Shower circuit confusion !

[powelly]

hello again ,
some advice needed please ? Im currently studying towards my full scope domestic electrical installer qualification. My confusion starts with my shower circuit at home , i currently have a 9.5kw instantaneous shower fitted with 10mm cable back to a 32A MCB. Is this correct because through my calculations and with reference to BS:7671 it doesn't seem to add up ?
With reference to the BS:7671 OSG cable selection theory it points me towards:
9.5KW/230V=(lb)41.3A so in order for : ln>lb it would need to

be a 50A MCB?

I apologise if im being thick but if so could somebody set me straight , thanks for your time !!!!!!

 

[OwainDIYer]

hello again ,
some advice needed please ? Im currently studying towards my full scope domestic electrical installer qualification. My confusion starts with my shower circuit at home , i currently have a 9.5kw instantaneous shower fitted with 10mm cable back to a 32A MCB. Is this correct because through my calculations and with reference to BS:7671 it doesn't seem to add up ?
With reference to the BS:7671 OSG cable selection theory it points me towards:
9.5KW/230V=(lb)41.3A so in order for : ln>lb it would need to

be a 50A MCB?

I apologise if im being thick but if so could somebody set me straight , thanks for your time !!!!!!

9500 W / 240V = 39.58 A

If you run it on 230V it will consume less power and take less current because the voltage is lower, the resistance remains the same.

If it's a new shower it might actually be rated at 230V, but an older one will be rated at 240V.

 

[ban-all-sheds]

But however you look at it a 32A breaker isn't right...

 

[riveralt]

With reference to the BS:7671 OSG cable selection theory it points me towards:
9.5KW/230V=(lb)41.3A so in order for : ln>lb it would need to

be a 50A MCB?

I apologise if im being thick but if so could somebody set me straight , thanks for your time !!!!!!

45 Amp should be enough if your consumer unit manufacturer makes it.

 

[Pants7478512]

9500 W / 240V = 39.58 A

If you run it on 230V it will consume less power and take less current because the voltage is lower, the resistance remains the same.

9500/240 = 39.6A

9500/230 = 41.3A

How does that work then? It will pull a higher current at a lower voltage.

 

[riveralt]

[9500/240 = 39.6A

9500/230 = 41.3A

How does that work then? It will pull a higher current at a lower voltage.

BS7671 17th Edition uses 230v as the standard throughout.

Shower manufacturers in particular promote the headline figure of say 9.5kw shower @ 240 volts.
which equates to 8.7kw @230v

 

[Pants7478512]

Shower manufacturers in particular promote the headline figure of say 9.5kw shower @ 240 volts.
which equates to 8.7kw @230v

The sneaky b@stards -

 

[ban-all-sheds]

9500/240 = 39.6A

9500/230 = 41.3A

How does that work then? It will pull a higher current at a lower voltage.

By what magic will the resistance of the heating element drop from 6.06Ω to 5.57Ω when the voltage reduces?