Line-Side Tap on Residence

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Hi,

This question concerns the interconnection of a PV system.

I would like to do a line-side tap on a home in the SF Bay Area (PG&E territory). The main panel is a bit weird. Basically, it's an MLO-type panel w/ only one circuit breaker in it (and only has room for one circuit breaker). That breaker protects a subpanel circuit. The customer does not want to interconnect in the subpanel because it's in the garage. Makes things a little difficult.

Essentially, I just want to know the appropriate way to do this to Code. As a designer/PM, I've figured out many different interconnection strategies, but this is new territory for me. For example, I believe the connection has to be protected by a fused disconnect (but I suppose a circuit breaker would be fine, too). What are the rules and confinements concerning this approach?

Thanks!

Andy
 
Hi,

This question concerns the interconnection of a PV system.

I would like to do a line-side tap on a home in the SF Bay Area (PG&E territory). The main panel is a bit weird. Basically, it's an MLO-type panel w/ only one circuit breaker in it (and only has room for one circuit breaker). That breaker protects a subpanel circuit. The customer does not want to interconnect in the subpanel because it's in the garage. Makes things a little difficult.

Essentially, I just want to know the appropriate way to do this to Code. As a designer/PM, I've figured out many different interconnection strategies, but this is new territory for me. For example, I believe the connection has to be protected by a fused disconnect (but I suppose a circuit breaker would be fine, too). What are the rules and confinements concerning this approach?

Thanks!

Andy

What is the wiring method between the meter and this circuit breaker enclosure? Often I will put a box or wireway between the meter and the service disconnect and make the splice there. Sometimes you could make the tap in the service disconnect enclosure with split bolts or other lay in type connector. Yet another option is to replace the meter socket with a class 320 that has dual lugs (usually more expensive than the other options, but it has its place in some situations).
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Hi,

This question concerns the interconnection of a PV system.

I would like to do a line-side tap on a home in the SF Bay Area (PG&E territory). The main panel is a bit weird. Basically, it's an MLO-type panel w/ only one circuit breaker in it (and only has room for one circuit breaker). That breaker protects a subpanel circuit. The customer does not want to interconnect in the subpanel because it's in the garage. Makes things a little difficult.

Essentially, I just want to know the appropriate way to do this to Code. As a designer/PM, I've figured out many different interconnection strategies, but this is new territory for me. For example, I believe the connection has to be protected by a fused disconnect (but I suppose a circuit breaker would be fine, too). What are the rules and confinements concerning this approach?

Thanks!

Andy

A lot depends on your AHJ; many of them have some specific ideas of how a line side interconnection should be made. Some will let you connect to the service conductors via insulation piercing connectors inside the panel and some will not. Of those who do, some will require that there be a main breaker in the main distribution panel and some will not. Some will consider the connection to be a separate service and have you connect neutral to ground in a fused disco with a ground rod and no EGC running from the PV AC disco back to the service. It goes on.

Interpretations of code differ; I suggest having a preconstruction meeting with your AHJ to get from them what they expect to see rather than trying what you think will work and then maybe failing your inspection.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
Hi,

This question concerns the interconnection of a PV system.

I would like to do a line-side tap on a home in the SF Bay Area (PG&E territory). The main panel is a bit weird. Basically, it's an MLO-type panel w/ only one circuit breaker in it (and only has room for one circuit breaker). That breaker protects a subpanel circuit. The customer does not want to interconnect in the subpanel because it's in the garage. Makes things a little difficult.

Essentially, I just want to know the appropriate way to do this to Code. As a designer/PM, I've figured out many different interconnection strategies, but this is new territory for me. For example, I believe the connection has to be protected by a fused disconnect (but I suppose a circuit breaker would be fine, too). What are the rules and confinements concerning this approach?

Thanks!

Andy

Your post is lacking on details, particularly whether you have a meter/main combo or field wiring between meter and main. If a meter main, what I often do is install a subpanel next to the main, and divert the existing sub feed through it. The new sub gets a solar breaker and a breaker for.the existing sub feed.
 

PWDickerson

Senior Member
Location
Clinton, WA
Occupation
Solar Contractor
It would be nice to have a more detailed description of the electrical components involved. It sounds like you have a meter base whose load side conductors feed a circuit breaker enclosure with the service disconnect in it, which then feeds a sub-panel in the garage. A circuit breaker enclosure is different from a MLO panel. The former does not have any bussing, and the latter does. This is an important distinction.

If it is in fact a circuit breaker enclosure with no bussing, than you should be able to do a load side connection by tapping the feeder conductors in the circuit breaker enclosure. If the garage sub-panel has a main breaker in it, then you can make the tap without having to upsize the feeder conductors. You are not limited by the 120% rule with this arrangement. Your backfeed capacity can be as large as the service. I am not sure what code cycle you are on, but the relevant code article in the 2017 code is 702.12(B)(2)(1)(a&b).

Also 705.12(B)(2)(2) modifies the calculation in the tap rules in 240.21(B). You will have to take into account the inverter current when determining the minimum ampacity of the tap conductors. I have seen this mis-applied several times, so here is an example. If you have a 200 amp feeder circuit to a 200 amp sub-panel, which has a 200 amp main breaker installed in it, and your tap conductors are 10' or less in lenght, and your PV inverter has a max output current of 32 amps, then your minimum tap conductor ampacity calculation looks like this:

200A + (32*1.25) = 240
240 * .1 = 24A

I am make a lot of assumptions here. Depending on your situation, this may all be irrelevant.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
...

Also 705.12(B)(2)(2) modifies the calculation in the tap rules in 240.21(B). You will have to take into account the inverter current when determining the minimum ampacity of the tap conductors. I have seen this mis-applied several times, so here is an example. If you have a 200 amp feeder circuit to a 200 amp sub-panel, which has a 200 amp main breaker installed in it, and your tap conductors are 10' or less in lenght, and your PV inverter has a max output current of 32 amps, then your minimum tap conductor ampacity calculation looks like this:

200A + (32*1.25) = 240
240 * .1 = 24A
...

Note that since the inverter output requirement is bigger in your example, the conductors would need to be sized for 40A.

I'm glad you agree that's how it should be applied. The actual language of the section is terribly worded. I submitted and input to have it fixed in the 2017 code but the CMP evidently didn't think it important enough to act on.
 

PWDickerson

Senior Member
Location
Clinton, WA
Occupation
Solar Contractor
Note that since the inverter output requirement is bigger in your example, the conductors would need to be sized for 40A.

I'm glad you agree that's how it should be applied. The actual language of the section is terribly worded. I submitted and input to have it fixed in the 2017 code but the CMP evidently didn't think it important enough to act on.

That's right. In the example, the inverter output x 1.25 determines the conductor size. If the tap conductors are between 10' and 25', then you would multiply by 1/3, and the ampacity of the tap conductors would be determined by the tap rules.

To say that the code section is poorly written is an understatement. I am pretty good at interpreting complicated code articles, but the only reason I understand how to apply it is because I took a class from one of the people who wrote the article. Thanks for your effort to simplify the language.
 
Hi, thank you for all of the responses. My contact did not mean to say "line side tap". He actually meant a "feeder tap", as PWDickerson wisely discerned. I have always shied away from feeder taps because the NEC language was so confusing. However, it's time to confront this head-on and finally learn the rules.

This is what I am understanding from the above conversation about feeder taps:

(In my case, the single breaker in the main panel is 200A, and feeds the subpanel in the garage [is it possible to post a picture of it here?]. The subpanel does not have a main breaker in it. Also, you were correct in guessing that my inverter output current was 32 amps. This connection will be made outside of the panel. NEC 2014.)

1. First, take the inverter output current and multiply it by 1.25 for continuous duty (32A x 1.25 = 40A)

2. Add this value to the value of the OCPD protecting the circuit (40A + 200A = 240A).

3. If the feeder tap is less than 10-ft., multiply the above value by 10%. If the tap is greater than 10-ft but less than 25-ft, multiply by 33%. (10-ft in this case.... 0.10 x 240A = 24A)

4. Size the wire according to the greater of..... A.) the inverter output circuit w/ the continuous duty factor, or B.) 10% of the inverter output current w/ continuous duty factor + OCPD

5. In this case, 24A < 40A, so we would size the wire to accommodate 40A of current.

Does this sound correct?

Also, the electrician proposed we do this using Polaris connectors (IPLD 3/0-3). This would be my first time working with Polaris connectors, too.

Andy
 

Zee

Senior Member
Location
CA
First, check if your CITY (not PG&E) even allows load side, AKA feeder, taps!
You may have it all figured out to NEC, but I know of several major cities in the Bay that do not allow them.

Second, PG&E offers a meter product just for this purpose. "Green Meter Adapter". AKA Renewable Meter Adapter in other areas.
Maybe a bit $$$.
https://www.pge.com/includes/docs/p...reenbook/servicerequirements/TD-7001B-007.pdf

Third, A new sub-panel is always a great idea, as mentioned above.
Added benefit of giving the customer more breaker space for future use in a new and often, more accessible location.

Note: this new s.p. installation work may trigger a separate electrical permit requirement in addition to the solar, not a big deal usually
Note: still stuck on how it can be "MLO" with "only one circuit breaker". Isn't that the definition of Main Breaker Only (MBO)?
Note: Photo :thumbsup::thumbsup: much appreciated when asking for sound advice!
Note: Interconnection in garage makes things more difficult? I cannot imagine how. Sounds ideal.
 

PWDickerson

Senior Member
Location
Clinton, WA
Occupation
Solar Contractor
Having no main breaker in the garage sub-panel complicates things a little when doing a feeder tap. You have to follow 705.12(B)(2)(1)(a), which usually requires upsizing the feeder conductors, and nobody wants to do that. To get around this you can land the feeder conductors in the sub-panel on a breaker with a tie-down kit, instead of the main lugs. That will allow you to qualify under 705.12(B)(2)(1)(b), which doesn't require upsizing the feeder conductors.

I was not aware that some municipalities do not allow feeder taps. It would be a drag to find that out after the install was done.
 
This is a photo of the main panel: https://ibb.co/iNsCbS

What kind of panel is this? I'm not sure if you would call this a main breaker type panel? It just looks a lot different than what I am used to seeing.

I would ultimately just like to relocate this breaker to a new subpanel right next to the main panel, and then put the PV breaker in the new subpanel, too. The feeder tap was just sort of a last resort.

Andy
 
What kind of panel is this? I'm not sure if you would call this a main breaker type panel? It just looks a lot different than what I am used to seeing.

Andy

I have wondered that myself. I call them circuit breaker enclosures. Its just a circuit breaker and an enclosure. I am not sure what the NEC considers them. Maybe they are still panelboards but I'm not sure. Anyone know?
 
Yeah I have used things like that, mostly as a service disconnect where the main panel cant be "nearest the point of entry". Sometimes I use a safety switch but sometimes a circuit breaker and enclosure - or whatever the technical name is.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
This is a photo of the main panel: https://ibb.co/iNsCbS

What kind of panel is this? I'm not sure if you would call this a main breaker type panel? It just looks a lot different than what I am used to seeing.

I would ultimately just like to relocate this breaker to a new subpanel right next to the main panel, and then put the PV breaker in the new subpanel, too. The feeder tap was just sort of a last resort.

Andy
It's not a panel at all; it's an enclosed breaker used as a main service disconnect. Panel bus rules do not apply.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
This is a photo of the main panel: https://ibb.co/iNsCbS

What kind of panel is this? I'm not sure if you would call this a main breaker type panel? It just looks a lot different than what I am used to seeing.

I would ultimately just like to relocate this breaker to a new subpanel right next to the main panel, and then put the PV breaker in the new subpanel, too. The feeder tap was just sort of a last resort.

Andy

You should see if it's possible to put a main breaker in the subpanel that that breaker is feeding. If so, a load side tap will probably be a lot easier. I've done the new subpanel thing a lot with 100A feeders. With 200A, the equipment is more expensive, there's fewer options, more space required, and much more difficult to handle 200A wiring. Looking at your photos and trying to imagine how you're going to get two 200A feeds in and out of that enclosure makes me wince.
 
You should see if it's possible to put a main breaker in the subpanel that that breaker is feeding. If so, a load side tap will probably be a lot easier. I've done the new subpanel thing a lot with 100A feeders. With 200A, the equipment is more expensive, there's fewer options, more space required, and much more difficult to handle 200A wiring. Looking at your photos and trying to imagine how you're going to get two 200A feeds in and out of that enclosure makes me wince.

After reviewing it with others, we decided to de-rate the "main breaker" in the circuit breaker enclosure down to 150A. This would allow us to keep the existing 4/0 aluminum conductors. From my understanding of the Code, the conductors on the load side of the inverter output connection have to be able to handle an ampacity equal to the value of the primary source overcurrent device plus 125% of the inverter output circuit. In this case, it would be 150A + (21A x 1.25) = 176.25A. 4/0 aluminum conductors have an ampacity of 180A.

As far as the 10-ft tap rule, the tap conductors would have a minimum circuit ampacity of:
0.1 x [150A + (21 x 1.25)] = 17.625 amps

However, 125% of my inverter output current is greater than that (26.25A), so I would size the conductors to the higher ampacity.

New questions:

1.) Do the tap conductors HAVE to be protected by a fused AC disconnect, or is okay if I use a circuit breaker?

2.) Can I do a feeder tap in any old NEMA-rated electrical enclosure?

Andy
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
That's a good way to do it.

You can use a circuit breaker instead of a fused disco. But the only reason I can think of for doing so is if you have a combined panel for your solar, and you want to save a piece of equipment.

And yes, you can use any electrical enclosure that has a NEMA rating appropriate to the location. There are also some size requirements based on the wire size and such.
 
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