Grid tied, non battery, line side tap question Maine

[33oneill]

Hi, I am going to be DIY installing a 7.2kw grid tied, non battery (Enphase IQ8) system here in Maine. I have a 100A service. I have a question re the line side tap connection I will need to make. I know what a line side tap is but I have never done one. Looking at my service all I see is two blades connecting to a 100a breaker. If I have to make the connection before the first breaker, where and how do I make that connection? Am I allowed to make the tap in the upper compartment where the meter is located? Does anyone know if my power company (Central Maine Power) allows me to do this?
Thanks Mike O

 

[Hedges]

You have a 100A main breaker only panel. No need to make a line-side tap.

I would use Polaris or other means to branch off downstream of the main breaker to a 40A fused disconnect, or a PV aggregator panel, then the inverters.

The existing circuit - does it go to a sub panel inside? I would like that to have 100A OCP, since it will now have available to it 100A + 40A.

Alternative - feed the 100A into a 125A breaker panel. Put up to 50A worth of PV breakers on it, and 100A breaker to feed existing sub panel.
Are you supposed to have visible blade disconnect, or is that optional?

What is the busbar rating of your existing sub panel?

 

[33oneill]

Thanks. Yes it goes to a 100a panel. A GE Model TM3210CCU There is a 100a main breaker. I didn't get the busbar rating. I won't be back there until the weekend. This is a seasonal cottage that I am converting to year round. The breakers w the white tape and X's are from the old electric baseboard heat and are not being used. I will remove the breakers as I remove the baseboard.

The line drawing that is coming with the system calls for the line side tap. I thought you could not add a 40a breaker to a 100a panel , but I did not check my panels busbar rating. What is Polaris?
Thanks again

 

[Hedges]

Reason for a line side tap would be to put in PV greater than allowed by 120% rule.
The sum of main breaker and backfed PV breaker at far end of busbar is not allowed to exceed 120% of busbar rating.
So if a 100A busbar with 100A main breaker, you'd be allowed to put 20A PV breaker at far end, and 16A continuous current.
If your busbar is 125A, then 125A x 120% = 150A, 150A - 100A = 50A breaker allowed, and your PV could go there.

With 100A breaker at meter, and 100A breaker on sub-panel, all you need to do is tap off the wires between those 100A breaker and add whatever you want.

One example of Polaris:

Polaris 3/0 - 6 AWG Bagged Insulated Multi-Tap Connector, Black IPL3/0-3B - The Home Depot

IPL insulated multi-tap connectors are suitable for connecting 3-wires. Will not support combustion. Cold temperature rated to minus 45 degree C. Dual rated for use with copper and/or aluminum cables.

www.homedepot.com

If you get one that can be fed from both sides, you can feed existing wire through middle. You'll be able to hang additional circuits off it in the future with fewer screw terminals.

I don't know if you only need one circuit for Enphase, or at that wattage maybe multiple 240V strings. For just one, fused disconnect switch. For multiple, (optional?) disconnect switch and a PV aggregator panel. It may be exempt from 120% rule if only backfed, no loads. If you size it suitably, you can use it for loads too. e.g. 125A panel, 70A main breaker, up to 70A PV. Or 125A panel, 100A main breaker, 50A PV.

 

[zanydroid]

NGL, seeing line side tap was clickbait for me to take a look at this thread

Who gave you the line side tap drawing, and why did it come about? Did not want to upgrade panel? Lineside tap is a call your POCO situation, pretty unlikely to find someone on forum that knows such hyperlocal info (on top of fewer people overall doing lineside tap). Hopefully you have a good relationship with them and can have the changes made to avoid line side tap. If POCO does not allow or adds a lot of annoying extra checks.

You can backfeed up to 80A (100A total of breakers) through that panel with judicious placement of the load side backfeed. I am backfeeding 70A through 100A service.

If you stick a 200A or 225A subpanel between the main and the subpanel you can tie into that. The problem with using the Polaris connector is that you will have to do feeder tap calculation/protection level for the feeder to the existing subpanel. Since you have 100A feeding it from grid and 40A feeding from Enphase, there is potential of 140A going into the feeder without a supply side OCPD. Feeder protection involves conduit and limited maximum length. If you put a subpanel there with 100A breaker feeding to subpanel, lug to 100a main disconnect, and 40A breaker to disconnect you don’t have to worry about it. It has to be at least 125A busbar, probably better to just max it just in case you add more solar.

Enphase trunk cable is max 20A OCPD per branch. Can do cheaper than Enphase TBH, even in microinverters.

 

[WindWizard]

I am in Maine also. CMP requires you to submit your plans for approval to them before you do anything. Go to the CMP website and then look for the approval forms. If you cannot find them then give them a call. Once they have approved your plans then after you do your installation whether you do it or an electrician, it needs to be inspected to make sure that all the wires and equipment is okay with CMP.

I have an off-grid system, so it does not apply to me.

 

[33oneill]

Thanks for the replies. I have to digest this - there's a lot to think about. To answer the question that came up: I am purchasing this system online. I filled out a form, included the pictures of my service and the breaker panel. They came up with the line drawing. I will contact them because in filling out my form I mentioned the line side tap (because I didn't think I could back feed 40a into my existing 100a panel) and maybe they just said 'ok line side tap then'. I don't mind changing out / upgrading my breaker panel but I don't want to have to pull larger feeder wires from my service breaker.

Eventually I will upgrade my service and my breaker panel and feeders to 200a but for now I am looking for the simplest, code compliant way to connect my PV to the grid. The Enphase IQ combiner box and the AC disconnect will be mounted outdoors next to the service entrance. To me, if I could use the Polaris line splices to tap into the wires going from the first breaker in the service entrance to my breaker panel - that seems the simplest.

If I am understanding this correctly another option is I need to check my busbar rating of my breaker panel. If my busbar is 125a then I could do some breaker rearrangement and back feed the panel with a 40a breaker? If my panel's busbar is rated 100a I could remove the existing panel and put a 125a panel with a 100a main breaker and backfeed my PV through a 40a breaker?

WindWizzard - Thanks. So far CMP has been easy to work with. I had to fill out some paperwork about my proposed system but they did not require plans from me. I do have to have the system signed off by a licensed electrician before they will change my meter over to a bidirectional one.

 

[Hedges]

Correct you can't put 40A PV breaker in existing panel, only 20A, if busbar in panel is 100A. Try to find out if that is 100A or 125A busbar. If 125A, then you can install 40A PV breaker.

Because sub panel has 100A breaker and meter box has 100A breaker, you can do everything without needing utility to shut off power (yank meter).
It would work to just splice a branch to PV, although as Zany says there are rules regarding a wire with excess power available on it's input, protected by breaker at far end.

I'm not personally concerned about that at all in this case, because the unlimited power from grid is protected with 100A OCP at meter. I'm not worried about 100A + 40A available to a 100A wire with 100A protection at far end because:
1) If the wire shorts out, it will fast trip the breakers feeding it.
2) If excessive load is applied at the sub panel, it will trip the 100A main breaker on the sub panel.
Only concern is being allowed to do it or not.

As Zany said and one of my suggestions was, Install a 125A or larger panel (main lug is fine.) Install 100A branch circuit breaker and move the sub panel feed wires over to that breaker. Install new wires feeding 125A panel from 100A main breaker in meter box. Install up to 50A of PV breakers at far end of the 125A panel.

If you want or are required to have a visible blade disconnect, it can be placed after the single 50A PV breaker. If you have multiple Enphase circuits, you'll need additional PV aggregator panel or fuses for them. (If two 25A breaker for two PV circuits, I'd be tempted to have switch break L1 of one circuit and L2 of the other. Likely not proper, but it would work.)

Or switch could be placed before the 125A panel (needs to be 100A switch), but then if shut off it shuts off the house.

Eventually I will upgrade my service and my breaker panel and feeders to 200a but for now I am looking for the simplest, code compliant way to connect my PV to the grid. The Enphase IQ combiner box and the AC disconnect will be mounted outdoors next to the service entrance. To me, if I could use the Polaris line splices to tap into the wires going from the first breaker in the service entrance to my breaker panel - that seems the simplest.

Have I got a deal for you!

Install a 225A busbar main lug panel beside the existing panel. Leave room above to install a meter box, but keep the B-hub cap on top for now.
Using 2" conduit and Tee, connect bottom of existing service entrance box to bottom of 225A box, and continue with Tee for PV circuit. Always leave a Tee with unused branch for further expansion.
Move existing 100A circuit to a 100A breaker in 225A box.
Feed main lugs of 225A box from service entrance.
Install up to 70A PV breaker at bottom of 225A box.

In the future, you can install meter and weather head above 225A box, install 200A main breaker, and 120% rule allows 70A PV.
The nice thing about 70A is it allows 56A continuous to feed through a hybrid or battery inverter and supply protected loads.
Well behaved Rule-21 PV inverters can AC couple with such battery inverter. (Enphase IQ8 is not well behaved.)

If you do use IQ8, likely have to go with Enphase ecosystem battery inverter. People here have had better luck AC coupling to IQ7. I favor high voltage string inverters, although those now require PV module level power electronics for RSD, which microinverters do not.

Take a look at Sunny Boy Smart Energy, which will be available in January. It outputs 7.7kW AC, can take in up to 15kW of PV, charges optional HV battery from BYD with up to 10kW. At this time only offered for time shifting power, not for grid backup (except for 120V 15A Secure Power.) I expect SMA to offer external transfer switch & auto-transformer in the future for full backup. It is mentioned for the European model and has been available for other products.

Instead of main panel with branch breakers, I like best having a 200A main breaker only panel for service entrance. I use Polaris to fan out to 100A and 200A panels and fused disconnects. I've got a lot of Square D QO boxes on my wall.

 

[33oneill]

Thanks for the replies. I have some homework to do. I will report back.