View Full Version : Yet another electrical thread

Frantically Relaxing
03-25-2013, 04:27 PM
sorry up front at this may get a little long winded :)

First- Our boat has been in an "amentity free" harbor since '06. We don't even have culinary water. The entire dock consists of 22 10x20' single slips, we're at the end of it. the first 2 years our power supply consisted of running extension cords from the utility building about 200 feet away, which itself was connected to temporary power. in 2008 the harbor got a decent power supply installed, after that, I ran some 8 gauge wire from the building to the dock, and installed a 30 amp plug. From there, I ran the boat power using a 10 gauge contractors extension cord. Our boat has two 30 amp input plugs, and I rigged up a junction box that allowed me to feed both inputs using the same cord. When I installed the 30 amp socket I attempted to install a GFCI breaker, but it always tripped. So I just installed the outlet without the GFCI. There are three GFCI's in the boat, and they operate properly without issue. And I've otherwise had no problems with the power. In 2009 I ran all new 8-3 wiring directly to the boat, from a 50 amp knife switch electric box that's attached to the building. The two hot leads split at a junction box at the boat, and each lead feeds a 30 amp outlet. I've had absolutely no problem with this setup. I find no ground leakage, I've checked hull voltage and voltage from the hull to the water several times and I've never found any stray current other than a few millivolts.

Our friend sold the harbor in January, and now we have new owners. The Harbor property is leased from the state, and they will be doing an inspection soon, so I thought I should upgrade the boat's power connection. I picked up a 50 amp GFI service disconnect box, and an electronic kilowatt meter which I mounted inside a Hoffman fiberglass electric box. I spent the afternoon Sunday installing the box, running conduit and wiring, only to have the same problem with tripping the GFI breaker once it was all connected.

FWIW, yes, I'm still using the 8 gauge and I know I should be using larger, but this has always been at my expense, and the new owner is planning on installing "official" dock power within the next 2 years. Until then, this should continue to get us by.

Part of the new install included hammering a new dedicated eight-foot long ground rod just below where the box is mounted. The incoming power was originally connected to a large A/C unit, consisting of two hot leads and a neutral. The ground and neutral connections are separate in the new box. I ran several tests with the voltmeter; neutral to each hot measured 122 V, ground to each hot the same, and even though they were not connected within the box, the neutral and ground wires showed continuity. With power off I also checked continuity between all the box connections, everything was fine. All tests were made while the boat was plugged in. Interestingly, I found that the breaker would trip even with either or both load wires disconnected from the breaker. Only the neutrals were connected. I disconnected the GFI neutral test wire, and the breaker was fine until I touched it to the neutral bus bar, then it tripped.

Once I unplugged the boat, the breaker didn't trip.

As I understand how GFI's work (like from this online explanation): "In normal operation the current that flows in from the 'hot' wire must return in full through the 'neutral' wire, and only way there could be an imbalance in the amount of current flowing in to the hot wire, and the amount of current flowing back through the neutral wire would be if an external source is adding current or current is being leaked through an external source.

-- How can there be any current for the GFI to measure when the loads are disconnected? If there's no current, why is the breaker tripping?

Any ideas on where to start looking? :confused:

Thanks in advance!

Here's a pic of the new setup--


03-26-2013, 07:04 AM
I'm thinking that though you've got your heart in the right place as far as safety is concerned the setup as it is now it simply isn't going to work. For one with the length of your run and marginal wire you'll be possibly subject to maybe enough amperage loss to trip it even without a load. Secondly when using a GFCI breaker it is measuring a balanced load on both legs such as would be applied in going to an appliance such as a hot tub for instance.

In your case you are attempting to feed a sub-panel or distribution point in your boat. As such I can't see any possible way that you could consume and disperse the power in both legs identically. So you're going to experience surges on one leg or the other throughout the day as you utilize different appliances on your boat.

-- How can there be any current for the GFI to measure when the loads are disconnected? If there's no current, why is the breaker tripping?

In a boat it is actually required that the AC and DC system be grounded and they are usually bonded at the motor itself. Chances are you are picking up some stray current or leakage at this point and though maybe a small amount it could be enough to trip the breaker because it's sensing there shouldn't be any current at all.

Frantically Relaxing
03-26-2013, 10:28 AM
The long-run causing the trip makes sense. I'll measure for stray voltage between the neutral wire and my new ground post and see what I get. My "distribution point" at the boat is just a small junction box where the 8-3 line enters and two short 8-2 lines with 30amp female plugs exit and plug into the boat. So the boat is essentially plugged into a 200' long 8-gauge extension cord. I have a few 120v GFI's and small breaker boxes kicking around, it would be a simple matter to put a GFI breaker in place of the junction box and see what happens.

03-26-2013, 11:04 AM
At 200 feet, using 8 awg and 2 30amp plugs (60 amps) you are get a 15 volt drop. here is a good calculator http://shop.genuinedealz.com/Store/Tab.aspx?tabid=2

03-26-2013, 12:12 PM
I believe this is a chart for DC current.

03-26-2013, 12:20 PM
Look to the left of the carts for the calculator. You plug in the wire size, voltage, length, an amps. It gives you voltage drop, voltage at the end of circuit and % of drop.

Frantically Relaxing
04-01-2013, 09:38 AM
Charts shmarts ;) .... How about some real world data?

As noted above, our boat is wired with #8 stranded wire, the run is at a bare minimum 225', probably closer to 250'. I don't have a pic of the measurement, but the supply box measured 122.2 to 122.4 volts.

volts no load on the boat:


volts with the 1200w microwave running--


volts with the coffee pot keeping coffee hot--


Frantically Relaxing
04-01-2013, 09:46 AM
Home voltage no load (122.4)


Home voltage with the 1200w microwave running-



I lost 3.3 volts at home (2.7%) and 12.7 volts on the boat (10.5%) with the same load. And the boat only lost .4 volts at most under no load.

04-03-2013, 06:09 AM
It seems you're experiencing a significant drop considering it's a single appliance running on the circuit. I'm left wondering where it's going to go when you're actually utilizing the circuits in real world typical conditions. Making coffee, with the microwave running while watching the morning news on TV very well may or will drop the voltage down to a point where the appliances may be damaged. In looking around on this topic on the web there seems to be more commonly shared information on the topic in the RV world. It seems RV parks are also plagued with voltage issues just like Marinas but there is a lot more discussion on the topic available to review. I did run into an example of an wire in available monitor that actually would or could serve about any boater pretty well but it's marketed more towards RV's.

Anyway here it is as an example:

Progressive Industries 30 Amp Permanent Electrical Management System Description (http://www.dyersonline.com/progressive-industries-30-amp-permanent-electrical-management-system.html)

High/Low Voltage Protection:
Whenever AC power falls below 104 volts, or rises above 132 volts, the EMS automatically shuts down power to the RV. The EMS will monitor the power and once the AC power rises above 104 volts, or below the 132 volt level, the time delay indicator flashes for the preset time and then automatically restores power to the RV.

Time Delay for A/C Compressor:
If the AC power is interrupted, or the EMS detects a fault condition, the built-in time delay is activated. There are tow settings on the EMS: one is 136 seconds (02:16), and the other is 15 seconds. Consult your air conditioner manual to see if it has a time delay built in. If so, use the 15 second delay, if not; use the 136 second delay. The factory setting is 15 seconds.

3-Mode Surge Protection:
This feature provides full surge protection L-N, L-G, and N-G. Total Joule rating is 1,790, 44,000A surge current. Response time of <1 nano second.

Surge Indicator:
In the event of a power surge, and the surge protector circuit is damaged within the EMS, L-N or L-G, the digital display error code will read E-10. This indicates the EMS needs to be serviced.

Reverse Polarity Protection:
If AC power is a reverse polarity condition, the EMS will not allow power to the RV and the error code will read E-1.

Open Neutral Protection:
If AC power has an open neutral condition, the display will not light, and the EMS will not allow power to the RV.

Open Ground Protection:
If AC power has an open ground condition, the EMS will read an error code of E-2 and power will not be allowed to the RV.

AC Frequency Protection:
If AC power frequency deviates +/- 9 hertz from 60 cycles per second, the EMS will shut down power. An error code of E-7 will be displayed when the frequency is high; and an error code will be displayed when frequency is low.

Accidental 240V Protection:
If 240 volts is detected when plugging into AC power, the EMS will NOT allow power to the RV. If this condition occurs while power is applied to the RV, the EMS shuts off power instantly. The display will read the voltage and E-3 for the error. (NEVER BYPASS THE EMS WHEN THIS OCCURS.)

Continuously scrolls all of the AC power information, including voltage, current, frequency, error codes and previous errors. Each reading is displayed for two (2) seconds.

Previous Error Code:
This feature tells the user what the previous error was and why power was interrupted to the RV. To read a previous error code, put a "P" in front of the "E" code. This is only displayed if an actual error occurs. The error is deleted when power is disconnected from the EMS.

Enclosed blue jumper wire allows the user to bypass the computer circuit in the EMS in the event of computer failure, thus allowing AC power into the RV. This does not disable the surge protection portion of the EMS; however, all other features are disabled.

Modular Design:
Replacement parts are designed for simple plug and play, making repairs extremely user friendly.

Microprocessor Controlled:
The computer is driven by a state-of-the-art microprocessor that is programmed with software to drive the entire EMS.

If something like the above isn't feasible but you'd still like to be able to easily manually monitor line voltage maybe something like this (http://www.dyersonline.com/prime-products-line-voltage-monitor.html) would serve you better though it offers no real protection of any appliances.

04-03-2013, 07:00 PM
I have a couple questions and I mean them respectfully but how is the marina allowing you to install your own electrical connections etc? Are the other slip owners aware of this?

What is your liability personally if you are not a licensed electrician? If something unfortunate happened, someone could sue the pants off you and I doubt your insurance would cover you?

I just know I wouldn't want my boat neighbor wiring a marina.

I will also note, electricity freaks me out. I do very little with that stuff because it can be so confusing.

Frantically Relaxing
04-05-2013, 06:31 PM
For all intents and purposes, my electric connection is nothing more than a high-tech extension cord. If I attached a 50amp plug on the line-side of my wires and a 50 amp receptacle in place of the breaker box and plugged into that, it WOULD be nothing more than an extension cord...

I'm the only one who has power on the dock, everyone knows about it, most of 'em hook up extension cords to my outside GFI outlets to vacuum their boats out. If something goes wrong I suppose I'm plenty liable, but after 6 trouble-free years I'm not too worried. As for licensed electricians, I'll just keep my mouth shut...

As noted above, I haven't wired "the marina", just our boat.