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Electical circuit question
Old 07-21-2009, 08:18 AM   #1
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Electical circuit question

I live on a lake and have a dock about 100 feet from my house. I just sold a small electric boat that had a small battery that I would carry to the house for recharging, then take it down when needed. I realize it's a violation of LBYM principles, but it gets harder and harder for me to handle the small tippy boat and carry the battery up and down a bunch of stairs, so I'm now considering getting a slightly larger, more stable, boat with a 48V system, using four 12V batteries and built-in charger (a Minn kota E-drive).

So I need to run a permanent circuit from the house down to the dock. I'm going to call an electrician to make sure everything is safe and done according to code, but before I get estimates I'd like some idea of the extent of the work.

My house fuse box is in the basement utility room and, unfortunately, is on the opposite side of the house from the dock. The rest of the basement is finished, so putting a separate circuit into the box, though ideal, may be a big deal.

My other option is to run the circuit from an existing outside circuit on the back of the house, which is closest to the dock. But that circuit feeds not only the outside plug but also two bathrooms (what were they thinking) and outside malibu lights, and on occasion trips the GFCI when DW uses her hair dryer.

My question, how much current would I expect a battery charger to draw? And it's not only the charger drawing, but with 100 feet of line, there would also be some voltage drop for that distance. I don't mind an occasional GFCI trip if tapping off that existing line will save me thousands over a separate circuit, but also don't want to do anything stupid.
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Old 07-21-2009, 08:39 AM   #2
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Well let's see. 2hp, = about 1500watts, runs 2 hrs on a charge according to Cabelas, so 3000WH. I could not find the charger (you should get info on the charger before calling the electrician), but 3000wh/8 hou charge would be 375wh charge per hour, gross up for 50% efficiency factor (just a guess) to 750wh charge per hour. 750/110= just under 7amps. It will definitely blow if your DW uses the hair dryer while this puppy is on...

Just back of the envelope, but probably not too far off.

get the facts on the charger before doing anything...

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Old 07-21-2009, 09:01 AM   #3
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Is the ceiling of the basement drywalled or suspended? If suspended, you may be able to snake a new wire across to the lake side wall. If not, you could trench around the perimeter of the house and upgauge to a 12 gauge wire for a 15 amp circuit.
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Old 07-21-2009, 09:53 AM   #4
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Can you put the charger on a timer and only charge on "off hours"? That way you could use that circuit and not interfere with the bathroom use.


An electrician *may* be hesitant to add another outlet to an already overloaded circuit though, no one can predict how someone might want to use that dock plug, and it's pretty inconvenient to blow a breaker while you are out 100' away.

Wait a minute - is the GFCI tripping due to a ground fault, or overload? If due to ground fault, I would investigate. I wouldn't rely on a GFCI for ongoing protection if there is an underlying problem. Fix the problem.

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Old 07-21-2009, 10:11 AM   #5
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Since this wiring job sounds like it could be a big deal, especially with cabling going the 100 feet to the dock (deep trench??), I'd wonder if it might be easier to find a good way to continue with the one battery system.

Can you find a way to make it a lot easier to transport the battery? Do you have a carrying sling or case so that you don't need two hands? Is it perhaps good exercise to carry the battery up the stairs? Can you make a protruding plank device to make it easy to get the battery off the tippy boat.

Will the number of hours spent setting up this new electrical subsystem be greater than the number of hours schlepping the battery?

I think we need pictures of the dock and the lake.
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Old 07-21-2009, 10:46 AM   #6
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Most common GFCI is 15 amps - check the feeding circuit and if it's a 20amp find & install a 20 amp GFCI. Electricians? Any issue with that course?
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Old 07-21-2009, 10:51 AM   #7
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Based on this model, the amperage would be 2.375 (285w/120v). Round up to 3A for "fudge factor"...

Black & Decker Power Tools

Using this calculator, required wire size is 14 gauge.

Wire Size Calculator

Maybe just use a heavy duty extension cord?
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Old 07-21-2009, 11:03 AM   #8
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Not sure what you have for a fuse box, but adding another circuit may or may not be a big deal. If you are going to go to the expense of adding a dedicated circuit down at the lake, go with a 20 amp GFCI. I agree with Ramblers bar-napkin calcs; the battery charger will probably only draw around 10 amps peak , 20 amps will leave you enough to run the beer fridge and an outdoor light. If you don't like humping up the hill to charge the battery, you sure as heck don't want to have to do it every time you need a cold one. (And you can always flash the light off and on as a signal for someone to bring you another if you run out...)

18" deep is code in most places- how hard is the digging going to be ? You may have to rent a walk-behind trencher (ditch-witch) if you have a loot of roots, etc to get through. I would probably come out of the ground in pvc conduit fastened to a 10'-12' long 4x4 pressure treated post, up to a pvc outlet box 24" above grade on the post, come out of the top of the outlet box in conduit to an outdoor switch at 48" above grade, then up the pole in conduit to a outdoor light at the top. You can make up the entire assembly before you plant it 24" deep at the end of the trench- will only have to wire incoming power into the outlet box on site. Consult a local electrician; they may want you to to upsize to 10/2 NMB direct burial wire for the 20 amp circuit; although the line loss at 100' should be negligible- depends on how far you will have to go to snake it through or around the house.. You could also go with 12/2NMB and drop to a 15Amp circuit- probably still more than what you have available on your current GFCI circuit- Who knows, maybe the DW will run down to the dock to blow-dry her hair when you finish this project...

If you hire this out, the labor costs could be substantial. If you do it yourself, the wire will will be your only big expense- the fittings and outdoor box/outlet will only cost a few $- assuming you have room for another circuit in the panel.


Let us know how the project goes. I agree with t-al, we need photos of the dock and the lake!

Have you looked into a Solar battery charger?
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Old 07-21-2009, 02:18 PM   #9
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Thanks, guys, great suggestions.

Rambler, pretty good envelope you have there. I checked the charger and it draws 5 amps. With the bathrooms and wife's hair dryer I would probably trip the GFCI, which I do now anyway, but ERD's idea of a timer is great, I could charge in the middle of the night.

Just had the electrician over, asked him for several options, existing circuit, new circuit, etc. I'll let you know what he says.

Westerskies, I'll post a pic when I can. And no, hadn't thought of a solar charger. That might be a problem, though, since I'd have to redo the boat's circuitry to plug in a DC solar charger.

OK, just took a photo of my dock (don't know how to resize it, it's pretty big). It's the one down the hill, just to the right of the pontoon boat with blue cover (a neighbor's). It's a 110 acre lake, opens up to the left. Already sold my smaller boat, so its not in the picture. Note the wooden steps going down the right side, that's where I would run the line. That's also where I carry the battery up and down. '

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Old 07-30-2009, 07:25 PM   #10
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I asked two electricians for quotes, but before either of them could give me a quote I finished the job myself.

Went to Lowes and asked a few knowledgeable people (including here) how to do it. Bottom line, I used UF cable tacked along my wooden steps to the dock. At the dock end I used an outdoor waterproof boc with GFCI, and at the house end I hooked into the existing 15A circuit that also feeds the bathrooms and outdoor lights, and is also GFCI protected. Right now everything is working, and I'm getting the pontoon boat tomorrow, so I'll see if it really works. And I'll ask DW to not use the hair dryer while I'm charging the boat, I'm sure she'll be OK with that

Biggest problem: sweat running down into my eyes from the Virginia humidity as I hammered away at the tacks to hold the cable. Should not have done it in the middle of the day.
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Old 07-31-2009, 12:20 AM   #11
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I can see why you didn't want to pack the battery up the hill. What is the vertical elevation differential between the house and the water? My last lake cabin had 52 steps- 32.5' and it was a lot of work packing gear up the hill after a day on the lake

Looks like a great location, very relaxing... especially with 110v down by the water .
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Old 08-01-2009, 12:02 PM   #12
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I can see why you didn't want to pack the battery up the hill. What is the vertical elevation differential between the house and the water? My last lake cabin had 52 steps- 32.5' and it was a lot of work packing gear up the hill after a day on the lake
Yeah, I bet it was. My elevation is only about 100 feet with about 25 steps, not a big problem to walk but carrying a battery gets pretty heavy. Besides, I got my new pontoon boat today and it's a 48V system with four big batteries, no way will I carry them up and down.

For the wiring, I told a buddy about what I did, with two GFCIs (one at the house and one at the dock) and he said two GFCIs cancel each other out. Is this true?

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Looks like a great location, very relaxing... especially with 110v down by the water .
Thanks, that 110v might just be good for a small beer cooler as well
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Old 08-01-2009, 12:26 PM   #13
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For the wiring, I told a buddy about what I did, with two GFCIs (one at the house and one at the dock) and he said two GFCIs cancel each other out. Is this true?
Not if you mean "cancel out" as in "render them useless".

It is redundant though - one OR the other will trip (possibly both, depends on reaction time), really no need for both. But I don't see how it can hurt.

But someone might assume that the work was not done by a real electrician, just based on that alone. Don't know if that matters to you. I'm guessing that stapling the wiring to the decking isn't to code either, but we have some tight codes around here, many of which I think are overkill.

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Old 08-01-2009, 01:46 PM   #14
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Not if you mean "cancel out" as in "render them useless".

It is redundant though - one OR the other will trip (possibly both, depends on reaction time), really no need for both. But I don't see how it can hurt.
Yes, ERD, that's what I meant, render them useless. I'm big on safety, so I'm OK with redundancy even if they trip twice as often. I'd rather have them trip when they don't need to than not trip when they need to.

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But someone might assume that the work was not done by a real electrician, just based on that alone. Don't know if that matters to you. I'm guessing that stapling the wiring to the decking isn't to code either, but we have some tight codes around here, many of which I think are overkill.

-ERD50
Well, there's probably ample other reasons for someone to know I'm not a real electrician I tacked the wire along the sides of my steps so it's visible and can serve as a warning that hey, there's wire here. An electrician would probably have tacked it underneath, with commensurate cost.

As far as the code, I searched the codes online and didn't see this addressed. I asked a local licenced electrician, a local contractor, and the guy at Lowes and they all thought that tacking outdoor grade UF to wooden stairs is OK with the county. They say the big thing with the code here is safety, they don't want the wire to be a tripping hazard or to be in a place where it can be accidentally cut by a weed wacker, etc. So I hope I'm OK but will probably go down to the county just to ask hypothetically what does the code allow. If I''m in violation I will change the wiring setup.

Another factor is my obstructionist POA. There are no covenants on wiring, not because it's not important, but because they don't want liability. But that would not stop them from sending my request through 3 or 4 different committees, taking 3-4 months to let me know whether I can proceed (even though every other dock is wired) and generally making themselves a PITA. So I'd rather ask for forgiveness (of what?) than permission.
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Old 08-01-2009, 02:27 PM   #15
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As far as the code, I searched the codes online and didn't see this addressed. I asked a local licenced electrician, a local contractor, and the guy at Lowes and they all thought that tacking outdoor grade UF to wooden stairs is OK with the county. They say the big thing with the code here is safety, they don't want the wire to be a tripping hazard or to be in a place where it can be accidentally cut by a weed wacker, etc.
I don't know what the codes are either (I am not an electrician), but I tend to agree with you that a potentially hazerdous thing is better where it can be seen than to be partially hidden.

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So I hope I'm OK but will probably go down to the county just to ask hypothetically what does the code allow.
Send a neighbor

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