EarthingPlasticPipes

You do not have to earth plastic pipes.

Plastic pipes make for a safer electrical installationand reduce the need for earthing. Festooning aninstallation that has been plumbed in plastic pipewith green and yellow earth wire is not necessaryand is likely to reduce the level of electrical safetyof the property, not increase it.

Everyone knows that water and electricity do notmix, that the risk of electric shock is greater whenthere is water around. They know that the risk andseverity of an electric shock is increased as a resultof the presence of water. This may be the reasonfor the concern that water in plastic pipes mayconduct electricity and that bonding is required.Because of this, the IEE commissioned theElectrical Research Association to carry outmeasurements of the electrical conductivity ofwater in plastic pipes.

The ERA tests confirm that tap water in a plasticpipe is a poor conductor of electricity. One metreof 15 mm diameter plastic pipe filled with tapwater from Leatherhead where the ERA are based,has a resistance of 100,000 Ω. This one metre ofpipe will restrict currents to less than fatal valuesand of course in practice, there would be manymetres of pipe between metal items of plumbingequipment and earth.

The resistance of water varies around the country,it is reduced by impurities, not all of which areharmful. The additives put into the water ofcentral heating systems to reduce corrosion makethe most difference, as can be seen from the tablebelow.

Resistance of the water in 1 metre ofplastic pipe

Resistance Ω

15 mm diameter, tap water20 mm diameter, tap water15 mm diameter, water withdouble dose of inhibitor at 60°C

115,000 65,000 20,200

So why do wet hands and immersion in a bathincrease the risk of electric shock?

The Human body plus clothes, particularly shoeshas an impedance of about 3,000 Ω - see table inthe next column. At 230 volts this will result in a

By Paul Cook of theInstitution ofElectrical Engineers

CD Revised Nov 2002 The IEE is not responsible for the

current of about 153 mA (153 thousandths of anamp). This is not nice, but it is unlikely to killyou. If there are no shoes and hands are wet, theimpedance falls to 500 Ω and the current at230 volts is 460 mA. This is getting decidedlyunpleasant. Immersion of the body in a bath, ineffect halves the impedance of the body andcurrent at 230 volts would then be as high as1,000 mA. This is dangerous, and can kill.

Situation BodyImpedance

Current at230 V

Dry with shoesDryWetBody ½ immersed

3000+ Ω1500 Ω500 Ω250 Ω

76 mA153 mA460 mA920 mA

Horny dry hands and feet are quite goodinsulators. However, if the hands are wet, saltsand contaminants improve the contact and reducethe resistance of the skin. Dry skin has a highresistance, wet skin has a relatively low resistance.

The other reason why bathrooms and such placesare relatively risky electrically, is the presence ofearthed metal. Should you be unfortunate enoughto touch the live parts of broken equipment andnothing else except say a well insulated floor,there would be little result. Electrical jointers andfitters regularly work live under such controlledconditions. However, if you touch a live part andan earthed metal pipe, then you get a verydangerous electric shock.

An earthy environment where there are lots ofmetal pipes is potentially less safe than an earthfree environment. We can now start to see whyplastic pipe installations are going to lead to saferinstallations. For a start, there is not all thatearthed metal around.

The bonding requirements for plastic piped andmetal piped installations is described below.

At the Service Position - Main Bonding

In each electrical installation, main equipotentialbonding conductors (earthing wires) are requiredto connect to the main earthing terminal for theinstallation the following :

• metal water service pipes

• metal gas installation pipes

• other metal service pipes and ducting

• metal central heating and air conditioningsystems

• exposed metal structural parts of the building

• lightning protection systems

opinions expressed in the above page. 1

It is important to note that the reference on theprevious page, is always to metal pipes. If theincoming service pipes are made of plastic, theydo not need to be main bonded.

If the incoming pipes are made of plastic, but thepipes within the electrical installation are made ofmetal, the main bonding must be carried out. Thebonding being applied on the customer side of anymeter, main stopcock or insulating insert and ofcourse to the metal pipes of the installation.

The connections of the bonding wired to the pipeshas to be made with a proper clamp to BS 951complete with the label “SAFETY ELECTRICALCONNECTION - DO NOT REMOVE.”

If the incoming services are made of plastic andthe pipework within the building is of plastic thenno main bonding is required. If some of theservices are of metal and some are of plastic, thenthose that are of metal must be main bonded.

Typical earthing arrangements and protective conductor csa - TN-C-S

TN-C-S: PME earthNote: i) Main equipotential bonding conductors may be separate (as shown) or looped with unbroken conductors.

ii) Local electricity supply network conditions may require larger conductors.iii) - Safety Electrical Connection - Do Not Remove.LABEL

LABEL

otherextraneous-conductive-parts

earthing bar

consumer unitor distribution board

meter tails 25 mm2supplier’s meter

10 mm216 mm2

mainearthingterminal

main equipotentialbonding conductors

metalwaterpipe

metalgas pipe

10 mm2

16 mm2

supply earthPME connection

LABEL

LABEL LABELintake•

In the bathroom - Supplementary Bonding

Supplementary or additional equipotential bonding(earthing) is required in locations of increasedshock risk. In domestic premises the locationsidentified as having this increased shock risk arerooms containing a bath or shower (bathrooms)and if you are lucky enough to have one, in theareas surrounding swimming pools.

Please note, there is no specific requirement tocarry out supplementary bonding in domestickitchens, wash rooms and lavatories that do nothave a bath or shower. That is not to say thatsupplementary bonding in a kitchen or wash roomis wrong (it would be wrong for plastic pipes) butit is not necessary.

For plastic pipe installations within a bathroom theplastic pipes do not require supplementary

CD Revised Nov 2002 The IEE is not responsible for the

bonding and metal fitments attached to theseplastic pipes also would not require supplementarybonding.

It seems to be the practice of some builders toeffect all the plumbing in plastic except for thosebits of the pipework that are visible. These shortlengths of metal pipework supplied by plasticpipes or metal taps connected to plastic pipes,metal baths supplied by plastic pipes and with aplastic waste do not require supplementarybonding.

However, electrical equipment still does require tobe supplementary bonded and if an electricshower, or radiant heater is fitted, they will requireto be supplementary bonded as usual.

Supplementary bonds are required to be connectedto the protective conductor of all circuitssupplying electrical equipment in the bathroome.g. at a flex outlet or switch.

Figure 1 shows the supplementary bonding in abathroom where the house is plumbed with metalpipes and Figure 2 shows the supplementarybonding required in a bathroom where thepipework is plastic.

Metal radiators supplied by plastic pipes shouldnot be supplementary bonded. It is not safer tosupplementary bond them, it is safer not to.Locations generally are safer if the location isearth free as discussed earlier.

There are many possible combinations of metaland plastic pipe arrangements in a bathroom. Totry and answer questions regarding thesupplementary bonding required in a number ofpermutations of copper and plastic pipe, Table A below has been prepared.

opinions expressed in the above page. 2

CD Revised Nov 2002 The IEE is not responsible for the opinions expressed in the above page. 3

Figure 1: Supplementary bonding in a bathroom - metal pipe installation

Figure 2: Supplementary bonding in a bathroom - plastic pipe installation

.

metal waste

Outside Zones

* Zone 1 if the space is accessible without the use of a tool. Spaces under the bath, accessible only with the use of a tool, are outside the zones.

Shaverunit

Cord

shower Switchfor fire

Radiant fire

metal pipes

Pull cord switch luminaire

0.6 m 2.4 m

3.0 m 2.25 m

Zone 2

Zone 2

Zone 0

Zone 1 Zone 3

Outside Zones

Ceiling

*

metalpipe

Zone 3

Notes:1. The protective conductors of

all power and lighting pointswithin the zones must besupplementary bonded to allextraneous-conductive-partsin the zones, including metalwaste, water and centralheating pipes, and metalbaths and metal shower basins.

2. Circuit protective conductorsmay be used as supplementarybonding conductors.

3. Metal baths not connectedto a metal building structuredo not requiresupplementary bonding if allmetal pipes connected tothem has been bonded.

4. Connections to pipes to bemade with BS 951 clamps(complete with “SafetyElectrical Connection” label).

Outside Zones

* Zone 1 if the space is accessible without the use of a tool. Spaces under the bath, accessible only with the use of a tool, are outside the zones.

Shaverunit

Cord

shower Switchfor fire

Radiant fire

plastic pipes

Pull cord switch

0.6 m 2.4 m

3.0 m 2.25 m

Zone 2

Zone 2

Zone 0

Zone 1 Zone 3

Outside Zones

Ceiling

*

plasticpipe

Zone 3

plastic waste

plastic waste

Notes:1. The protective conductors of

all power and lighting pointswithin the zones must besupplementary bonded. Thebonding connection may beto the earth terminal of aswitch or accessory supplyingequipment.

2. Circuit protective conductorsmay be used assupplementary bondingconductors.

3. Supplementary bonding ofshort lengths of copper pipeinstalled where the pipes arevisible, is not necessary.

luminaire

Table A: Supplementary bonding in a number of permutations of copper and plastic pipe

Pipework materialWastePipes

ColdWater

HotWater

CentralHeating

Supplementary bondrequired between

Comments

1 Metal Metal Metal Metal All metal pipes, earth terminalsof protective conductors ofclass I and class II equipment,and accessible exposed-conductive-parts of the buildingstructure.

Metal pipes can be used asbonding conductors ifjoints are metal to metaland electrically continuous.

2 Plastic Plastic Plastic Plastic Earth terminals of protectiveconductors of class I andclass II equipment andaccessible exposed-conductive-parts of the building structure.

Bonding of metal taps,metal radiators or metalbaths is not required unlessthe bath is connected to themetallic building structure.

3 Plastic Plastic Metal Metal Hot water pipes, central heatingpipes, earth terminals ofprotective conductors ofclass I and class II equipmentand accessible exposed-conductive-parts of the buildingstructure.

A bond is not required tothe taps either hot nor cold,or to metal baths unlessconnected to the metallicbuilding structure.

4 Plastic Plastic Plastic Metal Central heating pipes, the earthterminals of protectiveconductors of class I andclass II equipment and accessto exposed-conductive-parts ofthe building structure.

Bonding of metal watertaps is not required, normetal baths unlessconnected to the metallicbuilding structure.

5 Plastic Metal Metal Metal All metal pipes, earth terminalsof protective conductors ofclass I and class II equipment,and accessible exposed-conductive-parts of the buildingstructure.

Metal pipes themselves canbe used as bondingconductors if joints aremetal to metal andelectrically continuous.

6 Plastic Metal Metal Plastic All metal pipes, earth terminalsof protective conductors ofclass I and class II equipment,and accessible exposed-conductive-parts of the buildingstructure.

Metal central heatingradiator does not requirebonding.

Notes:

1. Supplementary bonding is carried out to theearth terminal of protective conductors ofclass I and class II equipment within thebathroom. A supplementary bond is not runback to the main earth,

2. Metal window frames are not required to besupplementary bonded unless they areelectrically connected to the metallic structureof the building.

3 Metal baths supplied by metal pipes do notrequire supplementary bonding if all the pipesare bonded and there is no other connection ofthe bath to earth

4 All bonding connections must be accessibleand labelled “Safety Electrical Connection -Do Not Remove”.

CD Revised Nov 2002 The IEE is not responsible for the opinions expressed in the above page. 4