VD calculation for long boat dock run.

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Mike410is

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Location
Florida
Occupation
Residential electrician
Hello everyone. I’m looking at rewiring an existing residential dock. Original branch circuit is supplied by a two-pole 40amp with 6-3 Romex from the panel that runs 75-85ft through the attic to a junction box on the side of the house. From there it is 165ft to the dock. So total length from the panel to the dock is 240-250ft. The load at the dock is a 12.5amps lift plus a few led lights.

I plan on running 6awg THWN in 1in PVC to the dock. By my calculation the VD wouldn’t be more than 5volts.

I used 2 x 12.9 x 20 x 250/26,240= 4.92 for my calculation.

I’m just wanting to make sure I’m correct, and also wanted to know what your thoughts are on changing the breaker out to a two-pole 40amp GFCI? Thanks
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I believe you are required to have a disconnect on shore adjacent to the pier. I would place my GFCI there.
 
kwired

kwired

Electron manager
Location
NE Nebraska
HEYDOG said:
If this is 240 volts only. The recommended voltage drop should not exceed 3% of the applied voltage. .03* 240= 7.2 volts. Your 4.92/240 =@ little over 2% voltage drop!
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In NEC that is just a suggestion as an informational note and not enforceable. If you have energy code that enforces this then it is a requirement, otherwise you can have whatever voltage drop is deemed acceptable by whatever reasoning.

I'd possibly disregard to some extent VD developed when using the boat hoist, simply because it is used infrequently and for fairly short time when it is used. Also other loads may not be in much use when using the hoist in many cases anyway.
 
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