Measuring Current

Section 2

MEASURING ELECTRICITY

engine speed governor. For models rated 60 Hertz, the governor is generally set to maintain a no-load fre- quency of about 62 Hertz with a corresponding output voltage of about 124 volts AC line-to-neutral. Engine speed and frequency at no-load are set slightly high to prevent excessive rpm and frequency droop under heavy electrical loading.

Clamp-on:

To read the current flow, in AMPERES, a clamp-on ammeter may be used. This type of meter indicates current flow through a conductor by measuring the strength of the magnetic field around that conductor. The meter consists essentially of a current trans- former with a split core and a rectifier type instrument connected to the secondary. The primary of the cur- rent transformer is the conductor through which the current to be measured flows. The split core allows the instrument to be clamped around the conductor without disconnecting it.

Current flowing through a conductor may be mea- sured safely and easily. A line-splitter can be used to measure current in a cord without separating the conductors.

Figure 2-2. – Clamp-On Ammeter

Figure 2-3. – A Line-Splitter

NOTE: If the physical size of the conductor or ammeter capacity does not permit all lines to be measured simultaneously, measure current flow in each individual line. Then, add the individual readings.

In-Line:

Alternatively, to read the current flow in AMPERES, an in-line ammeter may be used. Most Digital Volt Ohm Meters (VOM) will have the capability to mea- sure amperes.

This usually requires the positive meter test lead to be connected to the correct amperes plug, and the meter to be set to the amperes position. Once the meter is properly set up to measure amperes the circuit being measured must be physically broken. The meter will be in-line or in series with the component being mea- sured.

In Figure 2-4 the control wire to a relay has been removed. The meter is used to connect and supply voltage to the relay to energize it and measure the amperes going to it.

1.00 A

BATTERY
-	+	RELAY
		RELAY

Figure 2-4. – A VOM as an In-line meter

Measuring Resistance

The volt-ohm-milliammeter may be used to measure the resistance in a circuit. Resistance values can be very valuable when testing coils or windings, such as the Stator and Rotor windings.

When testing Stator windings, keep in mind that the resistance of these windings is very low. Some meters are not capable of reading such a low resistance and will simply read CONTINUITY.

If proper procedures are used, the following condi- tions can be detected using a VOM:

•A “short-to-ground” condition in any Stator or Rotor winding.

•Shorting together of any two parallel Stator wind- ings.

•Shorting together of any two isolated Stator wind- ings.

•An open condition in any Stator or Rotor winding.

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