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Grounding antistatic mat
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Evan



Joined: Aug 04, 2007
Posts: 35
Location: Australia

PostPosted: Sat Sep 08, 2007 1:33 am    Post subject: Grounding antistatic mat
Subject description: Major Tom to Ground Control...
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I have a brand new antistatic mat, complete with grounding wire.

So... where do I attach the other end of the grounding wire?

My work area is not really in a location that is conducive to easily getting to a ground. I have an electrical outlet handy, but the physical outlet itself is probably not grounded (unless it is different than every other outlet in the house). The outlet is a standard Australian 3-prong outlet (with ground prong).

There is an aluminium sliding-glass door frame nearby, but I don't think that it is grounded.

Can I connect the mat to the ground from the electical outlet (the 3rd prong)?

How do you determine if you have a good ground (without electrocuting yourself)?
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Randaleem



Joined: May 17, 2007
Posts: 456
Location: Northern CA, USA

PostPosted: Sat Sep 08, 2007 2:39 am    Post subject: Re: Grounding antistatic mat
Subject description: Major Tom to Ground Control...
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Hi Evan,

Getting and determining a GOOD ground is a lot harder than checking to see that you have a functional one.

To check for a functional GND at the outlet, set your meter to a High A/C voltage range (obviously something above 240VAC), and now probe all the combinations of the three holes. You should be able to see whether the gnd terminal is connected, and perhaps even a bit about its "goodness". From hot to neutral and from hot to gnd should be the same reading. From neutral to gnd there should be no reading. (you may find a low reading here. This shows the potential difference between the paths of the neutral and GND, and can point to a not-so-good gnd, neutral, or both.)

If you get no reading from hot to GND (or a low reading; or anything not equal tothe reading from hot to neutral); then your GND is suspect, not really being useful. Personally, If I found this to be the case, I'd fix it if at all possible. (were it my abode.)

Assuming you have a GND at the plug, that's where you could put the antistat wire. I'd make up a dummy plug with no connection to the hot and neutral. Only your antistat wire to the GND lug. That way you can move the mat by simply unplugging it from the mains socket. It also means you don't have to open the box and run the risk of contact to mains voltage. In the USA, the center screw between our typical Duplex outlets is connected to GND. So we can use a forked lug to that screw in your situation. I'm not familiar with how it is in Oz, so I don't know if something similar is possible for you?

Do note that usually there is a 1Meg or so resistor somewhere in that line from mat to GND. If you can't find it, I'd add it. Use a 1W or 2W size.

But what about if you don't have a GND at the outlet?

Sometimes you can use a coldwater PIPE to make a GND connection. This will depend upon the age of the abode; since plastic has largely replaced metal pipes in many plumbing situations. (at least here in the USA) Even with metal pipes, you need to attach to one that is going into the...

Ground! So if you're three stories up it might not be the best choice.

There is always the possibility of driving a copper or steel grounding rod into the EARTH outside that sliding glass door and running your wire directly to it. But even this can get tricky.

If you have any amateur radio operators nearby; ask one for help. You can usually spot them by their antennae! Laughing (And most all I've ever met were really decent, and helpful types.) Theseguys have to understand grounding to do what they do. A related resource is the ARRL handbook, which should be available online. (ARRL=American Radio and Relay League. You probably have an Aussie equivalent.)

Hard to see the best solution from here! I hope at least some of this is useful.

Randal
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Evan



Joined: Aug 04, 2007
Posts: 35
Location: Australia

PostPosted: Sat Sep 08, 2007 4:22 am    Post subject: Re: Grounding antistatic mat
Subject description: Major Tom to Ground Control...
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Randaleem wrote:
To check for a functional GND at the outlet, set your meter to a High A/C voltage range (obviously something above 240VAC), and now probe all the combinations of the three holes. You should be able to see whether the gnd terminal is connected, and perhaps even a bit about its "goodness". From hot to neutral and from hot to gnd should be the same reading. From neutral to gnd there should be no reading. (you may find a low reading here. This shows the potential difference between the paths of the neutral and GND, and can point to a not-so-good gnd, neutral, or both.)

I took the readings from a powerboard that is connected directory to the plug (the plug is not in a convenient place to get to with a multimeter).

OK, here are the readings:

nothing connected : .3 - .5 volts
Ground only : 2 - 2.5 volts
Hot - Ground : 243 v
Hot - Neutral : 243 v
Neutral - Ground : 0v

I'm taking from this that I have a good ground, and that the not connected/Ground only readings are due to the magnetic field put out by the AC.

Quote:
Assuming you have a GND at the plug, that's where you could put the antistat wire. I'd make up a dummy plug with no connection to the hot and neutral. Only your antistat wire to the GND lug.

Luckily, I have one lying around, it was for a Technics Audio Oscilliscope I have to re-cap. This is now wired, and I get the 2v that a Ground only connection gives me.

Quote:
I'm not familiar with how it is in Oz, so I don't know if something similar is possible for you?

I think that in Australia there is a screw terminal specifically for ground, separate from the mounting screws. My impression is that the electrical standards down here are safer than in America.

Quote:
Do note that usually there is a 1Meg or so resistor somewhere in that line from mat to GND. If you can't find it, I'd add it. Use a 1W or 2W size.

Already taken care of, the mat has one, and I have checked it with the multiometer.

Quote:
But what about if you don't have a GND at the outlet?

Sometimes you can use a coldwater PIPE to make a GND connection.
...
Even with metal pipes, you need to attach to one that is going into the...

Ground! So if you're three stories up it might not be the best choice

There is always the possibility of driving a copper or steel grounding rod into the EARTH outside that sliding glass door and running your wire directly to it. But even this can get tricky.

No problem, we are on the ground level. However, the house is built on sandstone, so there isn't a lot of 'earth' around. A ground from a pipe would depend on the pipe actually being buried in some ground somewhere.
Quote:
Hard to see the best solution from here! I hope at least some of this is useful.

Very useful. This is pretty much the avenue I was going to take. I just wanted some confirmation before playing around with 240 AC, and plugging a conducting mat into a power outlet (even if only wired to ground)!

Thanks.
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Evan



Joined: Aug 04, 2007
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Location: Australia

PostPosted: Sat Sep 08, 2007 5:03 am    Post subject: Reply with quote  Mark this post and the followings unread

All that being said, I am a little concerned about the 2 volts coming off the ground.

But then again, that is only with the ground connected to the multimeter, the other lead of the multimeter isn't connected to anything.
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blue hell
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PostPosted: Sat Sep 08, 2007 5:36 am    Post subject: Reply with quote  Mark this post and the followings unread

Evan wrote:
All that being said, I am a little concerned about the 2 volts coming off the ground.

But then again, that is only with the ground connected to the multimeter, the other lead of the multimeter isn't connected to anything.


With one terminal unconnected you are just picking up hum Very Happy

You made the right connection.

I don't know if you have a CV or other metal pipes in the vicinity of your workbench, but if so you might want to check if these are at about the same voltage level as your earth connection. If not you should get an electrician to fix that situation, or do it yourself when you know where and how to do it.

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also .. could someone please turn down the thermostat a bit.
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Uncle Krunkus
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PostPosted: Sat Sep 08, 2007 5:37 am    Post subject: Reply with quote  Mark this post and the followings unread

I would put another 1M resistor inside the plug if there is any possibility the other resistor could be left out of the circuit. Having a perfect (or near perfect) connection to ground strapped to your wrist, or under your elbow, is a big liability. It's like a little neon sign on your forehead that says to the nasty electrocution beastie "bite me".
I've been bitten by 240V about 4 times in my 40 years, and I know now that had been properly earthed on any of those occasions, I would not be here today.

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blue hell
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PostPosted: Sat Sep 08, 2007 5:42 am    Post subject: Reply with quote  Mark this post and the followings unread

Very wise words uncle !
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also .. could someone please turn down the thermostat a bit.
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Evan



Joined: Aug 04, 2007
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Location: Australia

PostPosted: Sat Sep 08, 2007 7:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
With one terminal unconnected you are just picking up hum Very Happy

Yup, this is pretty much what I thought. Especially as the voltage dropped as I moved the unconnected test lead away from the ground source.
Quote:
I don't know if you have a CV or other metal pipes in the vicinity of your workbench, but if so you might want to check if these are at about the same voltage level as your earth connection. If not you should get an electrician to fix that situation, or do it yourself when you know where and how to do it.

No pipes or anything near my work area.

One of the fun things about Australia is that permanent wiring must be dealt with by a licenced electrician, nd I'm leary enough about 240v to not want to touch the permanent wiring. Not like in America, where anyone can mess with the wiring in the walls...
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Evan



Joined: Aug 04, 2007
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PostPosted: Sat Sep 08, 2007 7:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Uncle Krunkus wrote:
I would put another 1M resistor inside the plug if there is any possibility the other resistor could be left out of the circuit.

This would make the total resistance 2M. Would this affect the antistaticness of the mat?

I guess I'll have to source the resistor.
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Scott Stites
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PostPosted: Sat Sep 08, 2007 10:08 am    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
Not like in America, where anyone can mess with the wiring in the walls...


Anyone can mess with the wires in the walls anywhere, whether it's legal or not. However, it's got to meet code here as well or you're truly hosed, should you survive. Very Happy

Edit: IE, at least where I live, the work has to be inspected by a licensed electrician. Generally, if you're not licensed and you're messing with the wires, and you only think you know what the f*ck you're doing, you have a fool for an electrician.

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blue hell
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PostPosted: Sat Sep 08, 2007 10:17 am    Post subject: Reply with quote  Mark this post and the followings unread

Evan wrote:
This would make the total resistance 2M. Would this affect the antistaticness of the mat?


No problem, the mat's resistance is much higher.

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Jan
also .. could someone please turn down the thermostat a bit.
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