MidNite Solar MNTRANSITION Box, PV Wire to Standard Wire Transition Enclosure, 1000Vdc, 4 String, Type 3R Outdoor Rated

About the MidNite Solar MNTRANSITION Box

PV wire is built for the array. It's UV-rated, sunlight-resistant, and designed to survive decades exposed to the elements between panels and junction boxes. It's also expensive, stiff, and miserable to pull through conduit. On a ground mount or any installation where the array is more than a few feet from your equipment room, you don't want to be pulling PV wire through 50 or 100 feet of conduit when standard building wire does the job for a fraction of the cost and pulls far easier.

The MNTRANSITION mounts at or near the array and gives you a code-compliant splice point. PV wire comes in from the panels on one side. Standard THHN/THWN (or 1kV-rated wire on systems over 600V) goes out through conduit on the other side. The savings on wire cost alone can pay for several of these boxes on a multi-string ground mount, and your electrician will thank you for not making them wrestle stiff PV cable through every bend.

Internal Layout

The box includes 2 tin-plated bus bars for combining and transitioning up to 4 PV strings across 2 isolated output circuits. This works well for charge controllers with 2 MPPT inputs, where you're combining 2 strings per tracker. A 15-position ground busbar handles equipment grounding conductors from #14 to 1/0 AWG. The enclosure itself is a 1000Vdc rated, ETL-listed junction point with enough internal volume and knockouts to accommodate additional splice methods if you need to keep more than 2 circuits isolated through the conduit run. A snap-in dead front covers all terminals after installation.

If you need 4 fully isolated string outputs (for 4 independent MPPT inputs), a single box with its 2 bus bars won't keep all 4 circuits separate. Either use a second MNTRANSITION with each box handling 2 strings, or use the box as a junction point with the additional circuits spliced independently of the bus bars.

Surge Protection at the Array

The MNTRANSITION is also a natural mounting point for PV-side surge protection devices. Lightning and induced surges are strongest closest to the array, so installing an SPD at the transition point (rather than only at the equipment end of the conduit run) gives your charge controller and inverter the best protection. The knockouts accept MidNite Solar MNSPD units, and the ground busbar provides a clean, short grounding path from the SPD to the equipment ground. On long conduit runs from a ground mount, this is especially important because a surge suppressor at the far end of 100 feet of wire is far less effective than one right at the source.

Enclosure and Mounting

The powder-coated aluminum enclosure is Type 3R rated (rainproof) for outdoor installation right at the array. A quarter-turn latch secures the flip-up cover, which props open during wiring and maintenance for easy access. At 4 lbs and 13.5 x 8 x 4 inches, it mounts on a post, rail, or wall without adding significant weight to the structure.

Wire Voltage Ratings

Standard THHN/THWN is rated to 600V. If your PV string voltage exceeds 600V, you need 1kV-rated wire on both sides of the transition, not just the PV side. The box itself is rated to 1000Vdc, but the wire you pull through conduit must match the system voltage. This is an easy detail to miss on high-voltage string designs.