Measuring Current; Measuring Resistance - Generac Power Systems 7 kW NG Repair Manual

Section 1.4
Measuring Electricity

MEASURING CURRENT

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 transformer with a split core and a rectifier type
instrument connected to the secondary. The primary of the
current 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 measured safely
and easily. A line-splitter can be used to measure current in a
cord without separating the conductors.
Figure 15. Clamp-On Ammeter
Figure 16. A Line-Splitter
Note: If the physical size of the conductor or ammeter
capacity does not permit all lines to be measured simul-
taneously, measure current flow in each individual line.
Then, add the Individual readings.
Page 20
PART 1
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 measure 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
measured.
In Figure 17 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
BATTERY
- +
Figure 17. A VOM as an In-line Amp 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, or checking a wire for an open or grounded
condition.
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 conditions can be
detected using a VOM:
• A "short-to-ground" condition in any Stator or Rotor winding,
or a short to ground on a specific control wire.
• Shorting together of any two parallel Stator windings.
• Shorting together of any two isolated Stator windings.
• An open condition in any Stator or Rotor winding, or an open
in a control wire.
GENERAL INFORMATION
A
RELAY