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Topic Title: 8.5kW shower, 6mm cable, 32A mcb
Topic Summary: Your thoughts!
Created On: 05 August 2014 08:37 PM
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 05 August 2014 08:37 PM
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Grumpy

Posts: 460
Joined: 09 January 2009

Evening all! Another low brow for you.
Theoretically not compliant. Client wants to change existing defunct shower (8.5kW) for a like for like. My view is that a fixed load of 35A is unlikely to trip the MCB (unless my son's in the shower of course), likewise overload the cable (no idea if it's run through six feet of insulation) and short circuit protection is provided y the mcb. TT. Up front 30mA RCD. I don't know why I'm bothering, you want to see the place!
 05 August 2014 08:52 PM
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daveparry1

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Joined: 04 July 2007

A 40 amp mcb would be more appropriate but a 32amp will be ok if there are no teenagers around Grumpy!
 05 August 2014 08:55 PM
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Grumpy

Posts: 460
Joined: 09 January 2009

Cheers Dave. Do you ever look at a place and lose the will to live? How much easier would one's life be if one was a cowboy?!
Mind you, I aint keen on horses.
 05 August 2014 09:00 PM
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daveparry1

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Quite often yes!
 06 August 2014 12:37 AM
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alancapon

Posts: 5831
Joined: 27 December 2005

Whether it complies or not will depend on what voltage the shower is rated at 8.5kW, as well as the voltage at the terminals of the shower when it is in use. For example, if it is 8.5kW at 250V, and there is 235V at the terminals (due to voltage drop), then the shower will draw (8500/250) x (235/250) = 31.96A.

Regards,

Alan.
 06 August 2014 10:29 AM
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davezawadi

Posts: 2809
Joined: 26 June 2002

A 32A MCB is perfectly fine, stop trying to work to decimal places, nothing is so accurate here! Whatever you do the cable is adequately protected, its life may be shortened a bit, but its still unlikely to melt as you well know (how many melted bits have you ever found?). Look in the BGB to see how long a 32A breaker takes to open at 35A, you may be surprised.

-------------------------
David
CEng etc, don't ask, its a result not a question!
 06 August 2014 11:09 AM
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Grumpy

Posts: 460
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Point taken. Maybe I'll just wire it to the lighting circuit and have done with it!
G
 06 August 2014 07:26 PM
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broadgage

Posts: 1356
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In practice, the stated cable and MCB sizes will be fine, but a pedantic inspection might rule it to be non compliant.

Q would I install it like that in my own home? yes.

Q would I accept the continued use of such an installation ? yes

Q would I install it like that for a paying customer, and put my name to it ? no I would not.
 06 August 2014 08:07 PM
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Grumpy

Posts: 460
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Originally posted by: broadgage

In practice, the stated cable and MCB sizes will be fine, but a pedantic inspection might rule it to be non compliant.



Q would I install it like that in my own home? yes.



Q would I accept the continued use of such an installation ? yes



Q would I install it like that for a paying customer, and put my name to it ? no I would not.


I agree with you on all the above. If I were starting from scratch I certainly wouldn't use 6mm on a 32A breaker. However, I am replacing an existing 8.5kW shower with another and it seemed a trifle pedantic to refuse to do that without ripping the house to shreds.
Thanks all for your responses.
G
 06 August 2014 08:35 PM
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daveparry1

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I can't see anything at all wrong with 6.00mm t/e on a 32 amp 60898 type B. Standard cooker circuit's work quite happily like this up to 15 kW and they're drawing current for far longer than a shower (even with teenagers using the shower!)
 06 August 2014 09:17 PM
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broadgage

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Originally posted by: daveparry1

I can't see anything at all wrong with 6.00mm t/e on a 32 amp 60898 type B. Standard cooker circuit's work quite happily like this up to 15 kW and they're drawing current for far longer than a shower (even with teenagers using the shower!)


Not strictly comparable.
A shower is a more or less fixed load, if it says 8.5KW, then subject to voltage variations and manufacturing tolerances it will use 8.5 KW.

A cooker consists typically of four or more boiling rings, one or more ovens, and often a grill. Each element is controlled by either a thermostat or an energy regulator, continuous full power operation of each component is most unlikely. Therefore the OCPD and cable can be sized at much less than the total rating of all the elements.

I would certainly not put a 15KW shower (if such an article could be obtained) on 6mm on a 32 amp MCB !
 06 August 2014 09:23 PM
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daveparry1

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Neither would I Broadgage, I was merely pointing out that as far as I can see 6.00mm t/e on a 32 amp breaker and feeding an 8.5kW shower is no problem!
 06 August 2014 10:01 PM
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leckie

Posts: 2014
Joined: 21 November 2008

Well subject to the installation method you may well be able to change the MCB to a 40A type B. So what is the problem?
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