Asked to bond a sink (table)

[LeeH]

I have been asked to ‘bond’ some tables or industrial sized wash bins by the engineering supervisor here at work. People stand and work out of these. Simple structure with water that’s filled from a hose.

Q “can you bond these tables, and what do you think?”

Me. “Well, seeing they are not part of the electrical installation, and are very unlikely to be extraneous then No”

I then explained about the 23K rule and how it comes about.

We had a professional chat about it all but couldn’t convince the other party completely and they still think it’s required . Now he’s probably forgotten more then I’ll ever know regarding the machinery here but I have spent long enough in electrical installation and design to be confident. He also cut his teeth back in the 15th which was obvious when I was told you have to bond sinks, ‘cross bonding’ etc.

Anyway I degress.....so I marched off my my AIO tester in hand. Tested the table to a known earth. With the floor wet and the table sat in the water, metal wall panels and with no surprise at 500V test voltage 0.1Mohms.

I’m aware that going around bonding anything metal including the tea bag caddy can increase the risk of shock and I’m trying to prevent this culture from starting.

So let’s discuss either my misunderstanding of electrical theory or how I can science my way out of this hole.

Discuss.

 

[telectrix]

0.1 Meg. is far in excess of the 22K threshold for testing for bonding.problem with IR tests is the resolution is not low enough to get an accurate figure. i'd say bonding not required.

 

[HappyHippyDad]

I agree with you. You've tested it to known earth and it does not test as extraneous. It's also not an exposed conductive part so I don't feel it needs bonding.

What were his arguments for it?

Is there any way of testing to earth in a worse case scenario? I.e tub full of water, water all over the ground etc? Might be good to take a few tests over time (to get a more accurate, stable figure) as even though 100,000 ohms is fairly well over the 23Kohms it's not hugely over.

 

[LeeH]

EDIT

0.01 M ohms. 10, 000 ohms which depending on which figure you use, 10mA or the upper 30mA is up for debate.

10mA threshold 23000
30mA threshold 7667


My eyes are going, just turned 40 and phone screens seem much smaller now.

 

[HappyHippyDad]

EDIT

0.01 ohms. 10, 000 ohms which depending on which figure you use, 10mA or the upper 30mA is up for debate.

My eyes are going, just turned 40 and phone screens seem much smaller now.

Did you mean 0.01 M ohms? If so, that's 10K ohms, so it does test as extraneous.

 

[Taylortwocities]

IMO, in those circumstances, you are introducing more of a risk if you connect an earth to these items.

 

[LeeH]

Yes, @hippyhapoydad that’s my point. It’s on a wet floor but so are so many random and movable objects throughout the factory.

Post edited to correct 0.01 Mohms

 

[HappyHippyDad]

EDIT

0.01 M ohms. 10, 000 ohms which depending on which figure you use, 10mA or the upper 30mA is up for debate.

10mA threshold 23000
30mA threshold 7667


My eyes are going, just turned 40 and phone screens seem much smaller now.

You're trying to justify it now!

In your first post you said you were explaining the 23K rule to the chap. 0.01M ohms does not meet the '23K rule'.

This is well out of my domestic remit as I expect there are other factors to consider in Industrial rather than just one test result, but it does test as extraneous.

 

[LeeH]

It test as extraneous, but so will the metal waste bin.

 

[Wilko]

Extraneous implies it's from outside. In this case the potential it will have is the floor it stands on in the room.

Out of interest are there any other conductive surfaces (that are connected to the MET) within reach?

A down side of bonding the sinks : if it's a TNCS installation and the supplier's N was lost (due to a local network fault completely independent from your good installation) then bonding may have decreased the safety of staff working at the sinks, IMHO .

 

[LeeH]

Extraneous implies it's from outside. In this case the potential it will have is the floor it stands on in the room.

Out of interest are there any other conductive surfaces (that are connected to the MET) within reach?

Yes, stainless control panels (enclosure), containment on the adjacent wall. The white wall is also aluminium clad foam which sits on the floor with a resin kurb. My known earth is from a supply to a panel on that wall.

I’ve just realised I’m having difficulty proving it ISN'T extraneous earthier than it is. I know it isn’t and it’s madness thinking it requires bonding but trying to explain that in a discussion is proving frustrating.

 

[LeeH]

‘Rather’ pesky auto correct.

 

[Pete999]

Yes, stainless control panels (enclosure), containment on the adjacent wall. The white wall is also aluminium clad foam which sits on the floor with a resin kurb. My known earth is from a supply to a panel on that wall.

I’ve just realised I’m having difficulty proving it ISN'T extraneous earthier than it is. I know it isn’t and it’s madness thinking it requires bonding but trying to explain that in a discussion is proving frustrating.

Show them this video
continuity of ring final circuit conductors - YouTube - https://www.youtube.com/results?search_query=continuity+of+ring+final+circuit+conductors

 

[Pete999]

Show them this video
continuity of ring final circuit conductors - YouTube - https://www.youtube.com/results?search_query=continuity+of+ring+final+circuit+conductors

No not this one sorry
This one dohhhhh

And this one

 

[telectrix]

whatever the outcome of bond or not bond, just make sure staff have their marigolds on when washing up. DNO use then when working live. so they must be a good idea.