Extraneous....Yes or No....

[tony mc]

Thats the reason for the test is my understanding or we would be bonding everything.

So if the test show that is is not extraneous over 22k then no need to bond.

Hope that makes sence.

 

[ELEKTRIC]

DETERMINING IF A PART IS EXTRANEOUS OR JUST A PIECE OF METAL​

A test should be made using an Insulation Resistance Tester set on MΩ, supplying 500 Volts.
Test procedure:
Connect one test lead to the metal part and the other lead to a known earth. (MET)

If the resistance value is 0.022MΩ (22000Ω) or greater, no supplementary bonding conductor is required.
If it is less than 0.022MΩ, supplementary bonding should be carried out.

From the Ohm’s law:

I = V / R;

I = 500V / 22000Ω = 0.023Amp

This shows that if the fault was on a single phase 230Volt supply the current that would flow between the conductive parts would of course be only 0.0115Amp (11.5 mA).

This current is unlikely to give a fatal shock.

Guidance Notes GN8 and GN5 state:
" If extraneous metalwork is above 22KΩ then it need not be supplementary bonded.

 

[IQ Electrical]

hello everyone, im new to the forum and this is my first post.... just been reading this thread and have a little thing to add....

Surely if the metal pipe has a high resistance to earth it would not be a bad idea to bond it as it would be sitting at around 230v under fault conditions?

or am i just stupid? haha.....

This is the problem when the reasons for bonding are not understood, during a fault, the voltage on the main earth terminal rises (sometimes significantly) this can then be distributed to bonded non extraneous conductive parts, creating a danger!

That is why it's important to actually establish whether an item is actually an extraneous-conductive part before we string green&yellow everywhere.

 

[Dave_]

gotcha.... if said pipe had a low resistance to earth and its bonded (extraneous) the dis. time would be faster (less danger), if not bonded and theres an earth fault anywhere on the property would just result in another live part to grab with no path to earth (thus no point in bonding it) ... i did know this.... living in Barcelona at the mo, of the tools, the brain is a bit slow at the mo.... i remember that equation regarding a touch voltage not exceeding 50v.... coming back now... thanks mr IQ!

Dave

 

[Dave_]

Here's a question for you all regarding this thread..... My poor first post got me doing a little thinking (yes im sad like that, but i am drinking a beer whilst posting)

During a periodic test and inspection of the installation in a butcher’s shop, it is revealed
that the circuit supplying an electrically operated compressor does not meet the maximum
earth fault loop impedance requirements. The circuit is protected by a 16 A
Type C CB, and the unit is situated 1 m from a steel sink. Explain how, under certain
conditions, this situation may be resolved by the use of supplementary bonding.
Support your answer with calculation.

This is not my work, its Brian Scaddan's the 2391 chief examiner.

lets get the old grey old matter going

ill post the answer later..........

 

[telectrix]

on a similar vein, used to be that all metal ( stainless steel) tables and such in a commercial kitchen were supplementary bonded, all linked together. do we now perform an IR test to see if they read > 22k, and so no longer need to be bonded?

 

[telectrix]

Here's a question for you all regarding this thread..... My poor first post got me doing a little thinking (yes im sad like that, but i am drinking a beer whilst posting)

During a periodic test and inspection of the installation in a butcher’s shop, it is revealed
that the circuit supplying an electrically operated compressor does not meet the maximum
earth fault loop impedance requirements. The circuit is protected by a 16 A
Type C CB, and the unit is situated 1 m from a steel sink. Explain how, under certain
conditions, this situation may be resolved by the use of supplementary bonding.
Support your answer with calculation.

This is not my work, its Brian Scaddan's the 2391 chief examiner.

lets get the old grey old matter going

ill post the answer later..........

sticking my neck out here as i may be way off the mark, but here goes. Zs is measured with all circuits , earths and bonding in place, thus creating parallel paths. if the machine were to be bonded to the metal sink, which we assume is in turn connected to the water pipe supplying it, this may then add another parallel path, thus reducing the measured Zs. this of course assumes that the sink is not fed by a plastic water pipe.

 

[IQ Electrical]

Yes, a supplementary bonding conductor between sink and compressor.

The resistance for the conductor must be not greater than 50/Ia

Remember that the rated current of the MCB must be multiplied by 10 for the 'C' curve.

 

[IQ Electrical]

Sounds like she has alot on her mind. Try asking her. If it doesn't work, then yes, it might be a yes t

But what does she think about the supplementary bonding?

 

[Cazmac1]

I've enjoyed reading this post and I've asked a similar question on another thread regarding. Bonding just want to know if your testing an old installation where there are metal sinks and food prep tables that are being constantly moved for cleaning and some of the bonds are loose some are broken off and some are still in-tacked. If I was to apply the 22K test I may encounter problems due to the poor condition of the bonding. Should I reinstate all the bonding or remove it and carry out the test with everything disconnected. I would all so like to pose the question that although this is not a special location there is a lot of water used in a kitchen and in wet condition's the readings may change. father than rely on bonding would it not be a better course of action to RCD protect all circuits or would this make no difference. It just don't make sense to rely on bonding where this bonding is put under such mechanical stress.

 

[IQ Electrical]

Think about what you are asking:

How can a food prep table introduce a potential to the installation?

Do the sinks have metallic waste pipes heading into the ground, thereby introducing true earth potential?

You need to get bonding requirements clear in your mind BEFORE doing PIRs, do you not have a copy of BS7671:2011?

 

[Cazmac1]

I don't understand your reply I am quite simply stating that the installation in is current state has lot of different metal tables and sinks at different earth potentials as some are bonded and some are not. These Item are in reach of one another so potentially if you had an item of electrical equipment on one table that is faulty and has failed to trip the CB and you then touch the other table that is bonded you have now created an earth path and could be electrocuted? I either take out all the bonding and start from fresh and determine if it is actually required or I reinstate all bonds and cross bonds as they were in the original install. Or is it me?

 

[IQ Electrical]

That's why the requirements were withdrawn, the potential-rise of bonded non-extraneous conductive parts under fault conditions created a far greater hazard than not having the metalwork bonded.

If you're doing a PIR just note that "some items are bonded together and some aren't however there is no requirement for bonding" under the current edition of BS7671.

 

[Cazmac1]

Thanks, I will get the GN8 and dig a little deeper. For now I'm going to put it down a Code 2 and they can take it from there.

 

[tony mc]

On the schedule what regulation are you going to refer too with regards to the bonded tables if you assign a code 2 unsatisfactory!!