Enphase IQ series +7 inverter

[jaggedben]

There's a pretty spirited fight going on over the 2020 NEC on this point. It's been going back and forth between making the PV disconnect on a supply side interconnection have a neutral-ground or not. Seems to be settling on the no bond side of things but a vocal group is still trying to change it to require a bond.

The second draft was awful. First draft needed a tweak or two but generally had the right idea in allowing either method.

 

[jaggedben]

The problem is AHJ enforces NEC and local amendments not a textbook or theory electrical engineer because NEC does not go into all that.

For example if one calculates 100kvA on single phase breaker 480V as 100/.48/1.732 = 120.2A and size breaker as 150A then AHJ has no code section to enforce and say 100/.48 =208A and next size is 250A. AHJ cannot enforce this and their is no code section for calculation. All of that makes it tough for the AHJ.

What's tough on the AHJ? The AHJ gets to make the call.

I believe that usually this sort of thing can be resolved by bringing in an electrical engineer to stamp the design and take the liability off the AHJ if the code is unclear.

 

[hhsting]

What's tough on the AHJ? The AHJ gets to make the call.

I believe that usually this sort of thing can be resolved by bringing in an electrical engineer to stamp the design and take the liability off the AHJ if the code is unclear.

Our AHJ has alot of electrical engineer blindly stamping, collecting money without looking at design so it becomes problem for AHJ.

 

[hhsting]

....At one point I posted a full list of all the code sections that could be used to argue 'for' or 'against'....

Can you please post the link for full list of all code sections for or against? I searched and searched but did not find any such post.

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[ggunn]

Can you please post the link for full list of all code sections for or against? I searched and searched but did not find any such post.

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Good luck with your argument, but in my experience, since either side can be argued AHJ's make up their mind about it and will not be swayed.

 

[hhsting]

Good luck with your argument, but in my experience, since either side can be argued AHJ's make up their mind about it and will not be swayed.

Yea but in this project I work as reviewer/contractor for AHJ and can at least have some authority over AHJ. I did like to see that list for and against link to see how others approach this from both sides.

 

[ggunn]

Yea but in this project I work as reviewer/contractor for AHJ and can at least have some authority over AHJ. I did like to see that list for and against link to see how others approach this from both sides.

It's pretty simple, actually.

Line side PV is not a service: EGC runs from array through the fused AC disco back to the service. No ground rod needed at the disco.

Line side PV is a service: EGC from array terminates at the fused AC disco, neutral is bonded to ground in the disco, ground rod at the disco tied to building ground, no EGC between disco and service.

Either way is compliant with the NEC as it is today.

 

[wwhitney]

Line side PV is a service: EGC from array terminates at the fused AC disco, neutral is bonded to ground in the disco, ground rod at the disco tied to building ground, no EGC between disco and service.

So this arrangement always puts neutral current from the main service on the bonding jumper between the solar service ground rod and the main service grounding electrode system? And if the PV array EGC is ever interconnected with the main service EGC elsewhere, it puts neutral current on both EGCs?

I guess the same issues would arise at any building with multiple services.

Cheers, Wayne

 

[ggunn]

So this arrangement always puts neutral current from the main service on the bonding jumper between the solar service ground rod and the main service grounding electrode system? And if the PV array EGC is ever interconnected with the main service EGC elsewhere, it puts neutral current on both EGCs?

I guess the same issues would arise at any building with multiple services.

Cheers, Wayne

Neutral is contiguous back to the service from the PV either way. But yes.

 

[wwhitney]

Neutral is contiguous back to the service from the PV either way. But yes.

Right, but under "line side PV is not a service" there is only one neutral-ground bond, so no neutral current on the EGC.

Seems like a strong argument for the "line side PV is not a service" side.

Cheers, Wayne

 

[hhsting]

Right, but under "line side PV is not a service" there is only one neutral-ground bond, so no neutral current on the EGC.

Seems like a strong argument for the "line side PV is not a service" side.

Cheers, Wayne

Yes and no what if you have load like post #1 Envoy communication fed from AC solar panel then its combination of service and non service? Does solar panel fed Envoy or utility service?

 

[jaggedben]

So this arrangement always puts neutral current from the main service on the bonding jumper between the solar service ground rod and the main service grounding electrode system? And if the PV array EGC is ever interconnected with the main service EGC elsewhere, it puts neutral current on both EGCs?

I guess the same issues would arise at any building with multiple services.

Cheers, Wayne

You don't need multiple services, just multiple service disconnects. And yes, all of that is very explicitly permitted in 230 and 250.

 

[jaggedben]

Can you please post the link for full list of all code sections for or against? I searched and searched but did not find any such post.

Originally posted here, I've made a slightly updated version.

---------

Is a supply-side PV disconnect a service disconnect?

'Yes'

Article 100 definitions of 'Service Conductors', 'Service Entrance Conductors' and 'Service Point.' Along with the requirements of 230.70, these logically entail that the conductors require what 230.70 calls 'a service disconnecting means'. Note that the definition of 'Service Point' is not negated even if the definition of 'Service' is not considered to apply. One would have to argue that the service has no 'Service Point' to avoid the requirements of 230.70.

230.2(A)(2) - allows an additional service for parallel power production systems. This code section calls this connection a service, even though that's not consistent with the article 100 definition for 'Service'.

230.40 Exception 5 - Refers (via reference to 230.82(6)) to the PV system using 'service entrance conductors', which along with 230.70 requires a service disconnecting means. Also uses the phrase 'supply side of the normal service disconnecting means', (emphasis added), which avoids the implication that all the service disconnecting means must be elsewhere, as opposed to just the 'normal' ones. (see below)

230.70 Titled 'Service Equipment Disconnecting Means,' it requires service entrance conductors to have a disconnecting means. It refers to this means with the phrase 'service disconnecting means' six times, as well as the phrase 'service disconnect' twice. Any installation with a 'Service Point' ends up having to meet these requirements. Any invocation of 230.40 Exception 5 to justify a supply side tap would also invoke 230.70. Notably, the Article 100 definition of 'Service Equipment' is not actually necessary for invoking the requirements of this section.

230.71 Note that nothing that can reasonably construed as applying to a PV system is included in 230.71(A)(1) thru (4).


'No'

Definition of a Service, which refers to 'delivering energy from the serving utility to the wiring system of the premises served.' [NOTE: changing in 2020 NEC to longer imply one direction.]

Definition of Service Equipment, which refers to 'load end of service conductors'.

230.82 and 705.12(A), 705.31: These sections use the phrase 'supply side of the service disconnecting means', which can be taken to imply that the service disconnecting means are elsewhere. (Note again that 230.40 Exception 5 avoids this implication with the additional of the word 'normal'.)

230.82(6): Notably this section does not include the same restrictions as 230.82(5).


All references are 2014 NEC.

 

[jaggedben]

Right, but under "line side PV is not a service" there is only one neutral-ground bond, so no neutral current on the EGC.

Seems like a strong argument for the "line side PV is not a service" side.

The generalized counter argument is that a PV supply side disconnect presents exactly the same safety issues as an additional service disconnect. And the code allows - actually it requires - multiple N-G bonds where there are multiple service disconnects. It also requires the neutral to be brought to service disconnects to provide a fault-current path. It does not require the GECs to create parallel paths but it permits that as an option.

 

[wwhitney]

And the code allows - actually it requires - multiple N-G bonds where there are multiple service disconnects. . . . It does not require the GECs to create parallel paths but it permits that as an option.

With multiple services on a single building, aren't all grounding electrodes present required to be interconnected, so that the GES will always be carrying some neutral current via the multiple N-G bonds?

Cheers, Wayne

 

[electrofelon]

Originally posted here, I've made a slightly updated version.

---------

Is a supply-side PV disconnect a service disconnect?

'Yes'

Article 100 definitions of 'Service Conductors', 'Service Entrance Conductors' and 'Service Point.' Along with the requirements of 230.70, these logically entail that the conductors require what 230.70 calls 'a service disconnecting means'. Note that the definition of 'Service Point' is not negated even if the definition of 'Service' is not considered to apply. One would have to argue that the service has no 'Service Point' to avoid the requirements of 230.70.

230.2(A)(2) - allows an additional service for parallel power production systems. This code section calls this connection a service, even though that's not consistent with the article 100 definition for 'Service'.

230.40 Exception 5 - Refers (via reference to 230.82(6)) to the PV system using 'service entrance conductors', which along with 230.70 requires a service disconnecting means. Also uses the phrase 'supply side of the normal service disconnecting means', (emphasis added), which avoids the implication that all the service disconnecting means must be elsewhere, as opposed to just the 'normal' ones. (see below)

230.70 Titled 'Service Equipment Disconnecting Means,' it requires service entrance conductors to have a disconnecting means. It refers to this means with the phrase 'service disconnecting means' six times, as well as the phrase 'service disconnect' twice. Any installation with a 'Service Point' ends up having to meet these requirements. Any invocation of 230.40 Exception 5 to justify a supply side tap would also invoke 230.70. Notably, the Article 100 definition of 'Service Equipment' is not actually necessary for invoking the requirements of this section.

230.71 Note that nothing that can reasonably construed as applying to a PV system is included in 230.71(A)(1) thru (4).


'No'

Definition of a Service, which refers to 'delivering energy from the serving utility to the wiring system of the premises served.' [NOTE: changing in 2020 NEC to longer imply one direction.]

Definition of Service Equipment, which refers to 'load end of service conductors'.

230.82 and 705.12(A), 705.31: These sections use the phrase 'supply side of the service disconnecting means', which can be taken to imply that the service disconnecting means are elsewhere. (Note again that 230.40 Exception 5 avoids this implication with the additional of the word 'normal'.)

230.82(6): Notably this section does not include the same restrictions as 230.82(5).


All references are 2014 NEC.

Seems like using preponderance of the evidence, the pv disco is a service disco. NO FURTHER DISCUSSION OF THIS IS ALLOWED

 

[jaggedben]

With multiple services on a single building, aren't all grounding electrodes present required to be interconnected, so that the GES will always be carrying some neutral current via the multiple N-G bonds?

Yes, all services would be grounded to one set of electrodes. But this does not necessarily mean that there would be neutral current on the GES because of multiple N-G bonds. Multiple services are likely to be supplied by different transformers, since the code doesn't generally allow multiple services in situations that wouldn't also be likely to call for that. Again, this is different from multiple service disconnects on a single service.

Residential structure GESs often carry some amount of neutral current regardless, by being connected to neighboring services' GESs though the water pipes. Again, the code doesn't try to prohibit this. The code really gives lots allowances for the possibility of parallel paths through the GES (besides the earth itself).

 

[synchro]

The language looks pretty straightforward to me. Look at a busbar and sum the ratings of all the breaker poles that land on it. They can't sum to more than the busbar rating. It makes no difference whether you have a three phase or a single phase system. Note that unlike the other sections of this part of the code, it's the breaker ratings that count rather than 125% of the inverter output current.

I have dealt with several AHJ's on this issue and that's the way all of them interpret it.

I'm late to the game on this thread but I agree with this comment.
I also don't think there's a good engineering justification to reduce the requirement on the busbar current rating by sqrt(3)/2=0.866 when combining single phase inverter outputs in a 3-phase delta configuration. Although the line current output that's available to feed the POCO or loads is reduced by this factor, the current going into the bus at the connection of a backfed breaker to the bus is the full current of the inverter. I think this needs to be taken into account in the heating of the bus because the bus is a three dimensional object with a distribution of currents along it, and not just the idealized single point or "node" as in Kirchoff's current law.

As an aside, at each connection point of a delta the current from one phase leads the line output current by 30 degrees while the other phase lags it by 30 degrees. So each of these two phase currents with magnitude Ip has a vector component Ipi with magnitude cos(30) x Ip = 0.866 Ip, and these two components are in phase with eachother and therefore can be directly summed to produce a line output current that has the same phasing. But no current has disappeared to get this 0.866 scaling factor. Instead, each phase current Ip also has a vector component Ipq that's at 90 degrees from Ipi, and with a magnitude sin(30) x Ip = 0.5 Ip. This current flows between the two phases at a delta connection. And although it does not appear in the line output, this current Ipq goes through the buss when the delta is constructed by connecting backfed breakers to the bus. So it therefore contributes to heating of the bus. Just to confirm this all works out, sqrt [ (0.866)^2 + (0.5)^2] = 1 by Mr. Pythagoras's theorem and so all of the phase current is accounted for and none of it has disappeared.

So I don't think you can rely on vector addition of phase components to reduce the bus rating requirement in this situation. Just like the current that flows through a breaker feeding a load can't be subtracted out, but instead often has to be added in.

 

[GoldDigger]

Your point is well taken. The extra current may not flow very far in the bus, but it certainly traverses the bus stabs.

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[jaggedben]

I believe there's a much better justification for using the vector math on the main breaker and output conductors for the panel than on the busbar. Just sayin'.