10 kw Electric Shower

[garash]

Hi Can anyone tell me if a 10ml cable is man enough to connect to a 10 kw electric shower?

 

[Iggifer]

It does depend on a few factors such as where the cable runs (insulation etc) and how long the run is.

But it could be, yes

 

[ericmark]

What is a 10 ml cable? There is a problem years ago cable was called by how many strands and how thick each strand was 7/0.044 for example but when we went metric we started to go by the cross sectional area 10 mm² for example. So a 10 mm² cable twin and earth is likely 7.9 x 15.9 mm overall and we get confusion where people measure the wrong bit.

The insulation in cable is made from different materials XLPE, LSZH, PVC etc and these mean the cable can run at different temperatures. Also the cable must be able to dissipate that heat so we talk about installation methods.

So a thermal plastic cable installed to Reference Method 100# (above a plasterboard ceiling covered by thermal insulation not exceeding 100 mm in thickness) being 10 mm² without any other de-rating factors like being with other cables is considered as being able to carry 45A.

But it could be as low as 32A if the conditions are not favourable.

45A = 10.35 kW with a 230 v supply.

However our cable is limited by heat which takes time to build up. Also our protection device takes time to trip until 3 to 5 times rated value so running something which only runs for a short time one can get away with exceeding the value of the protection device. Likely an 11 kW shower will never trip a 45A MCB or damage the cable.

 

[garash]

Just to be a bit clearer, the electric shower being used is only 4kw and we are replacing it with a 10.5 kw in the same place, so the length of the existing cable is adequate for connection. We do not believe that the cable itself needs to be changed/upgraded which is what we are being told. Sorry if I was not clear on that in my original post.

 

[mikeyd]

Cable sizes are not measured in millilitres. If you mean 10 mm² then how are you measuring it? Who is telling you it needs changed any why do you doubt them?

 

[JohnW2]

Likely an 11 kW shower will never trip a 45A MCB or damage the cable.

If it did trip, it would presumably be a faulty MCB ... a B45 MCB is required to carry 50.85A indefinitely without tripping and, even if the 11kW were quotes at 230V (unlikely), that would be under 48A.

Kind Regards, John

 

[ericmark]

Likely an 11 kW shower will never trip a 45A MCB or damage the cable.

If it did trip, it would presumably be a faulty MCB ... a B45 MCB is required to carry 50.85A indefinitely without tripping and, even if the 11kW were quotes at 230V (unlikely), that would be under 48A.

Kind Regards, John

Agreed however other people also read the posts and with 6mm² cable feeding a shower with a B32 MCB quite often it is overloaded, but will still hold for long enough to get a shower. I have found, when this is the case over time, the MCB gets more and more sensitive, and the time one can shower for decreases as the years go on. Likely this varies manufacturer to manufacturer, it really will depend on the temperature required to trip the device, and if that is high enough to cause oxidisation, and so weakening the element.

 

[JohnW2]

Agreed however other people also read the posts and with 6mm² cable feeding a shower with a B32 MCB quite often it is overloaded, but will still hold for long enough to get a shower. I have found, when this is the case over time, the MCB gets more and more sensitive, and the time one can shower for decreases as the years go on.

Indeed, that can happen. However, in the context of your comments, at least in theory a non-faulty B45 should really never trip with a shower of 11kW or less, even if it were run continuously.

Whatever, in the context of the OP's question, the crucial issue which needs to be ascertained is exactly what cable size he actually does have.

Kind Regards, John

 

[ban-all-sheds]

Just to be a bit clearer, the electric shower being used is only 4kw

Never heard of one so small - I can't see how it could ever have worked.

and we are replacing it with a 10.5 kw in the same place, so the length of the existing cable is adequate for connection

Not necessarily - the length might be too great given voltage drop for a larger load.

We do not believe that the cable itself needs to be changed/upgraded which is what we are being told

As per mikeyd, why don't you believe that?

Have you worked out what the current carrying capacity of the cable is, given its installation method(s), and checked that voltage drop will be within limits?

If you have, and it's OK, why has the person advising you not done the same, or reached the same conclusion?

Why do you not trust him, and why don't you get an electrician who you do trust?

 

[JohnW2]

Not necessarily - the length might be too great given voltage drop for a larger load.

As a matter of interest, what degree of voltage drop do you believe would "impair the safe functioning of" an electric shower?

Kind Regards, John

 

[ban-all-sheds]

I don't know. I do know that mine is full of electronics, and I don't know what voltage regulation is in place for those.

I don't know what the maker quotes as the minimum voltage for his shower. I do know what 525 says about that.

I don't know what size or length the OP's cable is. I do know that someone who does know has said it needs replacing.

 

[JohnW2]

I don't know. I do know that mine is full of electronics, and I don't know what voltage regulation is in place for those.

In practice, it obviously depends on what one's 'usual' supply voltage is. BS7671 deems any (no-lighting) equipment to be OK down to a "voltage at its terminals" of 204.7V, which represents ~15% VD for someone with a usual supply voltage of ~240V.

I don't know what the maker quotes as the minimum voltage for his shower. I do know what 525 says about that.

I don't. My copy of 525 talks about "the product standard relevant to the equipment (if there is one)" (whatever standard that might be for a shower), which may or may not specify a minimum voltage, but it says nothing about manufacturer's instructions.

Kind Regards, John

 

[ban-all-sheds]

So are we again facing the situation that when you don't KNOW something you are happy to GUESS and tell the OP that there IS NO CHANCE WHATSOEVER that an appliance where the maker specifies a minimum voltage won't work properly at a voltage below that?

 

[JohnW2]

So are we again facing the situation that when you don't KNOW something you are happy to GUESS and tell the OP that there IS NO CHANCE WHATSOEVER that an appliance where the maker specifies a minimum voltage won't work properly at a voltage below that?

I'm not really sure why you're getting so excited. To be adequate, current-carrying-capacity-wise, for a 10.5kW shower, the cable would have to be at least 6mm², possibly 10mm². Even if one uses the BS7671 guidance VD figure of 5%, that would be satisfied by any cable length less than about 37 metres for 6mm², or about 62 metres for 10mm², cable lengths which I very much doubt would be exceeded in a normal house.

The crucial unanswered question relates to what cable to OP actually has, and whether it has an adequate CCC for a 10.5kW shower. As above, voltage drop is most unlikely to be an issue.

Kind Regards, John

 

[ban-all-sheds]

I doubt it too.

But I don't KNOW.

And when I don't KNOW I won't assure someone that they can do XYZ because of my GUESSWORK.