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Thread: Solar PV Line Side Tap - Assistance desired

  1. #1
    Join Date
    Jun 2009
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    2

    Solar PV Line Side Tap - Assistance desired

    I'm installing a 12kw ( 56 Kyocera 210w and 2x SB7000US Inverters) system and want to make sure I connect my line side tap properly. I have a Square D 200A side by side combo meter and service main panel that is heavily utilized with underground utility feed.

    The 56 Kyocera's are in 4 strings of 14 each with 2 per SB7000 Inverter. They are connected on the AC side to a Square D 100A 6/12 current combining panels with 2 40A breakers from the inverters and an 80A breaker to a Square D AC disconnect with RK5 fuses toward the main panel line tap. The fuses then are to be tied into my Square D main panel at either the meter socket or at the two legs service side pairs of cables to the 200A service disconnect switch on service side through 4 grommets.

    The Squared D main panel has spare wire holes and set screws on each leg perfect and probably for a solar tap. Why else have 3 set screws per leg when only 2 are needed and 1 on each side unused. They are hot and to safely connect to them, I would need to remove the meter of course. That is ideal and very clean. The tap is identical to how the main disconnects are wired. Is it ok? Does it impact the UL rating? How could any change not impact UL? Anywhere, meter or cables to the disconnect? How would I find out? Would Square D actually tell me?

    Ok that is downright ideal! Spare set screws on the meter lugs identical to the ones used to feed my main breaker. It couldn't be done cleaner. Push in the wires and tighten the screws and the two hot 80A taps are done. Then there is the neutral and ground.

    The main panel is a top or bottom utility service so there is a spare ground and neutral lug also above the meter. Its not accessible without removing the meter but its perfect except very large. There are also screws that holds the ground bar going across to the service side which I could change to stainless and add a lock washer and lug with set screw also. Not as ideal but easily accessible and bullet proof and 1 inch from the ground point.

    I've read all Wiles papers and there is no formula except changing to a 400A panel (yuck) or finding higher rated buses for the Square D so it becomes capable of the extra 80A. Yuck.

    How are line side taps actually done when the panel supplier is UL rated and anything would void that! There are so many main panel models that it would be virtually impossible to verify every one's UL rating is ok with a change anywhere on the line side. How are line side taps done as a practical matter and is my using the spare set screws on the 2 hot legs and either using the existing lug and set screw upgraded plus a lug with set screw for the neutral and ground. The hot line tap wires are #4 AWG THWN-2 and the neutral/ground are #6 AWG THN-2 according to my solar suppliers calcs.

    My concern is not electrical integrity but how even touching the line side on any panel impacts UL and how the building department and NEC and PG&E would see that. I designed Telecom systems and we couldn't touch any OEM UL or agency approved electronics in any way or the UL testing was voided.

    How does he real world work?

    Just remove the meter, intall the taps and se what happens when the inspector looks at it? I know its electrically bulletproof since I'm using the exact hardware and not adding any current to any bus bar.

    Any comments appreciated!

  2. #2
    Join Date
    Jun 2009
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    4
    I am having a similar issue concerning the possibility of a line side tap. The Service entrance setup consists of a 400A Cutler Hammer Panel with (2) 200A mains, one of which feeds a 200A sub panel directly adjacent to the main panel.

    Currently there are two inverters that are set up where one back feeds the sub panel through a 35A breaker, complete with its one Utility Disconnect and Dedicated meter. The second inverter feeds into the main panel through a 30A breaker, again this feed has its own meter and switch.

    The utility and municipality both approved this setup on paper, where it was clearly draw in the manner it was installed. Now that it is time for it to be commissioned the inspector says we can not have two Utility disconnects/Dedicated meters.

    Leaving us with the option of combining the circuits and de-rating one of the 200A breakers (difficult due to the amount overcurrent devices inplace) OR a line side tap.

    As stated in the first post any suggestions on line-side taps and the effects on UL or safety would be appreciated.

    Thanks

  3. #3
    These are very interesting questions and pertinent to many Electricians currently looking into PV installations. It would be nice if someone knowledgeable from Mike Holt's staff could weigh in with a respectable answer.

    Many of us would appreciate it....

  4. #4
    Join Date
    Aug 2009
    Posts
    12

    My understanding...

    It is my understanding that when you have a 200 amp main and a 200 amp sub panel and split the breakers from each inverter across the two panels you are definitely still feeding the main busbar the combination of available current from your inverters.

    A supply side tap is definitely the preferred answer in both scenarios, and in our neck of the woods readily approved by pretty well-informed inspectors.

    I would think that with a 400 amp main calculating the load on the subpanel and downsizing the breaker for that panel would free up enough space for your pv array, a question I would ask is are you using a subpanel to combine the pv energy? there is a neat way to downsize the breaker rating in the main by using a subpanel to combine the output of your two pv inverters.

    Also, in my understanding the current to your subpanel is load and does not enter into your calculation of supply into the busbar, you should be able to correctly install up to 80 amps of pv current into the main panel, regardless of the sub.

    Could be wrong, hope I was helpful a bit.

    Brian

  5. #5
    Join Date
    Feb 2007
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    USA
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    It matters only what the buss rating is. I doubt the bus of a resi 400 amp panel is rated at more than 2 x 200 amps. That is unless you have one with a 400 amp main.

  6. #6
    Join Date
    Aug 2009
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    12

    Cutlerhammer

    I believe this is most likely the load center you have if it is a CH and this has a 400 amp bussbar, therefore all of your supplied current can max at 120% of the rating, or 80 amps.

    http://www.eescodirect.com/direct/Pr...roductId=60370

  7. #7
    If anyone has any info on the line side tap that would be great.

    I've got a similar install coming up out of town and haven't been able to get enough info to know whether it will be able to fit a breaker(s) with the 120% rule, downsize the main breaker, or do a line side tap (which I've never done).

  8. #8
    Join Date
    Feb 2007
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    USA
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    Quote Originally Posted by newenergy View Post
    If anyone has any info on the line side tap that would be great.

    I've got a similar install coming up out of town and haven't been able to get enough info to know whether it will be able to fit a breaker(s) with the 120% rule, downsize the main breaker, or do a line side tap (which I've never done).
    You need to be able to tap the wires after the meter but before the Main of course. Most Meter main combos do not have enough room for this. You might want to this if you AHJ will allow. If the connection from the meter LOAD to the Main breaker is done with wires than this may work.
    With the power off
    1) Remove Load side wires from the meter to the Main breaker. Install a gutter/box of proper size from the Load of the meter to the Main breaker.

    2) perform the tap using proper wire size in the gutter/box. I have used a terminal block made for this.
    3) us a service rated fused switch for the Solar feed. and you should be good to go.
    4) ground / bond as required.
    any coments?

  9. #9
    Join Date
    Feb 2003
    Location
    Massachusetts
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    48,188
    If your doing a line side tap the rating of the panel is irrelevant.

  10. #10
    Join Date
    Aug 2009
    Posts
    1

    Solar Line SIde Taps?

    If I understand you correctly you appear to be connecting a grid attached PV array. Does it have battery backup? If so refer to the design papers as your exclusive direction for installation. Your Rep should have provided you with engineering as an option with your package. If not, often it is installed after the main breaker and serves to reduce the load on the service tap (not buss) not increase it. If, however, you think there is possibility for a problem, a quick load calc. could give you some insight as to the potential demand on that panel. If you add your maximum PV output to the calc it will give you an idea what your total current might be in a highly unusual situation. I say this because most peak usages occur during the morning and evening hours while peak PV production occurs during mid day when people are not home. Your situation may have special considerations but this is a good place to start.

    Good Luck,
    Daniel B House

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