In our previous post, we gave you a basic overview of Galvanic Isolators, and why you need one on YOUR boat. If you haven’t read it, but would like to, please click HERE.
If you read the previous article, you now know why you need a Galvanic Isolator, and how to choose the right one for your boat. And it really wasn’t that bad, was it? But if you’d like to become a Certified Galvanic Isolator Nerd, read on.
What is the difference between Galvanic Currents and Earth Leakage?
Galvanic Currents, and Earth Leakage are often lumped together as one. But they are actually quite different.
Galvanic Currents, (AKA Corrosion Currents), are small currents that flow in the earth conductor of a boat’s shore connecting cable. They are quite low voltages, typically under 1 volt. They cause corrosion of a boat’s hull and stern gear, prop etc., and fast depletion of anodes. All metal boats connected to a mains supply have Galvanic Currents.
Earth Leakage comes from faults in the boat’s wiring or equipment, and also from “interference” from electronic equipment (TV’s, Battery chargers etc., etc) that’s connected to the boat’s electrical system. Not all boats have earth leakage, but many do. And it’s very, very damaging to your boat’s hull, propeller, anodes etc. If you have earth Leakage, you probably won’t know about it until your boat comes out of the water for maintenance.
Types of Earth Leakage:
AC Leakage. This is what the RCD (Earth leakage circuit breaker) on your boat and shore post are intended to protect against. AC leakage is potentially dangerous to life, but doesn’t directly cause hull damage.
DC Leakage. Also known as Stray Currents. Your boat’s circuit breakers do NOT protect against this! Stray Currents can flow as a result of faults in the boat’s DC wiring or equipment. Often, you won’t be aware of these currents, as there may not be any obvious symptoms. Stray Currents are very damaging indeed, because the voltages are higher than Galvanic Currents – 12 or 24 Volts.
Imprinted Leakage. This is variant of DC Leakage.Your boat’s circuit breakers do NOT protect against this! This type of leakage usually comes from equipment that uses Switched Mode Power Supplies – including battery chargers, power supplies, TV’s, and some LED light drivers. The Voltages involved can be up to and above 40v. Imprinted leakage can cause severe corrosion damage, and when it does, it’s often very rapid. Be aware that even brand new equipment can cause Imprinted Leakage.
Do I need a capacitor in my galvanic isolator?
Earth leakage can reduce the effectiveness of a galvanic isolator, and a capacitor can be fitted to a galvanic isolator to “bypass” this leakage around the isolator. Capacitors don’t work well at low frequencies, and because the frequency of the mains voltage is very low, to be effective, a very large value of capacitor is needed.
And that’s not all……
With modern technology, many earth leakage problems stem from high tech equipment like battery chargers, laptops, navigation equipment etc. This type of leakage is at higher frequencies, and is known as “Imprinted Leakage”. Because of the way they’re made, high value capacitors aren’t very effective at bypassing high frequencies to earth. They aren’t “perfect” capacitors – they are “inductive”, and that ruins their effectiveness at high frequencies.
We believe that the ultimate solution is to have a Galvanic Isolator that is fitted with a capacitor, and LED’s to warn you about earth leakage, so that you can take steps to resolve the problem. Earth Leakage problems never clear up on their own, and should always be taken seriously.
Galvanic Isolators are now available with circuits built in that monitor the current flowing in the earth conductor. Of course, there shouldn’t BE any current in the earth conductor, but if there is, our isolators alert you by illuminating LED’s. One LED lit indicates DC leakage, and two LED’s lit indicate AC leakage.
Which causes most damage, Galvanic Current or Earth Leakage?
At risk of repeating myself, the clear answer is…. Earth Leakage (AKA DC Leakage) – because DC leakage happens at higher voltages. There are two types of DC Leakage, (see above), and both will quickly damage your boat.
So, to confirm…. DC Leakage Currents are BY FAR the more damaging. That’s because the voltages involved are greater. But there is some good news. Whilst all boats connected to a shore supply will have Galvanic Currents, DC Leakage Currents are a problem for a staggering 1 in 3 boats. We estimate that almost EVERY boat will have issues with DC Leakage at some time in it’s life. Because DC Leakage can be SO destructive, it’s a something you should take very seriously indeed. We recommend that you choose a Galvanic Isolator with Earth Leakage detection, or some other method of checking that you don’t have an earth leakage fault.