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.

 

[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