Fitting a dual electric/central heating towel radiator

[DarrenSL]

I want to fit a dual electric/central heating towel radiator in my bathroom but have a couple of questions before I proceed...

Where should I fit the fused switch? Inside the bathroom or outside?
Do I need to earth bond all the exposed metal work in the bathroom if I go ahead with the radiator? Currently, all other appliances in the bathroom are LV so not earthed.

The bathroom is 2m x 2m in total and the radiator will be approx. 1 to 1.5m from the sink, toilet and bath (if thats relevant?)

Thanks.

 

[RF Lighting]

I want to fit a dual electric/central heating towel radiator in my bathroom but have a couple of questions before I proceed...

Where should I fit the fused switch? Inside the bathroom or outside?

This should be fitted outside the bathroom with a sutiable flex outlet plate inside the bathroom. I have also got a time clock fitted to mine (outside the bathroom) This might be worth considering fitting

Do I need to earth bond all the exposed metal work in the bathroom if I go ahead with the radiator? Currently, all other appliances in the bathroom are LV so not earthed.

Yes.
The bathroom should be 'cross bonded' even if there is nothing electrical in there at all

The bathroom is 2m x 2m in total and the radiator will be approx. 1 to 1.5m from the sink, toilet and bath (if thats relevant?)

The flex outlet for the towel rail needs to be in zone 3 or beyond, which this will be (0.6 meters from the edge of the basin)

 

[DarrenSL]

The bathroom should be 'cross bonded' even if there is nothing electrical in there at all

Pardon my ignorance, but where's the risk of shock if there's no electrical equipment? I read the IEC (I think) guidelines a while back and to be honest it went a little over my head. Am I right in saying that the risk is from the fact that there could be a PD between say a faulty appliance (earthed) case and the tap (earth) which would still result in a shock. So the purpose of bonding is to make all exposed metalwork the same zero potential.

I also don't understand the fact that if the appliance is faulty the circuit breaker will trip and hence no risk of shock?!


Thanks for the tip on using a flex plate. It didn't even cross my mind. I was planning to go straight through and under the floorboards. The flex plate should look neater and be safer too.

Like the idea of a timer too

 

[RF Lighting]

A potential could exist between the hot and cold tap. This could occour if there were say for example a fault which brought the hot pipe live (somewhere inside or outside the bathroom) and not to the cold pipe so the hot tap is now at mains voltage and the main bonded cold tap is at earth potential. If you were to grab both taps at the same time (especially with wet hands) then YOU would complete the circuit of live to earth. If the bathroom is cross bonded then the voltage will use the earth wire to complete the circuit rather than you. There will still be a risk of shock from this but it will be a lot less severe than an un-bonded situation. I know the chances of this happening are unlikely and the fuse for the circuit would blow but it could take upto 5 seconds for the fuse to blow and if you were unfortunate enough to have this situation occour and happen to grab the taps then the result will be

I hope this makes sense but it is not easy to explain the reasons in 'laymans' terms. (no offence)

 

[DarrenSL]

No offence taken. I understand the point your making. One more question though (Sorry but I do find this concept rather interesting as it seems to contradict my understanding of electricery (sic)).

My understanding is that water is a pretty good conductor of electricity, a lot better than skin and bone anyway. So, within the house the hot supply will at some point be connected to the cold e.g. at the boiler. So any potential difference will dissipate pretty quickly. Does it simply come down to the difference in resistance between say 20m of water filled copper pipe versus. ~1.5m of human tissue?

 

[RF Lighting]

This might be a shocking statement that goes against everything everyone is taught at school, but water does not conduct electricity. It is infact the impurities in water that do the conducting and I beleive this can not be a set value (for resistance value purposes). I beleive the NICEIC have an 'average resistance value' of 1 meter of water with a 'cross sectional area' the same as if it were in a 15mm pipe (but I don't have this to hand at the moment). To back my statement, have you ever had to top up a car battery? This uses distilled water (i.e. water with the impuritys removed). I have also seen a sealed light fitting that had filled with water as was still working

 

[DarrenSL]

Ah, fascinating stuff! Makes perfect sense now. I actually did a Chemistry degree some while back. Its all come back to me now ... electrolytes and free ions etc. Should have known better

Perhaps thats why I'm an accountant now

Thanks!

 

[Spark123]

In a bathroom, a person is at increased risk of electric shock owing to being wet and unclothed which reduces the resistance of the body. The hot and cold pipes may be at the same potential being cross bonded at the boiler, but this pipe will have a resistance which in the event of a fault where a live cable comes into contact with the hot water pipe may cause a potential divider effect between the hot - boiler - cold/gas - earth through main bonding etc, hence there may be quite a large potential existing between hot and cold pipes whilst the fault clears. This is why supplementary bonding is carried out local to the bathroom, to keep all metalic items which are likely to introduce a potential to the bathroom at the same (or thereabouts) potential.

 

[RF Lighting]

I'm an accountant now

Wish I'd known that earlier

Only kidding

 

[Adam_151]

Paul cook of the IEE quotes 115k-ohms for a 1m 15mm pipe filled with 'average' tap water, this drops to 20.2k if its a heating pipe with a double dose of corrosion inhibitor operating at 60°C

 

[Pensdown]

This might be a shocking statement that goes against everything everyone is taught at school, but water does not conduct electricity.

When I had hair on my head and not in my ears I remember going into a flooded basement in Catford.

The water was above the sockets and there were bubbles coming out of them where the water was boiling inside the socket. The consumer unit was in the basement & my brain would not let me walk in the water to turn it off even though I knew the water could not be live. Stupid I know but in the end I used a piece of 2x1 to reach over and turn it off

 

[DarrenSL]

The water was boiling?! Could have been electrolysing i.e. splitting the water into hydrogen and oxygen. Your biggest risk was probably being blown up!

 

[DarrenSL]

I want to fit a dual electric/central heating towel radiator in my bathroom but have a couple of questions before I proceed...

Where should I fit the fused switch? Inside the bathroom or outside?

This should be fitted outside the bathroom with a sutiable flex outlet plate inside the bathroom. I have also got a time clock fitted to mine (outside the bathroom) This might be worth considering fitting

Is this the type of switch you were referring to http://www.screwfix.com/app/sfd/cat/pro.jsp?id=12544&ts=46029

Also, are there any rules regarding the positioning of the flex plate. e.g. not directly beneath the radiator.

Thanks.

 

[Pensdown]

http://www.tlc-direct.co.uk/Main_In...Mk_Accessories/Flex_Outlets_Plates/index.html


The ideal location would be as close as possible to the rails connection point so the flex does not trail on the floor

 

[Steve]

The water was boiling?! Could have been electrolysing i.e. splitting the water into hydrogen and oxygen. Your biggest risk was probably being blown up!

Unlikely - electrolysis only happens with DC, AFAIK. Its impossible with AC because of the reversing polarity all the time.