Bonding and Plastic pipe

[noodle_26]

Hi

The situation is this;
PME supply
Dual consumer unit with 30mA RCDs
Incoming water pipe is MDPE into house where it is teed off copper to kitchen sink etc and copper to oil fired boiler in utility room
Boiler incoming in plastic
Tails to all taps and rads are in copper and remaining connecting pipework in plastic.
Supply pipework to shower is in plastic until under floor boards where it changes to copper and is embedded in wall up to shower.
The disconnection times required by Section 411 of BS 7671 are met
All circuits are protected by RCDs having the characteristics required by 415.1.1

As quoted in the electricians guide to the wiring regs "where there is a plastic incoming service and a metal installation within the premises, main bonding may be needed...."

Question 1. In the situation above is MEB required, can someone explain the "main bonding may be needed" in what circumstances is it needed or not with mixed metal, plastic pipework.

This brings me on to the next question,

"For new installations or alterations / additions in a location containing a bath or shower, supplementary bonding will not be required if:
1. The disconnection times required by Section 411 of BS 7671 are met, and
2. All circuits are protected by RCD’s having the characteristics required by 415.1.1, and
3. The building has protective equipotential bonding in accordance with 411.3.1.2, and
4. All extraneous-conductive parts of the location are effectively connected to the protective bonding."

Regarding the quote above if it is deduced that MEB is not required because of the plastic supply pipes then how can rules 3 and 4 above be met? Also if MEB is fitted to the copper side of the incoming then how can rule 4 be met as there is non conducting plastic pipe between rads taps etc?

Do i need supplementary bonding or not?

How should this situation be dealt with, I would really appreciate some advice.

Thanks in advance

 

[StuSpiers]

the formula to work out if you need supp bonding=

50v/30ma= 1667 ohms

continuity test between earth and all metalwork in bathroom if it is below that reading (1667ohms) and you are fully rcd protected you do not require supp bonding.

plastic pipes confuses things.

personally I would MEB regardless.
only supp bond if you are above that figure (which could be the case if plastic is being used)

 

[Moses]

[h=3]Legal Requirements[/h]If main or supplementary bonding is not present (or it is substandard), a householder is not legally obliged to upgrade it in line with current best practice. However it is considered to be a serious electrical fault (one which would be recorded as a level 1 failure on a periodic inspection report). As a result, anyone carrying out Part P notifiable modifications to any part of an electrical installation should also check and rectify any bonding faults at the same time. Note that any work that is part P notifiable cannot legally be carried out (either DIY or paid for) without the correct bonding being in place.
Note that if the main bonding is not to current standards, many professional electricians will refuse to undertake any electrical work (whether covered by part P or not) unless they are also instructed to perform the remedial work required. Contrary to popular opinion, this is not a revenue raising exercise, and is actually to avoid them getting into a very questionable legal position.
A similar situation exists where serious earthing faults are present in an installation such as Lighting Circuits Without an Earth.


[h=3]Plastic Pipework Installations[/h]Generally with plastic pipe installations, supplementary bonding of the pipes is not required. Note however it may still be required between the earths of, say, lighting and power circuits if they are both accessible in the room.
For rooms plumbed in plastic, where the only metal pipe used is for "show work" (i.e. the visible rises of chrome or copper pipe to taps and fittings), there is no requirement to bond the short sections of visible metal.
However if a bathroom is plumbed in a mixture of plastic and metal, and there is some exposed metal pipework connected to other metal pipework that runs between the bathroom and some other part of the building, this should be bonded since this could result in a potential being introduced into the room from elsewhere.
[h=3]Appliances[/h]Electrical appliances with exposed metalwork, may be adequately bonded just via the earth (aka circuit protective) conductor in their supply flex, and do not need separate bonding wires or earth clamps.
[h=3]Installations not in "Special Locations"[/h]In rooms which are not "special locations" (i.e. places likely to put you at increased danger from electric shock, typically because you might be wet), there is also no requirement. So for example a cloakroom with WC and basin would not require it (although it is commonly seen in such circumstances). Kitchens are also not special location for the purposes of supplementary bonding.
[h=3]Change to protection for Special Locations in 17th Edition[/h]Under the 17th edition of the IEE Regs (BS7671:2008) it is permitted to have no (supplementary) equipotential bonding in a room containing a bath or shower providing that the main equipotential bonding is in place, and that all the circuits feeding the room have additional protection from a RCD with 30mA (or lower) trip threshold.

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[Moses]

The best way to check this is with a wander lead attached to the MET of the installation go around and do an IR test on all the pipework that is metal and that your concerned about, if you get results of over 22Kohm then the metalwork is not classed as an extraneous conductive part and does not need bonding.

I would be amazed if your cold water feed to the boiler which is PVC will be able to produce a potential back to your metallic stop cock, but personally I would bond all pipes at the boiler.

I
The 22kohm rule is derived from the formula

Rcp>Uo/Ib - Ztl

Rcp = resistance between MET and metal structure

Uo = 230v

Ib = is the 'Let Go' current through human body (0.01A, 10mA)

Ztl = impedance of human body (1000 ohms)

For tns and tncs a resistance < 22kohms would need to be bonded.​

 

[Deleted member 9648]

Hi

The situation is this;
PME supply
Dual consumer unit with 30mA RCDs
Incoming water pipe is MDPE into house where it is teed off copper to kitchen sink etc and copper to oil fired boiler in utility room
Boiler incoming in plastic
Tails to all taps and rads are in copper and remaining connecting pipework in plastic.
Supply pipework to shower is in plastic until under floor boards where it changes to copper and is embedded in wall up to shower.
The disconnection times required by Section 411 of BS 7671 are met
All circuits are protected by RCDs having the characteristics required by 415.1.1

As quoted in the electricians guide to the wiring regs "where there is a plastic incoming service and a metal installation within the premises, main bonding may be needed...."

Question 1. In the situation above is MEB required, can someone explain the "main bonding may be needed" in what circumstances is it needed or not with mixed metal, plastic pipework.
As already stated...test to establish if INCOMING services are extraneous. You do NOT need to go round the entire installation with a wander lead. Test at the first metallic section after the stopcock,if that is extraneous main bond there. As the potential comes from outside the installation by bonding at the point of entry you have dealt with the problem,the rest of the pipework is irrelevant..... unless (highly unlikely) it can pick up an external potential once within the building.
This brings me on to the next question,

"For new installations or alterations / additions in a location containing a bath or shower, supplementary bonding will not be required if:
1. The disconnection times required by Section 411 of BS 7671 are met, and
2. All circuits are protected by RCD’s having the characteristics required by 415.1.1, and
3. The building has protective equipotential bonding in accordance with 411.3.1.2, and
4. All extraneous-conductive parts of the location are effectively connected to the protective bonding."

Regarding the quote above if it is deduced that MEB is not required because of the plastic supply pipes then how can rules 3 and 4 above be met? Also if MEB is fitted to the copper side of the incoming then how can rule 4 be met as there is non conducting plastic pipe between rads taps etc?
If MEB is not required my proceedure is to test between conductive parts within the location and metallic services entering the location,if the reading is <1667 ohms no supplementary bonding is installed. Remember an extraneous CP in a bathroom is likely to be metallic pipes where they enter the location.....therefore that is where you may need to supp bond. Radiators,taps etc are unlikely to intoduce an earth potential unless they are fixed to metallic structural parts.....once again,by bonding at the point of entry to the location,the hazard has been dealt with,what happens to pipework within the location ,such as plastic inserts is irrelevant.

Do i need supplementary bonding or not?

How should this situation be dealt with, I would really appreciate some advice.

Thanks in advance

My red

 

[noodle_26]

Hi

Thankyou all for taking the time to help, it is really appreciated, I have one more question that I forgot to ask initially;

'If' it is deduced that MEB is required by testing as described above how would the following situation be dealt with; as stated in my original post the incoming plastic pipe is teed I forgot to mention it is teed in plastic not copper, the plastic arrives into the building from below, the plastic tee is actually below ground, one side of the tee rising above the screed where it connects to copper, the other part of the teed plastic pipe continuing under kitchen floor (approx 4m) then out the ground into utility then to copper and supplying boiler.

Quoting from electricians guide regarding MEB it states ".....connection must be made before any branch pipework......"

Am I correct that as this is impossible as the branch is in plastic that if MEB is required then two connections should be made back to MET, one from utility and one from kitchen?

Thanks in advance

 

[Moses]

Hi

Thankyou all for taking the time to help, it is really appreciated, I have one more question that I forgot to ask initially;

'If' it is deduced that MEB is required by testing as described above how would the following situation be dealt with; as stated in my original post the incoming plastic pipe is teed I forgot to mention it is teed in plastic not copper, the plastic arrives into the building from below, the plastic tee is actually below ground, one side of the tee rising above the screed where it connects to copper, the other part of the teed plastic pipe continuing under kitchen floor (approx 4m) then out the ground into utility then to copper and supplying boiler.

Quoting from electricians guide regarding MEB it states ".....connection must be made before any branch pipework......"

Am I correct that as this is impossible as the branch is in plastic that if MEB is required then two connections should be made back to MET, one from utility and one from kitchen?

Thanks in advance

You can loop the bonding wire from the first bond to the second bond and then on to the CU with the single wire, ( Loop not cut the wire)

 

[noodle_26]

Thank you all so much, very helpful

 

[currie123]

Hi I know this is an old thread but I am wondering whether all the above calculations etc regarding if main bonding is required if service pipes are plastic are also applicable to TT earth systems ?

 

[Johnuk]

these sound like college questions lol

 

[currie123]

No its not a college question mate

 

[Guest55]

Hi I know this is an old thread but I am wondering whether all the above calculations etc regarding if main bonding is required if service pipes are plastic are also applicable to TT earth systems ?

Yes.....

 

[Guest55]

In fact only today i bonded a water mains that was plastic incomer with all copper house pipework.
Didnt bother doing any of the calcs / testing / measurements either.
Why ?
because even though it didnt need bonding i cant be arsed explaining the technical in's and out's to anyone who comes along after and questions why it wasnt done basically.
Ever tried talking wiring theory with estate agents or building control officers ?
Their eyes glaze over in seconds lol.

 

[currie123]

Ok thanks biff, the one I was looking at is plastic incomes with partial copper and partial plastic inside house, TT system obviously, when I suggested to the customer it should really be bonded he said he was getting a bit sick of me finding problems with his electrics !

 

[Jayways]

The problem with everyone not bonding on basis of calculations / Testing and plastic service water pipes will be if circumstances change and something then becomes connected to earth. I cant imagine a plumber sorting it out