ohmmeter, contact by a single strand of wire will give reading of 0
ohms. This would indicate a good circuit. When the circuit operates,
this single strand of wire is not able to carry the current. The single
strand will have a high resistance to the current. This will be picked
up as a slight voltage drop.
Unwanted resistance can be caused by many situations as follows:
Undersized wiring (single strand example)
Corrosion on switch contacts
Loose wire connections or splices.
If repairs are needed always use wire that is of the same or larger
gauge.
Measuring Voltage Drop ? Accumulated Method
1) Connect the voltmeter across the connector or part of the cir-
cuit you want to check. The positive lead of the voltmeter
should be closer to power and the negative lead closer to
ground.
2) Operate the circuit.
3) The voltmeter will indicate how many volts are being used to
?push? current through that part of the circuit.
Note in the illustration that there is an excessive 4.1 volt drop
between the battery and the bulb.
SGI974
Measuring Voltage Drop ? Step by Step
The step by step method is most useful for isolating excessive
drops in low voltage systems (such as those in ?Computer Con-
trolled Systems?).
Circuits in the ?Computer Controlled System? operate on very low
amperage.
The (Computer Controlled) system operations can be adversely
affected by any variation in resistance in the system. Such resis-
tance variation may be caused by poor connection, improper
installation, improper wire gauge or corrosion.
The step by step voltage drop test can identify a component or wire
with too much resistance.
MA
EM
LC
EC
FE
CL
MT
AT
AX
SU
BR
ST
RS
BT
HA
SC
EL
IDX
HOW TO PERFORM EFFICIENT DIAGNOSIS FOR AN ELECTRICAL INCIDENT
Circuit Inspection (Cont?d)
GI-31