I'm a new member, experienced contractor and this is my first post. My brother has recently purchased a cliff side river home. A new boat dock will have a 13 amp 120 volt boat lift. My question is getting the power down the cliff to a new sub panel mounted to an existing deck that is 10' above and adjacent to the water and dock. It's about a forty-foot drop down at a 45/60° angle to this location. It is very rugged terrain. If I was to run underground to the existing staircase and strap my conduit to the stringers to get to this panel location the total run length would be at least 400' from the main panel due to where the staircase starts. Another option would be to run 1" PVC underground from the main panel to the cliff's edge and then transition from a post mounted junction box down the cliff to the new panel using 1" RMC w/3#8 &1#10 EGC. This path would shorten the run length to approx. 200' and almost a straight line point to point. Trenching the cliff is not an option due to the rocks, trees and slope. My thought was to surface mount the RMC to struts embedded into the cliffside at the proper intervals. I'm concerned about voltage drop and calculated that the #8s will carry the motor load at the 200' distance with around a 3% drop. Does anyone see a code problem with the pipe running exposed down the cliff? It appears to be stable ground. This is my first job like this in 40 years and before I contact the AHJ, I'm looking for a little input. I thoroughly understand the branch wiring requirements for the dock connections from previous Mike Holt forums and the feeder will be GFCI protected. Thanks.
Boat dock panel feeder
- Thread starter DaveN
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synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
There was a somewhat similar post which was for an industrial setting and it didn't have a steep drop, and they settled on having RMC up on posts maybe 10 to 12 feet above the ground (if I recall correctly). I think this would be better than having a trip hazard close to the ground.
GeorgeB
ElectroHydraulics engineer (retired)
- Location
- Greenville SC
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- Retired
Engineering perspective, I don't know where the NEC might bite;
If the motor is your ONLY load (well, maybe some 90V-250V cell phone chargers and similar), have you considered a boost transformer after the GFCI and supplying perhaps 140V to the cable? 20A GFCI, #10 conductors. You'd be able to use the modern lighting fixtures rated for 100-300V. I don't see any negatives.
That idea is intriguing. Been over 20 years since I did any type of boost transformer job. Those were for 240v rated machines running on 208v. I don't know what the future holds for the dock area but I'm sure there's going to be a battery charger and probably some sort of lighting.
It's about a 40' drop at between 45 and 60 degrees. I would probably exit the bottom of the jbox and immediately drop over the edge. I would enter the lower side ko of the panel to insure that any moisture would drain out the bottom of the panel. Wedges or not, I would ductseal the upper conduit opening. Thanks
There definitely would never be foot traffic on this slope. I'm going to need climbing gear to do this install. I was thinking maybe 12" high minimum and would adjust for any irregularities on the way down for a nice straight run.
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