Tapping main line for solar install

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  #1  
Old 03-02-16, 08:59 AM
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Tapping main line for solar install

Hey guys, I keep searching for the proper solution and I've realized I am better off seeking opinions from people who know.

I'm drafting up designs for a DIY solar project on my house. The problem I ran into, which appears to be common, is I easily hit the 120% busbar rule, so I need to switch from Load-Side to Supply-Side. Basically, I need to splice the main line between the meter and my electrical panel.

So what I have figured out so far:
I believe my mains are 4/0 ( I have 150A service )
I have a 2" conduit on the outside going from the meter into the house.
I should be able to get the power company to cut power for a day which would allow me to disconnect the mains from the load center & meter box, cut the conduit, put a junction in, splice the lines and hook up my fused 60A disconnect for my solar.

I have found some insulated multi-tap lugs for splicing wires that are 4AWG-4/0AWG.

The problem I am having is finding the proper supplies for the rest of this, and I'm trying to make sure I'm not violating code.

My understanding (maybe I'm wrong) is that I need a metallic NEMA 3R box with 2" conduit openings large enough to install the splices on, I am having a hard time finding anything that fits that description.

My other alternative to splicing in the middle of the line, is to splice inside the circuit breaker panel by disconnecting the lugs, using the insulated splices and adding a few extra inches of 4/0 to connect back into ... assuming there is enough space to work in there with the splices and extra 4/0 wire.... (And looking at it now, there really isn't that much space, it could be done, but the splices would be sitting on top of all the incoming branch circuits, that makes me a bit uneasy that something could short if it came loose)

Does anyone know what the proper solution is?
I have enough experience wiring my house that I don't have a problem doing this work myself, I just need to know what the right solution is and if someone can point me to the correct parts.

Thanks
 
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  #2  
Old 03-02-16, 09:58 AM
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I doubt your proposed method would be allowed by the power company. What do their solar interconnection and net metering standard say?

I would approach this by replacing the meter with a 225A meter/main combo. This would require converting the current main panel to a subpanel and updating grounding on both. The solar inverter then feeds into a breaker in the new meter/main box, and the old "main" panel is fed with a 150A breaker.
 
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Old 03-02-16, 10:16 AM
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What the power company allows vs what code allows is of course two different things.

I have their interconnection guide, it doesn't show what they recommend in these situations.

The NEC allows you to split supply lines, one of the reasons you would use it with PV is it completely gets rid of the 120% rule. Once you go directly on the supply side, you can size your PV system up to the size of the lines feeding your property. You just need a AC disconnect with fuses, with a minimum rating on the box of 60A (though you can use smaller fuses if the inverter & wiring beyond it aren't rated for 60A). Supply side connections from what I read are very common with PV, but no one seems to document it, most likely because its generally performed by an electrician.

I have no trouble hiring an electrician if I absolutely need to.... but I'm trying to spec out the design for Xcel to send to their approval department and they want specifics... I still could be a few months out on doing an install and don't want to go find an electrician and waste their time if it leads nowhere.

The real issue for me is where to make the split and to do it within both code and how the power company wants it.

There are splice blocks, you can splice at the lugs if its allowed (most lugs aren't rated for two connections), there are piercing splice connectors that can be installed on live lines that cut into the mains, etc. So there is the "how" and then there is the "where"..... can I do it in the meter box, can i do it in the main panel, should I cut the conduit between the meter and the panel, and if so, what is the proper type of box to house this connection.
 
  #4  
Old 03-02-16, 10:39 AM
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there are piercing splice connectors that can be installed on live lines that cut into the mains,
Those are called Ilsco L taps.

I have seen them used to attach the solar supply wiring directly to the main wiring just before it enters the main breaker. This requires that added on wiring to be the same size as the service wiring. It doesn't look terribly neat and it doesn't fit well in a tight service panel but apparently is allowed as I've seen this in several customers home.
 
  #5  
Old 03-02-16, 01:03 PM
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Yes and no. In my area at least the local inspector and the power company both have to approve a service entrance before it will be connected, so the codes and standards aren't different, they have to work together. I personally have never seen a solar tap ahead of the main breaker. Might be something that is regionally allowed or forbidden.

If you're going to DIY this, I recommend you request that the power company do the disconnect at the pole or transformer, even if it costs more for the service call. If you have to do any work in or directly around the meter can, you want the service completely dead, If you just have them pull the meter it will still have live unfused supply in that box which is not safe for DIY work.

On the tactical side, if you have rigid or even IMC conduit, there is no practical way you will be able to cut it unless you pull out the conductors and remove the conduit from the house to make the cut and rethread. If it's PVC you might be able to do it in place if you're careful.

Instead of looking for a junction box, you'll probably want to look at making the taps in a gutter. You may even be able to replace the conduit entirely with a length of gutter and use pipe nipples and/or condulets to enter the meter box, solar disconnect box and main panel box. It's very common in commercial and multi-occupancy service entrances. A local electrical supply house would be able to get you want you need. The 2" openings you'll need to cut with an electrician's punch kit (rental maybe) or a bi-metal hole saw and clean up burrs with a file.

There are many DIY friendly insulated taps and splice blocks Ilsco and Polaris are two common brands. Any of these are OK given you have a box or gutter with adequate clearance for all of that #4/0 conductor. Depending on what kind of panel, meter box and main breaker you have, double lug options may be available which would obviate the need for splice blocks.
 
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Old 03-02-16, 04:37 PM
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Might be something that is regionally allowed or forbidden.
I have to agree with that.

I know in one particular customers house I was at.... the inspector is a stickler. I was called by the customer to replace a rusted out meter pan. I did that as an emergency repair and the inspector signed off on the solar install just after that. I know he had the panel cover off as that is his style.
 
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