Copyright Goodheart-Willcox Co., Inc. Chapter 10 How Electric Meters Work 173 the meter, a shunt is used. A shunt is a resistor that produces a low-resistance path for current to pass through another part of the circuit. This prevents the device from overheating. Analog ammeters typically have four or more current ranges that use internal and external shunts. Shunts are available in the hundreds of amperes. The magnetic coil is wired in parallel to the shunt. See Figure 10-4. In this example, we see if the coil has a maximum capacity of 1 mA (0.001 A), then shunt 1 is used for a 10 mA range. When a 10 mA current is measured, 90%, or 9 mA, flows through the shunt. 120 V on 250 V range 120 V on 50 V range 50 V on 50 V range Goodheart-Willcox Publisher Figure 10-3. A voltage measurement using two ranges is shown. The measure 120 V the 250 V range must be selected. If the 50 V range is selected, the pointer will be off scale and the movement can become damaged. Coil Range selector S1 S2 Common probe Load + Probe Meter in series with load 90% of current flows through shunt 1 and 10% flows through the coil. 99% of current flows through shunt 2 and 1% flows through the coil. Goodheart-Willcox Publisher Figure 10-4. The meter is configured to measure current.