How to Test a Galvanic Isolator

Ed Watt is the General Manager of the Galvanic Isolator Company

The easiest way to test a Galvanic isolator is using a simple multimeter. The results you get won’t be of laboratory standard, but you should be able to check that your isolator is working, and isn’t either short or open circuit.

You’ll need a multimeter with  Diode or Semiconductor test setting - a diode symbol like the one in the photo below.

The Galvanic isolator must be completely disconnected before testing - it can not be tested whilst installed.

galvanic isolator test on narrowboats and cruisers

If you’re testing a Wire In Galvanic isolator, it’s really simple, because the connections are readily accessible. A Plug in Galvanic isolator is  slightly more tricky - because the earth terminal on the socket end is inset. It’s important to get a really good contact between the multimeter and the terminals, or you could get unreliable results.

To help with this, it’s a good idea to attach a small crocodile clip to each of the multimeters probes, as shown in the picture.

marine galvanic isolator test with multimeter

Calibrate the Multimeter

First we need to calibrate the multimeter. Set the multimeter to the Semiconductor Test or Diode Test position, and with the  probes NOT touching, write down the meter reading. This is the “Open Circuit” reading.

Next, connect the probes together, and write down the meter reading. This is the “Short Circuit” reading.

Now we’ve calibrated the multimeter, and we’re ready to carry out the actual test.

Testing a Galvanic Isolator with Stud connections

testing a marine galvanic isolator with a multimeterTo test a Galvanic isolator with connecting studs...

1). Set the multimeter to the Semiconductor Test or Diode Test position, and attach one crocodile clip to each stud. Wait 5 seconds then note the reading on the meter. The reading will typically be between 0.9 (Volts) and 1.2 (Volts). 

2). Now reverse the connections. Wait 5 seconds then note the reading. Your Galvanic isolator is OK if the reading is similar (within about 10%) of the previous reading.

If the multimeter reading is equal to either the Open Circuit or Short Circuit readings you noted when you calibrated the multimeter, or if the readings in both directions are widely different, your isolator MAY be faulty, and we’d suggest getting it professionally checked.

Testing a Plug In Galvanic Isolator

To test a Plug In Galvanic isolator, it’s a  good idea to extend one of the probes by clipping a thin terminal screwdriver to one of the crocodile clips (See photo). This will make it easier to connect to the socket end.

how often should a galvanic isolator be tested

Completely disconnect the isolator from the boat and the shore supply.

As you can see in the photo, the connections you need to check are the BIGGEST ones in the plug and socket - the ones nearest the locating nibs in the body of the connectors. 

First calibrate the multimeter as explained above.

marine galvanic isolation for boats
how to test a plug in galvanic isolator

1). With the multimeter set to the Semiconductor Test or Diode Test position, connect one of the crocodile clips to the earth connection of the plug, and insert the terminal screwdriver into the earth connection of the socket, ensuring that it makes good contact with the metal connection in the hole. Wait 5 seconds then note the reading on the meter. The reading will typically be between 0.9 (Volts) and 1.2 (Volts). 

2). Now reverse the connections, and wait 5 seconds. Your Galvanic isolator is OK if the reading is similar (within about 10%) of the previous reading.

If the multimeter reading is equal to either the Open Circuit or Short Circuit readings you noted when you calibrated the multimeter, or if the readings in both directions are widely different, your isolator MAY be faulty, and we’d suggest getting it professionally checked.

MARINE GALVANIC ISOLATORSmarine galvanic isolators uk

If you don't already have a Galvanic isolator, you almost certainly need one! Whenever you plug into an electric hook up, a Galvanic Isolator is essential! Below is a link to our most popular model. It just plugs into your hook up cable. No tools, no wiring - just plug it in.

 For more information please Click Here