Advice about earthing an ESD wrist-strap & mat

Forums › Home Workshop DIY › Advice about earthing an ESD wrist-strap & mat

brad.wright

67 posts

Master Geek

#177192 25-Jul-2015 21:44

Hi All,

I have found a couple of local products (NZ) that allow you to connect your ESD equipment to an Earth / bonding plug (utilising existing earth in the house) . Some have plastic live / neutral pins and others have metal live / neutral / earth. Are these safe / legal or would I be better off installing a separate (new) earth rod?

Thank you!

gzt

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#1351754 25-Jul-2015 22:40

Imho using existing earth is a very bad concept. There is a risk that a ground fault will a) damage components b) damage humans.

I imagine the bonding gear will be resistive but even so.

Having said that, geekzone has a few elec engineers posting and I'm sure one will pass by to give an educated view : ).

elpenguino

3419 posts

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#1351755 25-Jul-2015 22:44

Check your house wiring. Old installations (cant tell you when the cut off occurred) did not actually require an earth rod and the house earths are joined to the neutrals. This means your house earth has to run all the way back to the sub station or transformer.

If you have an earth rod linked to your domestic installation, you should be ok with something that links your earth mat to the domestic earth. In the past I have used a normal 3 pin plug with the mat connected to the earth pin through a 1M ohm resistor.

A resistor is helpful to limit current in the event you touch something live while wearing your earth strap.

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brad.wright

67 posts

Master Geek

#1351760 25-Jul-2015 22:51

Thanks for the replies. My sparky installed an earth rod when my house was re-wired 4 years ago.

I know the connection point has a 1 meg ohm resistor.

Excuse my ignorance but aren't neutral and earth sill connected in the distribution board?

Thanks Again!

Brad

gregmcc

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#1351783 26-Jul-2015 06:40

brad.wright: Thanks for the replies. My sparky installed an earth rod when my house was re-wired 4 years ago.

I know the connection point has a 1 meg ohm resistor.

Excuse my ignorance but aren't neutral and earth sill connected in the distribution board?

Thanks Again!

Brad

they sure are, and at the transformer the neutral is also connected to an earth mat

Niel

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#1356603 1-Aug-2015 13:27

Anti-static mats are high impedance, and supposed to be sufficiently insulated from mains. Normally you connect them to mains earth (in a lab environment), and I would if I know the circuit is on an RCD. Or if I'm working on an item that is not connected to mains, then an anti-static mat is anyway essentially useless and I clip it to the chassis of the equipment I'm working on. Remember electric field comes from a potential difference, and managing ESD is not a matter of just discharging the person but rather bringing the person, equipment, and tools to the same potential.

You can never have enough Volvos!

richms

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#1356625 1-Aug-2015 14:12

Assuming the 1 meg resistor is actually good for 230 volts then even if you earthed to the phase pin you would have under a miliamp to the real earth so not likly to do anything. Have seen more leakage current on the chassis of crap DVD players.

Not that connecting it to the phase pin is a good idea, but with a megaohm inline, I am not seeing the huge concerns.

Richard rich.ms

Niel

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#1357202 2-Aug-2015 17:44

Even the cheapest 1/4W resistors are rated 250V operating, and 400V overload. At 240V, a 1M resistor will dissipate only 60mW. And the mat itself is carbon loaded rubber covered by normal rubber, not a metal plate. If you are still concerned over knock-off parts, then add your own mains rated resistor in series so you know it is safe.

You can never have enough Volvos!

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brad.wright

67 posts

Master Geek

#1357453 3-Aug-2015 08:35

Thank you for all the replies - very helpful!

Brad W

1101

3122 posts

Uber Geek

#1357552 3-Aug-2015 09:43

A anti static station is not just a mat on the bench.

Also think about the carpet, the chair you sit on, the type of material in the clothes your wear :-)