Any 400A Solar Ready panelboards available?

[Garbluck]

Doing a larger Residential job in Vegas. The resident currently has a 400A MSP w/ 2, 200A Disconnects (going to their own 200A Panelboards).

We're going to upgrade their MSP, but we're not sure what we're going to upgrade it to. My hopes, are that we can get a 400A Solar Ready MSP so that we aren't placing our 150A PV on the load side. We could go for a 600A MSP, but we'd need to find a smaller Main Disconnect to fit our PV on the load side (per 120%).

Any thoughts?

 

[ggunn]

Doing a larger Residential job in Vegas. The resident currently has a 400A MSP w/ 2, 200A Disconnects (going to their own 200A Panelboards).

We're going to upgrade their MSP, but we're not sure what we're going to upgrade it to. My hopes, are that we can get a 400A Solar Ready MSP so that we aren't placing our 150A PV on the load side. We could go for a 600A MSP, but we'd need to find a smaller Main Disconnect to fit our PV on the load side (per 120%).

Any thoughts?

What makes a panel "solar ready"?

 

[TommyO]

What makes a panel "solar ready"?

I think it's a marketting name for a panel that has a dedicated spot for PV breaker (or wind,etc).

ex:
http://w3.usa.siemens.com/powerdist.../meter-load-center/Documents/SIE_BR_SOLAR.pdf


Wouldn't a 600A main panel work with 2 of 200A for the existing and 1 of 150A for PV?
(It'd even be less than 100% of the panel rating - wouldn't have to use the 120% rule)

 

[Carultch]

Doing a larger Residential job in Vegas. The resident currently has a 400A MSP w/ 2, 200A Disconnects (going to their own 200A Panelboards).

We're going to upgrade their MSP, but we're not sure what we're going to upgrade it to. My hopes, are that we can get a 400A Solar Ready MSP so that we aren't placing our 150A PV on the load side. We could go for a 600A MSP, but we'd need to find a smaller Main Disconnect to fit our PV on the load side (per 120%).

Any thoughts?

I've never heard of a "solar ready" panelboard.

What you need to do, is size the busbar in excess of the main breaker, and leave an available space at the opposite end for interconnecting a system to all phases/lines.

In general, it ends up being a busbar size up. So for a 200A service, building a main panel with a 400A busbar and a 200A main will allow plenty of room to add solar. Or a 600A busbar with a 400A main. Or an 800A busbar with a 600A main.

The formal rule is that (interconnection breaker + main breaker) cannot exceed 120% of the busbar ampacity. In 2014, a new rule rewords this language so that rounding errors on "interconnection breaker" are not a show stopper, as long as 125% of nominal operating current is used instead.

 

[GoldDigger]

The rounding errors on breaker size are at their worst when an AC combiner and/or PV connection to a sub panel are used. It is great that [2014] takes care of this.

 

[Carultch]

The rounding errors on breaker size are at their worst when an AC combiner and/or PV connection to a sub panel are used. It is great that [2014] takes care of this.

Absolutely. That is why you generally try to interconnect at as main of a panel as possible/practical.

The other "gotchya", is when breakers aren't suitable for backfeed. And it is like trying to prove a negative, looking for the fine print, hoping it doesn't exist.

 

[jaggedben]

Doing a larger Residential job in Vegas. The resident currently has a 400A MSP w/ 2, 200A Disconnects (going to their own 200A Panelboards).

We're going to upgrade their MSP, but we're not sure what we're going to upgrade it to. My hopes, are that we can get a 400A Solar Ready MSP so that we aren't placing our 150A PV on the load side. We could go for a 600A MSP, but we'd need to find a smaller Main Disconnect to fit our PV on the load side (per 120%).

Any thoughts?

If you're on the 2014 code, or can talk your AHJ into following its provisions, I'd suggest the following under 705.12(2)(1)(b)...

Find a way to insert a 200A fused disconnect (or circuit breaker enclosure) into one of those 200A feeders, along with a tap box between the main service and the new disconnect. From the tap box also feed a 150A fused disconnect (or circuit breaker enclosure) for the solar.

This gives you a feeder tap that's got appropriate overcurrent protection on all sides and doesn't involve any busbars that have to be subject to the 120% rule.

 

[Smart $]

If you're on the 2014 code, or can talk your AHJ into following its provisions, I'd suggest the following under 705.12(2)(1)(b)...

Find a way to insert a 200A fused disconnect (or circuit breaker enclosure) into one of those 200A feeders, along with a tap box between the main service and the new disconnect. From the tap box also feed a 150A fused disconnect (or circuit breaker enclosure) for the solar.

This gives you a feeder tap that's got appropriate overcurrent protection on all sides and doesn't involve any busbars that have to be subject to the 120% rule.

Aye... but the tap (PV) must comply with 705.12(D)(2)(2) so tap ampacity must be 125% of inverter output rating plus the OCPD rating protecting the feeder... hmy:

What shall we call that? The 225% rule. :lol:

 

[Carultch]

Aye... but the tap (PV) must comply with 705.12(D)(2)(2) so tap ampacity must be 125% of inverter output rating plus the OCPD rating protecting the feeder... hmy:

What shall we call that? The 225% rule. :lol:

The reason you are thinking of "225%", is due to the fact that the PV system is treated as a continuous load, and the existing feeder loads are not necessarily continuous. In any case, it is the value driving the OCPD that matters. 1.25*continuous, or the mix of 1.25*continuous + 1*noncontinuous.

It works more like a 200% rule, the way we are familiar with the calculation that corresponds to the famous "120% rule". Breaker for source #1 plus breaker for source #2, cannot exceed 200% of the feeder's ampacity. Not really that this is a practical case to worry about, because most people would intuitively not believe the breaker on either side, could exceed a feeder's ampacity.

But more simply, it is best stated that the wire must be protected from both sources at its ampacity per standard Article 240 rules that apply to overcurrent protection. The wire can be fed in either direction, up to its ampacity with the appropriate safety factor that applies based on continuous/non-continuous load. Because the current from the line-side source, and the interconnected source, will never ADD UP, the wire will not become overloaded if it is protected from overload at or below its ampacity, from the direction of both sources.

 

[don_resqcapt19]

If you are installing a new panel, you can use a MLO panel with 400 amp bus and 3 breakers. That makes the solar connection a line side connection and you could install two 200 amp breakers for the loads and up to a 400 amp breaker for the solar connection.

 

[Smart $]

The reason you are thinking of "225%", is due to the fact that the PV system is treated as a continuous load, and the existing feeder loads are not necessarily continuous. In any case, it is the value driving the OCPD that matters. 1.25*continuous, or the mix of 1.25*continuous + 1*noncontinuous.

It works more like a 200% rule, the way we are familiar with the calculation that corresponds to the famous "120% rule". Breaker for source #1 plus breaker for source #2, cannot exceed 200% of the feeder's ampacity. Not really that this is a practical case to worry about, because most people would intuitively not believe the breaker on either side, could exceed a feeder's ampacity.

But more simply, it is best stated that the wire must be protected from both sources at its ampacity per standard Article 240 rules that apply to overcurrent protection. The wire can be fed in either direction, up to its ampacity with the appropriate safety factor that applies based on continuous/non-continuous load. Because the current from the line-side source, and the interconnected source, will never ADD UP, the wire will not become overloaded if it is protected from overload at or below its ampacity, from the direction of both sources.

I think you better take a step back and read it as if for the first time ever...


Nowhere does it say the sum of 125% IOCC and feeder OCPD shall be not more than 200% feeder ampacity. It plainly says size shall be based on the sum of 125% IOCC and feeder OCPD... period.

 

[Carultch]

I think you better take a step back and read it as if for the first time ever...


Nowhere does it say the sum of 125% IOCC and feeder OCPD shall be not more than 200% feeder ampacity. It plainly says size shall be based on the sum of 125% IOCC and feeder OCPD... period.

I never intended to imply that. I was mainly saying that if you are trying to force the rule for tapping onto feeders to be written in the same language as it is for a connection onto a busbar, you end up with a 200% rule instead of a 120% rule. This of course makes it more complicated in a way no one would ever want to think about it.

The bottom line is that feeders need to be protected from sources at both sides at or below their ampacity, per standard OCPD practices from Article 240. You can feed a 100A feeder from a 100A breaker on the utility side. You can feed a 100A feeder from a 100A breaker on the solar side. Or you can do (up to) both at the same time.

 

[ggunn]

If you're on the 2014 code, or can talk your AHJ into following its provisions, I'd suggest the following under 705.12(2)(1)(b)...

Find a way to insert a 200A fused disconnect (or circuit breaker enclosure) into one of those 200A feeders, along with a tap box between the main service and the new disconnect. From the tap box also feed a 150A fused disconnect (or circuit breaker enclosure) for the solar.

This gives you a feeder tap that's got appropriate overcurrent protection on all sides and doesn't involve any busbars that have to be subject to the 120% rule.

I didn't see where the main is MLO, or possibly I am misunderstanding what you are proposing. If the main is 400A and has a 400A main breaker, then you are still limited to 80A from PV anywhere on the load side of the main, including a tap on a feeder from the main.

 

[SolarPro]

If you are installing a new panel, you can use a MLO panel with 400 amp bus and 3 breakers. That makes the solar connection a line side connection and you could install two 200 amp breakers for the loads and up to a 400 amp breaker for the solar connection.

Exactly. Just eliminate the load side connection altogether.

 

[Smart $]

I never intended to imply that. I was mainly saying that if you are trying to force the rule for tapping onto feeders to be written in the same language as it is for a connection onto a busbar, you end up with a 200% rule instead of a 120% rule. This of course makes it more complicated in a way no one would ever want to think about it.

The bottom line is that feeders need to be protected from sources at both sides at or below their ampacity, per standard OCPD practices from Article 240. You can feed a 100A feeder from a 100A breaker on the utility side. You can feed a 100A feeder from a 100A breaker on the solar side. Or you can do (up to) both at the same time.

I still think we're not on the same page.

Let's say we have a supply-side feeder OCPD of 200A and a load-side OCPD of 200A, and a PV (at 160A IOCC; 200A OCPD) tied in mid-run of feeder. Which "leg" or "legs" of this circuit is the feeder, and which are taps? What is the minimum required ampacity of each "leg" (there are three)?

 

[Garbluck]

If you are installing a new panel, you can use a MLO panel with 400 amp bus and 3 breakers. That makes the solar connection a line side connection and you could install two 200 amp breakers for the loads and up to a 400 amp breaker for the solar connection.

The municipalities in the area will just calculate the 120% rule into that (400A x 1.2 = 480A / 80A PV Available).
The municipalities also do not allow Line side taps.

It appears my options are to somehow find a 400A Solar ready, or to have a 600A MLO (or protected by a 400A Disconnect).

 

[ggunn]

The municipalities in the area will just calculate the 120% rule into that (400A x 1.2 = 480A / 80A PV Available).
The municipalities also do not allow Line side taps.

It appears my options are to somehow find a 400A Solar ready, or to have a 600A MLO (or protected by a 400A Disconnect).

I don't see how a 400A "solar ready" helps you. Either the solar is load side (limited to 80A) or line side (disallowed by your AHJ). That is, unless "solar ready" means the bus is rated enough higher than the main breaker to fit the solar in on the load side and under 120% of the bus rating.

 

[jaggedben]

Aye... but the tap (PV) must comply with 705.12(D)(2)(2) so tap ampacity must be 125% of inverter output rating plus the OCPD rating protecting the feeder... hmy:

What shall we call that? The 225% rule. :lol:

Thanks for reminding me that I intend to submit a revision to that wording. I think what they intended was for taps be sized according to 240.21(B) where the rating of overcurrent device ahead of the tap is the sum of both sources.

If you are installing a new panel, you can use a MLO panel with 400 amp bus and 3 breakers. That makes the solar connection a line side connection and you could install two 200 amp breakers for the loads and up to a 400 amp breaker for the solar connection.

Can you point to an actual product that fits this description? That was the OP's question, essentially. FWIW, I googled for 20 minutes and could find no such thing.

I didn't see where the main is MLO, or possibly I am misunderstanding what you are proposing. If the main is 400A and has a 400A main breaker, then you are still limited to 80A from PV anywhere on the load side of the main, including a tap on a feeder from the main.

He described the service as having two 200A service disconnects, which fits every 400A residential service I've ever seen (admittedly only a handful). And in the 2014 code the 120% rule only applies to busbars in panelboards, and not to conductors or feeder taps. If you are misunderstanding you should review the changes to the 2014 code.

The municipalities in the area will just calculate the 120% rule into that (400A x 1.2 = 480A / 80A PV Available).
The municipalities also do not allow Line side taps.

It appears my options are to somehow find a 400A Solar ready, or to have a 600A MLO (or protected by a 400A Disconnect).

If the municipalities accept a 'Solar Ready' panel but not a 400A MLO, that's highly illogical and not according to Code. If they apply the 120% rule to an MLO panel, a 600A panel still isn't enough for you. Seems to me it's worth quite a lot of money to kindly, patiently explain what the code actually says.

 

[Zee]

It's possible the OP meant that the AHJ does not allow line side TAPS (taps meaning here stripping or piercing insulation on service conductors for split-bolts etc, or some double lugging, if you are lucky, on Main lug terminals....) ?
the prohibition being on the physical method of connection less than the point of connection (supply side or load side).

...but maybe a line side (supply side) connection in the form of a PV breaker on a MLO only panel is permissible?
As many have suggested here?
Though on re-reading his last post he says they would still apply the 120% to that! I guess i do not want to believe it!

(SOLAR READY PANELS:
Essentially that is what the "solar ready" panels I have seen specs on do: they have a pre-mounted supply side aka main breaker spot for up to a 2p60 A pv breaker)

 

[don_resqcapt19]

The municipalities in the area will just calculate the 120% rule into that (400A x 1.2 = 480A / 80A PV Available).
The municipalities also do not allow Line side taps.

It appears my options are to somehow find a 400A Solar ready, or to have a 600A MLO (or protected by a 400A Disconnect).

Assuming that they have written rules that amend the NEC they can do that. If not, then they have to apply the rules as written in the NEC.