Upgrade shower - cable size

[Alison556]

My mum was wanting to upgrade her shower - it's an 8.5kW that she has in and she was looking to get a 10.5kW shower.

I'm not sure that the cable is thick enough though. I got a bit of 10mm cable to compare the sizes and it's marginally thicker to what's in. It's on a 40amp fuse.

I'll say it's 4m from the fusebox to the shower but that's being generous as the fusebox is just outside the bathroom door.

Could a 10.5kW shower safely run on this cable (I know I'd need to put a bigger fuse in). If not, what would be the highest watt shower we could put in?

 

[EFLImpudence]

No good 'saying' what it is. You will have to make sure.

If it is 6mm² cable and runs through NO insulation or conduit then you can fit a 10.5kW shower.

 

[Alison556]

You mean I need to know exactly how far the shower is from the fuse box? I'll measure it. The cable goes under the floor and there's no insultation there and I'm pretty certain there's no conduiting - not sure how I'd check on that though - I can't get under the floor any more.

 

[Taylortwocities]

Bearing in mind that 10.5kW pulls around 45amps. You said a 40amp FUSE. IS it really a fuse, or an MCB?
I ask, because a 40A type B MCB will allow 45A through it for around 16 minutes before it will trip, so that will probably be OK, providing she doesnt have long showers!
A 40amp fuse will last a lot longer.

 

[EFLImpudence]

You mean I need to know exactly how far the shower is from the fuse box?

No, I misread your post - just the correct size of cable.

 

[Alison556]

Bearing in mind that 10.5kW pulls around 45amps. You said a 40amp FUSE. IS it really a fuse, or an MCB?
I ask, because a 40A type B MCB will allow 45A through it for around 16 minutes before it will trip, so that will probably be OK, providing she doesnt have long showers!
A 40amp fuse will last a lot longer.

Sorry, my bad - it's a 40amp MCB. I tried taking pics to show the cable that's there and the 10mm cable they gave me to compare but the cable that's in looks a little bit narrower.

Mother doesn't take long showers, but niece does!

 

[ban-all-sheds]

a 40A type B MCB will allow 45A through it for around 16 minutes before it will trip, so that will probably be OK

No, it won't.

Ib ≤ In ≤ Iz

[EDIT]Formatting changed to focus on the relevant part of the rule[/EDIT]

 

[Alison556]

Ive no problem about replacing the MCB for a 50amp but it's the cable that I'm concerned about. I can't even gauge what cable is in the existing one - I had a look at how to work it out in the wiki but it went over my head

 

[flameport]

Ive no problem about replacing the MCB for a 50amp but it's the cable that I'm concerned about.

The cable is 6mm. There are no sizes between 6 and 10mm, so if it is smaller than the 10mm piece, it is 6.

You can't use a 50A MCB, as that is greater than the cable rating, which is 47A assuming it is not contained in insulation or conduit.
A 45A MCB could be used, if one can be obtained for your consumer unit.
A 10.5kW 240V shower is 43.75A.

 

[EFLImpudence]

The shower won't/can't overload the cable so 50A is alright.

 

[jj4091]

You need to ensure that any isolators in the circuit are correctly rated also.

 

[deadshort]

Ive no problem about replacing the MCB for a 50amp but it's the cable that I'm concerned about.

The cable is 6mm. There are no sizes between 6 and 10mm, so if it is smaller than the 10mm piece, it is 6.

You can't use a 50A MCB, as that is greater than the cable rating, which is 47A assuming it is not contained in insulation or conduit.
A 45A MCB could be used, if one can be obtained for your consumer unit.
A 10.5kW 240V shower is 43.75A.

Listen to this man

DS

 

[scousespark]

Who is installing the circuit? If you are hiring an electrician he will be better positioned than us to confirm what you have and can have.

 

[ban-all-sheds]

Listen to this man

DS

Why?

Better off listening to EFLI - he knows wot whereof he speaks.

 

[deadshort]

BAS, i have no idea why? As i was referring to Flameport's post

Kindest regards,
DS.

keep taking the tablets