Earth checking for grounding

[S87134]

I want to be sure that a wall socket is truly earthed. I propose to do a continuity test on the earth pin back to the gas meter. Would that be sufficient? I have a cheap volt/ amp meter and a long cable.

I have no reason to believe the socket is faulty but because I have ordered a grounding sheet to sleep on I would like to be certain. They supply a 3 pin earthing plug, only the earth is connected, with a resistance in case the earth becomes live. The resistance is a current limiting resistor IMω ± 5%. I also propose to put an ordinary 5 amp inline fuse on the earth in case it goes live for some reason.

Robin

 

[RF Lighting]

Don't bother with the fuse. It will afford you no protection what-so-ever.

You can run a lead from the earth pin of the socket back to the Main Earthing Terminal (MET) of your electrical installation and test for continuity between the end of the lead and the MET, but this does not prove that the socket is actually earthed, just that it is continuous between the socket and the MET.

The only way to properly check would be to test the socket with an Earth Fault Loop Impedence tester, which every electrician will (should) own.

 

[PrenticeBoyofDerry]

As RFL says only sure way to confirm the socket outlet is earthed is by the use of a EFLI tester.
You can check for continuity between socket and main earth terminal/earth busbar but this will only tell you that you have continuity not that you actually have a connection to earth via the earthing arrangement.

 

[ericmark]

I would agree with RF Lighting. I know some years ago when I was in university there was questions raised about the use of earth straps with sensitive electronic components.

I seem to remember it was considered safe where the installation complied with 17th Edition i.e all sockets had earth leakage trips installed and the 1Mohm resistor see here which is a similar situation.

These plugs

seem to have more than a simple connection with a resistor. Not sure why one wants to be grounded but the problem with the wrist straps is due to flexing they do fail I think the plug is more to ensure the band has not failed then connecting to it.

Anyway the sheet could be connected to mains supply and while you are lying on it no problem only when you come to get on or off is there a problem. So as long as you have RCD protection then the chances of a fault being there just at the moment you get on or off it is very slim.

 

[EFLImpudence]

I also propose to put an ordinary 5 amp inline fuse on the earth in case it goes live

I presume you have been dissuaded but, out of interest, where were you proposing to put it?

 

[Spark123]

What on earth is a grounding sheet??
If I sleep with my antistatic wrist band on will it help?

 

[S87134]

What on earth is a grounding sheet??
If I sleep with my antistatic wrist band on will it help?

From what i have read, I think that it will help provided it is earthed. Here is a paper on the health benefits of grounding:

http://downloads.hindawi.com/journals/jeph/2012/291541.pdf

Robin

 

[S87134]

I also propose to put an ordinary 5 amp inline fuse on the earth in case it goes live

I presume you have been dissuaded but, out of interest, where were you proposing to put it?

I have tried it by rewiring an ordinary plug. Taken out the negative, and cut short the pos so that it does not come through the plastic of the plug. I need it to hold the other end of the fuse. Sealed the pin holes with hot plastic glue as an insulator. Thus only the earth pin comes out of the plug. Rewired inside so that the earth goes first to the fuse connector. The outside cable is routed to the other side of the fuse. It is a single connection through the fuse to the earth.

Robin

 

[Taylortwocities]

Untitled

• Taylortwocities
• 11 Jun 2011
• 8

 

[Peet]

Like RF says the fuse is of no use here. People often think that fuses protect people, they don't they protect the installation. The resistor choice however, could need careful consideration.

Note that in the Wiki pointed to by ericmark that it says there are often two resistors. One at either end. There's more than one reason for this. One reason is redundancy, failure of one doesn't compromise the whole. Another is that you have double the safe working voltage of a single resistor. Take for instance a very common resistor used the world over, the Philips MRS25 metal film. It has a maximum permissible voltage across it of 350V. 240vAC mains at its peak is 340V. So to use a single one in this application you're coming close to the limiting element voltage. A 1Meg one wouldn't fail through excessive power dissipation but it might fail due to voltage breakdown. And remember this is a safety application. So reliability and stability are high up the list. As these cost negligible amounts of money I wouldn't be using one of them. Buy a proper antistatic plug by a known good make. Not a chinese copy. Sometimes they even have distributed resistance down the connecting wire.

Antistatic protection equipment resistors are a two way street. One way it protects the kit being used by dissipating charge in a controlled way. That means not with excessive current which might damage it. Which is why antistatic bags are plastic with a coating that runs at xMeg per SQ inch rather than tin foil. The other way is by protecting the user and avoiding the need for a direct connection to an electrical system but still working for the application.

If you want to be grounded then why involve the electrical system? Why not bang in your own earth rod and use that? No plug, no connection to the electrical system, less variables. and possibly better performing as there's no guarantee the mains earth is clean. I'd still incorporate the distributed resistors though as you're bringing a wire from A to B and probably through an electrical installation.

Also RCD protection is no excuse for taking chances. Yes they help and undoubtedly save lives but do something that, as far as is reasonably practicable inherently safe. RCDs are a backup device, not a means to an end.

Interesting stuff. I'm sure the human body is effected by phenomena we don't understand yet, and we currently struggle to measure.

If you want to be grounded then why involve the electrical system? Why not bang in your own earth rod and use that? No plug, no connection to the electrical system, less variables. and possibly better performing as there's no guarantee the mains earth is clean. I'd still incorporate the distributed resistors though as you're bringing a wire from A to B through an electrical installation.

 

[Peet]

I know some years ago when I was in university there was questions raised about the use of earth straps with sensitive electronic components.

I seem to remember it was considered safe where the installation complied with 17th Edition i.e all sockets had earth leakage trips installed and the 1Mohm resistor

Do you mean safe from the point of view of the user or the electronics EM?

 

[ricicle]

Snake oil ?

 

[bernardgreen]

Why not bang in your own earth rod and use that? Why not bang in your own earth rod and use that?

Yes you could do that but then wouldn't that be an "extraneous service" which like gas and water pipes have to be "earthed" to the main "earth" terminal to prevent them bringing "extraneous" potentials ( like true ground ) into the equipotential zone.

Is it snake oil to sleep on a grounded mat ? Who knows. Some will prove it is, expecially the people who sell the mats.

This useful grounding block might be useful to connect more than one mat to the "earth"

http://www.russandrews.com/images/products/1839l.jpg

price reduced to £216.00 (was £240.00)

 

[S87134]

If you want to be grounded then why involve the electrical system? Why not bang in your own earth rod and use that? No plug, no connection to the electrical system, less variables. and possibly better performing as there's no guarantee the mains earth is clean. I'd still incorporate the distributed resistors though as you're bringing a wire from A to B and probably through an electrical installation.

Most of the sellers of grounding sheets, etc do recommend using a grounding rod and they do sell them. In my case I have a flat on the first floor and do not have access to the garden. I therefore have to look to something that is earthed in my flat. In terms of convenience and the avoidance of trailing cables, a socket is best, but there is the central heating pipes, and also the gas and water pipes. I could easily check the bonding continuity to the external gas pipe. May be that is the safest and likely to give the best grounding. In that case I would not appear to need added protection.

Robin

 

[ricicle]

Your earth in the flat could be several volts above true earth so what are you trying to achieve by sleeping on a mat that may not be tied to mother earth ?
Do you want to be at one with true/mother earth or at one with the electrical earth ?