A 705.12 question: Load side connection to the MSP without PV breaker?

[fandi]

Hello All,
If a PV inverter connects to the load side of a main service panel (MSP) without a PV breaker at the MSP (basically it's a tap at the MSP), is it a violation of which of the following code sections:
- 705.12(B)(1) Dedicated Overcurrent and Disconnect.
- 705.20 Disconnecting Means, Sources.
- 705.21 Disconnecting Means, Equipment.
- 705.22 Disconnect Device.
- 705.23 Interactive System Disconnecting Means.
- 705.30 Overcurrent Protection.
Note: There's a separate fusible disconnect switch between the PV inverter and the MSP.
Thank you.

 

[wwhitney]

Information is limited, but there are compliant configurations that match all the specifications provided. So I'll say "None of the above."

Cheers, Wayne

 

[fandi]

Information is limited, but there are compliant configurations that match all the specifications provided. So I'll say "None of the above."

Cheers, Wayne

Sorry I wasn't clearer. Please see the diagram. The question is not about which option of 705.12(B)(2)(3) Busbars to be used (from a through e according to NEC 2017). It's about: For a LOAD side connection, is it OK to tap directly to the MSP without a PV breaker at the MSP?

 

[jaggedben]

That's absolutely fine. The fusible disconnect satisfies all those code sections you cited.

 

[wwhitney]

For a LOAD side connection, is it OK to tap directly to the MSP without a PV breaker at the MSP?

Sure, no problem. The conductors between the 400A service disconnect and the 40A fused disconnect just need to be of sufficient size and length to be properly protected per Article 240.

Cheers, Wayne

 

[jaggedben]

Although I'm assuming you are talking about tapping wires. Tapping directly to MSP busbars could be a violation of 110.3B, depending on details.

 

[fandi]

Although I'm assuming you are talking about tapping wires. Tapping directly to MSP busbars could be a violation of 110.3B, depending on details.

Exactly. If the MSP does not have a provision allowing to tap directly to the bus then it's a violation to 110.3B

 

[fandi]

On a side note, 705.12(B)(2)(3)(c) is used in this case as a compliant method. The total load breakers at the MSP (excluding the main 400A breaker) is 390A plus max 40A coming from the PV inverter > the MSP bus rating of 400A. But because there's no PV breaker at the MSP, now the equation is just 390A < 400A even though there's max 40A current from the PV inverter. Any potential violation to 705.12(B)(2)(3)(c)?

 

[wwhitney]

On a side note, 705.12(B)(2)(3)(c) is used in this case as a compliant method. The total load breakers at the MSP (excluding the main 400A breaker) is 390A plus max 40A coming from the PV inverter > the MSP bus rating of 400A. But because there's no PV breaker at the MSP, now the equation is just 390A < 400A even though there's max 40A current from the PV inverter. Any potential violation to 705.12(B)(2)(3)(c)?

The 2017 NEC 705.12(B)(2)(3) doesn't properly address bus connections without OCPD. Really the bus connection should be treated as 40A (or rather, 125% of the inverter output current) regardless of whether the OCPD is directly on the bus or downstream. The 2020 NEC, which will be in effect in CA starting January 1, tries to clear this up but kind of bungled the language. The 2023 NEC has somewhat better language.

So if you figure out how to tap the bus compliantly, you could use the 120% rule, 705.12(B)(2)(3)(b) by putting the tap at the end of the bus. Or is one of the existing breakers at either end of the bus supplying a feeder you can tap under 705.12(B)(2)(1)? Then the busbar would be fine, also under 705.12(B)(2)(3)(b).

Cheers, Wayne

 

[fandi]

The 2017 NEC 705.12(B)(2)(3) doesn't properly address bus connections without OCPD. Really the bus connection should be treated as 40A (or rather, 125% of the inverter output current) regardless of whether the OCPD is directly on the bus or downstream. The 2020 NEC, which will be in effect in CA starting January 1, tries to clear this up but kind of bungled the language. The 2023 NEC has somewhat better language.

So if you figure out how to tap the bus compliantly, you could use the 120% rule, 705.12(B)(2)(3)(b) by putting the tap at the end of the bus. Or is one of the existing breakers at either end of the bus supplying a feeder you can tap under 705.12(B)(2)(1)? Then the busbar would be fine, also under 705.12(B)(2)(3)(b).

Cheers, Wayne

It's 2017 NEC at the moment for me. I agree with you that the connection is a 40A or 125% inverter output current. It's not my design so I can't move things around.

 

[Phil Timmons]

WHY would they do this? Trying to stay under the 120% limit?

For example -- would take 200 Amp Main + 50 Amp Solar PV Breaker? But you are showing a 400 Amp Main (inferring a 400 Amp Bus) . . . so this is not likely.

or out of space in the existing panel?

Otherwise a 40 or 50 Amp C/B is a pretty easy / cheap connection point. Is this just a 240/120 V, single phase? $20, or so, right?

But even it is an I-Line 480V, three phase (that is the most expensive, right?) . . . it is easier than trying to do home-made taps.

Yunno they make Main C/B panels with factory lugs on the bottom IF you really really wanted to this.

 

[fandi]

WHY would they do this? Trying to stay under the 120% limit?

For example -- would take 200 Amp Main + 50 Amp Solar PV Breaker? But you are showing a 400 Amp Main (inferring a 400 Amp Bus) . . . so this is not likely.

or out of space in the existing panel?

Otherwise a 40 or 50 Amp C/B is a pretty easy / cheap connection point. Is this just a 240/120 V, single phase? $20, or so, right?

But even it is an I-Line 480V, three phase (that is the most expensive, right?) . . . it is easier than trying to do home-made taps.

Yunno they make Main C/B panels with factory lugs on the bottom IF you really really wanted to this.

Like mentioned in the single line diagram, It's a 400A bussed 240/120V single phase 3 wire service panel.
I think their intent of not installing a PV breaker at the MSP is to use 705.12(B)(2)(3)(c) as a compliant method (total breakers excluding the main is 390A < MSP bus rating of 400A). This is to take advantage of the 2107 NEC not addressing PV connection without a PV breaker.

 

[Phil Timmons]

Is there space in the panel for a 50 amp, 2 pole? $20, Home Depot. ;P Easy Win.

There is no "advantage" in this. ;P Were there submitted and reviewed plans by the city? If not, you can comply by any method.

If there were plans submitted and approved with a bus tap, I would tell the AHJ that the feeder is better protected with the breaker, and expect them to smile and nod, and get the project Green-Tagged.

You follow that section of the code is a Logical OR? You can comply by any of the listed methods.

 

[wwhitney]

I think their intent of not installing a PV breaker at the MSP is to use 705.12(B)(2)(3)(c) as a compliant method (total breakers excluding the main is 390A < MSP bus rating of 400A). This is to take advantage of the 2107 NEC not addressing PV connection without a PV breaker.

While not against the letter of the 2017 rules, I'd say it's clearly against the spirit. Is there some reason the PV connection can't be made at either end of the bus? If that's done, all will be well with the 120% rule, whether the connection is a bus tap or another breaker.

Cheers, Wayne

 

[fandi]

Is there space in the panel for a 50 amp, 2 pole? $20, Home Depot. ;P Easy Win.

There is no "advantage" in this. ;P Were there submitted and reviewed plans by the city? If not, you can comply by any method.

If there were plans submitted and approved with a bus tap, I would tell the AHJ that the feeder is better protected with the breaker, and expect them to smile and nod, and get the project Green-Tagged.

You follow that section of the code is a Logical OR? You can comply by any of the listed methods.

This is a peer review and I did tell the engineer to provide a PV breaker but he said there's nothing wrong with his design under 2017 NEC. So either I come up with a code section to show a violation or I should shut up.

 

[fandi]

While not against the letter of the 2017 rules, I'd say it's clearly against the spirit. Is there some reason the PV connection can't be made at either end of the bus? If that's done, all will be well with the 120% rule, whether the connection is a bus tap or another breaker.

Cheers, Wayne

I think at the MSP, they run out of a slot for a PV breaker.

 

[wwhitney]

In your situation I might try:

"Based on fundamental engineering principles, it is implicit in applying 2017 NEC 705.12(B)(2)(3)(c) that the bus tap be counted at the size of the downstream OCPD. Relocating the OCPD from the bus to the downstream disconnect makes no change in the bus loading."

Cheers, Wayne

 

[wwhitney]

I think at the MSP, they run out of a slot for a PV breaker.

How are they tapping the bus, and can that be done at the end of the bus? The breaker vs tap is not really an issue. And as I commented earlier, they could tap the feeder supplied by one of the breakers at one end of the bus.

But the above is about how to improve the design, not about establishing that the current design is insufficient.

Cheers, Wayne

 

[Phil Timmons]

This is a peer review and I did tell the engineer to provide a PV breaker but he said there's nothing wrong with his design under 2017 NEC. So either I come up with a code section to show a violation or I should shut up.

So the bus has factory taps at the bottom? We sometimes order that way, but I think it is a request item?

Or does this guy think you are supposed to add them along with the 133 Amp Wire? (25 foot Tap Rule?)

I suppose if you wanted to mess with him, suggest 500 MCM (the panel feeder wires, right?) Vampire Taps on the incoming lines. ;P

 

[fandi]

So the bus has factory taps at the bottom? We sometimes order that way, but I think it is a request item?

Or does this guy think you are supposed to add them along with the 133 Amp Wire? (25 foot Tap Rule?)

I suppose if you wanted to mess with him, suggest 500 MCM (the panel feeder wires, right?) Vampire Taps on the incoming lines. ;P

LOL.