What cable am I looking at - 6mm or 10mm?

[zappastix]

Hi

I've got to replace an electric shower, which was probably installed around 12 years ago.

The shower that needs replacing was a Mira Sports 8.5kW which never tripped the MCB B32

If possible I'd like something around 9.8kW - but I want to confirm that the cable can handle it.

As I live a long way from places like B&Q I can't go there and confirm sizes in store.

The cable that is installed is chunky.

I've removed the consumer unit cover, and can confirm that the cable to the shower is the same size as the cable running to the electric cooker/oven.

MY QUESTION

Do you think I have 10mm cable installed?

These are the measurements (I've Googled for ages to determine how a cable is measured, but no joy).

The outer sheath of cable is between 14mm and 15mm across.

Each core (black and red) are between 4mm and 5mm in width.

Each black & red core is made up of '7' individual copper wires.

What do you think - have I got 6mm installed or 10mm

I need to know because if it's 10mm I can replace the MCB B32 for MCB B40.

However, I've read that you can run a 9.8kW rated shower on 6mm cable on MCB B32 - is this possible?

Many thanks in advance.

Stephen

 

[Taylortwocities]

The way to check, for certain, is to use a micrometer and measure the diameter of the conductor. Then work out the area of the cable using
PI r²

Personally I use a selection of butt crimps. A 10mm² cable won't go into a 6mm crimp but will go into a 10mm crimp.

Cable outside dimensions differ from make to make so its not a sure way of finding out but look here for a list of different twin and earth cables and NOMINAL sheath sizes.
http://www.tlc-direct.co.uk/Main_Index/Cable_Index/Twin_and_Earth/index.html

If your existing cable is protected by a 32A cb then I would expect that it will be 4mm or 6mm.

Re your last comment. Do you know about Ohm's law? If you did then you will know that 9.8KW is more than 42amp. So, how can you think that a 32A CPD will be OK

 

[Steve]

The cable that is installed is chunky.

Do you think I have 10mm cable installed?

Yeah, its chunky. It must be 10mm².

Chances are, its 6mm².

I wouldnt use anything other than 10mm² or higher to feed a shower.

 

[mikhailfaradayski]

everything TTC says is valid, the only downside is that you need a mic or vernier, or some crimps.

The nominal size for the sheaths of 6mm and 10mm T+E are
6mm = 13.5x7 mm
10mm = 17.1x10mm

You may be able to use a simple ruler to discern the difference.

However, you mention the rd/blk cores are stranded, what about the earth core? stranded or solid?

Do you have a multimeter? The resistance of the cable will define its csa

Also, one last bit, are you aware that changing the cable and its protective device is 'notifiable' work and means you have to part with a lump of cash to the council who will provide very little in return?

Might i suggest you ring a sparky and get an idea of how much he might charge you before you jump in and give your self a problem/extra cost

 

[ban-all-sheds]

What do you think - have I got 6mm installed or 10mm

//www.diynot.com/wiki/electrics:flatpvccables

I need to know because if it's 10mm I can replace the MCB B32 for MCB B40.

1) Not necessarily

• http://www.tlc-direct.co.uk/Book/4.3.1.htm
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

2) //www.diynot.com/wiki/electrics:part-p

 

[zappastix]

Thanks mikhailfaradayski.

The earth is solid.

From your help it looks like the cable is 6mm.

Not to worry - a 8.5kW shower it is.

 

[Taylortwocities]

And what current is 8.5KW?

 

[davelx]

And what current is 8.5KW?

And a 32A MCB will support that load for how long, TTC?

 

[mikhailfaradayski]

And what current is 8.5KW?

And a 32A MCB will support that load for how long, TTC?

a very long time indeed, but do you think that means its ok???

 

[ban-all-sheds]

And a 32A MCB will support that load for how long, TTC?

That's not the point.

 

[Taylortwocities]

Fig 3.4 indicates a load of 37A will trip a 32A breaker in approx 900 seconds. So if you take a long shower you'll be all soapy when the CB trips.

The OP is designing a circuit. In doing this your first step is to determine Ib = 37A.
Then you'll need a protective device In = 40A because

In > Ib

Doing it your way In would be less than Ib

Bad bad man for even suggesting it.

We haven't even started talking about correction factors, oh yes, and cable size.

 

[mikhailfaradayski]

Fig 3.4 indicates a load of 37A will trip a 32A breaker in approx 900 seconds.

are specsavers open tomorrow?

 

[Taylortwocities]

curses, I followed the wrong line on the graph

Nurse, the screens!

 

[jaysean1]

I would put a b40 rcbo on it

 

[ban-all-sheds]

Why do you think that's an evil and twisted suggestion?