Earthing Stainless Steel Bench?

[SparkB]

I have been asked to 'earth' a metal/stainless steel bench inside a workshop.
The bench is used with hand tools and power tools - there is a socket directly above it where power tools being used are plugged in to.
Also staff are complaining of receiving static shocks when touching the bench, and hopefully the earthing would help with this also.
My thought is to earth the bench via 6mm Green/Yellow to the earth at the socket (metal clad socket).
I have had a few conflicting views on this so just wanted anyone's thoughts?

 

[Marvo]

I'd suggest finding the fault (probably more than one fault) that's giving the tingling shocks would be the highest priority. Also ramp test the RCD that protects the sockets and if there isn't an RCD then consider installing one.

 

[yellowvanman]

I would have thought this is similar to supplemenatry bonding in which case 544.2 applies.

 

[SparkB]

Hi Marvo, There is no fault present, the staff are getting static shocks when touching the workbench after walking across the room due to new flooring - no electrical appliances involved when the static shocks are felt.
The request to earth the bench is to try and alleviate the static shocks.

 

[SparkB]

Hi Yellowvanman, Thanks for your reply. I realise that there is no actual requirement to earth the bench, but if it's requested and alleviates the issue with the static then I cannot see a problem but wanted to get others views on it

 

[ruston]

Then the build up of static in the employees will have to earth out elsewhere, you will just be moving the problem. Not sorting the cause.

 

[SparkB]

Hi Ruston, thanks for your reply. The issue with static has only been present since the new flooring was fitted - despite staff wearing anti-static soled safety shoes etc. They asked for bench earthing as a hopefully quick solution

 

[snowhead]

If the Staff are discharging static to the bench it must already be Earthed / Bonded to earth.
Have you checked.?

If it isn't then the static must be in the bench and discharging to them.

Unless of course there's a fault on an appliance lead and the bench is live and static is not the problem.

Or they're all wearing nylon underwear because it's hot.

 

[SparkB]

Hi Snowhead, thanks for the reply. The bench definitely isn't earthed, and like I say even when no appliances are in use and stored elsewhere staff still get a small shock

 

[SparkB]

The issue seems to be with the new flooring, as nothing else had changed and no issues previously at all

 

[ruston]

Dare I ask what the floor is made of , and is the bench on top of the new floor?

 

[Marvo]

What type of flooring is it? If they're wearing anti-static shoes then there's a very high chance it's not static.

You'll have to forgive me for being skeptical, I'd still suggest test the bench with a wander lead for elevated voltage wrt earth and impedance to earth and just for good measure test the socket circuit as well. There's many times a low insulation fault has been mistaken for static and even on the slim chance it is static, earthing the table will just make the shocks worse.

 

[SparkB]

Yes the bench is on top of the new flooring. It appears to be plastic/synthetic sheeting put down on top of the old concrete flooring

 

[ruston]

Is there any way that the bench fixings could of compromised the electrical installation or be into the rebar?

 

[SparkB]

The bench isn't fixed or secured to the floor or walls it's just like a large metal table, freestanding.

When I was there I felt the shock too - a small quick sensation, just like static, that was over in an instant

Thanks for the replies everyone

 

[sean_ork]

Just bond the bench using a 1M ohm resistor, the static will still be discharged when the bench is touched - but it won't be noticed by the user.

 

[SparkB]

Hi Sean
Do you mean bond the table to the earth/casing of the metal clad socket above, with a 1M ohm resistor in series with the bond?

 

[sean_ork]

Yes, that's pretty much all a ESD kit does

 

[VoltzElectrical]

I kept getting one helluva belt off the missus car the other week, but not her, I started closing the door with my foot but one day when we got back, I steadied myself against the wall and got a belt off that! It must have been something building up in my clothing, as it only happens when I am wearing one particular top.

I remember another thread about someone getting a belt from radiators, but it turned out that they were feeling the static discharge TO the radiator that they had built up.

In my opinion, if the feeling is fleeting, but painful and no voltage is apparent during testing, then further earthing the bench will only enhance the sensation?

 

[sean_ork]

The trick is to manage the rate of discharge such that it's not noticeable - hence the series resistor