boat lift

dellOctober 2, 2009

My question is about cable choice and conduit size, please help if able.

I need a circuit to protect two 3/4hp motors (240V/15amp about 150' run) Will use 10 guage cable.

I want to run another circuit to protect two GFI outlets and two lights. Will use 12 guage cable.

Should I use a direct burial wire within my conduit? What size conduit do I need to comfortably pull and contain both cables? This is in Florida where they are using NEC 2005 codes, how deep should my trench be for the conduit?

Any other thoughts on this typical boat dock/lift wiring?


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Instead of running two cables from the house, why not run one bigger one and put a small subpanel at the dock? Then branch off for your motors, lighting, etc. It also gives you room for expansion should you find the need down the road.

If you're going to use conduit, why use cable too? Just use wire rated for wet locations (most wire today has multiple ratings so whatever your home center/electrical supply house will probably work).

    Bookmark   October 2, 2009 at 4:18PM
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Do NOT put direct burial cable (e.g., Type "UF") in conduit. (That's not optional--it's against code.) THWN individual wires are the way to go. (Look for "THHN/THWN" at a big box store.)

First, let me make sure I understand your requirement correctly. That'd be one 15-amp 240V circuit (not 120/240V!) for the two motors and one 15- or 20-amp 120V circuit for lights and outlets, right?

To start with, I see no reason to use #10AWG for the 240V circuit. At 150', if you use #12AWG copper instead, the voltage drop for a full 15-amp load is only about 3.7%, which should be quite acceptable. If anything, it's the 120V circuit that may need the larger wire guage if you plan to draw more than approximately 10 amps.

(Keep in mind that a 240V circuit is more efficient with respect to voltage drop over distance than a 120V circuit.)

So you'd probably be pulling 2 x #12 (one red, one black for the motors) and 2 x #12 (or #10) for the hot and neutral of the 120V circuit. Plus, you need one equipment ground wire (green or bare) sized according to the largest of the current-carrying conductor (i.e., #10 or #12).

That is: 5 #12s or 2 #12s and 3 #10s.

Assuming a fairly straight and uncomplicated 150' run, 1" PVC conduit oughta work out OK with some lube. 1 1/4 might be slightly easier and 3/4" is possible, but definitely a good bit harder to manage. (I wouldn't use 3/4" for this myself.)

Unless there are complications (a driveway or a goofy local code requirement, for example), the conduit needs to be buried a minimum of 18" deep.

    Bookmark   October 2, 2009 at 11:28PM
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Multiple circuits run to a detached outbuilding ?

Not according to the NEC

    Bookmark   October 4, 2009 at 9:24AM
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This is a dock, not a building.

Also, UF is certainly "allowed" in conduit, it's just a really bad idea, for several reasons.

PVC conduit needs to be 18" in a residential setting.
UF cable needs to be 24" unless under a residential driveway which can then be 18".

    Bookmark   October 4, 2009 at 9:45AM
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Thank you all.

Based on the input I will put a 30amp two-pole gfi breaker in the main box and run 10ga wire to a subpanel at the dock. With the subpanel (back fed to a 30 amp breaker as a main breaker)and with a 15 amp two-pole breaker for the motor control panel and a 20 amp gfi outlet for convenience plugs and lighting.

Any last thouhts appreciated as well, I will dig this over the weekend. Thanks Again

    Bookmark   October 21, 2009 at 11:36AM
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Ron Natalie

This is a dock, not a building.
The code says "structure or building". A pier is a structure.

A dock is the spot in the water the boat is in. The thing it gets tied up to is a pier.

    Bookmark   October 21, 2009 at 3:06PM
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Salt water ? Use good stuff !!
Corrosion ... as you know.

    Bookmark   October 25, 2009 at 7:10AM
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I have a 4 motors boat lift with 2 controllers on the post of the dock. It is a sealed double latch weather tight control box with 2 up and down manual switches.

It is too far away from the boat and I would like to reposition the control box on the water side of pole so I can reach it from on the boat to lift up and down easily.
Is there a code that specifies an EXACT location for up and down manual lever control panel box?

It seems the neighbors all have installed where it is easiest for the electrician and not convient for the boater. no offense meant.

    Bookmark   April 30, 2011 at 10:56AM
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"...the neighbors all have installed where it is easiest for the electrician and not convient for the boater..."

There may be a simple reason- "Easiest for the electrician" often equates to "less expensive".

    Bookmark   April 30, 2011 at 1:07PM
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Ron Natalie

Yep, we charge more for things that aren't easy :)

    Bookmark   May 1, 2011 at 9:24AM
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.........and people like to pay less for the things that are. ;)

    Bookmark   May 1, 2011 at 10:13AM
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I have a 100' foot pier and boat lift and ran # 10 stranded with no problems. 220v for the lift and 110 for lights and outlet plug. The 110 for the lights was for a transformer for 12v lighting for 20 lights and 110v lights and plug for the lift.
Instead of going into the house, I put a water tight double switch box at the beginning of the pier.

Hope this helps

    Bookmark   August 10, 2012 at 6:54PM
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I have a Dayton 1 hp single phase motor turning a Dayton reduction gear box. It has ben use for over 20 years with no problems. Last week I was lowering my boat and when I turned off the switch the boat continued to lower at a quicker pace. I hit the lower switch and it slowed the boat down. It will hold in the up position but not in the lowering position.


    Bookmark   August 10, 2012 at 7:06PM
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My idea is to please start a new thread instead of continuing a three year old conversation. Most boat winches have an integral brake. Basically, when the motor isn't running, the brake engages. It sounds like your brake is in need of service.

    Bookmark   August 10, 2012 at 9:43PM
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