EMIT - Questions And Answers

Where would I find any articles/information on 1 meg verses 2 meg resistors in heal straps? - Anonymous, Redmond, WA

The information you are looking for I can provide to you now, as there is very little information on our web site concerning the reasoning for 2 Megohm vs. 1 Megohm series resistance in foot grounders.The primary reason for having any additional or discrete resistance, and in particular 1 Megohm or greater is for personal safety. If the grounded operator comes into contact with live power (under 250 VAC), then this discrete resistance (minimum 1 Megohm) will limit the current the body receives to a safe level of below 0.25 mA. The MIL-STD-454 recommends that the current be under 1.0 mA, UL recommends that it be below 0.25 mA. All of our resistorized foot wear and wrist straps are UL approved. 1 Megohm versus 2 Megohm? Why a choice? There is a very simple, but important reason for the choice. One Megohm will get the unit UL approved, but since it is highly recommended to wear a pair of Foot Grounders (one on each foot) there is a problem when both foot grounders are grounding the body. The equivalent resistance of resistors in parallel can be much less than any individual resistance series. In the case where the circuit consists of only 2 identical values, the equivalent resistance is half of one of the identical values. Two 1 meg resistors in parallel is equivalent to 0.5 megohms, which is considered “unsafe” by UL but OK by MIL-STD-454. 2 Megohm resistor foot grounders when worn and ground by both feet would bring the equivalent resistance to 1 Megohm, considered safe by UL. This is why it is recommended to use 2 Megohm resistor foot grounders when wearing one on each foot.

Related Categories: