Not another shower question lol

[Gregm879]

Hi all and as ya can guess from the subject its another shower query. I think i've read through most the recent threads and from that hope ive got most the info lol basically the flat im living in had a 7.5kw shower fitted before i lived here and it has pretty much given up. Im looking to replace it and for the cost, an 8.5kw seems to come up cheaper than the current 7.5kw??
so heres the info.............. Its running out of crabtree starbreaker on a 40amp MCD. Its on the protected side of a RCD 63A 3MA on a 6mm cable through conduit with other cables for about 8m before going into the wall. where it goes throught a pull cord switch then down to shower. i have no knowedge of technical terms and hope thats most of what ya need??? This post is really jus to help me and me missus to decide on whats the best course of action. of course if work needs doing we will be using a proffesional tradesperson. really hope some1 can give us a bit of advice and look forward to reading any comments many thanks

 

[oharaf]

How many other cables in this conduit? Is the conduit passing through insulation of any form?

 

[Gregm879]

thanx for reply it looks like there are 3 other cables running through it. and no its running along the top of the wall so no insulation.

 

[oharaf]

8500/230 = 37A so based on this your are fine

However

You say there are 3 cables running in this conduit (probably trunking!!)

So grouping factors need to be taken in to consideration

The design current is 37A the Nominal current is 40A (by the MCB)

We need to establish It

It>= In/(CaCiCgCr)

Ca = 1.0 Ci = 1 Cg=0.70 Cr=1


So

It = 40/(1x1x0.7x1)

= 57.1A

So what you will need is a 60A MCB

10mm cable has a maximum capacity in these conditions of 57A you are right on the limit!!!!

You may need 16mm cable!!


However if you can run this cable outside of the trunking it would allow you to use the 40MCB (with RCD protection naturally) and 6mm cable would suffice however I would highly recommend installing the 10mm cable as a matter of course for future proofing


Anyone want to second check my calcs?



THIS IS UTTER DRIVEL!!!!!

 

[Goldberg]

8500/230 = 37A so based on this your are fine

Your calculation is wrong - 8500 kW at the rated voltage of 240VAC is 35.4A.

BTW, at 240V + 10% the upper limit of the design load is 40.0A.

...So what you will need is a 60A MCB

Are you completely mental?

Anyone want to second check my calcs?

It's not your "calcs" that should be checked.

 

[stargazer]

I think Oharaf was having a blond moment

OP, you might get away with 6mm for your new 8.5kw shower but suggest you upgrade to 10mm to take care of any correction factors and future proofing. You have indicated you will be employing an electrician for this work, and he will calculate the necessary cable size after examining your installation.

You should not need to change your protective devices – you already have RCD protection and a 40A MCB.

 

[oharaf]

I looked at the wrong table!!!!!!!!!

~So to correct myself

8500/230=36.9A (I was taught use 230 unless it is cetain the accessory is
rated at 240VAC)

36.9/(1.03x0.7x1x1) = 51.1A

From the (CORRCET)table = 10mm

As for the 60A I admit talking out my arsche!!!! Probably due to late night again


Goldsberg I thank you!!!

 

[ban-all-sheds]

As for the 60A I admit talking out my arsche!!!!

Goldberg will be along presently to check that for you.

Please lie on your side with your knees drawn up to your chest.

 

[oharaf]

NO!!!!! Not the Standard British IndexFinger!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[electronicsuk]

8500/230 = 37A so based on this your are fine

Your calculation is wrong - 8500 kW at the rated voltage of 240VAC is 35.4A.

8500kW?!

 

[ColJack]

oh good, not just me that saw that then?
he likes pointing out others piddling mistakes.. but never admits when he's wrong..

 

[ban-all-sheds]

NO!!!!! Not the Standard British IndexFinger!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

OK - how about the 5" BSF?























































































British Standard Fist

 

[mikhailfaradayski]

you gonna squeal like a piggy bwouy.



Have you seen Deliverance?

 

[ban-all-sheds]

I have.

I've also had a prostate biopsy, and that thing is bigger than a finger...

 

[Goldberg]

8500 kW...

This was wrong. I typed a "k" where there shouldn't have been a "k".

I apologise unreservedly for this typing error.

If anyone thinks that typing a "k" where there shouldn't be a "k" results from an error of understanding or of calculation, then you need some tuition in the difference between what matters and what doesn't.

8500/230=36.9A (I was taught use 230 unless it is cetain the accessory is rated at 240VAC)

That's a pointless and misguided rule of thumb, and one that leads people into making habitual mistakes by discouraging thinking.