PRODUCT SAFETY SOLUTIONS
© 2012 Educated Design & Development, Inc. All rights reserved. Rev B: February, 2012 Page 10 of 19
OPERATING INSTRUCTIONS:
This chapter explains the proper use of the LT-952. This includes instructions on how to perform leakage
measurements through the product under test’s power cord grounding conductor and measuring leakage
current from surface to ground or neutral and between surfaces. All of these tests generally need to be run
to test compliance with IEC60950. As such, they assume the product is completely isolated from ground.
Finally, this chapter will show how to measure leakage current in field-testing situations where the product
cannot be isolated from ground.
For these examples, assume that the product under test is a 120 Volt cord-connected piece of equipment
that is being tested for compliance. Please refer to
IEC60950 for complete testing specifics
Measuring Through the D.U.T. Power Cord Ground
1. Isolate the product under test from ground. This can be accomplished by placing the product on a rubber
pad or other suitable insulator. This may also include disconnecting any accessory cables connected to the
product under test (i.e. a shielded monitor or printer cable).
2. To verify that there are no other grounds to the equipment under test, connect an ohmmeter between the
ground pin on the product under test and the power system ground. Readings of close to 0 Ohms indicate
the presence of an extraneous ground that needs to be removed. This step can probably be omitted for
simple test setups. The only penalty for an extraneous ground may be a blown meter fuse in the LT-952.
3. Secure the work area so that you or another person cannot accidentally come into contact with the
product during the test. Since the product ground is disconnected while the Ground switch is toggled
OPEN, the product under test poses a potential shock hazard.
4. Set the controls on the LT-952 as follows:
Voltage selector 115
Power OFF
Neutral CLOSED
Line FORWARD
Meter Connection D.U.T. GROUND
Range 20mA
5. Connect the product under test to the front panel receptacle. Make sure that the product under test’s
power switch is ON.
6. Turn the Power switch of the LT-952 to ON. Observe that the leakage indicated on the LT-952 is ZERO.
This is normal as the leakage current is flowing through the still connected product ground.
7. To measure leakage, depress and hold the Ground switch to the OPEN position. Within a few seconds,
the display on the LT-952 should settle to the final leakage current value. If the displayed result is less than
20mA, change the Range switch to the 2mA position.
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