Bonding 😣

[bennie]

No waffling, going to get straight to the point. Main water on the exterior of the building in plastic. Changes to copper inside the building. According to regs doesn't need main bonding. Incomer to building is 120mm SWA, TNS with a 70mm earth. Current bonding to the water is 10mm but as said according to the regs it's not needed. Many water heaters & showers on the installation so when an insulation resistance test was carried out between the MET & the stop cock it was showing a dead short. As main bonding isn't required but there is still resistance between the pipework & the MET should there just be supplementary bonding & if so does that mean 6mm would be sufficient.

 

[newfutile]

I take it you measured with the bonding disconnected?
There are a few other ways a pipe can be connected though to earth ,via boiler or cylinder CPC ,or via a gas bond if there is one.
Try a low ohm test to give you a clue .
If with all parallel paths disconnected it's less the was 23 K ohms I would bond it.

 

[bennie]

I take it you measured with the bonding disconnected?
There are a few other ways a pipe can be connected though to earth ,via boiler or cylinder CPC ,or via a gas bond if there is one.
Try a low ohm test to give you a clue .
If with all parallel paths disconnected it's less the was 23 K ohms I would bond it.

Yes tested with bonding disconnected. With all parallel paths disconnected the reading is <999 so no main bond required. So as I said is only supplementary bonding required. Also if I'm testing to see if it needs to have a main bond surly I only need to do an insulation resistance tests?

 

[Pretty Mouth]

the reading is <999

Please clarify: the reading is less than 999 what?

 

[westward10]

One minute you have a dead short then you have <999?

 

[bennie]

One minute you have a dead short then you have <999?

Sorry greater than 999, that what it says on the meter. If you read what I said, with all parallel paths disconnected there is no read but with them connected it's a dead short, which is what you would expect. My only question is does it need a main bond or would supplementary suffice.

 

[bennie]

Please clarify: the reading is less than 999 what?

Sorry greater than with all parallel paths disconnected

 

[newfutile]

Unless you can't meet disconnection times why would you need supplimentary bonding ?

 

[bennie]

Sorry greater than 999, that what it says on the meter. If you read what I said, with all parallel paths disconnected there is no read but with them connected it's a dead short, which is what you would expect. My only question is does it need a main bond or would supplementary suffice.

Unless you can't meet disconnection times why would you need supplimentary bonding ?

Why wouldn't I need supplementary bonding even if disconnection times are met? So it's ok to have no main bond because the water supply is plastic and no supplementary to the copper pipe work inside even though with all accessories connected there is a path between said pipe work and the MET?

 

[newfutile]

are there more than 1 items of conductive parts that you want to prevent from different potentials ?this is what supplimentary bonding is usually for in my experience , whether it needs main equipotential bonding is another mattter,you have said it was a dead short but also stated its over 999 i guess you mean Meg Ohms?.
if its able to intoduce a potential (usually earth potential) you would need to bond it with a suitably sized cable to the met.

 

[oscar21]

I don't think there are many people who actually understand what main bonding does even though they are installing 10mm "earth" cable about on every job.

 

[bennie]

are there more than 1 items of conductive parts that you want to prevent from different potentials ?this is what supplimentary bonding is usually for in my experience , whether it needs main equipotential bonding is another mattter,you have said it was a dead short but also stated its over 999 i guess you mean Meg Ohms?.
if its able to intoduce a potential (usually earth potential) you would need to bond it with a suitably sized cable to the met.

Only the pipe work no extraneous. I suppose the question I should have asked is is any type of bonding required if no main bond is needed even though there are water heaters and showers in the installation which will mean the pipe work will be connected to earth?

 

[bennie]

I don't think there are many people who actually understand what main bonding does even though they are installing 10mm "earth" cable about on every job.

I'm carrying out an EICR so trying to determine if it should be removed.

 

[westward10]

I'm carrying out an EICR so trying to determine if it should be removed.

Why didn't you say this in the first place?
I am carrying out an EICR.................................................................................

 

[bennie]

Why didn't you say this in the first place?
I am carrying out an EICR.................................................................................

Wanted to see peoples responses. This a commercial site. I understand that because the service is provided in plastic above ground it is insulated from earth & I have tested to prove that. The internal pipe work is all copper & with all accessories connected under fault conditions it could become live. Not all circuits have 30mA protection so supplementary bonding is required, yes? No? But is that the case if no main bonding is required? I also know if main bonding isn't required we don't put it in because it could create a potential difference but if through the earth of accessories the pipe work could become live should it have a bigger earth back to the MET than what is in the flex. I may be over thinking this as the pipe work may not be at a potential difference & if disconnection times are met & it's a TNS it should all be good but should the main bond that is there be removed or have I just answered my own question?

 

[Pretty Mouth]

Wanted to see peoples responses. This a commercial site. I understand that because the service is provided in plastic above ground it is insulated from earth & I have tested to prove that. The internal pipe work is all copper & with all accessories connected under fault conditions it could become live. Not all circuits have 30mA protection so supplementary bonding is required, yes? No? But is that the case if no main bonding is required? I also know if main bonding isn't required we don't put it in because it could create a potential difference but if through the earth of accessories the pipe work could become live should it have a bigger earth back to the MET than what is in the flex. I may be over thinking this as the pipe work may not be at a potential difference & if disconnection times are met & it's a TNS it should all be good but should the main bond that is there be removed or have I just answered my own question?

You have established that the pipework isn't an extraneous part, so main bonding isn't required. You can leave the bond there if you like, or take it out, it doesn't really matter as the pipework is connected to the MET in many places anyway. So far so good.

Not sure you're on the right track regarding supplementary bonding. Supplementary bonding is additional protection, so only required in certain situations, as specified in the regulations. One example of where it is required would be a bathroom where not all circuits serving the location have 30mA RCD protection. We can't determine whether sup bonding might be required in the property you describe, so you'll need to catch up on the regs for this to decide yourself. Start with the note to reg 415, then read 415.2, then head to the index.

 

[7029 dave]

You have established that the pipework isn't an extraneous part, so main bonding isn't required. You can leave the bond there if you like, or take it out, it doesn't really matter as the pipework is connected to the MET in many places anyway. So far so good.

Not sure you're on the right track regarding supplementary bonding. Supplementary bonding is additional protection, so only required in certain situations, as specified in the regulations. One example of where it is required would be a bathroom where not all circuits serving the location have 30mA RCD protection. We can't determine whether sup bonding might be required in the property you describe, so you'll need to catch up on the regs for this to decide yourself. Start with the note to reg 415, then read 415.2, then head to the index.

It amazes me that a lot of Electricians dont understand the difference between equipotential bonding and supplementary bonding.

 

[bennie]

You have established that the pipework isn't an extraneous part, so main bonding isn't required. You can leave the bond there if you like, or take it out, it doesn't really matter as the pipework is connected to the MET in many places anyway. So far so good.

Not sure you're on the right track regarding supplementary bonding. Supplementary bonding is additional protection, so only required in certain situations, as specified in the regulations. One example of where it is required would be a bathroom where not all circuits serving the location have 30mA RCD protection. We can't determine whether sup bonding might be required in the property you describe, so you'll need to catch up on the regs for this to decide yourself. Start with the note to reg 415, then read 415.2, then head to the index.

I though I was on the right track but sometimes it's good to have another opinion. I've always felt that they need to clarify the bond or not to bond reg because the majority of the time it doesn't matter if your services are insulated from earth as there will most certainly be a path back somewhere in the installation.

 

[bennie]

It amazes me that a lot of Electricians dont understand the difference between equipotential bonding and supplementary bonding.

Most do it's just in certain circumstances a helpful reminder is needed. Better to ask than be wrong,no?

 

[bennie]

You have established that the pipework isn't an extraneous part, so main bonding isn't required. You can leave the bond there if you like, or take it out, it doesn't really matter as the pipework is connected to the MET in many places anyway. So far so good.

Not sure you're on the right track regarding supplementary bonding. Supplementary bonding is additional protection, so only required in certain situations, as specified in the regulations. One example of where it is required would be a bathroom where not all circuits serving the location have 30mA RCD protection. We can't determine whether sup bonding might be required in the property you describe, so you'll need to catch up on the regs for this to decide yourself. Start with the note to reg 415, then read 415.2, then head to

What if the same situation arose in a TNCS system?

 

[westward10]

In general terms the earthing system is not relevant regarding supplementary bonding.

 

[bennie]

In general terms the earthing system is not relevant regarding supplementary bonding.

Disregard the supplementary bonding question. If services are insulated from earth but still have a main bond in a TNCS system & have accessories that give a pathway surely that would be an issue & would need noting.

 

[Pretty Mouth]

Disregard the supplementary bonding question. If services are insulated from earth but still have a main bond in a TNCS system & have accessories that give a pathway surely that would be an issue & would need noting.

Not quite following you. Is your concern diverted neutral currents, or is it open supply neutral causing a rise in voltage on the earthing system?

 

[bennie]

Not quite following you. Is your concern diverted neutral currents, or is it open supply neutral causing a rise in voltage on the earthing system?

Open supply neutral

 

[Pretty Mouth]

Open supply neutral

Any metalwork connected to the MET could rise in voltage compared to true earth under an open supply neutral fault (on TN-C-S), and that would include the bonded pipework. However, in the property you're inspecting, the pipework is connected to the MET in numerous places, so removing the main bond isn't going to make a real difference.

Either way, the regulations permit the general use of TN-C-S, so it wouldn't be something you would code on an inspection. There are circumstances where TN-C-S is not permitted (eg caravan hookups) in which case you would code it