Hey man,

Big thanks for your support with getting the PV system up and running. No pressure at all — I don't mind getting back down there soon if my hunch here is wrong.

When the SMA inverter (model SB3.8-1SP-US-40) tried to get going this morning, it detected an electric arc on the DC side. Error 8206.

On the roof, I feel good about my MC4-connector crimps and my junction-box connections. The modules are directly connected to each other (there are no "module-level power electronics" up there).

The modules and racking are bonded / grounded.

I assume the fail is the PV-wire connections in the inverter.

This inverter's user manual is here. The section on connecting the PV array(s) starts on page 48. Here's the tl;dr...

Disconnect the grid side of the inverter first (to turn it off). To do that, use the wall-mounted disconnect switch that's about 6' to the left of the inverter.

On the left side of the inverter, there's a switch to disconnect the PV from the inverter. Turn that switch to the *O* position to disconnect. This switch just separates inverter electronics from the PV input while you're working in there. ...It doesn't protect you.

In the daytime, the PV wires are energized... several hundred volts (the big-boy module spec sheet is here).

Before proceeding, please either wait until it's dark out or disconnect one of the MC4 connectors up on the roof. The two MC4 connectors are on the outside edges of the far left and far right modules, in the middle. You should be able to disconnect without a tool... pinching down in the middle. But probably easier to go with the dark option.

Step 13 of the related user-manual section includes:

First insert the connector into the terminal point all the way to the lock (round opening). Then insert a flat-blade screwdriver (blade: 3.5 mm (0.14 in)) as far as it can go into the actuation shaft (rectangular opening). Hereby the lock opens and the conductor can be placed into the terminal point as far as possible.

I assume that the dude pushed the wires in but didn't use a screwdriver to get them all the way in. (I was lame / hasty with my wire-pull check.)

Before putting the wires farther in... Please pull them out and inspect. The user manual says they should be stripped about 11/16. If the bro nicked the wires or cut off strands (in a sloppy strip), please cut that off and re-strip.

When you're ready to fire the inverter back up... turn the DC switch on first, and then the grid side.

You're welcome to call or text anytime with questions.

SMA is a great inverter brand to get more familiar with. Solid German engineering.

It'd be excellent to collaborate on getting the other modules installed.

BTW: I have a blog where I write about my failures in the field, etc. I'd be honored if you checked it out (here).