Wrist Straps – Q&A – Part 1
We get a lot of inquiries in regards to wrist straps: what they do, why the different types, how they are used, etc. So we thought it might be helpful for you to collect the most common queries in a Q&A style blog post. There is quite a bit of ground to cover in regards to wrist straps so to make it easier on your eyes and head, we spread the information over 2 blog posts. The first post will cover the basics from what a wrist strap is to introducing the different styles. The second post will focus on the correct use of wrist straps. Let’s get started!
What is a wrist strap?
A wrist strap is made up of two components:
- a wrist band that is worn comfortably around your wrist and
- a coil cord that connects the band to an Earth Bonding Point (EBP).
Wrist band and coil cord of a wrist strap
Why do I need a wrist strap?
In an ESD Protected Area (EPA) all surfaces, objects, people and ESD sensitive devices (ESDs) are kept at the same potential. This is achieved by simply using only ‘groundable’ materials that are then linked to ground. Wrist straps are the most common personnel grounding device and are used to link people to ground. They are required if the operator is sitting (see question below).
Are wrist straps necessary?
Wrist straps are not necessary if an operator is wearing two foot grounders on a conductive grounded floor and doesn’t lift both heels/toes at the same time. As some people lift both feet off the ground while seated, wrist straps are essential for sitting personnel.
Does a wrist strap work if it’s near your forearm?
Yes. The key to the wrist strap is the intimate contact of the conductive band to your skin and of course the coil cord connecting it to ground. It doesn’t matter if the contact point to your body is on you wrist, finger, forearm, ankle, etc., as long as it is in direct contact with your skin. The skin is electrically continuous over you whole body. The wrist is just a convenient place to couple the band to.
What styles of wrist bands are available and how do they differ in their effectiveness?
Operators can choose between elastic and metal wrist bands:
- Elastic wrist bands are the most popular wrist band as they are comfortable to wear and easy to adjust. Compared to metal wrist bands they are also less expensive.
- Some people prefer metal wrist bands as they are generally longer lasting and easier to clean.
The key to personal grounding is to have an adequate path to ground so that there is never a potential difference with respect to ground on the human body for longer than 150 milliseconds (ms) body movement time. Such rapid grounding is accomplished well by elastic or metal wrist straps. So in terms of their effectiveness to protect against ESD, there is no difference between elastic and metal wrist bands.
What size wrist band do I need?
Both elastic and metal wrist bands are (to a certain degree) adjustable. Metal wrist bands offer less adjustment, so you will find those are generally available in different sizes depending on the circumference of your wrist. However, you are still able to adjust metal wrist bands if you needed a tighter/looser fit.
To adjust your wrist band, follow the below steps:
1. Elastic wrist bands:
- Place the wrist band on the wrist.
- Pull the “tail” of material that extends out from the clasp to tighten the elastic material until the wrist band fits snugly but comfortably.
Adjusting an elastic wrist band
2. Metal wrist bands:
- Insert the link end of the wrist band into the slotted opening on the cap. Insert it at a downward angle to allow the links to slide inside the channel in the backplate.
- Change the size of the band by sliding the links in or out of the stainless steel backplate. For extra small you can cut off excess links with cutters.
- Lock the links into place by pulling down on the band, seating the band securely over the lip on the edge of the backplate.
Adjusting a metal wrist band
What is the difference between single-wire and dual-wire wrist straps?
Single-wire wrist straps have one conductor inside the insulation of the coil cord. They offer significantly lower life-cycle costs compared to dual-wire wrist straps. While they would not be suitable for the most critical applications, single-wire wrist straps are an economical way to ground an operator.
Dual-wire wrist straps have two conductors. They offer a reduced risk of damaging ESD sensitive devices because even if one conductor is severed, the operator still has a reliable path-to-ground with the other conductor. For that reason they are generally used in critical applications. For maximum benefits dual-wire wrist straps should be used together with dual-wire continuous monitors.
Find part 2 of this series here.