Newly Qualified - Own House re-wire

[MDJ]

I doubt you will need to change them, I was just having fun regarding trying to use a 16mm2 cable, 10mm2 would be fine IMO, unlikely a 10mm2 won't cope with a 9.5kw shower in a domestic situation, have you ever tried to connect 2 16mm2 cables into a 45 amp double pole switch? Lets see your formular for working out why the 10mm2 cable won't do.

 

[MBEINST]

I joined this forum to seek guidance and assurance from those who are already in the game earning a crust. I referred to table '4D5' pg 282 of the regs. Running the cable above a plasterboard ceiling covered by thermal insulation exceeding 100mm - current carrying capacity of 10mm is 36A. By my reckoning the showers demand will exceed this (9500w/230v=41A or 9500w/240v=39.5A).

I am not saying that the 10mm will not cope but it doesn't strictly adhere to the regs. Don't forget that I am new to this and could be way off the mark with my thoughts/calculations. As previously stated I am looking for guidance and assurance.

It appears to me that the manufacturers of fittings should know the regs and manufacture their products to allow adherence to said regs.

Please forgive my naivety.

 

[MDJ]

When I mean how did you come to your calculation I mean have you actually confirmed there is 300mm2 of insulation / how far is the run? can you actually install the cable in the loft so it is clipped around the sides above insulation and in fresh air? no need to be defensive, we are trying to help, I wouldn't personally see the need to install a 16mm2 cable to a 9.5 kw shower in a house, if insulation is the difference between a 10 and a 16 then look for other ways to get to a 10mm2 cable.

 

[MBEINST]

We just had the loft insulation topped up to 300mm. I could take the cable above the insulation obviously this means that I could not clip to the joists but I could attach to the hangers and purlin before dropping it back down through the stud wall. Is this a better way to go? The length of the cable run would be approx 12metres.

I appreciate that you are offering your help and advice which is obviously why I posted in the first place. Can you please confirm that I have read the regs correctly.

 

[richy3333]

Using the rule of thumb for diversity that's around 120A. Hope nobody in the house wants to flit between both showers, whilst roasting the sunday joint and welding the car in the garage and ironing the kids uniform

 

[MatthewC]

Its really up to you about the hangers if it would put your mind at ease them use them. You could maybe install a couple bits of conduit across the beams that will keep the insulation off it and its such a short run the cable will easily carry 45A. Also i was taught to always place your shower off its own 45amp RcBO. (Good practice)
Best of luck.

 

[MBEINST]

I would like to thank you all for your contributions and I am taking the advice given.

The new board will have every circuit on its own RCBO and the showers will be re-wired in 10mm which will be run above the insulation.

My last remaining question is again regarding the shower circuits.

10mm cable current carrying capacity = 45A

9.5Kw shower demand = 41A

The RCBO should be rated lower than the current carrying capacity of the Cable (45A) but obviously higher than the demand of the shower (41A). As far as I can see RCBO's are available in 40 and 45 Amp? Help?

Am I looking at this too deeply?

 

[wade88]

Damn, i was sort of hoping you were going to go away and wire the buggers up in 16mm because i would have LOVED to see how that worked out!

 

[SafetyFirst]

Is the garage only using low loads? If so i'd just incorporate it into the whole downstairs ring.

 

[MatthewC]

Lol man your more pedantic than me

1. A 1.5mm cable is rated at 13amps it actually can hold nearly 16amps.

2. A 2.5mm cable is rated at 20amps but can actually hold 25amps.

3. A 10mm cable is rated at 45amps but can actually hold nearly 55amps.

The B.S standards are set for maximum safety and are to be used correctly. The reason they lower them is to stop people making cloudy judgments and overloading circuits. As long as your run of cable is less than 30M you can use a 45amp RCBO to protect your 10mm cable because its to the standards and nowhere near the maximum demand of the cable. Try googling Shower packs.

 

[High Tower]

1, cable values are worked out at 230v nominal, you probably have around 240v if you measure it.
So...

9kw shower @ 230v = 39.1 A
9kw shower @ 240v = 37.5 A

So 10mm2 is all good!!,

Don't take offence about the 16mm ribbing its the normal reaction of all sparks when someone suggests using 16 on a shower!, I'm guessing that if this is your first job then you have not had the pleasure of two 10's in a pull cord!!!, now when your sweating with bleeding fingers, just think.......I wonder how hard a cable half as big again would be lol

If you are re wiring the showers then as you suggested clip it direct to gable walls and along the underside of the purlins and where it needs to pass through the insulation vertically to the ceilings use a off cut of 4" waste pipe cut to 350mm long.

For what my opinion is worth, the kind of money you are paying for your board then as its your house, pay a little more and get a Hager board!!!, u will be glad you did!!!!

 

[vjsmarwick]

Have been reading all the posts here ant the reason some over 8kw showers are on 6mm is they have been upgraded but people never think of upgrading the cables but they are right 10mm will be fine for your needs. As for garage sockets personally I would use a circuit of its own so many things you might plug in you never dream you will use now but do in the future.
We are all here to help and welcome.

 

[MBEINST]

Once again fellas thanks very much for the feedback.

It appears that I hadn’t grasped the Sparks sense of humour and have taken some of the comments a little too literally. Lesson learned.

I will spend a little more on a better board but still intend to have an RCBO on every circuit. I applied for an account with Denmans and Electricfix so will see about a decent board and RCBO’s.

MatthewC, it appears that I am using the tables in 7671 too literally and I never imagined that the 10mm would actually be capable of carrying 55 amps. It appears that the regs have confused me when I thought they were there to help.

My circuit when installed will be a 9.5kw shower supplied by a 10mm cable and protected by a 45amp RCBO. The cable will run above the insulation.

My garage will be wired on its own circuit. I will be using a bench grinder, compound mitre saw and table saw but obviously not all at the same time.

This is my first solo installation and I will be using it for my application to join ELECSA which is why I am concerned about getting everything bang on according to the regs and what ELECSA will be looking for.

I look forward to the near future when hopefully I can share in the Sparks sense of humour and offer a little gentle ribbing myself.

Thanks again

‘Example is the school of mankind, they will learn at no other’

 

[MDJ]

My circuit when installed will be a 9.5kw shower supplied by a 10mm cable and protected by a 45amp RCBO. The cable will run above the insulation.

Good man there you go, you did it and you will understand why I suggested avoiding a 16mm2 cable if possible after connecting the 2x 10mm2 cables into the pull switch.

 

[bigbaddave]

Lol man your more pedantic than me

1. A 1.5mm cable is rated at 13amps it actually can hold nearly 16amps.

2. A 2.5mm cable is rated at 20amps but can actually hold 25amps.

3. A 10mm cable is rated at 45amps but can actually hold nearly 55amps.

The B.S standards are set for maximum safety and are to be used correctly. The reason they lower them is to stop people making cloudy judgments and overloading circuits. As long as your run of cable is less than 30M you can use a 45amp RCBO to protect your 10mm cable because its to the standards and nowhere near the maximum demand of the cable. Try googling Shower packs.

Where did you get theses figures from? What reference method ?