Procedures for Testing with the DX Host
70 Baker DX 71-030 User Guide EN V10 www.megger.com
DC Tests Using the DX Host
NOTICE: Review all safety information provided with the equipment and presented in chapter 1 —“General
Operating Information” before setting up or operating.
Confirm that the Baker DX setup procedure has been followed. Refer to chapter 5 —“Setting up the Baker
DX Tester” as needed.
Refer to chapter 7 —“Setting up Fixtures, Test Accessories, and Lead Connections” for information needed
on this topic.
WARNING: DC tests of high-voltage motors will be automatically discharged
when releasing the Start (PTT) button (unless PTT lock is active). To avoid injury
or death from electrical shock, wait for discharge to reach zero before removing
any leads.
Some standards resources suggest allowing a winding to discharge four times
the total amount of time that DC voltage is applied to the winding.
When performing DC tests, all three red leads are hot (with voltage). When
performing a single-phase set of tests, typically leads 1 and 2 are connected to
the two coil leads. Lead 3 is not connected, but is still hot. Ensure that the
unused lead is safely set aside to prevent accidental contact with equipment,
unit under test, or the operator to avoid injury or damage.
NOTE: DA start/stop, Step Voltage, ramp rates, and other test settings are specified in the System Settings
mode. Refer to the “Using System Settings” section in chapter 4 —for more details.
DC tests of electric motors help determine the integrity of the ground wall insulation of a
motor’s coil. Ground wall insulation consists of wire insulation, slot liner insulation, wedges,
varnish, and sometimes phase paper.
The DC tests performed by the Baker DX include:
Insulation Resistance (IR)
Dielectric Absorption (DA)
Polarization Index (PI)
DC High Potential (HiPot)
Step Voltage
Each test type was designed to answer specific questions regarding the properties or integrity of
the ground wall insulation system. The following example includes procedural details.
1. Always begin DC testing by conducting a MegOhm test using a test voltage based on
the motor’s operating voltage and the appropriate standards and/or company testing
guidelines.
2. Look for an unusually low MegOhm value when compared to previous measurements or
industry accepted limits for the type of insulation in the motor.
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