBJ thereby creating an effective ground-fault path back to the utility source which can provide high levels of fault current into the your installation under a fault condition.

Ask you AHJ what he requires and get back to us.

Thanks.
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
Connecting 600-amp SE conductors to the line side of a 200-amp disconnect just wouldn't work...something would meltdown and burst into flames.

Ok but did you take a look at post #8 you have three separate 200A PV disco enclosures each connecting to 3 main service 200 disconnect line side terminal lug. What is wrong with this scenario?


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hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
On post #1 let’s say main service disco is 400A and PV AC disconnect is 100A. Let’s assume simultaneous fault occurs on 400A side and 100A side then would the main bonding jumper in 400A main service disco be sufficient size to handle both fault same time? I think not since it’s sized for 400A main disco and so two options:

1. Either provide separate main bonding jumpers in each enclosure 400A and separate in 100A or

2. Re size the main bonding jumper in main service disconnect to handle both the 400A and 100A incoming service entrance conductor sizes.

Not sure. What are your thoughts about two options above and are both per code?


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No takers. Nobody knows?


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baserunner4

Member
Location
CA
Solar is not a service but a lot of people/ utilities treat us as one therefore having the MBJ or grounded neutral kit in PV disco.

There is no wrong or right answer in this case and there are arguments for both sides. I can think of plenty. Usually go with what the AHJ says.
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
Unfortunately I am contractor to AHJ reviewer and AHJ does not have any rule about this.

Spoke with the engineer and he replaced and modified post #1 sketch with attached sketch this post. He provides main bonding jumper in main PV AC disconnect however supply side tap he is brining 4#3Awg + 1#6 AWG in 1 inch conduit from 125A main service disco to 80A PV AC disco. The grounding electrode system is still in main AC service disco.

Was wondering few questions and people who encountered how different AHJ handle or what are their opinion:

1. Is their anything wrong per code attached sketch?

2. Can you have EGC coming from supply side tap as shown sketch?If no then please which code section it does not comply and if yes then which code section it comply?

3.What are both arguements for both for and against NEC 2014 grounding electrode system and main bonding jumper at PV AC Disco?

4. Can you have grounding electrode system in main AC service disco and EGC going to PV AC disco as shown?
 

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shortcircuit2

Senior Member
Location
South of Bawstin
1. The EGC may carry objectionable current in violation of 250.6(A) and it could be considered an installation of the grounded conductor in parallel in violation of 310.10(H) 2014/2017 NEC or 310.10(G) 2020 NEC

2. Same comment as 1.

3. Advocates against say that PV is not a "service"...
Advocates for say bonding creates a more effective low-impedance ground-fault path back to the utility source.

4. The GEC generally needs to land in each separate enclosure per 250.64(D)


2020 changed the definition of "service" to "The conductors and equipment connecting the serving utility to the wiring of the premises served."
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
I am hard time finding in NEC 2014 what the attached pictures shows: AC PV disconnect is not counted as service disconnect. I looked in NEC 2014 Section 230.71(A) but does not say AC PV disconnect not counted. Does anyone know exactly what section it is in NEC 2014? If none then please say none.
 

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shortcircuit2

Senior Member
Location
South of Bawstin
Well you were asking for input on the Main Bonding Jumper in this thread and now Grouping.

2014 section 230.71(A) has what your asking about in that it says "or for each set of service entrance conductors permitted by 230.40, exception No. 1,3,4 or 5" and 230.40 ex # 5 specifies systems connected per 230.82 (5) & (6)

It is amusing in that here these conductors are regarded as Service Entrance Conductors through these Code references, but refer to them as the Inverter Output Circuit conductors in 690... service entrance conductors should terminate in a...Service Disconnect.

I'm happy to see that Mike Holt guides his readers to install the Main Bonding Jumper and line side bond in the photo you have uploaded.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
Am I right in assuming that the PV inverters drive little or no current through their neutral connection if they have one? If so then there does not seem to be a good technical argument that a bonding jumper in the PV disconnect creates a problem, because it will be conducting essentially no current in normal operation. But during a ground fault on the PV side, as shortcircuit2 mentioned, it provides a more direct and lower impedance path for the fault current.
 

hhsting

Senior Member
Location
Glen bunie, md, us
Occupation
Junior plan reviewer
Am I right in assuming that the PV inverters drive little or no current through their neutral connection if they have one? If so then there does not seem to be a good technical argument that a bonding jumper in the PV disconnect creates a problem, because it will be conducting essentially no current in normal operation. But during a ground fault on the PV side, as shortcircuit2 mentioned, it provides a more direct and lower impedance path for the fault current.

Not sure about Enphase Microinverters IQ7+. Do they have neutral current flow?


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