I am upgrading the electrical service to a floating boat dock in a home I purchased last year. The lake is managed by the Army Corps of Engineers and has specific regulations I'm required to follow.
Currently, 12/2 NM UF is run from the main house on a 20amp breaker to a mast at the shoreline, where it terminates at a flood light and a GFCI receptacle. Is it possible to use this existing 20amp feed to power a remote weatherproof subpanel (required by the Corps for remote shut-off) with a single 20 amp breaker inside? The sub-panel is rated for 70 amps.
From my perspective, the amperage isn't changing, and all I'm adding is a shut-off switch, therefore nothing should be wrong with this setup. Is this a correct assumption?
From this shut off panel at the shore and a locking outlet, 12/3 (black/white/green) SJOOW is run to the dock ramp, and is junctioned to 12/2 NM UF (black/white/bare), which is run through 1/2" schedule 40 conduit beneath the ramp and onto the dock.
I am a heavy duty DIYer, but want to be sure I'm not doing anything wrong with this 20amp sub-panel since this is a first for me. Thanks in advance for any advice or answers you can provide.
Best Answer
12/2 is awfully, awfully light for a 300 foot run. It's not a bad installation, and it's legal and safe to breaker that 20A. It just won't be very satisfying if you try to run a heavy draw appliance. As things are, your tiny 60W / 0.5 amp load won't be a probem. Punch your actual amp load into a voltage drop calculator (and specify 99% allowable voltage drop) to see what the voltage drop will be.
You new setup will delete the GFCI receptacle, but that's a good thing. The problem with GFCI's at beachside is that if the GFCI itself gets wet, electricity can leak from the unprotected line side of the GFCI and kill you. A better place for the GFCI is actually as a breaker in the main service panel, so the entire wiring run and the panel and the receptacle are all protected.
Since this is only one circuit, all you need here is a shutoff switch, provided you have a GFCI back at the main panel. This can be a $19 fuseless shutoff switch, or a $20 2-space subpanel with a $5 breaker installed in it (using the breaker as shutoff switch). Guests need to be able to shut off power FAST if needed, so get a panel where the main breaker is obvious, not hidden among the other breaker(s).
If you want the GFCI at beachside, figure on a $65 hot tub subpanel which has a GFCI "main breaker".
GFCI breakers for your main panel are $40, so this is a wash costwise. If you do have that, you will not need any GFCI devices beachside, and you can satisfy GFCI requirements with a sticker that says "GFCI Protected".
Using SJOOW cord between the flexing sections is correct.
If you're actually using the conduit wiring method where all boxes are connected by continuous conduit, 12/2 UF is a very tight fit in 1/2" conduit and a miserable pull (some manufacturer's UF are actually too big!) THWN-2 individual wires are the right thing for conduit, and you get to use stranded wire, which is a joy to work with. Only downside, you'll need 3 colors of wire.
If the conduit location is exposed to direct sun, PVC will take UV damage inside 3-4 years (so paint it). Sched 40 PVC also won't hold up to physical damage (so use Sched 80 or EMT at sensitive areas).