There is just a DC + / - pair of USE-2/RHW-2 10AWG for each string, plus the bare copper bonding conductor.
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At the roof top, all the PV wiring comes back into a PVC junction box
where it goes into PVC conduit down to the inverter collocated by the
main service panel.
There is just a DC + / - pair of USE-2/RHW-2 10AWG for each string, plus the bare copper bonding conductor. |
The exposed wire is special, It has to be rated for moisture resistance (it rains) and UV resistance (the sun shines). But even with wire that is supposed to stand up to a rooftop environment, it is a good idea to protect it. Some people like to use a stainless steel shield. I used a couple of small pieces of PVC conduit, and cut the bottom out so I can just clip it over the exposed wiring, as shown below.
| Here are the small pieces of 1" conduit, with a slice taken out of
the bottom so you can just slide them over exposed wiring. I
did the same thing in the one spot where I had to run exposed PV wiring
between modules.
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Here's what it looks like when done, secured with a couple of zip
ties.
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From the junction box down to the panel is nothing special, just PVC, through the roof, but past the eves so the conduit never goes into the interior of the house.
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Conduit on top of roof |
Conduit under eaves, down to inverter |
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The last bit before the inverter was done with waterproof flexible conduit; its expensive, but I only needed a few of feet and it makes for very simple hookup. This also shows the mounting bracket for the inverter and the SMA DC shutoff switch. |
| Notice in the picture of the wiring from the roof to the DC cutoff switch the wires from the roof are capped off with insulating wire nuts. There's an important reason for that, the modules are always live. If the sun is shining, the modules are producing electricity. You really want that 400V DC safely insulated until you are ready to put it somewhere safe. |
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Since my inverter is only about a foot away from my AC panel, the wiring from inverter to panel is pretty straightforward. Since I had a few feet of flexible conduit left over I used it along with some 90 degree elbows to make the connection.
The schematic for the wiring is on the Design Page. But the actual connections are very, very simple.
DC: Two series strings of 12 modules each give you two pairs of DC + / - running down to the inverter where they are wired into the DC shutoff switch in parallel. The bonding conductor from the modules and track on the rooftop is tied into the inverter's equipment ground lug.
AC: Two phase L1 / L2 / N out of the inverter goes to the main panel where L1 / L2 are wired into a DPST 30 amp 240V AC circuit breaker, and the N is tied into the main panel N bus. And the inverter ground lug is bonded to the main panel ground bus.
With the SMA inverter, all the voltages and phases are autosensing. That means commissioning is as easy as being sure your wiring is correct, turning on the AC breaker, letting the inverter sense the AC, and then switching on the DC cutoff and observe the startup messages on the inverter.
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Page lasted updated May 30, 2011
