Shower cable - how hot ?

[miffy93]

Hi, The mains cable from the shower runs on the inside of an airing cupboard, I've noticed that the cable feels warm to the touch when the shower has been used (for a normal 3-5 minute shower).

Is this normal ?

How hot should it get ?

Thanks.

 

[breezer]

Is this normal ?

How hot should it get ?

no

it shouldn't

 

[JohnD]

Looking at it differently, do you know what size the cable is (or measure its width if not) and what the rating of the circuit is (will be engraved on the MCB or fuse carrier). this will tell of it is overloaded.

You will get a bit of warmth on a big load, and if the cable is in a hot airing cupboard it will not lose the heat as quickly as if in a cold loft or under the floor. Feel the on/off switch to see if that is getting hot and tell us how big it is, and if it is the pull-cord ceiling mounted type.

 

[miffy93]

Thanks for the quick replies.

The airing cupboard get's quite warm, as there's a mini-radiator in it.

The Shower switch is a ceiling mounted pull switch.

The shower is 8.5kw

The MCB says "B40" (40A ?).

By putting a tape measure up against the cables it reads approx 10-12mm from left to right (if i'm reading it right).

As a by the way we've recently had the consumer unit changed & I asked the electrician to take a look at the shower - he said both the size of cable & the size of fuse were ok - I didn't mention the 'warm' cable at the time as i've only just noticed it.

Does this sound about right or shoud I be worried ?

Thanks again.

 

[JohnD]

I'm hoping someone else will know the numbers here. You get a slight heating effect in cables from a heavy current, provided the cable is up to size it isn't much, the cable will lose this heat to the air before it gets worryingly hot, and you can calculate the rise above ambient temperature.

If the cable is in a warm area, like an airing cuoboard, then the rise is above that higher starting point so it will end up a bit warmer; and you're supposed to re-rate and use a bigger cable in warm areas, though this often overlooked. I haven't got tables to hand to work it out but I bet someone will be along in a minute who can.

 

[Adam_151]

we need to know what size the cross section of the conductors are, I'd hazard a guess that its 6mm² (which measures 13.5mm across in the dimension you measured), 4mm² measures 11.9mm*

6mm² can comply in the situation you describe (36A load) presuming its not bunched, or run through insulation or anything else which might de-rate it, cables do get warm in use (which is why they must be derated in thermal insulation, or bunched, when heat can't escape), it has a maximum working temperature of 70C (FWIW, its allowed upto 150C under fault conditions)

if your cable just gets slightly warm and your sparky has said it complys, then there is nothing to worry about

*I might be wrong, but I don't think 4mm² could ever comply, well maybe if it was on its own along a cable tray :s

 

[miffy93]

Thanks for all your help, it's made me feel a bit better - i'll keep an eye on it though.

 

[russellsmiler]

Just been reading this post as i have just bought an Infra red thrmometer, one of those that sends a shines a red dot on the surface you are wanting to determine the temperature of.

I will recieve it in a few days, however i am interested if anyone knows of any correlation between
Watts, and cable temperature??

I know there is ratings for cables etc, but just as a question

what temperature on the outer sheaving of a twin and earth 2.5 standard cable be, if the cable is suppling a 3KW load and the cable is in a ambient 20 Degeree C ambient temperature, and lets say 20m from fuse to appliance (heater) on a radial circuit.

I know British standards will cover the cables integrity, however should temperatures be consistent with different cables?? (is there a scale)

and if so would a surface check with my IR thermometer on any loaded cable that i may have concerns about (like OP here) be able to give me or any person reassurance.

Russell


Russell

 

[russellsmiler]

Scuse spelling and repeating words....I need some food!!

 

[ban-all-sheds]

Conductors are not supposed to get to more than 70°C

Short of material properties data on the insulation and sheath, I don't see what you can do except consider more than &#8805;70°C on the surface bad, and <70°C possibly/probably OK.

And breezer was wrong - even a correctly sized shower cable will feel "warm" after a while.

 

[Click4]

can concur with BAS.

We have a 10mm cable feeding our shower, and it does indeed get a little warm to the touch.