Anti static wrist strap

[idris]

I have an anti static wrist strap with a 4mm banana plug on the end (and an optional crocodile clip).
My Breadboard has 4mm binding posts.
So I could connect the wrist strap to the Breaboard. But I'm sure this won't help when handling static sensetive components away from the breadboard.

I can't find an earthing mains plug that will accept a banana plug, And none at all at a sensible price.
(NB - using UK 3 pin plugs.)
So I was wondering about the merits of removing the live and neutral pins from a standard mains plug (for safety) and mounting a 4mm socket in the casing. Then plugging it into a switched wall socket with the power off.

Genius or madness?

 

[jackorocko]

Couldn't you just use a grounding cable screwed into the metal box and run through a small hole in the face plate?

 

[daddles]

Here's one solution -- it was a couple of minutes of work on a lathe. It's a chunk of 6mm (i.e., 1/4 inch) brass bar stock drilled for a 4 mm banana jack in one end and of a suitable diameter for a grounding jack in a power outlet on the other end. It's for a US outlet, but obviously could be made to work with others by changing the dimensions. That's a chunk of green vinyl tape insulating it.

If you don't have a lathe, something like this can still be made with e.g. a hand drill and a file (it just takes more time).

 

[idris]

Thanks guys.
Jackorocko - metal box of what? The power socket?
Daddles - do you mean basically the same principal as what I was thinking of?

 

[daddles]

Daddles - do you mean basically the same principal as what I was thinking of?

I'm not sure of exactly what you were thinking, as you didn't include a sketch. I just showed you what I use when I want to connect something with a 4 mm banana plug to a ground in a standard 15 A NEMA 120 VAC outlet, commonly found in US homes. It's been decades since I've seen a UK outlet, but I'd imagine you could do something similar to what I did. I'm assuming you want to connect your static strap's 4 mm banana plug to grounded conductor.

You can also use an alligator clip that accepts 4 mm banana plugs and connect it to something that is grounded. But I'm not as big a fan of this, as the alligator clips have a tendency to pull off if you accidentally apply a pull to them.

Another choice is to screw a spade connector as shown in the attached picture to something that's grounded, as there's a 4 mm socket in its end. Lots of choices, as these are all pretty common parts easily purchased.

 

[poor mystic]

You'd do well to put a 10MegOhm resistor in series with the strap. This keeps you safer than if you would be with the strap connected low-resistance to earth.

 

[daddles]

You'd do well to put a 10MegOhm resistor in series with the strap. This keeps you safer than if you would be with the strap connected low-resistance to earth.

Good point -- although the 3M ones I've used for 30 years have a 1 Mohm resistor in the cord (made e.g. by Desco).

 

[idris]

What does the resistor do? I assume it just provides a load for any static to discharge through. yes?

 

[poor mystic]

Sure, the resistor is a useful conductor, but the reason it is set high is to reduce the electric shock hazard to people, who might be working on live equipment while they are earthed.

 

[jackorocko]

What does the resistor do? I assume it just provides a load for any static to discharge through. yes?

As PM suggested, imagine your left hand touching a live wire while your right wrist is tied straight to ground with no resistance in series. I see a quick way for you to meet your maker.

 

[poor mystic]

Actually, it sounds like Idris might have one of daddles' very 3M straps. I used to use the reptile clip on mine and join it to the antistatic mat. I would quite happily have connected it to a mains-derived earth.

 

[idris]

I see a quick way for you to meet your maker.

With 4.5 volts? Jeez, a AAA battery must be more dangerous than I ever realised











Just in case anything was lost in translation - that's a well meant joke, not sarcasm.

 

[(*steve*)]

Just in case anything was lost in translation - that's a well meant joke, not sarcasm.

What was lost in translation was the important safety information.

The whole point is that if you tie yourself to ground via one wrist, you place yourself in a much higher risk situation for a fatal electric shock if you touch anything (perhaps your soldering iron) which develops an earth fault.

You also are at similar risk if the device you are earthing yourself to becomes live.

The series resistance is there to save your life, and whilst you may joke about with your life, I do not do the same with mine.

 

[idris]

Thanks Steve. I was not meaning to make light of safety or seem ungrateful for the advice - hence my addendum. I had not appreciated the inherent danger of a wrist strap. It had not occurred to me that, in the circumstances, there were any concerns other than damage to components. I assumed that you were talking about using mains powered equipment like PSUs and since I am currently only working with small batteries and Breadboard it had no occurred to me to think about things like soldering irons.
Humblest appologies for any offence unintentionally caused.

 

[(*steve*)]

The most dangerous risks are the ones you're not aware of.

So now you have one fewer.

And that's a good thing.

 

[daddles]

Another safety tidbit: if you work around electrical stuff, your power circuits should have a GFI (ground fault interrupter) protecting you (also called residual current devices). These things can protect you from ground faults and AC leakage. There's absolutely no reason why an experimenter shouldn't be using one -- they cost far less than a trip to the emergency room or a one-way trip to the morgue.