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There was a very informative article seen recently in Power and Motor Yacht magazine regarding ground fault interrupters. Nowadays these items may be found in differing guises at both ends of a shore power cable; i.e. on the pedestal on the dock and installed on the vessel, as well as installed in certain 110v outlets on board.

So, what exactly is a ground fault interrupter? Good question.

First, some basics. To power up an appliance, or any other electrically powered item, there must be an electrical circuit. That word “circuit” indicates that there is a loop, with the electricity flowing from the power source to the appliance and back to the source again. So, we need two wires, one supplying power, and one returning it to the power source, and because electricity is a nasty, dangerous thing, we need to keep it safely contained within those two wires.

The wire feeding power to the appliance is typically referred to as the “Hot Wire”, although if it ever were to be truly smoking hot, there would be a mighty big problem somewhere! I prefer the more appropriate “Live Wire”, as it is indeed the wire that is live and loaded with power.

The other wire is known as the “Neutral” or “Common” wire, and although this wire is effectively dead and doesn’t do much of anything when the appliance is switched off, hence the boring, bland monikers, it becomes live when the appliance is working and serves as the return wire in the circuit.

There is also a third wire, the ground wire, which connects to any metal components of an appliance and provides an alternate return path to ground in the event of a mechanical failure. The ground wire is a good safety device but it has limitations, hence the advent of the ground fault interrupter.

A ground fault interrupter device is essentially a very sensitive meter coupled to a very fast-acting switch. The meter monitors the electrical current flowing in and out of the circuit on both the live and neutral wires simultaneously, and is on the alert for any mis-match or imbalance between them.

If everything is hunky-dory and there are no issues that would cause some of the current to leak to ground somewhere, then the switch stays closed and the circuit remains powered.

But if there were to be a leakage to ground, such as a finger inserted into a light socket or a knife slid into a toaster during a frantic waffle rescue, then the meter would sense the imbalance and operate the switch to quickly disconnect the power.

FunctioningThe standard device we have installed in selected power outlets in North American homes is known as a Ground Fault Circuit Interrupter or GFCI. These are designed to trip when a leakage current as low as 3 or 4 milliamps is detected, and can cut the power in less than a tenth of a second, hopefully fast enough to prevent a jolt that might otherwise stop ones ticker ticking.

Ground FaultOn board new and newish vessels these days you might find an Equipment Leakage Circuit Interrupter, or ELCI, installed immediately downstream of the shore power inlet. These should be standard on all new boats and appear to work in an almost identical way to GFCI’s, and will cut the power to the vessel when a leakage current above 30 milliamps is detected.

Docks in marinas and boatyards are now being equipped with power pedestals that incorporate Ground Fault Equipment Protector (GFEP) breakers that will also trip with a leakage current above 30 milliamps. These also seem very similar in operation to GFCI’s, and are being stipulated in response to the rising numbers of deaths from individuals encountering lethal currents flowing in the water around boats due to faulty wiring or appliances on board vessels.

So, with GFEP’s on power pedestals; ELCI’s on vessels; and GFCI’s on outlets, there is a whole slew of highly worthwhile protection, so what could go wrong?

Well, for one thing if your older “classic” yacht has a few slightly dodgy electrical connections, you may find yourself tripping the GFEP on the power pedestal at a new or refurbished dock that has them installed. On newer vessels it may be a toss-up as to whether the GFEP on the power pedestal or the ELCI on the boat trips due to some wiring anomaly. Oh yes, new vessels are not immune from iffy wiring connections and other glitches, so new-boat owners may be in for a head-scratching search to find the cause of a bad trip. 

I recall back in the ‘90’s we would have problems with some new European boats wired for the North American market that had some sort of ground fault interrupter installed right after the shore power cable inlet. These seemed to be a hyper-sensitive Euro version, and would trip if you so much as sneezed near them, so they were quickly by-passed while the boat was commissioned and then reinstalled in order to let the owner find a solution.

The most obvious suspect of tripped ground fault interrupters must surely be shore power cable connections. These are temporary connections, and both the cable ends and receptacles can quickly become loose and corroded and cause a poor connection and/or a leak to ground. Inspection and replacement and/or repair is the best policy, and there are some great new designs of shore power connectors available nowadays that are a very worthwhile upgrade from the once-standard plug-it and (then try to remember to) twist-it style.

These ground fault interrupter devices are all worthy developments and all in the name of safety, which is a very good thing. Now all we need is a device that will turn someone into a muppet if they attempt to unplug our shore power cord and steal our juice.

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