ideal setup for 3 Phase 208V 43.2KW SolarEdge Inverter 175-200 OCPD

[gporter85]

I like the ideal of a 600A rated busbar with 400A OCPD also. This would allow me to use a breaker in main panel as my disconnecting means instead of a disconnect outside. My local PO allows us to waive the requirement for the manual disconnect switch.

To prevent a net metering customer from back-feeding a de-energized line, the customer
shall install a manual disconnect switch with lockout capability that is accessible to
Company personnel at all hours. This requirement for a manual disconnect switch will be
waived if the following three conditions are met: 1) The inverter equipment must be
designed to shut down or disconnect and cannot be manually overridden by the customer
upon loss of Company service; 2) The inverter must be warranted by the manufacturer to
shut down or disconnect upon loss of Company service; and 3) The inverter must be
properly installed and operated, and inspected and/or tested by Company personnel

I have done a lot of work in CA. PG&E the main utility has no problem whatsoever tapping any service. Be it double lugs on the line side of a disconnect between meter and Switch, Polaris lugs or IPC's. Some of the smaller utilities that are local irrigation districts want a UL inspector on site to watch you perform the tap... To a tune of $5-10,000. In that case having a custom panel built to accommodate the 120% rule is less expensive and easier. But every single commercial job i have ever installed has required knife blade disconnects fused or not.

 

[pv_n00b]

But the line is blurry for what is a supply side connection vs a 230.40 exception 2 or 3 install. Can i only have one ocpd for a supply side connection? Does a supply side connection become not a supply side connection once I put in an inverter output combiner panel and feeder?

It's really not a grey area here. If someone wants to connect a PV system on the utility side of the main disconnect it's supply side and not allowed. If it walks like a duck and quacks like a duck they call it a duck.

 

[electrofelon]

It's really not a grey area here. If someone wants to connect a PV system on the utility side of the main disconnect it's supply side and not allowed. If it walks like a duck and quacks like a duck they call it a duck.

No its really not always clear. Due to vagueness in the NEC, a given installation (depending on specifics) could be a supply side connection or fall under 230.40 exception 2 or 3.

 

[ggunn]

No its really not always clear. Due to vagueness in the NEC, a given installation (depending on specifics) could be a supply side connection or fall under 230.40 exception 2 or 3.

I disagree. Whether a PV system is connected load side or supply (line) side is very clear. The code is indeed ambiguous as to whether a line side connection is or is not a service entrance, but the Point Of Interconnection is either on the line side of the first OCPD or it isn't. Even if it is at the opposite end of a panel busbar from the utility feed, if that panel is the MDP and MLO, the PV is connected on the line side. If an AHJ's policy is "no line side PV connections" you won't be able to use 230.40 to get around it.

 

[jaggedben]

I'm pretty much with electrofelon here. Do these AHJs even allow 230.40 Exception 2 or 3 installs? Let's say you legitimately contract with the customer for something that's unrelated but bundled into the same contract. Like an EV charger, just for example. Would the AHJ allow you to put in an additional service disconnect just for an EV charger if you weren't doing PV? And now let's say you want to put a panel on the load side that new disco and put both the EV breaker and a PV breaker in it? Do the rules suddenly change? And if they would allow it for just the EV charger then how is doing this an illegitimate way of 'getting around' their prohibition on supply side connections? And, finally, if they recognize that 230.40 allows the EV charger, how would it not allow the PV?

 

[electrofelon]

I disagree. Whether a PV system is connected load side or supply (line) side is very clear. The code is indeed ambiguous as to whether a line side connection is or is not a service entrance, but the Point Of Interconnection is either on the line side of the first OCPD or it isn't. Even if it is at the opposite end of a panel busbar from the utility feed, if that panel is the MDP and MLO, the PV is connected on the line side. If an AHJ's policy is "no line side PV connections" you won't be able to use 230.40 to get around it.

Think about it: take a 400 amp service with 2 side by side 200 amp panels (230.40 ex 2). "Slowly" change that over to a line side PV connection. At what point does one of those panels and sets of conductors change to a pv line side connection? When there are only pv loads in that panel? When it "looks" like a pv system (perhaps change the panel to a fused safety switch and put pv labels in it.)?

 

[hevnbnd]

Because they think it's solar and solar makes bags of money on the huge markups so they want some of that? Just speculating here.

If they say the unit is fine for bi-directional current flow there is nothing special about a "solar transformer" in the LV range of dry-type transformers that requires customization. Maybe they want to specify a particularly high-efficiency copper wound transformer. I'm all for the high-efficiency units but I can still get those off the shelf at that size.

Per Federal Pacific they said that Solar inverters often put a large stress on the neutral. The Solar transformer they add core steal and extra insulation on the windings to help with the neutral stress that the inverter puts out.

Not sure what to think.

 

[electrofelon]

Per Federal Pacific they said that Solar inverters often put a large stress on the neutral.

Hogwash. Maybe in the past.

 

[ggunn]

Per Federal Pacific they said that Solar inverters often put a large stress on the neutral. The Solar transformer they add core steal and extra insulation on the windings to help with the neutral stress that the inverter puts out.

Not sure what to think.

How could that be? Unless it's three phase cobbled together from mismatched or a number not divisible by three single phase inverters, there should be no current on the neutral.

 

[jaggedben]

Only things I can think of are:
- neutral circulating currents if hooking up through a wye/wye, as debated elsewhere
-excess current on neutral when one leg of a three phase system fails and the system is not designed to shutdown inverters on the other legs.

But neither of those sound like problems addressed by the 'solution' described above.

 

[Adamjamma]

Could it be due to the number of people using individual 120v inverters to try to feed the meter? Rather than using a 240/120 inverter or a three phase inverter? Just wondering.. still trying to learn the basics

 

[jaggedben]

Could it be due to the number of people using individual 120v inverters to try to feed the meter? Rather than using a 240/120 inverter or a three phase inverter? Just wondering.. still trying to learn the basics

No. 120V inverters aren't really a thing. Most inverters these days output 240V or balanced three-phase.

A few years ago people did a fair amount of putting inverters at 277V line-to-neutral on a 480/277 wye. If there was an uneven number of inverters there would be significant current on the neutral. This could still happen with micro-inverters in a 208/120 wye.

But none of that should mean there is 'stress' on the neutral of the transformer that wouldn't be there under a typical load use. The explanation from Federal Pacific sounds like hogwash. I can't even think of what 'stress' would mean, other than overcurrent, which can be addressed with overall system design and shouldn't need a special transformer AFAIK.

 

[hevnbnd]

So got quote from POCO to change to 208V Y 3 Phase.... Drumroll... $15K

Will a 45KVa (125A calculated) T24SH2Y-45 be large enough? Max output of PV inverter is 125A. Thoughts on using a 45KVA transformer?

 

[pv_n00b]

Per Federal Pacific they said that Solar inverters often put a large stress on the neutral. The Solar transformer they add core steal and extra insulation on the windings to help with the neutral stress that the inverter puts out.

Not sure what to think.

Never heard of it. I looked on the Federal Pacific website and they have no information about special solar or photovoltaic transformer requirements listed. If it was a problem they would have a white paper explaining why someone should pay extra. I recommend finding another transformer vendor. Never buy the dealer applied undercoat.

 

[pv_n00b]

I'm pretty much with electrofelon here. Do these AHJs even allow 230.40 Exception 2 or 3 installs? Let's say you legitimately contract with the customer for something that's unrelated but bundled into the same contract. Like an EV charger, just for example. Would the AHJ allow you to put in an additional service disconnect just for an EV charger if you weren't doing PV? And now let's say you want to put a panel on the load side that new disco and put both the EV breaker and a PV breaker in it? Do the rules suddenly change? And if they would allow it for just the EV charger then how is doing this an illegitimate way of 'getting around' their prohibition on supply side connections? And, finally, if they recognize that 230.40 allows the EV charger, how would it not allow the PV?

We can argue this to death here, but the bottom line is that the local utility here will not allow any supply-side PV interconnections and as far as I know has no problem with 230.40 supply side load connection exceptions. They see a load as different than a generation source. I like to discuss these fine points but it does not matter to them.

 

[jaggedben]

I'm not really arguing with anyone. I just can't get the better of my curiosity. The post you quoted was a series of genuine questions, for you or ggunn. They remain unanswered for me.

 

[wwhitney]

the bottom line is that the local utility here will not allow any supply-side PV interconnections and as far as I know has no problem with 230.40 supply side load connection exceptions.

So what does your local utility say if you have a residence with one service disconnect and you propose to set a second service disconnect next to it (230.40 Exception 2), move one load over to the second service disconnect, and add PV to that second service disconnect? 705.12(B) is pretty easy to comply with if there is only one load breaker, so you'd get almost all of the benefit of a line side interconnection.

Cheers, Wayne

 

[hevnbnd]

I see now that you mentioned a new service in your first post.

It would still be useful to know what the load requirements on the building are. (Is 400A your building load?) Broadly speaking, your solar could be done at the opposite end of a main panelboard or switch board if it is rated 900A or more. There are probably other scenarios (e.g. 600A rated busbar with 400A OCPD) where it could work, but again specifics depend on the buildng load requirement. I'm not sure I'd bother with a supply side connection if one of these scenarios is easily feasible.

Regarding your idea of a 400A disconnect with multiple lugs ; you would need another fused disconnect for the solar. Consider whether a tap box and two service diconnects would be a cleaner solution. While I have done taps inside an exiting main disconnect many times, some AHJs might ask 'Why did you bring the solar into the main disconnect when you had a chance to keep them separate on a new service?"

That's an interesting page of the SolarEdge manual, but I think per code you are still only required to provide a 150A output circuit and OCPD. That's what will figure into article 705 calculations.

Read Article 705 carefully in your relevant code cycle.

Why would you need a 600A rated Busbar? If I am following 705 in 2014 code correctly I could use a 400A bus bar with 300A main breaker and 175A PV Breaker and come in at 119% of current rating of bussbar. Did i miss calculate some where? Or were you thinking 600A busbar because it would be hard if not impossible to find a 300A Main Breaker?

 

[jaggedben]

Why would you need a 600A rated Busbar? If I am following 705 in 2014 code correctly I could use a 400A bus bar with 300A main breaker and 175A PV Breaker and come in at 119% of current rating of bussbar. Did i miss calculate some where? Or were you thinking 600A busbar because it would be hard if not impossible to find a 300A Main Breaker?

I thought somewhere you said you needed 400A for the load. If your load calc only comes in at 300A or less then what you're proposing here is fine. You don't get to size the service disconnect smaller than the calculated load, regardless of your installing solar.

 

[hevnbnd]

I thought somewhere you said you needed 400A for the load. If your load calc only comes in at 300A or less then what you're proposing here is fine. You don't get to size the service disconnect smaller than the calculated load, regardless of your installing solar.

Correct. I am leaning toward a 400A service disconnect outside and 300A main breaker. Thanks!

So I am going to use a transformer to go from my 240 Delta to either 208Y or 277Y. I can get inverters for both voltages with the 277/480 being cheaper. See any reason to go 208V? I suspect the transformers are similar in cost.