Electrical puzzle

[Aidan]

Mine if definitely Period electrics. No RCD/MCB, just a good ol' fuse box with bits of wire strung through china thingies. You know where you are with stuff like that. But when my immersion heater has split asunder it just stopped working. No blown fuses or other excitements. It has puzzled me

It probably just burnt out the resistance wire thingy.
My fuses were vintage until fairly recently. Now RCD/MCBs in a split load consumer unit, well worth buying. The lights usually trip the MCB now when a bulb goes (non-RCD protected side) , but I'm much more confident that the current would be disconnected if there were ever a serious need. I uncovered quite a few horrors whilst doing it; optional earth connections mainly, sockets wired to lighting circuits. Part P makes DIYing that very verboten now, probably many people will stick with vintage fuse boards; which seems to be achieving the opposite effect to that required.

The Neutral does go to earth anyway after it leaves your house. There isn't an earth wire running all the way back to the power-station.

I know; there weren't RCDs in those days so it didn't make a lot of difference, providing the earth resistance is low enough to stop any exposed metals bits becoming live. I think it's connected to earth at the local sub-station/transformer.

I heard of someone whose nickname was Earth; he had zero potential.

 

[NT]

> If it's split, the electric resistance heater will be in contact with the water; the heater should be isolated and replaced asap. It is hazardous and they can kill.

Split immersion heaters function as electrode heaters and are no safety problem at all. As children we're taught that electricity and water must never mix, but real life is not nearly as simple. I'd estimate there are around a million split immersion heaters in daily use, and no-one even gets a shock let alone dies from them. I am qualified in this subject. If you think people die from this then feel free to offer us a reference along with your deaths per year figure.


> Some, or all, of the current could flow from the heater element to the cylinder's metal casing. If the pipework is properly earthed, this would trip an RCD.

yes it will if one is fitted, but this is true regardless of pipe earthing. Domestic waterworks are not electrically isolated systems, and one with no connection to earth anywhere at all is unheard of. There are multiple earthing opportunities, most of which are normally present, and it would be quite exceptional to find a system with no path to earth. Such systems would be a genuine safety issue if they existed.


> If the pipework is not earthed, the cylinder and attached pipework will be at mains voltage, 230V.

not by a long way. It makes no difference in fact. You miss many factors.


> If you should happen to touch the live parts and something that is connected to earth ( say a radiator, bath) current will flow through you to earth.

you cant touch any live parts with a split element because there arent any. You'd have to open the tank and stick your hand in the water to do so.

Fwiw an electrified bucket with a coin in the bottom used to be a popular fair amusement once. I've tried touching things in electrified water when younger, but the initial mild shock makes it impossible to keep your arm in the water long enough to reach anything, no matter how determined. Even in extremis an open top tank with an electrode heater inside would not electrocute anyone sticking their hand in - not that I'd recommend it.


> If it is earthed, the fuse/MCB should pop/trip if the current exceeds it's rating.

another common myth. Fuses can pass many times their rated current and not fuse. Plus a good percentage of immersion heaters are fused well above their power rating.


> If the break is near the end of the heater element, it is possible that the current will be low enough not to trip the MCB. The heater might still work with current flowing to earth, rather than to neutral.

it always will


If you think this is a dangerous condition, maybe instead of just telling us your assumptions you can explain why its standard industrial practice in line with all current laws and regulations. Here's some more on electrode heaters and British safety regulations:

http://www.tlc-direct.co.uk/Book/7.11.2.htm


NT

 

[NT]

MCBs have much lower breaking capacity than fuses, and much higher failure rates. Sometimes its worth consulting an electrician.


NT

 

[Aidan]

Split immersion heaters function as electrode heaters and are no safety problem at all. As children we're taught that electricity and water must never mix, but real life is not nearly as simple. I'd estimate there are around a million split immersion heaters in daily use, and no-one even gets a shock let alone dies from them. I am qualified in this subject. If you think people die from this then feel free to offer us a reference along with your deaths per year figure.

The vast majority of people on this forum will never encounter an electrode boiler and have no interest in them. One person who has some experience of electrode boilers is.................me. Granny, eggs, etc..

They're much used in humidifiers. The casings on the ones that I dealt with were plastic. The heating effect is caused by the resistance of the water and the current is passed through the water from live to neutral electrodes; or between the 3 phase electrodes. The heat output can be varied quite simply by varying the water level & immersion depth of the electrodes.

If you think this is a dangerous condition, maybe instead of just telling us your assumptions you can explain why its standard industrial practice in line with all current laws and regulations. Here's some more on electrode heaters and British safety regulations:

http://www.tlc-direct.co.uk/Book/7.11.2.htm

I explain.

The water heaters shown in that link are purpose-made electrode boilers and are shown with a metal casing connected to both earth and to neutral. This is an illustration of a safe installation.

You are making an assumption that a defective immersion heater will operate safely as an electrode heater. It is designed as a resistance immersion heater, not as an electrode heater and it should be replaced if it starts working an electrode heater.

You have assumed that the copper cylinder is correctly earthed AND that the earth conductor is continuous AND has negligible impedance, so that the cylinder and attached pipework are always at zero potential. If the cylinder is not effectively earthed (plastic pipework?) it will be live and there is a shock risk. If the only connection to earth is through the water, the water has some resistance and the cylinder will be live.

Yes or No?

yes it will if one is fitted, but this is true regardless of pipe earthing. Domestic waterworks are not electrically isolated systems, and one with no connection to earth anywhere at all is unheard of. There are multiple earthing opportunities, most of which are normally present, and it would be quite exceptional to find a system with no path to earth. Such systems would be a genuine safety issue if they existed..

There might be a path to earth, but it's resistance will probably be excessive for it's safe use as an earth conductor.

> If the pipework is not earthed, the cylinder and attached pipework will be at mains voltage, 230V.

not by a long way. It makes no difference in fact. You miss many factors.


> If you should happen to touch the live parts and something that is connected to earth ( say a radiator, bath) current will flow through you to earth.

you cant touch any live parts with a split element because there arent any. You'd have to open the tank and stick your hand in the water to do so...

The live conductor is, errrrr, live. If the cylinder is not connected to earth (zero potential) , it will be live too.

My understanding is that immersion heaters are liable to cause nuisance tripping of RCDs because the insulation is hygroscopic and this can cause a small leak to earth (mAmps) on first switching on the heater, after which the insulation dries out. This is very different from an element with a split sheath with large currents passing directly to earth.

> I am qualified in this subject.

I think not.

 

[Ian Bond]

Part P makes DIYing that very verboten now, probably many people will stick with vintage fuse boards; which seems to be achieving the opposite effect to that required.

/quote]

According to Bristol LA's guidelines for electrical work...

http://www.bristol-city.gov.uk/ccm/...F211BFA40F815F17AF4C8C9999B0?asset_id=395008&

A DIYer can do the work and get it tested and certified by a qualified electrician, when using the 'submit a Building Regs application' route.

A very small percentage of people will DIY a full rewire to modern standards, as I did. But if you want to, it is certainly not forbidden by Part P.

Of course, your electricity board's electrician will make final connections to your new CU. I'm not suggesting you'd tamper with their end of the supply and work live with the meter tails.

It really is not a problem - I've done it! And I've also installed an unvented mains pressure hot water system, again by making a Building Regs applications.

 

[NT]

Re Aidans reply

Mistake after mistake after mistake, as always. You dont even know the subject.

Cut it short and answer one simple question. How many people die per year from split immersion heater elements, and where do you get your figure from. If you can manage that, the discussion will be ended.


NT



> I am qualified in this subject.

> I think not.

classic

 

[Aidan]

Re Aidans reply

Mistake after mistake after mistake, as always. You dont even know the subject.

Mistakes that you have not specified.

I have answered your query and as requested, provided an explanation of how the cylinder and attached pipework could become live and a shock hazard. I have not provided the answer that you'd anticipted, you have realised that you were mistaken and have asked some more questions to avoid that issue.

If the cylinder is not effectively earthed (plastic pipework?) it will be live and there is a shock risk. If the only connection to earth is through the water, the water has some resistance and the cylinder will be live.

Yes or No?

So, could the cylinder become live or could it not?
That is the only question.
You know that the answer is 'yes' but you can't reconcile yourself with the fact that NT has made a mistake.

Cut it short and answer one simple question. How many people die per year from split immersion heater elements, and where do you get your figure from. If you can manage that, the discussion will be ended.

No idea.
You're implying that such a fault has never killed anyone and that therefore it is not dangerous. It is hazardous. If you have information to show that no one has ever been killed by a split immersion heater, then post it here.

I am not having a discussion with you. My qualifications are in Mechanical Engineering. I feel obliged to post a contrary opinion to the misleading information you've posted. Anyone reading it will be able to work out their own opinion from our two conflicting views.

I contend that an immersion heater does not become a properly designed and safe electrode heater when it develops a fault. We are talking about vintage properties with, in some cases, vintage electrical installations.

> I am qualified in this subject.

> I think not.

classic

But true, Nigel.

 

[biffvernon]

Children, children.
All I know is that my immersion heater has split of three occassions. I noticed the problem because my water was cold not because I had been electrocuted.

 

[NT]

>> Cut it short and answer one simple question. How many people die per year from split immersion heater elements, and where do you get your figure from. If you can manage that, the discussion will be ended.

> No idea.

> My qualifications are in Mechanical Engineering.

enough said.


NT

 

[Aidan]

So, could the cylinder become live or could it not?

.

> My qualifications are in Mechanical Engineering.

enough said.

NT

So that's a 'Yes', then.

 

[NT]

lol