Advanced Marine Electrics and Electronics Troubleshooting A Manual for Boatowners and Marine Technicians

or reject that suspicion. Alternatively, many

people will use the clamp-on leak tester dis-

cussed earlier. If excessive leakage is found,

they’ll just replace the piece of equipment.

Using a Megohmmeter

Meter lead connections and screen displays

vary from one brand of megger to another, but

there are some commonalities among meters:

• multiple voltage test ranges


• a low ohms scale for checking continuity
  and resistance values below 200 


• the ability to measure voltage up to 600
  VAC


• a “3-minute” lock test function (a com-
  mon time parameter used by equipment

manufacturers who recommend periodic

insulation tests)

It is common practice to select a voltage

range that is approximately twice the value of

the rating of the appliance or cable being

tested:

• For a 120 VAC appliance, use the 250 V
  scale (or the nearest equivalent on the
  meter).


• For a 220 VAC appliance, use the 500 V
  scale.


• For 600 V boat cable, use the 1,000 V
  scale.

Connecting the meter to the circuit or

appliance in question is easy once you’ve

sorted out any isolation requirements and

100 electrical systems troubleshooting

multiple voltage

test ranges

positive test lead

negative test lead

master test button

3-minute lock

test function

The Extech 380360 megohmmeter measures resistance up to 2,000 M. It also has a 3-minute lock test func-

tion. Also shown is the unit’s master test button.