Ground Resistance Measurement - 3-Pole (3-Point) - AEMC 6470 User Manual

4.5 Ground Resistance Measurement - 3-Pole (3-Point)

The Model 6470 measures the ground resistance of an electrical installation.
One terminal, E (X), is connected to the ground under test. Two other terminals, S
(Y) and H (Z), are connected to two auxiliary rods some distance away.
NOTE: It is important that the auxiliary rods be sufficiently far away to not inter-
fere in the measurement. If the rods are too close, the reading will be too low. If
the rods are too far away, the readings will be too high.
The actual resistance of the auxiliary rods also may affect the measurements if
they are too high. High resistance actually comes from poor or very dry soil. To
have a good measurement, the instrument needs to "punch" through and provide
enough signal strength.
The Model 6470 provides two test voltages 16V and 32V associated with a higher
test current than other instruments on the market (>200mA max). The test voltage
is set to 32V when it leaves the factory and may be lowered to 16V by the user. The
Model 6470 can also measure the resistance of the auxiliary rods.
The nominal test frequency is 128Hz (Square Wave) which is typical for ground
testers. In certain cases measurements, at nominal test frequency may be affected
by stray signals in the ground. The Model 6470 automatically scans the stray volt-
age noise and internally selects the best test frequency between 41Hz, 55Hz,
92Hz, 110Hz, 119Hz, 128Hz, 476Hz for the optimum measurement. For advanced
users, the test frequency can be manually selected between 41Hz and 513Hz.
Details on ground resistance measurements and rod distances are available in the
AEMC Understanding Ground Resistance Testing Workbook CD that was
®
included with the instrument.
Please note that the AEMC
terminals to facilitate connections and to ensure that adequate test lead lengths
are provided.
Shop for AEMC products online at:
34
ground kits include color-coded leads which match the
®
ShopAEMC
www. .ca 1.877.766.5412
Ground Resistance Tester Model 6470