Electric shower cuts out after 5 mins

[CrazeUK]

Also would it be safe to just swap the cable for a 16mm² for future proofing when this shower dies to upgrade to a 10.5kw?

 

[terryplumb]

The 2.5 refers to the CPC's cross sectional area.
10 mm² cable is sufficient, you don't need 16 mm² , and it runs from the consumer unit all the way ( not just the bit between the isolator and shower)

 

[CrazeUK]

Oh I see. 10mm² it is. Oh yes,for me CU to the isolator is the easy bit. I guess injust get concerned when it involves a wet area and electricity

 

[CrazeUK]

Quick update. I haven't swapped the cabling or anything as yet.

I did however purchase a Flir Camera for my phone.
Here are the results:
Picture 1

picture 2

picture 3

Picture 1 and 2 are about 4 minutes apart after I had a 5 min shower and ran the shower a bit longer.

Picture 3 is the isolater switch in between that 4 mins.

The temperatures shown are surface temperatures of the housing,I assume it is around 10c higher underneath.

When someone goes in the shower, I'll remove the cover and do it again

 

[Johntheo5]

If the shower is designed for 9.5kw at 240V then the heating element(s) resistance is 6.06 ohms.
If your voltage is 230 (UK?) then the current draw is 37.96A say 38A and its output is 8.73kw.
You require a 40A MCB.
Regulations may specify 10mm2 cable but as the shower is not continuously running then the 6mm2 cable temperature rise is probably very modest. The current flow will be ~ 37.8A with 8M (4M to&from) of 6mm2 cable with a resistance of 3.08mohm/m. 8M of cable will have a heat loss of 35 watts at 37.8A or ~ 1.34 watts/ft??, hardly set the world on fire if my calcs are correct.

 

[CrazeUK]

If the shower is designed for 9.5kw at 240V then the heating element(s) resistance is 6.06 ohms.
If your voltage is 230 (UK?) then the current draw is 37.96A say 38A and its output is 8.73kw.
You require a 40A MCB.
Regulations may specify 10mm2 cable but as the shower is not continuously running then the 6mm2 cable temperature rise is probably very modest. The current flow will be ~ 37.8A with 8M (4M to&from) of 6mm2 cable with a resistance of 3.08mohm/m. 8M of cable will have a heat loss of 35 watts at 37.8A or ~ 1.34 watts/ft??, hardly set the world on fire if my calcs are correct.

Thanks for the calcs. With electricity and water I would rather be safe lol.

Earlier in the thread someone suggested the switch maybe tripping because it's getting hot. This eas just to prove the case.

 

[CrazeUK]

I wanted to double check before changing the MCB.

Here is the thermal image of tge shower running 5 mins after someone had been in.

Here you see the wire getting warm / hot.
Would changing the mcb help? Or do I just change the wire too?

The wire is a more expensive job as 10mm is quite expensive.

 

[Johntheo5]

That looks very like a bad wiring termination, if the remainder of the wiring is ~ 25C ish then definitely the termination.

 

[CrazeUK]

That looks very like a bad wiring termination, if the remainder of the wiring is ~ 25C ish then definitely the termination.

I actually think it's the whole wire.

The first image is of the trip switch and the second is a length of the wire.

All the wires are in trunking, so that temp wont be the actual temp of the wire, more the dissipated heat through the trunking.

 

[Johntheo5]

I calculated 35watts heat dissipation in 8 meters of trunking = 1.34 watts/Ft the live and neutral are each dissipating 1.34 watts/ft = 2.68 watts/Ft side by side? so perhaps raising the temperature to 54C in 5 minutes, very interesting to say the least and if the whole trunking/wiring is at this temperature then quite revealing.

 

[CrazeUK]

I calculated 35watts heat dissipation in 8 meters of trunking = 1.34 watts/Ft the live and neutral are each dissipating 1.34 watts/ft = 2.68 watts/Ft side by side? so perhaps raising the temperature to 54C in 5 minutes, very interesting to say the least and if the whole trunking/wiring is at this temperature then quite revealing.

So the wire is the problem? The MCB or both?

 

[bernardgreen]

Ok.
A 32amp circuit is wholly unsuitable for a 9.5kw shower. That would draw around 41 amps at 240 volts.
Hence the 32amp MCB is tripping. How many years has the shower been running on that breaker ?

That is the reason the shower is cutting out, the overheating wire is a secondary effect of the shower taking more current than that which the MCB and wiring are designed for.

 

[CrazeUK]

That is the reason the shower is cutting out, the overheating wire is a secondary effect of the shower taking more current than that which the MCB and wiring are designed for.

So both then. I will change the MCB first as that is the more economical and shorter time change. See if that has any impact. Then swap the cable out.

Thank you very much

 

[terryplumb]

You should not change the MCB for one with a higher rating if that's your intention.
The person that installed the circuit has judged that a 32amp breaker was suitable to protect the circuit cable.
Your shower appears to be drawing current at a level that the existing cable is carrying at its upper limit within its method of installation.
Do yourself a favour and engage an electrician to install an upgraded circuit

 

[Johntheo5]

The MCB is cutting out because its rated for 32A and carrying ~ 38A but there is a time factor involved, the greater the overload the shorter the time factor, 5 minutes does seem very short but changing it to a 40A will certainly sort that problem out, the electrician who replaces it should check the current draw even before he changes it, in case of any other problems.

So the wire is the problem? The MCB or both?

The higher the wiring resistance the less current flow since they are in series, not a significant amount anyway, only ~ 0.15A (35watts).

That is the reason the shower is cutting out, the overheating wire is a secondary effect of the shower taking more current than that which the MCB and wiring are designed for.