Cable Identification

[Adebisi]

I am trying to find out what cable is currently set up for my electric shower. It measures 13mm in width would that tell me anything?

TIA Simon

[RzB]

I take it you are talking about twin & earth?

Well I imagine there is a standard somewhere with dimensions and tolerances.

However - for what it's worth - I have some 6mm T&E that is 13.6 mm across the flat dimension - if you understand what I mean.

Disclaimer follows.... :-) I have no idea if this means you also have 6mm T&E.

Roy

[Phil L]

Yes, it tells you that the cable isn't the right size, the cable for your shower should be the same as cooker cable, IE about 25mm across the width, what you have is cable used for normal sockets etc, about 15amp, you need

45amp.

[Nick Dobb]

Unless he means electric as in power shower (no heating involved), in which case 15 amp ought to be plenty?

[Phil L]

I think he'd have said 'power shower' rather than the bog standard, 'electric shower'

[chris French]

Well what he *needs* depends on the current rating of the shower, which can vary.

However, as Roy said in another post, if the cable is 13mm across the widest dimension then it does sound like 6mm ^2 (I've just measured some and my measurement concurs.)

Current rating of 6mm is IIRC 40A? depending on the length of run and draw of the shower this may well be sufficient.

[Adebisi]

Thanks. Yes it's T&E I was wondering if it was 6mm or 10mm. I bet 10mm would be a lot wider?

[John Rumm]

No it does not.

It tells you the cable is probbably 6mm^2 T&E and that is all.

Whether it is correct or not will largely depend on the rating of the shower and the details of the cable run.

There is no such thing a "cooker cable" - again the cable for a cooker will need to be sized based on the actual appliance in question.

Huh? Are you just making up numbers? 25mm across any axis is wider than all the standard T&E cables.

Since when were sockets typically wired in 6mm^2.

Where do you get the 15A from - I can't think of any standard T&E cable size that has that rating (1.0mm^2 as used on lighting circuits would be closest at 16A best case).

Normal socket circuits are typically wired in 2.5mm^2 T&E, with a rating of upto 27A best case)

Again you are plucking numbers from the air.

Cable CSAs Vs Physical Dimensions (table pinched from one of Andy Wade's postings):

CSA (CPC) Strands Overall mm^2 No./dia. mm approx.

--------- ------- ----------

1.0 (1.0) 1/1.13 4.5 x 8.2 1.5 (1.0) 1/1.38 4.7 x 8.2 2.5 (1.5) 1/1.78* 5.3 x 9.9 4.0 (1.5) 7/0.85 6.1 x 11.4 6.0 (2.5) 7/1.04 6.8 x 13.1 10 (4.0) 7/1.35 8.4 x 16.8 16 (6.0) 7/1.71 9.6 x 19.5

• or 7/0.67

This does suggest the OPs cable is 6mm^2 and that will handle 47A when clipped direct to a surface. It also assumes there are no other derrating factors that need to be taken into account.

10mm^s would usually be the cable of choice for the modern more powerful showers.

[Phil L]

I think we can assume that it's in his bathroom? We can also assume that his bathroom is upstairs? And his meter is under the stairs?

Most modern showers are above 8KW, ergo it needs 10mm cable, he's got 6.

So you agree with me then that the cable he's got isn't big enough? - pretty much what I said but with more willy-waving.

[Christian McArdle]

Reasonably likely.

Hardly an assumption that can be made. Loads of houses have downstairs bathrooms.

About 50/50 IME. However, completely irrelevent, I'd have thought.

Try again. In many cases 6mm is more than adequete. 10.5kW @ 230V on a 45A MCB 6mm clipped direct is good for 28 metres on voltage drop and cable rating. I haven't checked the earth loop impedence, but it is usually OK.

I don't. I would say that 6mm is adequete for a large proportion of even higher powered electric shower installations. Personally, I would install

10mm as a matter of course to reduce voltage drop, decrease running temperatures and prolong cable life. However, there is no need to replace existing 6mm in many cases, which could be very destructive to the decoration.

Christian.

P.S. You were wrong on "15A" cable for socket circuits. Most standard socket circuits, including 20A radials and 32A rings, require cable rated at 20A.

15A socket circuits went out with rubber cable and round pin sockets and were often converted to 30A rings.

[John Rumm]

No I don't agree with you. In fact I expect there is a very good chance that the OPs cable is appropriate for his shower. However unless he posts more information we won't know for sure.

I was highligting that the information/advice you were giving was at best flawed, and the conclusion to which you had jumped was not a logical progression based on the information given. Sorry if you think this is "willy waving", but where matters of electrcity, water, and people are involved in close proximity, I feel it is important to get these things right and not make unsupported assertions, or seemingly invent technical data on the fly.

[Rob Morley]

Why? The CU could be on the wall in the hall or kitchen, and the shower just the other side of the wall.

[Andy Wade]

Hmm, be very very careful there. It may well be OK with a type B MCB and a PME supply, but if the protective device is a 45A BS 1361 fuse and the bathroom wiring is pre the bathroom amendment (so 0.4 second disconnection needed) then you'd need Zs < 0.6 ohm. If the service is TN-S (Ze max. = 0.8 ohm) then you're stuffed unless there's an RCD fitted.

You also need to check adiabatic compliance of the CPC - with a 2.5 mm^2 CPC protected by a 45 A device, no assumptions should be made...

[Phil L]

Hell his meter could be in the bathroom, but I think we all know that it isn't...in most houses the meter is usually downstairs and the bathroom upstairs, stop being pedantic, you are guesing the same as everyone else, the OP hasn't said where it is so it's safe to assume it's in the 'normal' range.

[Rob Morley]

Why do you keep banging on about the meter? It's the CU that matters, as that's where the cable will be connected.

I know no such thing. Nor does anyone else, based on the information given. If you think you know then you are deluded.

I'm not being pedantic, I'm pointing out your faulty reasoning. What makes you think we're talking about an upstairs bathroom? Plenty of houses have downstairs showers.

I'm not guessing anything - you're the one who said the cable is undersized without knowing all the significant facts.

He didn't state whether it's a house or a flat. If it's a flat then my scenario is more likely to be correct than yours is. He didn't even state the rating of the shower ...

[Christian McArdle]

Indeed. By saying I hadn't checked it, I meant that it needed to be checked, not that you shouldn't bother.

However, I would always RCD an electric shower and it would always be on a Type B MCB. Not that I would install something that required an RCD to meet earth loop impedence requirements, though. Even on a TT system, I would ensure that it would be compliant when the earthing is upgraded.

Christian.

[manatbandq]

I would dearly like a link to some of this domestic mains cable that is

25mm across. Please provide one, OR STFU!

MBQ

[Phil L]

Who the f*ck are you meant to be? Have you *ever* worked with electrical cable? His cable is 6mm, he needs 10mm, unless he likes his cables glowing every time he has a shower.

[Phil L]

And the meter is always a mile away from the CU? - pedant not over yet?

So you think his CU is in the bathroom? - curiouser and curiouser...

What makes you think we are talking about a downstairs shower?, *most* houses have showers upstairs.

I know that 6mm cable isn't suitable for modern (9.5KW and above) showers, and yes, we are all guessing, I was edging on the side of caution while you are clutching straws that it /might/ be /ok/ if this and if that.

Exactly, and I'll wager that more poeople live in houses than flats in the UK, and that most people in those houses have a shower upstairs, of course we could all be wrong and he lives in a tent.

[manatbandq]

I am who I am.

Yes.

You still haven't shown that you have any idea what you are talking about.

Show us the "cooker cable, IE about 25mm across the width" and you may be able to redeem yourself.

MBQ