10mm cable for shower - Why?

[Big_Spark]

Who's so in favour of regulations being followed even if they don't understand them that he thinks that Part P is b*11*cks and has no intention of using electricians because of it?

Who advises people to move their electricity meter themselves if the supplier asks £too much?

Who thinks that AC means that the neutral conductor is at 240V 50 times a second, and when people tell him he's wrong he accuses them of being mad?


Surely not....

My first post will be a bit controversial I think, but here goes in response to these comments.

Many parts of BS7671 (The 16th Edition Regs) are contradictory, vague and generally ambiguous at best. The IEE would not understand the term clear English if you droped a boat load of dictionaries of Faraday House. Having said that, if you bother to read the regs, and actually understand what they are saying, and you then carry out work as per they advocate, then you will at least be safe.

Part P...don't get me started on that load of unadulterated, self interested cr*p. Part P in the brain child of the NICEIC, which is a charity not a government body, and controlled, indirectly, by the big 4 in the contracting industry, T.Clarke's(Tommy Clarkes), Bailey's, AMEC, andMathew Hall.

I have personal experience of work from all of those, and most of their Guys I would not trust to wire a plug.

The concept behind part P is sound, however the joke that was the consultation, and the conclusions are very questionable.

The NICEIC and the ECA only have their own interests at heart, not that of the Industry or the public.

Moving your Electricty meter is a CRIMINAL OFFENSE. It is also an offense under the Electricty Supply Regulations Act and the Electricity Supply Act, however you will likely just be prosecuted by the the company for interfering with the meter, often called "Abstraction of Electricity" by the law.

Moving an Electricity meter is foolish.

AC..means ALTERNATING CURRENT, this also means the voltage alternates. 50 times a second the "Live" Phase conductor will be at a peak of around +338V (The RMS is 240V), further 50 times a second it will be at 0V and conversly it will be at -338V 50 times a second.

The same is true of the "Neutral" phase conductor, however due to the complexity of electricity, in an everday sense it is usual to think of it as "dead"..I won't bore you with the maths and technical reasons, but this is actually the case.

And if you think you cannot get a shock from the "Neutral" then you would be very wrong, just as you can get a shock from and "Earth" point or conductor if the circumstances are right.

HOWEVER, if you always turn the supply off to the circuit you are working on, then you will never recieve an Electric shock regardless.

 

[AdamW]

just as you can get a shock from and "Earth" point or conductor if the circumstances are right

Anyone who has set up a very large apparatus for an experiment may have found this. Particle accelerator labs such as CERN go to great expense and effort to level their earths. The potential difference across two earths can be significant: just try sticking one terminal of a multimeter on one earth contact and then stick the other terminal on an earth contact on a different circuit and see what you get!

"no two earths are equal"

 

[paulh53]

HOWEVER, if you always turn the supply off to the circuit you are working on, then you will never recieve an Electric shock regardless.

We won't mention shocks from "Borrowed Neutrals" will we

 

[Big_Spark]

HOWEVER, if you always turn the supply off to the circuit you are working on, then you will never recieve an Electric shock regardless.

We won't mention shocks from "Borrowed Neutrals" will we

Oh be fair to the DIYers here, that will simply confuse the hell out of them

 

[Northernladuk]

And on a practical example I had a 7.5Kw shower unit internals replaced by an 'electrician' but soon after I would come down stairs and there would be an acrid smell. Went down stairs to the electrics and sure enough it was a right mess. Caught it just in time.

The tw*t had only put a 9.5 Kw in instead without telling me so my 6mm cable was burning. Swapped it all out for 10mm (like my hot strong showers ) and all was well...

Number arn't there just for the good of the beauracrats and to keep regulation people in a job. They are there to safe your life!!!

 

[securespark]

Going to make enemies, here but your 6mm2 could be good for 9.5 in certain circs.....

 

[ban-all-sheds]

HOWEVER, if you always turn the supply off to the circuit you are working on, then you will never recieve an Electric shock regardless.

We won't mention shocks from "Borrowed Neutrals" will we

Oh be fair to the DIYers here, that will simply confuse the hell out of them

No it won't. I was going to point out b-n's as a source of risk, but could't find my round tuit. Not just a DIY error, either, I believe - didn't it used to be fairly common practice to have landing lights with live from the downstairs lighting circuit and the neutral from the upstairs?

 

[ban-all-sheds]

Going to make enemies, here but your 6mm2 could be good for 9.5 in certain circs.....

Yes but circumstances likely enough, or unrestricted enough in practice to make it worth bothering with?

 

[Big_Spark]

No it won't. I was going to point out b-n's as a source of risk, but could't find my round tuit. Not just a DIY error, either, I believe - didn't it used to be fairly common practice to have landing lights with live from the downstairs lighting circuit and the neutral from the upstairs?

That is the problem with round tuits, they are never there when you need them!!

However, in the 20 odd years I have been in the trade, I have rarely come across borrowed neutrals. As far as I can recall, the only time they have been encountered is when correcting problems caused by DIY electricians, with one notable exception.

Takingn a neutral from one circuit and using on another circuit if foolhardy at best, reckless and at worst potentially fatal. Anyone that has had a neutral shock will tell you it hurts more than the live..although I think some of that is psychological as you don't expect it!

 

[ban-all-sheds]

Hopefully you're never expecting an electric shock....

 

[securespark]

BAN

Like I've said on a previous post, in an ideal world, I would replace a shower circuit cable with 10mm2 any day when feasible.

Sometimes, though, the circuits is to be upgraded and for one reason or another you're stuck with the 6mm2 cable, which by careful calculation turns out to be sufficient. So you keep it....

My customer's favourite tricks are having some decorating done then ringing up and saying "I've just had my lounge/whatever decorated. Can you fit me a socket/whatever??"

Decoration is the main reason it is not feasible to replace a cable.

 

[Big_Spark]

Secure is partially correct, but totally wrong, here is why.

The load on a 9.5kW shower is 41.3A, if you assume a maximum run from board to shower of 20 meters, then taking the worst case possible for installation method from Table 4D2B we are given a volt drop of 7.3mV per A per Meter for 6mmsq T&E

So.. 7.3 x 41.3 x 20 / 1000 = 6.02V, so in this it would comply, however this same table also states that 6mmsq T&E only has a current rating of 38A at best in a domestic situation. You cannot used the 46A of the clipped direct as this would never occur in a domestic premises. Further, due to the use of insulating materials today and central heating, I would, and do, always lean toward the side of column 2 for the cable being enclosed in insulated walls, this gives a max rating of 32A for 6mmsq T&E.

The problem you then have is that 10mmsq is only rated at 43A.

I have seen recently that 11kW and 12kW showers will soon be available in the UK, this means that we will soon be pulling in 16mmsq cable and installing 63A breakers to handle the loads involved!!

Personally I would use SWA as it has better operating qualities and a smaller cable can be used for a given load..in fact 6mmsq SWA with Thermosetting insulation will handle up to 62A in the worst scenario your likely to find in a house.

The cost of 6, or even 10mm SWA over the cost of 10mm or 16mmsq T&E is very pleasing too....Its a LOT cheaper to buy

 

[securespark]

We'll have to beg to differ, FWL. I have checked my calcs reasoning with IEE and got agreement.

How do you terminate your SWA in shower??

 

[Big_Spark]

I suppose we will disagree on this then. I will conceed that in practise 6mm T&E will easily handle a 9.5kW load, HOWEVER it will not be in line with BS7671:2002...

Regarding the Armoured.

If you actually use 3 core you need not be concerned about the SWA and thus this can be left under the insulation and not exposed, using the showers cable clamp to hold the cable in place as you would T&E. The other end could be terminated as usual in the board or enclosure to ensure the cable is secure.

Alternatively, you could run SWA out and terminate it in the normal way in a metal adaptable (Glavanised) box flushed into the wall. Then the shower could be mounted over this so that a set of cables from the adaptable box could connect into the shower. The connection between the SWA and the link cables being made by heavy duty through crimps.

 

[ban-all-sheds]

Personally I would use SWA as it has better operating qualities and a smaller cable can be used for a given load..in fact 6mmsq SWA with Thermosetting insulation will handle up to 62A in the worst scenario your likely to find in a house.

But doesn't that higher rating come about because the insulation of the cable will tolerate a higher temperature? If you install a circuit such that it runs with a higher conductor temperature than you would encounter with normal T&E, can you be sure that the switchgear and appliance(s) will be happy at that temperature?

If you actually use 3 core you need not be concerned about the SWA and thus this can be left under the insulation and not exposed, using the showers cable clamp to hold the cable in place as you would T&E. The other end could be terminated as usual in the board or enclosure to ensure the cable is secure.

Doesn't 3-core SWA have a lower rating than 2-core? Or is that only on the assumption of multi-phase currents?