Earthing Pipes?

[sterose]

Gees, er.... yes, but it wont save bills because the bloody radiator will never give out any heat and the heating will run constantly

Duh!

 

[Gees]

All points noted but I say again what about the RCD?
I tried an experiment a few mins ago. 2 lenths of 22 mm copper with 6 inches of plastic pipe in between, filled with tap water = 500 k ohms or so.
(Thats with a 500 volt megger) Add a little salt and down it goes to 20 k.
With all the stuff floating around in a heating system goodness knows what the resistance of the water would be? So in theory the current would probably be very small it would certainly "tickle" a bit...

By the way I DO have a completly earth free area here. I have a workshop that is supplied by a 3kva Isolation transformer. There are literally NO earths that can be reached from this area. ( no rad. in this room ) so I can touch anything I like ( with one hand ) and be completly safe...

AS for heating running all the time.... Hasnt your boiler got any stats in it then?

 

[sterose]

An RCD prevents electrocution by measuring the current going in the live and out the neutral. If it earths out, the neutral current is less and there is an imbalance in the RCD and it trips.

Remember, i dont make the rules, im sure you could get away without earth bonding and survive an electric shock - but im explaining the theory behind earth bonding.

By the way, do people realise that Neutral is Earth, which is why you complete a circuit when you touch live to earth

 

[ban-all-sheds]

You dont earth steel shelves and towel rails because there is NO path to earth (assuming is is fixed to brick or wood) unless it is connected to something with a path to earth.

You do earth radiators though because they are generally somewhere conencted to earth, usually at a boiler (because the metal of the boiler must be earthed).

Water does conduct electricity but has a high resistance.

This means that, without me knowing the exact resistance, a current that is less than the fuse rating can flow through you.

Like i said, if the resistance of water means that a current of 39 amps flows from your shower into you, but the shower fuse rating is 40amps, the fuse will never blow because it is still below its rating.

However, 39amps can damage you if not set you on fire.

Please ask further if you dont understand.

As a final point, a totally earth free environment is the safest place to be, eg. you could touch the 240volts mains and not be electrocuted. BUT no place in a house is totally earth free, eg. there is always something that will conduct electricity. The problem in bathrooms is that there is plenty of water and metal, and electricity if you have a shower. If an electric appliance fails somehow, it is the most likely place for you to come into contact with the faulty appliance AND be touching something with a path to earth.

Also, save yourselves time by simply learning about this instead of arguing with me. I know im right. Because when I argue, i always know im right.

Sterose - I don't know who rattled your cage, but I sincerely hope you don't think it was me - I wasn't arguing with you, I was doing exactly what you requested - asking further.

I do understand why we don't earth shelves and towel rails.

I do understand why we earth radiators and metal pipes and metal baths and taps and electric towel rails and showers etc etc etc.

I do understand that water conducts electricity, and therefore makes bathrooms particularly risky environments.

I do understand equipotential bonding requirements.


I don't understand your example of the shower, though. If we assume the worst case of Zs being zero, 39A implies an Rp of 6.15 ohms, and I always thought the accepted worst case value was around 500 ohms. Again - if I dare ask, not argue - does it drop to that low a value for a wet body?

Anyway - from what little I know, I think it's irrelevant - 500 ohms will get you 480mA, which probably won't set you on fire, but probably will kill you in a very short space of time.

Data on the actual levels of current required to injure or kill people are understandably hard to obtain, but the IEC have had a stab at it, and Publication 479 has a chart showing shock hazard curves (this one has the tripping characteristics of MEM RCDs superimposed):

and a quick summary - in Zone 1 you are unlikely to get any adverse reaction, Zone 2 - usually no harmful effects, Zone 3 is where you start to get problems.

So we should be concerned if the Zs of the water in plastic pipes drops below 240k ohms, and really concerned if it drops below 24k ohms, as you can't guarantee that someone would let go of (in this case) a radiator.

Gees experiment showed 500k ohms for 6" of 22mm plastic pipe, 20k ohms when you add salt, i.e. 3.3M ohms and 131k ohms respectively per metre. More for 15mm pipe. And as he says, who knows what values when you consider the corrosion inhibitors in the water.

But even so it doesn't look, at first glance, as if the resistance of any reasonable length of water in a plastic pipe would be low enough to allow a hazardous current to flow through someone - your radiator would be, for practical purposes, earth-free, and therefore safer than one with a bonding cable attached.

We can't use Gees experiment as a guide, and personally this isn't something I've ever bothered to research as I don't have plastic pipes.

What do the regulations say? Do they assume that pipes will be copper, and therefore that radiators should be earthed, or do they make a distinction for plastic pipes?

 

[sterose]

I'm sorry, ban-all-sheds for my apparent tone of voice, I was just stressed with an unrelated issue.

I accept your explaination for the shower example, I have not analysed the actual resistance for it. I was just making an eggagerated example of what could happen of the current was just below the rating of the fuse.

I personally don't know the value at which someone can be killed. But I once heard that a sustained current of only 1/millionth of an amp is enough to kill in certain circumstances (please correct me...)


"But even so it doesn't look, at first glance, as if the resistance of any reasonable length of water in a plastic pipe would be low enough to allow a hazardous current to flow through someone - your radiator would be, for practical purposes, earth-free, and therefore safer than one with a bonding cable attached."

Yes, i have considered this myself, but as i say i dont make the rules.


Just for a moment, lest assume your radator, that is practically "earth-free", becomes live due to an electrical fault - and lets say that the appiance in question is 13 amps (maybe a heater)- there will be a *very* small amount of current flowing through the radiator to earth, not enough to burn the fuse in the portable heater.
Next lets assume, for some (unlikely) reason, you happen to touch something that IS earthed, maybe a tap, with a very low resistance, but still not enough to let the fuse burn out. It will then proceed to inflict a current on you without the fuse burning out.
The effects of that current are, for this explaination, irrelevant.
The point is that if the radiator was earthed in the first place, the >13amp current would have earthed and burned the fuse out. Saving you the unzzzzsavoury (laugh) experience of being electrocuted, and also avoiding the possibility of fire because of the heat that may, or may not, have been produced by the faulty appliance earthing out.

 

[climberjim]

I'm sorry, ban-all-sheds for my apparent tone of voice, I was just stressed with an unrelated issue.

I accept your explaination for the shower example, I have not analysed the actual resistance for it. I was just making an eggagerated example of what could happen of the current was just below the rating of the fuse.

I personally don't know the value at which someone can be killed. But I once heard that a sustained current of only 1/millionth of an amp is enough to kill in certain circumstances (please correct me...)


"But even so it doesn't look, at first glance, as if the resistance of any reasonable length of water in a plastic pipe would be low enough to allow a hazardous current to flow through someone - your radiator would be, for practical purposes, earth-free, and therefore safer than one with a bonding cable attached."

Yes, i have considered this myself, but as i say i dont make the rules.


Just for a moment, lest assume your radator, that is practically "earth-free", becomes live due to an electrical fault - and lets say that the appiance in question is 13 amps (maybe a heater)- there will be a *very* small amount of current flowing through the radiator to earth, not enough to burn the fuse in the portable heater.
Next lets assume, for some (unlikely) reason, you happen to touch something that IS earthed, maybe a tap, with a very low resistance, but still not enough to let the fuse burn out. It will then proceed to inflict a current on you without the fuse burning out.
The effects of that current are, for this explaination, irrelevant.
The point is that if the radiator was earthed in the first place, the >13amp current would have earthed and burned the fuse out. Saving you the unzzzzsavoury (laugh) experience of being electrocuted, and also avoiding the possibility of fire because of the heat that may, or may not, have been produced by the faulty appliance earthing out.

But why is your radiator any more likely to become live than any other isolated metal object? To exaggerate slightly you suggesting that when you pour water from a kettle you need to earth the tea spoon!

See
http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf

BTW as you know the regs, I have radiators with metal pipework. Currently the pipework is earthed but there is no additional earth strap between the radiators themselves and the pipes. Does this need to be the case or can I just rely on the pipe fittings making the earth connection.

Thanks

Jim

 

[sterose]

Drole, Jim. Very drole.

The radiator is not an isolated metal item. It is a large fixed item. There is an infinitely greater chance of me toughing a radiator and getting electrocuted than there is with a teaspoon.

After all, i find it laughable that someone might not notice a live electric cable connected to a teaspoon!

I also suggest anyone with further issues reads Jim's suggestion - http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf

I'm not exactly sure what you are saying, but i think what you are syaing is that the pipes leading up to the radiator are earthed but the actual radiator itself isnt.

I think you can get radiator earthing straps, but i would think that just earthing the pipes would do. Thats what I did.
Basically, what people should do is get a length of cable, and earth straps, and if its metal... earth it.

 

[climberjim]

Drole, Jim. Very drole.

The radiator is not an isolated metal item. It is a large fixed item. There is an infinitely greater chance of me toughing a radiator and getting electrocuted than there is with a teaspoon.

After all, i find it laughable that someone might not notice a live electric cable connected to a teaspoon!

I also suggest anyone with further issues reads Jim's suggestion - http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf

I'm not exactly sure what you are saying, but i think what you are syaing is that the pipes leading up to the radiator are earthed but the actual radiator itself isnt.

I think you can get radiator earthing straps, but i would think that just earthing the pipes would do. Thats what I did.
Basically, what people should do is get a length of cable, and earth straps, and if its metal... earth it.

OK. to change my analogy slightly. Girl semi-naked wanders from the bathroom, still wet, and starts to dry her hair with an electric hairdryer. She's resting her other arm/body on the radiator.

If she drips enough water into the hairdryer she could get a shock.

If the radiators not eathed and her feet are dry - maybe not a bad one.
If the radiators earthed it will be worse, possibly much worse (short to earth accross her chest etc.).

If the radiator becomes live she would get a bad shock if it wasn't earthed. BUT how does this happen there are no electrical connections - more improbable?.

Both earthing and not earthing have a risk attached but I would suggest that not earthing presents the lesser one.

I guess it all depends on where you think the balance of probabilites lies

Jim

 

[ban-all-sheds]

I'm sorry, ban-all-sheds for my apparent tone of voice, I was just stressed with an unrelated issue.

No worries - if I had a pound for every time I'd done something like that, I'd be able to afford to employ an electrician

.. I once heard that a sustained current of only 1/millionth of an amp is enough to kill in certain circumstances (please correct me...)

I'd be very surprised if 1 microamp was ever enough to kill. Does anybody know what current flows through your body when you use a neon tester?

"But even so it doesn't look, at first glance, as if the resistance of any reasonable length of water in a plastic pipe would be low enough to allow a hazardous current to flow through someone - your radiator would be, for practical purposes, earth-free, and therefore safer than one with a bonding cable attached."

Yes, i have considered this myself, but as i say i dont make the rules.

Indeed not - but it seems from the document on the IEE website, that you don't have to earth radiators that are fed by plastic pipes - in fact you shouldn't:

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

So there we have it - I was right after all, thankfully. And I say that not out of smugness, or "yah boo you were wrong" - I was beginning to worry that I'd given dave12 bad advice, and I'm relieved that I didn't.

I have radiators with metal pipework. Currently the pipework is earthed but there is no additional earth strap between the radiators themselves and the pipes. Does this need to be the case or can I just rely on the pipe fittings making the earth connection.

You don't have to connect an earth directly to the radiator, but if you've used PTFE tape on the joints it might be a good idea. Certainly wouldn't do any harm.

 

[climberjim]

Thanks Ban-all-sheds,

The annoying thing is that every time I look into to something like this I discover something else I should have done. In this case it appears I needed to cross bond the earth from the new shaver socket (to the water pipes). Can't see much point in it though (I think the isolating transformer should limit the current to safeish levels - not certain though) - possibly it needs cross bonding because of the screws holding it to the pattress but mines plastic).

Seems to me like work for the sake of the regs and I'm inclined not to bother. Can you (or anyone else) think of a reason why I should. I'm only too happy to be put straight on this.

Thanks

Jim

 

[ban-all-sheds]

Ah yes - shaver sockets.

Never understood these. Yes, there is a transformer in them, so any short circuits caused by water will be limited in severity and won't affect anything else.

But safe? They will deliver 200mA.

Although a useful feature of a transformer is that it is a high-impedance supply, so connecting a load with a lower impedance (e.g. a body) than designed for will drag the voltage down, I'm not convinced. Does anybody here fancy grasping the live output from a shaver socket in one wet hand and a well earthed tap with the other wet hand, to show how either the internal trip or the natural current-limiting effect of the transformer means that they don't get hurt?

Don't all rush at once

You'd think that in this day and age you'd be allowed something with a built in 10mA RCD. I wish you were, as I have a toothbrush charger which I would like to have in the bathroom, but I can't because it takes too much juice for a shaver socket.

As for your question, yes, you do have to bond it. The reason you should is that the regs say you must. Is it safe not to? Almost certainly, but don't look for logic in the regs - that way lies madness.

Grow a beard

 

[bonus]

Before you get too heavy in to shaver sockets.

I am in the middle of some bathroom projects at present. My house is around 7 years old. I have recently moved from a house that is two roads away and it is of the same age.
After, stumbling across this thread, it has just ocured to me that none of the pipes in my bathroom and shower room are earthed. In fact, I've had a look around the house and no pipes whatsoever are earthed.
Am I living dangerously or is there another way of doing this

Help!

PS.
I have an electric shower which I am replacing this week. I have had to endure an electric shower every day since moving in earlier this year. Two blew up on me when I was a kid, I hope I haven't inherited my Dad's DIY skills

 

[ban-all-sheds]

...I am in the middle of some bathroom projects at present. My house is around 7 years old. I have recently moved from a house that is two roads away and it is of the same age.
After, stumbling across this thread, it has just ocured to me that none of the pipes in my bathroom and shower room are earthed. In fact, I've had a look around the house and no pipes whatsoever are earthed.

Am I living dangerously or is there another way of doing this

Well, yes and no.

"Dangerous" is a bit emotive - certainly not as safe as it could be, and potentially dangerous. My first thought is that at 7 years old, your house is still under NHBC guarantee, and the electrical installation was installed in contravention of the wiring regulations, as they became compulsory on Jan 1 1993.

Get in touch with the builder - demand that he put this right, tell him exactly why is is wrong, and leave him in no doubt that you will sue him if he doesn't sort it out.

I have an electric shower which I am replacing this week. I have had to endure an electric shower every day since moving in earlier this year. Two blew up on me when I was a kid, I hope I haven't inherited my Dad's DIY skills

So do we all... If you're in doubt about your ability to install a shower, get a professional in.