9KW Shower on 4mm cable

[soulman]

Hi, While carrying out a periodic inspection I came across a 9kw shower on 4mm cable, 40A type B ocpd, 30ma rcd.

I have given a code 3, for the following reasons;

1. No sign of thermal damage at any termination.
2. Shower cannot overload as fixed load.
3. Short Circuit & Earth loop impedance well within limits.
4. Shower will not run at maximum 9kw.

I have also noted to the customer that the manufacturers recommend a 10mm cable. I would just like your opinions on the above.

Cheers

 

[telectrix]

i would have been tempted to clamp the load, see what it actually pulled. but i think C3 is right.

 

[andyb]

Won't the shower will always run at 9kw?

 

[GEOFF S]

Its pushing it, but no real drama, 9kW at 230 V or 240 V?

As long as its clipped direct and no insulation.

Cheers

 

[Paul.M]

Clamp the tails, it will be drawing around 32A. This is on a 4mm?

 

[polo1]

C2 for me, unless the cable is swinging in free air! (Would encourage derating the mcb to 32).

 

[assegayer]

im a trainee but surely 4mm is too little for 39A or 37.5A on 240volts. the cable is in a wall isnt it?!? and i thought showers will always use the load thats stated...

9000/230 = 39.13

9000/240 = 37.5

 

[Guest77]

Hi, While carrying out a periodic inspection I came across a 9kw shower on 4mm cable, 40A type B ocpd, 30ma rcd.

I have given a code 3, for the following reasons;

1. No sign of thermal damage at any termination.
2. Shower cannot overload as fixed load.
3. Short Circuit & Earth loop impedance well within limits.
4. Shower will not run at maximum 9kw.

I have also noted to the customer that the manufacturers recommend a 10mm cable. I would just like your opinions on the above.

Cheers

Hmm guess again.

 

[davesparks]

im a trainee but surely 4mm is too little for 39A or 37.5A on 240volts. the cable is in a wall isnt it?!? and i thought showers will always use the load thats stated...

9000/230 = 39.13

9000/240 = 37.5

Yes you are quite right that a shower should be considered at its full load as, without disconnecting one of the heating elements in the shower, you can't guarantee that it will be run in half power mode.

Your second current calculation is right, the first one is not quite there. (I'm assuming the 9kW is the 240V rating)
If you look at the rating plate on a shower (or anything else) you will find that it has a different rated power at each voltage.
The power dissipated by a load is determined by the electrical resistance and the voltage applied across that resistance. As the resistance remains constant a change in voltage will result in a relative change in power.

As a result the current at 230V will be a bit less than that at 240V.

 

[davesparks]

4. Shower will not run at maximum 9kw.

Cheers

Bearing in mind the actual mains voltage in this country is not what it says on the tin, it will almost certainly run at a shade over 9kW

 

[Welchyboy1]

The heating element will always run at 9kw its the speed of the water passing through it that governs the heat

its not like diversity on a cooker!!!!

What install method?

c2 for me

 

[soulman]

Thanks for replies, much appreciated. I did forget to mention that the shower has been installed for 9 years.

cheers

 

[Dave OCD]

It probably started out as a 7KW or even less when first installed, it also worries me that the big DIY chains are always promoting 10.8KW showers, ridiculous power rating IMO !

 

[JBL]

What type of cable? 4mm 90 degree should be ok depending on installation method.

 

[Darkwood]

What type of cable? 4mm 90 degree should be ok depending on installation method.

Welcome to the forum JBL..

Just in response to your post - how will it be sufficient if the equipment it is connected to will more then likely be 70c rated thus you would have to add a derating factor to the cable.... always take your CCC values off 70c rated cables unless your working with high temperature equipment including connections.