Trying to electrocute myself

[Christian McArdle]

Indeed. If you can eliminate earths altogether the protection is better. The IEE recommend that you use plastic pipework so that you can avoid the need for supplementary bonding.

However, if you DO have metal pipework, then supplementary bonding is safer because that earth fault that makes something 240V does one of two things:

1. It causes a major short to earth, tripping an MCB/RCD before you have a chance to be shocked.
2. If (1) doesn't occur, it means that everything is at 240V, so you don't get shocked. Have you seen those pictures of people working on live multi-kilovolt systems safely simply by only touching the live and not the earth?

Christian.

[roger]

Christian McArdle writes

Unfortunately, you do. Even if all the metalwork is only at 120V. Everything was fine until someone used bath salts so that the water going down the plastic drain to the old [broken?] earthenware drain in the yard was conductive. Stand in draining water, get nasty belt off mixer. I didn't altogether believe this, went over to the friends house and tried it. Once was enough. Contractor had used armour of cable for earth continuity, terminating it very professionally in a proper gland onto the Consumer Unit casing. Which was plastic. Filters on a big PC system, TV's etc then took "earth" to 120V.

[stefek.zaba]

Not quite sure they go that far; certainly with plastic plumbing there is less that needs bonding, e.g. taps don't; but other electrical gear such as electric showers, heaters, shaver points, etc. will still need cross-bonding.

[Lurch]

Not sure if you're agreeing or disagreeing with me, I'm sure it'll come clear in a minute. Meanwhile:- That's what I said. Connecting the metalwork in the bathroom together is half the job, connecting all the other bits of metal in the building together and also to a reliable earth point would be the other half.

SJW A.C.S. Ltd.

[Lurch]

Although if you add all the seperate bits of bonding and earthing regulations it basically all adds up to "connect all metal bits together" The supplementary bonding connected to metalwork will be connected to the main service pipes, (even with plastic in the middle, those bits need to be 'bridged'), they will be connected to each other at the mains end with equipotential bonding thus connecting all exposed metal work. This will also connect all socket screws, light fittings etc.. So there is no 'direct' regulation stating that supplementary bonding should be connected to earth but the earthing system as a whole is designed so that it is.

SJW A.C.S. Ltd.

[usenet]

If there are mostly plastic pipes there is no requirement to bond any metal bits on them (e.g. taps or maybe the odd union), thus this

*won't* be connected to the main incoming pipework, which is quite likely to be plastic nowadays anyaway. So no necessary connection to earth here.

There shouldn't be any socket in the bathroom. If there is nothing electrical with exposed metal parts (quite likely in a bathroom) there is again no need for the supplementary bonding to be connected to the electrical earth. (Is that right, I don't have my OSG to hand, it

*may* be that electrical equipment earths should be connected to supplementary bonding, not absolutely sure - however if there's no electrical equipment in the zones my comment still applies)

[Christian McArdle]

Indeed. However, they are keen to have you install plastic plumbing so that the metal bath and radiators don't need bonding. These are large areas likely to be touched.

Yes, but these are often not large areas. Also, I have none of these devices in my bathroom. Nor does my mother's house and nor did my last house. I do have metal pipework, though, so I've still got to have bonding.

Christian.

[Bob]

interrupting

implementation

240V relative to the floor they were standing on, of course. Just because all the metal bits are joined together doesn't mean that if they end up connected to the live instead of earth wire that you won't get a shock. You could always try holding a live wire if you don't think I'm right.

I did post a couple of years ago about this subject - ie what is the point of earth bonding, but no-one could answer at the time. From recent posts I can see what the reason is, but my point is that earth bonding protects against one kind of fault only. I'm just giving an example where it made the fault more dangerous.

Bob

[Christian McArdle]

What sort of bathroom floor has enough conductivity to give you a powerful enough shock to kill you? Typically, a bathroom floor will be timber, plastic, stone or ceramic. All are excellent insulators and will not support the levels of current needed for a dangerous current flow.

Christian.

[Lurch]

O.k, if the installation is all in plastic then yes, but my comments were more based on the more common installations of metalwork, (which is what the posters saying it is wrong to have supplementary earthing have so that is what I chose to comment on, plastic isn't relevant to this particular conversation).

I never said there should, I was meaning in the property in general.

No, you would still have to bond pipework together.

I didn't say connect it directly, I said it is connected by default, i.e. all earths connected together at the CU. More than likely the earth path from supplementary bonded metalwork will end up connected here.

SJW A.C.S. Ltd.

[Dave Plowman]

Do you really need to cross-bond a shaver socket given that the only exposed metalwork is the fixing screws?

[Lurch]

So you're saying it wasn't the bonding that caused the metalwork to become live but two seperate faults elsewhere in the installation. If you didn't have the bonding you would have found other faults or problems from not having bonding anywhere. If you would care to have go on google you will find plenty of articles on bonding, why you should do it, how it works etc..

SJW A.C.S. Ltd.

[Dave Plowman]

I'd not fancy my chances of standing barefoot on a wet concrete floor and touching a 240 supply with wet hands. You try it if you want. ;-)

[Lurch]

According to the regs, yes. I did a bit of sub-contacting to a firm a few years back, before earth bonding became daft. Being useless in every other aspect, (the firm, not me), I was surprised when I went on a 2nd fix of a bathroom extension to find a 4mm earth connected to anything in the room, the shower and exposed metalwork as normal but also to the light fitting, fan, shaver light, and anything else with a screew on it, whether it could be touched or not. Everything in the room was double insulated, bar the shower.

SJW A.C.S. Ltd.

[usenet]

But the whole point is that "supplementary bonding" *isn't* an earth connection and doesn't work by being connected to earth.

It may well be that in many installations (e.g. where all pipework is copper) the supplementary bonded metalwork in the bathroom is connected to earth but that isn't what makes it useful.

[usenet]

The floor isn't conductive so, no shock. You most certainly *can* grap a live wire and not get a shock, in fact it's the commonest situation in my experience as one nearly always wears rubber or plastic soled shoes nowadays and floors are nearly always covered with a layer of material which is afairly good insulator.

It's only of your other hand is leaning on something earthy that one gets a shock usually. I can't remember when (if ever) I've got a shock which was anything other than hand to hand (bad, across chest) or, more often in my case, simply across my fingers.

It can only make things more dangerous if there's something conductive at earth potential in the bathroom, if there is then the bonding is faulty because that item should be connected too. If the bonding is done correctly then even a damp floor will be at the same potential as the bonded metalwork, where else can it get its voltage level from?

[usenet]

How many bathrooms have bare concrete floors? Even then if the bonded metalwork is at 240 volts it's odds on that the floor will be too.

[Christian McArdle]

Urgh! You have a wet concrete floor in your bathroom?

Besides, what do you think the conductivity is of set unreinforced concrete with surface water?

Christian.

[Lurch]

I know.

It works by bringing all simutaneously touchable exposed pieces of metalwork to the same potential, (not neccesarily 0v though). See, I do know. In 'most' cases it would be connected to earth, fine, I'm not disagreeing.

SJW A.C.S. Ltd.

[John Laird]

Which, if they are like normal socket outlets, are earthed anyway...