|Introducing the ELCI|
|Written by Ed Sherman|
|Monday, 18 January 2010 10:56|
Introducing the ELCI.................Ed Sherman
One of the projects I've been working on for the last five years is lobbying for a requirement for an important new safety device that would be installed on all new boats and hopefully will get retro-fitted to old boats as well. The device is known as an ELCI, an acronym for "electrical leakage circuit interrupter". The concept here is nothing new, in fact boats built in other countries outside of the US have been employing similar devices for years, which is really what got me on to the idea. Basically I asked a simple question, is the rest of the world wrong and the US right in all of this? As I began to hear more and more about in water electrical shock deaths around boats, especially in marinas, I began to believe that we were off base and the rest of the boating world was right on target.
You already have similar devices installed in your home and on your boat, they're known as GFCI's or ground fault circuit interrupters. A photo of one is shown here and if you look really closely, you can just see the corrosion seeping out of the terminals.
Most of the GFCI units out there now have a small label on them that tells you to "test monthly". My comfort level is always reduced because I know nobody ever tests these things as part of a monthly routine, either at home or on their boat, and they do fail. The trouble is they don't fail in the open circuit mode, i.e. so the power is shut off. They fail in such a way that they won't do what you need them to do in the case of a short circuit from an appliance to its case. These devices are supposed to prevent you from getting electrocuted! Testing them monthly actually exercises the mechanical mechanism inside the unit so that it will react in a timely manner when needed to shut off the power to the appliance plugged into the socket. Without this periodic exercise, they sometimes start to stick and corrode to a point where the mechanical mechanism can't move to shut the power down.
The primary difference between the GFCI in your bathroom or kitchen and the ELCI I'm introducing here is the amperage level they trip at. The units in your house or on your boat are engineered to trip at a nominal 5 milliamps (mA), the ELCI that effective in July of this year will be required equipment on new boats is engineered to trip at 30 milliamps. You will still be required to have the 5 mA units in places like your head or galley area on the boat, but these 30 mA units will be required on your shore power system as it comes into your boat.
You might be thinking, hey why don't the marina people just put a GFCI in the circuit supplying my boat and be done with it? That's the rub, the 5 mA trip level is just too low in most cases to be effective. They would likely be nuisance tripping quite often. You see many of the typical appliances on your boat have some inherant, low level ground fault leakage already, not enough to shock you but leakage non-the-less. Battery chargers and motor circuits are classic examples of circuits where some low level leakage may occur normally. This leakage current is cumulative within the grounding system on your boat and on the dock. Five battery chargers and ten motor circuits all tied to the same grounding circuit might just trip a regular GFCI device on a regular basis. Hence, the 30 mA trip level of the ELCI. This specification incidently is the same as the devices used in Europe, New Zealand and Australia already. The 30 mA value is a good compromise between nuisance tripping and electrical shock hazard safety. What do these new devices look like? Two are shown below, one for a 30 amp shore power circuit and one for a 50 amp service.
The above units will either be mounted on the main AC distribution panelboard on your boat or may be located in a separate box somewhere near the shore power inlet to the boat, depending upon access limitations.
What's the problem? Why do I need this thing anyhow?
The problem here centers itself around the way in which boats today are wired. You see a modern boat is wired with all of its grounding system connected, both the AC and DC sides of you electrical system are connected. This is as it should be for several reasons. One is that by doing this an alternate path for ground fault current leakage ends up being established with the water the boat is floating in. Originally, this was thought to be a good option because even if the dock wiring had a faulty ground, the fault current would leak out of your boat and find a path back to the source of power and trip a regular circuit breaker, shutting the power down. A second reason is that by connecting everything together, corrosion issues are minimized, a way too complex topic to discuss as part of this entry. The idea here is that if your electric water heater devellops a short circuit to ground, the fault current will go through the green wire grounding circit back to its power source and trip the breaker, minimizing the risk of you touching the metal case of the heater and getting zapped by 120 volts of AC power. This is all well and good, but there is a problem. You see the heater in this example might be protected by a 15 or 20 amp circuit breaker, which in fact may never trip because the short circuit is of low quality simply meaning that the fault connection to the case of the heater might be very highly resistive and not able to conduct the full current supplied. You need to know that one amp of electrical current is enough to kill you if it travels through your heart, that's right one, uno. Hence, the 30 mA trip level for the ELCI. 30 mA (there are 1000 mA in one amp) will certainly be fealt, but it won't stop your heart. Its important to note here that all of the shock incidents we have documented have occured in fresh water, none in salt water. So, what's up with that?
You see fresh water is actually a rather poor conductor of electricity, salt water is really a good conductor. When electrical leakage current enters into a freshwater environment it has to struggle to find a path back to its source, typically along the surface of the water. Saltwater, being a good conductor dissipates the leakage current rather rapidly. In a freshwater scenario, the fault current forms a gradient on the surface that moves around the source boat. If a swimmer enters into this fault gradient, the current will enter the swimmers body at one point and exit at another. If the current path includes the person's heart (quite likely), the heart muscle can seize, you know the rest of the story......
The ELCI will shut down the power to a boat if a low level, but not too low, fault occurs, eliminating stray leakage current from entering into the water the boat sits in. The fault will then be noticed, traced and the faulty component replaced.
You're going to hear a lot more about these new devices over the next few years. If you buy a new boat built in 2010, it'll have one installed. If your boat is built before this year, get one installed or DIY. I'll be providing more information and a bunch of DIY instructions in posts this Spring as people get ready for the upcoming boating season and the ELCI's become more readily available in the market place, but please, consider this as a must have upgrade to your existing shorepower system, I'm really sick of hearing about people getting killed swimming around their boats.
|Last Updated on Monday, 01 March 2010 21:30|