# help wiring a dock



## seacern (Nov 1, 2010)

I need help on wiring a new dock. I’ll have a 420-foot run from my main service panel box to the sub-panel on the dock.

All wiring is copper THWN-2. I used #4 on the load and neutral lines and #6 on the ground. I pulled a black, red, white, and green.

The house is built on stilts with the meter base and electrical service panel box on one of the pilings. The electrical service panel is a Square-D QO with a main service disconnect breaker and eight other positions. Two positions are being used for the submersible well and a 30-amp circuit to the old dock. I’ll be replacing the 30 amp breaker to power the new dock.

I ran 1.5” pvc conduit at 18” underground for 185-feet to a non-fused pullout 60 amp disconnect at the base of the dock walkway.

From the disconnect, 1.25” pvc conduit is suspended beneath the dock for 235 feet to termination at the dock t-head.

I’ll terminate in a 60 amp sub-panel with eight circuit positions to feed a ¾ hp 240v boat lift, a 1 hp 240v boat lift, and 120v lights and outlets.

Due to the 235 feet run over the water and the disconnect at the dock base, I’d like to ground fault protect the whole circuit at the main service supply panel at the house versus running to the dock on a standard breaker and then providing GFI protection in the dock sub-panel using 15 amp GFI breakers and 20 amp GFI breakers.

Square D makes a QO-260GFI that I understand will not fit my application because it lacks a neutral terminal screw. This breaker is only for 240v GFI applications. It cannot be used as a 120/240v breaker to feed a 120/240v sub-panel. Uneven pull across the legs will have the breaker in a constant ground fault state.

Square D makes a QO-250GFI that does have the neutral terminal screw. I understand that this breaker can be used in a 120/240v sub-panel application.

Given the above:

1) Does anyone see a problem with my overall design?
2) Do I understand correctly that the QO-260GFI will not work in my application?
3) Is there another brand that will interchange with the Square-D QO that is 60 amps and provides for a 120/240v application?
4) Will the QO-250GFI at 50 amps meet my needs?

Thanks


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## nap (Dec 4, 2007)

> I ran 1.5” pvc conduit at 18” underground for 185-feet to a non-fused pullout 60 amp disconnect at the base of the dock walkway.


what does that mean? Where is the disconnect in relation to the water, both vertically and horizontally?



> Due to the 235 feet run over the water and the disconnect at the dock base,


how did you install the wire over the water?

do you have a floating dock? Is the electrical service mounted to the dock?

what is the NEMA rating of your disconnect and panel at the dock?

is this a single family home for private (non-commercial) use?


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## seacern (Nov 1, 2010)

Nap...

all wire is in pvc conduit. 1.5" pvc was trenched across yard to a min. depth of 18" from house service entrance panel to the beginning of the pier(walkway) which is the 185 ft run. 

There is a GE 60 amp non-corrosive, non-fusible, pullout disconnect at this point, the beginning of the dock, basically an air conditioner disconnect. The disconnect is at at height of 84" above the seasonal high tide. 100 year flood shows a 60" tide. I'm well above the 100 flood projection for the highest tide.

Watertight flexible pvc conduit was used from the disconnect to get under the pier/walkway to tie into 1.25" ridgid pvc that is mounted through holes drilled in the dock girders. The pvc is supported every 8' by the girders and ever 4' by clamps. This run is the 235' to the end on the pier/walkway to the t-head.

At the t-head, watertight flexible pvc conduit is used to route the run up a piling to ridgid 1.25" ridgid pvc conduit which terminates to a non-corrosive 60 amp subpanel located on the inside of the band of a hip roof shelter. The subpanel is 8' above the seasonal high tide.

This is a single family private home for personal use.

NEMA rating, not a clue. It's what everyone else in the area uses. We're talking saltwater and hurricanes. I bought exactly what several friends have on their docks, which were built and wired by contractors.

My main concern is the GFI protection. Whether to put multiple 15 and 20 GFI in the pier head sub-panel or a single GFI at the main house service entrance panel. 

If I go with the main GFI, is 50 amp enough since Square D doesn't make a 60 amp per my understanding of the 60 amp not having a netural wire terminal.

My work does not require a permit since it is for personal use in a single family home and the work is being done by me. I've talked with the county building inspector and he's fine with either option. I want to choose the safest.

Total run is 420 ft- 185' trenched in the yard and 235' over marsh and/or water suppended under the dock.

The dock is 100% wooden pilings with wooden girders, and marine structural concrete panels.


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## nap (Dec 4, 2007)

> My work does not require a permit since it is for personal use in a single family home and the work is being done by me


It's not that. It's that there are a lot of different rules if it wasn't a single family residence.

to the GFCI: obviously, if you use a GFCI on the feeder, if it trips, you lose everything. Since there is no point of use between the house and the panel, while it would provide protection if the conduit was damaged and there was an exposed wire, it would provide no purpose typically. I would go with the individual in the sub-panel.

Your wire is undersized though.


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## frenchelectrican (Apr 12, 2006)

There is first red flag it caught my attetion is the conductor size and distance and with 50 amp breaker that is too small and what more you allready raise new issue If you have to keep that conductor size then you only can use the 40 amp breaker { I am not joking on this part I have see it happend before }



> All wiring is copper THWN-2. I used #4 on the load and neutral lines and #6 on the ground. I pulled a black, red, white, and green.


The 16mm² { #6 AWG } is too small a EGC for this distance of run you should done get a 25mm² { #4 AWG } due the distance the reason why I say that due if you have any fault going on the 16mm² may be not engough power to trip the breaker so the code did written on that part so any time you have to increase the conductor accounting of voltage drop you have to increase the EGC as well. 

I am sorry but that is in Black and White in NEC code.

For the dock panels they typically come in either NEMA 3R or 12 depending on the local codes and how it set up.

And use the RCD { GFCI } at the dock panel due the distance the RCD will trip out on that distance.

Merci.
Marc


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## nap (Dec 4, 2007)

frenchelectrican said:


> The 16mm² { #6 AWG } is too small a EGC for this distance of run you should done get a 25mm² { #4 AWG } due the distance the reason why I say that due if you have any fault going on the 16mm² may be not engough power to trip the breaker so the code did written on that part so any time you have to increase the conductor accounting of voltage drop you have to increase the EGC as well.
> c


I was coming up with significantly larger that that even Marc.

this calculator says http://www.elec-toolbox.com/calculators/voltdrop.htm

#3 for a 120 volt 15 amp circuit at 420 feet 

#2 for 240 volt 40 amp, 420 feet
1/0 240 volt, 60 amp, 420 feet


How are you calculating for a 120/240 service like this when you are figuring for voltage drop?


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## frenchelectrican (Apr 12, 2006)

nap said:


> I was coming up with significantly larger that that even Marc.
> 
> this calculator says http://www.elec-toolbox.com/calculators/voltdrop.htm
> 
> ...


Nap I have Electrican Caluactur { Both NEC and European verison } and I ran on staight 240 volt circuit with 50 amp OCPD with max of 3.5% VD { it came up 3.4%VD ( 8.1 Volts } so it will be borderline on 120 volt side and that baised by using THHN/THWN 75°C copper conductors If I did use the 60°C then yes it will be much larger conductor as you mention.

Merci.
Marc


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## seacern (Nov 1, 2010)

Thanks for the help so far.

Line size: I sized the line based on the recomendation from the boat lift manufacturer. Their table showed #4 was good for up to a 500ft. run. 

Keep in mind that the lift motors only draw about 7-8 amps and only one will be operating at a time at 220v.

The most that will be running on the 120v circuits at one time will be a sercurity pole night light, a flood/spot light, and a radio.

What size standard breaker should I put in the main panel box to feed this circuit if I'm going to put GFI breakers at the dock subpanel?

Thanks


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## frenchelectrican (Apr 12, 2006)

seacern said:


> Thanks for the help so far.
> 
> Line size: I sized the line based on the recomendation from the boat lift manufacturer. Their table showed #4 was good for up to a 500ft. run.
> 
> ...


If it was pretty light load and you can get away with smaller conductor size.

I genrally don't really follow the boat lift manufacter instruction all the way espcally with voltage drop and belive me they are pretty picky with voltage drop. { I have allready see couple did fail due serious voltage drop } 

so with very light load you can use smaller conductor size and breaker size so let give you a example 30 amp breaker and with that distance you will need 25mm² [#4 AWG ] that baised on THHN / THWN copper conductor with 75°C rating with voltage drop at 3.4% but I know the NEC code can allow up max of 5% VD but once you get over 5% VD you may run into some issue. espcally with motor loads. { if you want to know what size conductor on 5% vd let me know } 

As far for the breaker it will depending on what brand name you have in your main load centre and type.

At the dock subpanel ditto it will depending on what brand it is and IIRC all circuits are have to be GFCI both 120 and 240 volts circuits so give you a head up on that one.

Two pole GFCI breaker are not cheap AFAIK they are over 60 + Euros.

And the single pole GFCI breakers are typically about 30 Euros.

Merci.
Marc


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## jbfan (Jul 1, 2004)

You could replace the pull out disconnect with a 60 amp spa panel, whitch has a 2 pole gfci breaker.
Finding one to fit the needs of sea air may prove to be a problem.

It will still be a 500' round trip to reset the breaker.


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## seacern (Nov 1, 2010)

Gentlemen, it's been five and a half years with everything working perfect. The spa GFI at the base of the dock has been tested once with great success when my son dropped the end of an extension cord into the water.

I have developed an issue that I'd appreciate advice on before I start checking all the connections for corrosion. 

The Dusk-to-Dawn metal Halide cheap Lowes Utilitech light has started kicking off and then slowly coming back on when either of my two boat lifts are operated at night.

The light could certainly have corrosion due to moisture intrusion- several hurricanes and tropical storms in the last five years.

Main breaker at house, a Spa GFI disconnect at the base of the dock, subpanel on dock with breakers independently feeding 1hp 240v boat lift, 3/4hp 240v boat lift, 120v outlets in weather proof box covers and a 120v circuit for the security light.

Thanks


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## jmon (Nov 5, 2012)

I know this is an old post, but glad everything has been working for you seacern.

I agree with your theory of the corrosion, sea water, etc., causing issues with your light. I would start there. Sounds like corrosion somewhere. Verify the connections as you have mentioned. Just a suggestion.

Please wait for the electricians to respond, they will have better advice/suggestions. Thanks.


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## psgama (Jan 30, 2016)

Loose or corroded connection causing too great a voltage drop to the ballast in your metal halide lamp, providing this only happens on motor load, and the lights operate fine otherwise.


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## seacern (Nov 1, 2010)

The guts of the light are probably corroded. Twice with significant wind and rain the GFI has tripped.


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## lenaitch (Feb 10, 2014)

Sounds like quite the setup you have. I don't know enough about your environment or weather-exposed electrical issues, but if it is corrosion when you are repairing/replacing things you might want to consider a sealant for both your fixtures and electrical connections.


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## Jim Port (Sep 21, 2007)

The ballast and/or capacitor could be dropping out on the reduced voltage.


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## Paulusgnome (Nov 13, 2014)

seacern said:


> ... Dusk-to-Dawn metal Halide cheap Lowes Utilitech light has started kicking off and then slowly coming back on when either of my two boat lifts are operated at night.
> ...


This may just be the metal halide lamp tubes getting past their use-by dates. As the lamp tubes age, their operating resistance increases and hence so does the voltage across the lamp terminals (note DO NOT attempt to measure this, dangerous HV ignition pulses!). Eventually it gets to where you are now, where they just hang on until a small voltage dip occurs, such as when you operate your boat lifts. The next stage is where they spontaneously cycle on and off every 15 minutes or so.
If you replace the lamp tubes with new, the problem should go away.


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## seacern (Nov 1, 2010)

I appreciate all the replies. It's a good possibility that the bulb is past its hours of usable life. I figure it has between 16000 and 18000 hours. Lowes advertises that the fixture has a bulb life of 8000 hours.

Great explanation above on how a metal halide bulb acts as it begins to fail. I figured it just "blows" like an incadesent bulb.

Now to decide if I replace the bulb @ $28 or the fixture @ $78 given the age and environment.

Either way I have to climb the ladder with these bad knees.

Great help.

For those wondering this is the fixture. In this application, cheap and throwaway works.

http://m.lowes.com/pd/Utilitech-100...-Halide-Dusk-to-Dawn-Security-Light/50222737=


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## rjniles (Feb 5, 2007)

Replace with LED. Payback in 2 years.

http://www.lowes.com/pd_595898-337-AL3050LPCGY_1z10fipZ1z11964__?productId=50278199&pl=1


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## rjniles (Feb 5, 2007)

deleted double post


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## lance80 (Jan 22, 2015)

Buy a new fixture, get an LED. At this point your ballast will need replacing too, which with a lamp change costs just about as much as a new fixture. 

If you just replace the lamp for now, that stressed ballast will most likely fail in the next year, which means you will be back up there changing it out anyways. 

Save yourself the hassle. 


Sent from my iPhone using Tapatalk


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