PRODUCT SAFETY SOLUTIONS
© 2012 Educated Design & Development, Inc. All rights reserved. Rev B: February, 2012
Page 4 of 19
Understanding Leakage Current: (Continued)
etc.), it may be appropriate to measure the leakage current in the grounding conductor or
from any exposed surfaces to ground. (Refer to “Field Testing Grounded Products”, Chapter 2,
for additional details.)
During this test, the unit is energized and any switches within the product controlling primary power (and
likely to be operated in normal use) are opened and closed in all possible combinations. Since the amount
of leakage current is proportional to the supply voltage, this test is typically done at the product's maximum
rated input voltage.
C. The Human Body Model
As previously indicated, a meter with precision impedance correlating to the impedance of the human body
is used to represent the human body. Extensive tests have been done to approximate the impedance of the
human body. These tests have shown that in different environments, with the user subjected to different
physical situations, the body impedance differs. On average, the human body impedance is equivalent to
1500 ohms shunted by a 0.15 µF capacitor.
It should be noted that most of the body impedance is a result of skin resistance. Therefore, in cases where
a person’s skin is likely to be cut (such as in a hospital), the human body resistance model may be different.
Similarly, moisture lowers the skin resistance. Most Standards deal with these issues by lowering the
leakage current limit for hand held products and products that may be exposed to moisture. Furthermore, it
has been proven that the perception to shock (threshold of perception) is directly related to frequency and
therefore, different body impedance models may be used when testing products whose leakage current
contains significant high frequency leakage.
D. Leakage Current Limits
The limits for leakage current vary among Standards. Depending upon the environment the product is
being used in and assumptions concerning the user, different limits may be imposed. These limits are not
only imposed to reduce the Risk of Shock, but also to minimize the possibility of reaction by the intended
user. This is important to emphasize because many assume the limits are only imposed to minimize injury
from electric shock. Although currents in the low milliampere range can cause injury or death in children
and some adults, they can also cause involuntary reactions that cause injury. In other words, a person may
touch a product and receive an unexpected shock, which in itself does not cause injury, but instead causes
the individual to react in a manner that results in injury.
Before using:
Read the entire manual before attempting to use the Leakage Tester. Operation and use of the LT-
952 is to be performed by Qualified Personnel ONLY.
WARNING:
The person(s) using this device should have proper education/training in its use.
CAUTION:
Be aware that there are no user serviceable parts. Do not open any product enclosure.
Return unit to ED&D for servicing.