POWERBOATER’S GUIDE TO ELECTRICAL SYSTEMS
Fig. 3-2. Ancor/Prova clamp-type meter. This unit retails for around $300 and offers amperage reading capability up to 200 amps and a frequency-checking function, useful for some AC tests. Made by Prova, marketed in the United States by Ancor.
Fig. 3-3. Fluke Model 336 clamp-type meter. This is a true RMS (root-mean-square) meter that can read up to 600 AC or DC amps. This is an excellent choice if you do a lot of AC work. Its shortcoming is that its ohms scale is not as sensitive as other meters I’ve used. This model sells for about $275.
marine applications, such as those used in battery isolators. It does work for testing most alternators, but it may not be adequate for many inboard or inboard-outboard starter-current tests. The Ancor (part number 702070) is available through major marine retailers such as Defender Industries and West Marine for about $300.
Both of these meters come with fairly easy-toread instructions, but be warned that the meter companies in general assume that you know how to attach the meters to the circuit correctly for the measurement you’re making. Reading the sections that follow will assure that you do!
Fluke Model 336
Using Your Multimeter
If you’re the type that simply has to have the best, Fluke Corporation makes what I consider to be some of the finest multimeters available anywhere. There are other fine meters, of course, but Fluke’s top-ofthe-line Model 336 offers one additional feature that will be useful if your boat is equipped with extensive AC circuitry such as a generator, inverter, or airconditioning and refrigeration systems. This meter will measure up to 600 amps DC and 600 amps AC, far beyond what most boaters need. It does not have a diode-test function, however, nor will it measure AC frequency. Figure 3-3 shows a Fluke Model 336 true RMS clamp-type inductive meter. It’s available through all the major marine supply houses in the United States for about $275. 30
There are literally hundreds of checks and tests that you’ll be able to carry out with your new multimeter. However, at least 90 percent of everything you’ll ever need to do will involve some form of the following four basic procedures: voltage measurement, voltage drop, amperage measurement, and resistance measurement. These procedures are so important that we discuss each in detail. Measuring voltage is the easiest, so let’s cover that one first.
Measuring Voltage To test for voltage, first make sure that your meter is turned on and that the leads are inserted into the correct sockets (the leads that came with your new meter probably have spike-like probes on the ends,
