ESD mats + grounding

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mdf

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#273120 5-Aug-2020 13:43

I'm renovating a hobby / workroom and have installed some nice wooden benchtops. I've been looking for a large(ish) mat to protect the benchtops when working (especially soldering) and to add a bit of slip resistance to vainly try and limit the amount of stuff that will get lost after falling on the floor.

Most of the ones I have found (e.g. this one) also offer anti static features. I've never especially bothered with this but probably should (I plan on building a new PC at some stage).

What's best practice for this in NZ? Does it need to be grounded to work? Most of the online stuff I've been able to find suggests either a special plug to use the AC earth wire, or attaching to a "grounded socket" (which seems to be a US thing). I will not be messing about with AC, but do have a socket right where the mat will go if there is an easy adapter/socket to use (just a normal plug only using the earth wire?).

Lias

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#2535180 5-Aug-2020 14:42

It's been awhile but I'm pretty sure when I used to work in a tech bay back in the day we just had ours straight wired to the earth pin in a wall plug. E.g. in your linked example mat, snip the spade connector off, wire that to to the earth pin of a plug and plug it into the wall socket. Whether or not that's safe to do I have no idea, but it's what my memory says we did.

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Jase2985

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#2535225 5-Aug-2020 15:04

the connection to earth should be a high resistance to create a slow (about a second) discharge to ground, not a straight wired connection.

the ESD mats you buy will have this built into it

neb

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#2535398 5-Aug-2020 17:36

mdf:
What's best practice for this in NZ?

If you're working from home, or more specifically in a non-airconditioned building, NZ's natural humidity is high enough that you don't need to be excessively cautious about static electricity. I've never experienced it in NZ, while in the US and Europe it's annoying enough that I open doors in buildings I've worked in with my keys to avoid getting zapped all the time. So if you've been walking on a carpet in rubber shoes or similar touch something earthed, but you probably don't need to go overboard with protection.

Technofreak

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#2535483 5-Aug-2020 20:57

Jase2985:

the connection to earth should be a high resistance to create a slow (about a second) discharge to ground, not a straight wired connection.

the ESD mats you buy will have this built into it

This most definitely this ^^^^^^^^^

Having it hard wired to earth is a recipe for causing death through electrocution if you happen to be working on or with a device which has a faulty 230 connection.

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1101

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#2535592 6-Aug-2020 09:45

I wouldnt bother

unless...
....You are willing to follow ALL the recomended ESD safe procedures
Get rid of the carpet would be no.1
only wear clothing made from natural fibres
Antistatic wrist strap
Look at the fabric your chair is covered with , change that . You can build up plenty of static just off your chair
And some others that I cant remember, so long ago

Unless you are working with individual components , just be carefull and ground yourself .
Of course it wont hurt to setup an antistatic mats . We used to have heaps of them, in long lengths. Now they are used for other things (floor mats etc)

DonH

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#2535620 6-Aug-2020 10:28

Technofreak:

..

Having it hard wired to earth is a recipe for causing death through electrocution if you happen to be working on or with a device which has a faulty 230 connection.

By your reasoning, my stainless steel kitchen bench should have a high resistance to earth in case any of the appliances I use on it develop a fault. 😉

As has been pointed out, antistatic work mats have the resistance built into the connection between the mat and the drain wire. The free end goes to a suitable grounding point. I had mine connected to the earth pin in a "tapon" (piggyback) plug, with my soldering iron plugged on top.

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Technofreak

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#2535641 6-Aug-2020 11:06

DonH:

Technofreak:

..

Having it hard wired to earth is a recipe for causing death through electrocution if you happen to be working on or with a device which has a faulty 230 connection.

By your reasoning, my stainless steel kitchen bench should have a high resistance to earth in case any of the appliances I use on it develop a fault. 😉

As has been pointed out, antistatic work mats have the resistance built into the connection between the mat and the drain wire. The free end goes to a suitable grounding point. I had mine connected to the earth pin in a "tapon" (piggyback) plug, with my soldering iron plugged on top.

Most definitely if you use your stainless steel bench as a place where you work on or repair electrical/electronic equipment. Otherwise under normal circumstances with modern double insulated appliances there shouldn't be a problem.

I would suggest using a stainless steel kitchen bench as a work place for such as repairing electrical/electronic devices as being very fool hardy. The very fact you are repairing something generally means you will have the case off or open thus vastly increasing the risk of contact with bare terminals that may have 230 VAC on them.

Not all ESD mats used to have a resister built into the earth lead. I have a portable ESD mat and as a matter of fact check the earth lead for two reasons. One to check for continuity otherwise the mat is useless and also for resistance for safety.

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tripper1000

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#2535811 6-Aug-2020 14:42

DonH: By your reasoning, my stainless steel kitchen bench should have a high resistance to earth in case any of the appliances I use on it develop a fault. 😉

No, different strategies for different risk profiles.

On an electrical work bench it is likely that live and open appliances are being worked on, so the risk of shock is substantially higher than simply operating an appliance in the kitchen. The consequences of shock are reduced when there are no low resistance return paths from the live internal part, through the body to earth, hence ESD leads and mats have a resistor added in series to earth. This is also why electrical work bench tops are usually made of high resistance material - it is almost always wood, plastic, rubber or ESD matt.

A stainless bench is inherently conductive, so unsuitable for working on live appliances. In normal kitchen use, if unearthed and a faulty appliance is place upon it, the whole bench becomes live, amplifying the risk to potentially multiple people. When earthed the bench can not become live. The most common source of shock from a stainless bench is via the hot water system when the cylinder element starts to fail - you may have heard of people getting "tingles" off the bench or off the taps. Earthing the bench sinks away the stray currents and tops this.

tripper1000

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#2535815 6-Aug-2020 14:49

To answer the OP, don't get too hung up about earthing the ESD matts to the mains earth system, or any earth in particular.

What is most important is that the bench, the sensitive devices being worked on, and the human and tools working on them is at equal potential - ie that they are all electrically connected together. If that potential is higher than mother-earth or not, isn't overly important - the aim of the game is to prevent sudden static discharge to/from the sensitive component and whatever is about to touch it and to have slow and controlled equalling out of the potentials - another reason why ESD leads and mats have resistance built in.

1101

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#2536183 7-Aug-2020 11:30

I would have presumed that ESD mats would have a high resistance anyway, so a earth resistor may not allways be 100% necessary ?

But, if you're going to connect the mat to earth, take an extra 5 minutes effort and add that resistor anyway :-)