Redring electric shower - fuse keeps blowing

[postflop]

I have a redring electric shower which blows the 30amp fuse everytime its used. Just started to do this over the past few days. Seems to last a bit longer if the shower water temperature is kept a bit lower. Have looked inside and wiring, etc. appears ok. See pictures. Grateful for any advice on what the problem could be.

Redring internal layout

• postflop
• 5 Nov 2011
• 4

Redring casing

• postflop
• 5 Nov 2011
• 4

 

[holmslaw]

..

 

[postflop]

Thanks for that, and I understand your comment. However, the circuit is dedicated to the shower unit and has been operational without problem for 6/7 years, with the same shower unit. The issue has only arisen in the past number of days

 

[riveralt]

What is the rating for your shower? It actually looks like an older version of the current slimline 650 which is a 9.5kw shower.

As Holmslaw stated if this is the case your fuse is way too small to handle this potentional load and your cable will probably need to be uprated to 10mm2 T&E as well.

 

[postflop]

Thanks Riveralt, I'll check the shower rating and also the size of the cable. Just wondering why it has been ok for 6/7 years and now all of a sudden the fuse keeps blowing. Surely if the fuse and cable have been unerated I would have had a problem much earlier after installation?

 

[RF Lighting]

I was on a job today where similar was happening.

It was a 9.5kW shower on a 30A BS1361 fuse box, and the fuse carrier was burning up. The heat was casing the fuses to blow much quicker than they should according to the fuse graphs.

 

[postflop]

RF did you replace the casing, or are you planning to run with an alternative solution? Thanks

 

[RF Lighting]

It needed the shower circuit replacing with a 45A circuit, and a new consumer unit.

 

[riveralt]

Thanks Riveralt, I'll check the shower rating and also the size of the cable. Just wondering why it has been ok for 6/7 years and now all of a sudden the fuse keeps blowing. Surely if the fuse and cable have been unerated I would have had a problem much earlier after installation?

Fuses (fuse wire) have a degree of tolerance built in - sometimes up to 1 1/2 times the face value. But if you think about your shower being turned on and off several hundred times (or several thousand times - if you household is like mine) over the past seven years the constant overheating of the fuse, like RF Lighting stated, has possibly caused physical damage to the fuse carrier itself perhaps the ceramic or the brass contacts.
The purpose of the fuse is to protect the cable from damage so in this case it has worked. The current carrying capacity of 6mm2 T&E is around 46 Amps in ideal conditions. This is close to the 41Amps that a 9.5kw shower might pull at full load.

 

[postflop]

Attached are a couple of photos of the fuse carrier for the electric shower circuit.......

Untitled

• postflop
• 28 Feb 2012
• 1

Untitled

• postflop
• 28 Feb 2012
• 1

Untitled

• postflop
• 28 Feb 2012
• 1

 

[RF Lighting]

You're never gonna beleive this


Here's mine from today!

 

[holmslaw]

..

 

[riveralt]

That melted plastic stuff should be telling you that it is time to move the shower circuit off that Consumer Unit.

I would have an electrician come out and examine the internal part to see if the damage is just confined to the visible area in the photograph or has it spread.
It could spell the end for the whole of the consumer unit.

In broad terms you will have two options.

Assuming the current consumer unit is 'knackered' then you will need to have it replaced - this will give you the opportunity to put the shower circuit on a proper footing regarding RCD protection and the correct size MCB.

If the current consumer unit can be saved then I would suggest you get an additional shower consumer unit. This will involve splitting the incoming supply. This new unit will give you both RCD protection and the correct size MCB.

Whatever you do - DO NOT put another fuse back in the Consumer unit or swop the shower circuit to another fuse.

 

[postflop]

Dont know the size of the cable by looking at it but it appears to be of the order 6.5/7.5mm T&E. I note it was mentioned earlier that 10mm T&E should be used with 45amp fuse. What is the maximum fuse size that should be used on say a 6.5mm T&E cable

 

[riveralt]

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