Antistatic mat

[tony3d]

Hi All, I just bought an antistatic mat which has a banana plug for earth ground. Is it safe to plug this into my Korad's green ground on my power supply? There would be no chance of hurting the power supply from a large static shock correct? My new solder station does not have a banana plug like my old one did. I checked with my multimeter, and the Korad does have continuity between the plug, and the ground lug on the power cord. Thanks.

[ejeffrey]

This is fine.  The ground strap has a high resistance anyway, so there will be no large current flows.  The idea is to slowly bleed away charge and avoid a sudden discharge.  The only potential problem is that you might unplug the power supply and forget that your mat is no longer grounded.  For that reason it would be preferable (but not necessary) to have a dedicated ground connection. This should only be a problem if you physically unplug the supply.  The main power switch should not disconnect the ground pin.

[wraper]

Connect mat through 1M resistor to the mains earth.

[wraper]

or maybe it already have that resistor.

[rolycat]

For optimum safety, don't use any old 1M resistor - not all of them are rated for mains voltages.

Our very own free_electron recommends three 470K resistors - 1/2 Watt or better. Solder in series, cover in heat-shrink tubing and wire into a mains plug between the earth pin and a firmly attached banana jack. Remove the supply pins or insulate them with hot snot glue.

Or if you have the money, you could always just buy an earth bonding plug.

[gotvolts]

Do not plug your anti-static mat into your power supply.

Why?  Because your power supply may become unplugged and at that point you will lose your ground connection without even knowing it.  Just run a wire from your antistatic mat to a hard ground connection at the outlet or nearby.

Also, do not use anti-static mats when running voltages over 30V, and ESPECIALLY do not use wrist straps for any energized voltage period over 30V as well, especially if there is line voltage present.  Major safety hazard.

[rolycat]

Do not plug your anti-static mat into your power supply.

Why?  Because your power supply may become unplugged and at that point you will lose your ground connection without even knowing it.  Just run a wire from your antistatic mat to a hard ground connection at the outlet or nearby.

ejeffrey made this point earlier. A power supply earth terminal is better than nothing if the OP doesn't (yet) have a safe earth bonding point. However, running a wire directly to any hard ground is potentially dangerous, and the connection should have a suitable resistance in series.

Also, do not use anti-static mats when running voltages over 30V.

Dave recently did a teardown of a 250V power supply. The PCBs were sitting on his anti-static mat while he probed voltages in excess of 500V. Are you saying he doesn't know what he's doing?

[tony3d]

Connect mat through 1M resistor to the mains earth.

The mat does have a 1 mega ohm resister in line.

[G7PSK]

Either get an antistatic plug or a bench connector like one of these. They are cheap enough not to have to bother with compromises.

http://www.ebay.co.uk/itm/Antistatic-ESD-Earth-Bonding-Plug-UK-1M-OHM-Multi-Listing-/321092991965?pt=LH_DefaultDomain_3&var=&hash=item4ac2a23bdd

http://www.ebay.co.uk/itm/ESD-Ground-Block-Under-Bench-Common-Point-for-Anti-Static-Armband-Wrist-Strap-/281157859534?pt=UK_Computing_Other_Computing_Networking&hash=item41765078ce

[rolycat]

Either get an antistatic plug or a bench connector like one of these. They are cheap enough not to have to bother with compromises.

http://www.ebay.co.uk/itm/ESD-Ground-Block-Under-Bench-Common-Point-for-Anti-Static-Armband-Wrist-Strap-/281157859534?pt=UK_Computing_Other_Computing_Networking&hash=item41765078ce

I think I'd rather trust a competently home-made earth bonding plug than that Chinese POS, and you're still going to need a grounding point to connect it to.

From the description:

 "Wrist strap group withou resistor"

Sounds like it doesn't have a high value resistor, and even if it does would you trust it?

Also, UK earth bonding plugs like the one linked to aren't going to be much use to the OP, who is in the States. I couldn't find a US plug for a reasonable price; maybe that's why free_electron suggests making your own?

[SLJ]

AS I said somewhere else, just make your own.

[Nerull]

Either get an antistatic plug or a bench connector like one of these. They are cheap enough not to have to bother with compromises.

http://www.ebay.co.uk/itm/ESD-Ground-Block-Under-Bench-Common-Point-for-Anti-Static-Armband-Wrist-Strap-/281157859534?pt=UK_Computing_Other_Computing_Networking&hash=item41765078ce

I think I'd rather trust a competently home-made earth bonding plug than that Chinese POS, and you're still going to need a grounding point to connect it to.

From the description:

 "Wrist strap group withou resistor"

Sounds like it doesn't have a high value resistor, and even if it does would you trust it?

Also, UK earth bonding plugs like the one linked to aren't going to be much use to the OP, who is in the States. I couldn't find a US plug for a reasonable price; maybe that's why free_electron suggests making your own?

Most straps put the resistor in the cord not the bonding point.  A resistor in the bonding point will not protect you against something plugged into the second grounding point from touching something grounded directly.

[rolycat]

Most straps put the resistor in the cord not the bonding point.  A resistor in the bonding point will not protect you against something plugged into the second grounding point from touching something grounded directly.

My bonding point was bought from a company specializing in ESD products and contains three 1M resistors; one for each connection:



I believe Dave has a similar item mounted under his bench.

The cord for the wrist strap also has a 1M resistor.

[SLJ]

Grounding points don't need resistors.  As was said above wrist straps have a 1M resistor already and mats are about a zillion ohms anyway.
If you have a wrist strap without a resistor that goes straight to ground throw it away as it's dangerous as f*#!.

[G7PSK]

All  grounding points seem to have built in resistors as do the wrist strap and mat leads so you end up with 2 meg of resistance, dose not appear to make any difference to static bleed off though.

[rolycat]

All  grounding points seem to have built in resistors as do the wrist strap and mat leads so you end up with 2 meg of resistance, dose not appear to make any difference to static bleed off though.

I'm beginning to suspect that - as usual - US practice differs from the rest of the world on this issue.

[zapta]

All  grounding points seem to have built in resistors as do the wrist strap and mat leads so you end up with 2 meg of resistance, dose not appear to make any difference to static bleed off though.

The one I got did not have resistor on the long wire, just on the one that connects to the wrist.

[Avotronics]

Mine has 1M resistor in wrist strap, none n the long wire, then another 1M in the plug. UK

[Fsck]

my system has a 0.2ohm grounding point to which I connect the mat or the 1M wrist strap.

so, only one 1M resistor between me and earth.

[nanofrog]

No resistor in the grounding block I have at all.
So only the 1M in the wrist strap in my case.

[Avotronics]

1M is fine.

[wilheldp]

How important is it that you wear the wrist strap when working on the mat?  Will the mat just dissipate the static if you touch it periodically, or do you need to be in constant contact with either the mat or strap?

[lewis]

No resistor in the grounding block I have at all.
So only the 1M in the wrist strap in my case.

Crimp terminal 

[rolycat]

How important is it that you wear the wrist strap when working on the mat?  Will the mat just dissipate the static if you touch it periodically, or do you need to be in constant contact with either the mat or strap?

Any static-safe workstation in industry has a minimum requirement that a table mat and a wrist strap are both used and both grounded through a safety resistor.

You can build up a static charge in seconds just by wearing polyester clothing, so if you happen to touch a sensitive component after building up such a charge you could damage it.

Also, bear in mind that the surface of an ESD mat will typically have a resistance to ground in the hundreds of megohms, so discharge will be much slower than through a wrist strap.

You can work out how long it will take using the equations for capacitor discharge, since the human body has a capacitance of around 10 to 200 pF, depending on environmental conditions. For example, a static charge of 3 kV will take around a third of a second to discharge to below a volt, assuming a body capacitance of 200 pF and a mat with a 200 megohm resistance to ground.

[nanofrog]

1M is fine.

Just putting it out there for comparison's sake between US & UK grounding products/practices.

No resistor in the grounding block I have at all.
So only the 1M in the wrist strap in my case.

Crimp terminal 

Yeah, the one in the pic is really pathetic.