Another pricing question

[Nicky Tesla]

iv fitted a 10.5kw on a 30a rewireable no probs.

 

[Northern Electric]

iv fitted a 10.5kw on a 30a rewireable no probs.

Nice! ROTFWL

 

[batty]

[No message]

 

[Northern Electric]

I've been giving this shower thing a bit of a thought. OK, we all know the shower is rated at 9500w. This rating is at 240V. OK, basic power calculation P=V*I, transposed I=P/V,9500/240 gives us a current demand of 39.58A. The shower element resistance can be determined by ohms law I=V/R, transposed R=V/I, 240/39.58= 6.06 ohms.

Now, at 230V the resistance of the shower is still the same, 6.06 ohms. Therefore the actual current demand at 230V will be I=V/R 230/6.06= 37.95A.

So you lot are right, a 40A mcb will be fine, even if the voltage rises to 250V the current demand will be 250/6.06= 41.25A and, as we all know, the voltage doesn't rise much above 240V these days.

I will keep my mouth shut in future on that subject! ROTFWL

Fancy having to prove myself wrong. Blushing

 

[Bez]

I've been giving this shower thing a bit of a thought. OK, we all know the shower is rated at 9500w. This rating is at 240V. OK, basic power calculation P=V*I, transposed I=P/V,9500/240 gives us a current demand of 39.58A. The shower element resistance can be determined by ohms law I=V/R, transposed R=V/I, 240/39.58= 6.06 ohms.Now, at 230V the resistance of the shower is still the same, 6.06 ohms. Therefore the actual current demand at 230V will be I=V/R 230/6.06= 37.95A.

So you lot are right, a 40A mcb will be fine, even if the voltage rises to 250V the current demand will be 250/6.06= 41.25A and, as we all know, the voltage doesn't rise much above 240V these days.

I will keep my mouth shut in future on that subject! ROTFWL

Fancy having to prove myself wrong. Blushing

Nice calcsB-) another one to throw into the mix is a 40A MCB will quite happily carry 50A indefinately, (BRB Page249)(cheers by the way Andy)

So I think we're all agreed on the shower, 10mm T&E with 40A protective deviceGuinness

 

[Andy™]

I've been giving this shower thing a bit of a thought. OK, we all know the shower is rated at 9500w. This rating is at 240V. OK, basic power calculation P=V*I, transposed I=P/V,9500/240 gives us a current demand of 39.58A. The shower element resistance can be determined by ohms law I=V/R, transposed R=V/I, 240/39.58= 6.06 ohms.Now, at 230V the resistance of the shower is still the same, 6.06 ohms. Therefore the actual current demand at 230V will be I=V/R 230/6.06= 37.95A.

So you lot are right, a 40A mcb will be fine, even if the voltage rises to 250V the current demand will be 250/6.06= 41.25A and, as we all know, the voltage doesn't rise much above 240V these days.

I will keep my mouth shut in future on that subject! ROTFWL

Fancy having to prove myself wrong. Blushing

if you check the power rating of the shower(usually on the actual unit), they are often quoted as X at 240v and Y at 230v

 

[Northern Electric]

Yeah, 10mm with 40A!

Andy, that's what got me thinking, all the ratings are usually stated at both 240V and 230V, obviously for different markets. I looked up a few showers (google again) and they were all 9.5KW at 240V, 8.7KW at 230V. That's when the old penny dropped.

 

[SPECIAL LOCATION]

Yeah, 10mm with 40A!Andy, that's what got me thinking, all the ratings are usually stated at both 240V and 230V, obviously for different markets. I looked up a few showers (google again) and they were all 9.5KW at 240V, 8.7KW at 230V. That's when the old penny dropped.

Well I was reading down this thread and I was about to jump in and say the manufactures quote their main rating @ 240v NOT 230v...

But then realised as I scrolled down ...

you had all finally got to the same point!Applaud Smiley:x

Just to add:-

I don't think its specifically to do with different markets...

more just so manufactures can say all of their literature is in accordance with specifications of current regs....

and current regs 'nominal Voltage' IS 230 +10% -6%, aka 216V - 253V

BUT if they started quoting 8.7K or 8.8k for what used to be a 9.5k shower....

Joe public would think he is being short changed!!!!

Bit like how good ole British Leyland used to state a 1.3L (1300cc) Maestro....

But actually it was the 1275cc engine out the old Mini!!!! :| :^O :^O

Back to the showerey bit... Can I also just add...

There IS a MCB rating between 40A & 50A

45A

which personally I find does the jobbie nice for a 9.5k or 10k shower "on 10.0mm"Blushing:x

or even

45A RCBO

] Guinness

 

[SPECIAL LOCATION]

Been to have a look at a job today. First big one for me and a promise of more similar jobs to come. 3 bed 1970s terrace. Been totally gutted so nice and easy to work in. Bloke who owns it is a builder so no making good.

Complete rewire including bonding.

Lounge: 4 x sso, 1 x TV, 1 x pendant drop

Hall: 1 x sso, 2 way switching to 2 x pendant drop, 2way switching to landing

Kitchen: 10 x sso, FCU x 2 for washer, drier. 2 x lights. Cooker circuit. Radial for freezer. Light in store cupboard

Rear utility/Toilet: 2 x pendant drop, outside light, 1 x sso, Xpelair.

Bedroom 1: 3 x sso, 1 x pendant drop, Light in store cupboard

Bedroom 2: 2 x sso, 1 x pendant drop

Bedroom 3: 4 x sso, 1 x pendant drop

Landing: 1 x sso, 1 x pendant drop

Bathroom: 2 x SELV downlights, 9.5Kw shower

Loft: 2 x lights

Smoke alarms

I'm looking at the following as far as circuits go:

Up Ring 32

Down Ring 32

Kitchen Ring 32

Utility radial 20

Freezer radial 20

Cooker 32

Shower 40

Up lights 6

Down lights 6

[/COLOUR]

All lights are going in existing locations as are most switches. Access to loft easy. Wooden floorboards up and down. Kitchen floor concrete.

May have missed something obvious so gentle reminders welcome.

Doing this myself - 2 weeks work. Worked out materials at under

 

[Couleddie]

Thanks Specs. Excellent post. Very much appreciate your comments as it's exactly the type of advice i'm looking for.

May change up and down rings to 20A radials.

Point taken on freezer. Will change to 16 as fridge may be separate and on same circuit.

 

[Bez]

May change up and down rings to 20A radials.

QUOTE]

As long as there's not two ladies in their bedrooms drying their hair at the same time

2 x 2300 watt hair dryers = 20A

Stick an X box, tele, couple of clock radios, hair straighteners, curling tongs etc, you wont be far off the cable current rating.

20A breaker is ok for upstairs but I would stick with a ring circuit.

Bez

 

[matt.leung]

2k sounds far to less for a re-wire, and yes get a helping hand on board, makes life easier when drawing in cables etc...

 

[Nicky Tesla]

its the

 

[musicspark]

May change up and down rings to 20A radials.

QUOTE]

As long as there's not two ladies in their bedrooms drying their hair at the same time

2 x 2300 watt hair dryers = 20A

Stick an X box, tele, couple of clock radios, hair straighteners, curling tongs etc, you wont be far off the cable current rating.

20A breaker is ok for upstairs but I would stick with a ring circuit.

Bez

4m from CU and 2.5 to sockets Check BRB

According to BRB a 6m cable will take 47A (as specs will tell you) as long as you can keep it out of the demon rockwool insulation.

10 m is future proof though

 

[Bez]

4m from CU and 2.5 to sockets Check BRB

According to BRB a 6m cable will take 47A (as specs will tell you) as long as you can keep it out of the demon rockwool insulation.

10 m is future proof though

Ah, now i was working on the assumption of a 2.5mm radial. Agree with 4mm radial.

Think I would still rather do a 2.5mm ring than a 10mm radial:O

 

[Apache]

Ah, now i was working on the assumption of a 2.5mm radial. Agree with 4mm radial.

Think I would still rather do a 2.5mm ring than a 10mm radial:O

the 6/10mm refers to the shower - you do know that?

 

[Bez]

the 6/10mm refers to the shower - you do know that?

I'de kinda guessed it, but we were discussing the upstairs ring so I did wonder

 

[musicspark]

I'de kinda guessed it, but we were discussing the upstairs ring so I did wonder

sorry I should have made that clear(47A for 5m shower )

for radial you take 4m to the CU then spur from JB to sockets in 2.5 - you can have a 32A radial circuit (20A if all in 2.5)

Appendix 15 of BRB

 

[binky]

It may well never trip, but I don't agree with installing an mcb which is rated less than the demand current. Ib In Iz.

I have installed numerous 9.5Kw showers and there has never been a problem on a 40A MCB. Had a neighbour who changed his shower for 10.5Kw (6mm and 40A MCB) it would still run for 20 minutes before tripping. Persuaded him to change back to 9.5Kw eventually as re-wiring the circuit would have been very difficult, and its worked fine ever since.

I don't disagree with your position on this but experience has shown me that its not an issue. If my memory serves me correctly there quite a few showers available now at 9.3Kw - keeps everyone happy

 

[Northern Electric]

I have installed numerous 9.5Kw showers and there has never been a problem on a 40A MCB. Had a neighbour who changed his shower for 10.5Kw (6mm and 40A MCB) it would still run for 20 minutes before tripping. Persuaded him to change back to 9.5Kw eventually as re-wiring the circuit would have been very difficult, and its worked fine ever since.I don't disagree with your position on this but experience has shown me that its not an issue. If my memory serves me correctly there quite a few showers available now at 9.3Kw - keeps everyone happy

See my later posts on this subject. A bit of maths proved myself wrong.