Shower Fuse Replacement?

[summerisle]

Hope I can explain this properly

My electric shower (9.5kw) has packed in and upon inspecting the fuse, etc I noticed that it whilst it is running off its own CU (Memera 2000 ASN100 100A) and has 10mm cable it only has a 30A fuse. This shower was replaced about 5 years ago and a 30A fuse may well have been suitable for the previous shower but the installer obviously never bothered his ass upgrading to a 45A fuse.

The CU has 2 HRC fuse carriers, one being the 30A and the other is blanked off. My question is can I get a 45A fuse into that unit? Is the 30A carrier easily removed and replaced or do I need a complete new CU?

Pic attached

Untitled

• summerisle
• 13 Jan 2015
• 2

 

[ban-all-sheds]

has 10mm cable it only has a 30A fuse.

The capacity of 10mm² cable can be as low as 32A, depending on how it's installed.

http://www.batt.co.uk/upload/files/4d5.pdf

Do you know how yours is installed?

The CU has 2 HRC fuse carriers, one being the 30A and the other is blanked off. My question is can I get a 45A fuse into that unit?

Depends what type of fuse it takes. With some types the physical size is the same for different current ratings, with others it is not.

Sooner rather than later someone who knows what sort that carrier takes will show up here and give you a definitive answer.

Is the 30A carrier easily removed and replaced or do I need a complete new CU?

It's easily removed and replaced if necessary, either with a different capacity one or an RCBO.

What isn't so easily done (by you) is the necessary testing. You also need to verify that your cable, as installed, can cope with the load you want it to.

 

[EFLImpudence]

the installer obviously never bothered his ass upgrading to a 45A fuse.

9500W @ 240V = 39.6A (38A @ 230V)

 

[summerisle]

has 10mm cable it only has a 30A fuse.

The capacity of 10mm² cable can be as low as 32A, depending on how it's installed.

http://www.batt.co.uk/upload/files/4d5.pdf

Do you know how yours is installed?

Thanks for the speedy response.
Not sure what you mean exactly but a 10mm cable runs from the CU straight to the shower which is nearly directly above where the meter box is?

 

[JohnW2]

Not sure what you mean exactly but a 10mm cable runs from the CU straight to the shower which is nearly directly above where the meter box is?

BAS was referring to the 'route' of the cable - is it clipped on the surface of a wall, buried in plaster, surrounded by insulation (e.g. within a wall) or what? Only if it is totally buried in insulation would the current carrying capacity be anything like as low as 32A. With more common installation methods (clipped to the surface or buried in plaster) it would be about double that.

Kind Regards, John

 

[summerisle]

Not sure what you mean exactly but a 10mm cable runs from the CU straight to the shower which is nearly directly above where the meter box is?

BAS was referring to the 'route' of the cable - is it clipped on the surface of a wall, buried in plaster, surrounded by insulation (e.g. within a wall) or what? Only if it is totally buried in insulation would the current carrying capacity be anything like as low as 32A. With more common installation methods (clipped to the surface or buried in plaster) it would be about double that.

Kind Regards, John

I'm with you. In the garage it is in conduit clipped to the wall and then attached to rafters before disappearing into the wall - from there it probably goes between floor and ceiling clipped to the joists and into the shower room. There would be no insulation in the equation.

I take it this is a good thing and that it means that it can adequately carry more current than what is necessary for a 5 minute shower?

I was also thinking of downgrading to a 8.5kw shower which would mean only a 35A fuse required?

 

[JohnW2]

I'm with you. In the garage it is in conduit clipped to the wall and then attached to rafters before disappearing into the wall - from there it probably goes between floor and ceiling clipped to the joists and into the shower room. There would be no insulation in the equation.

Fair enough. In that case, assuming it is 10mm² cable, it's likely to have a current-carrying capacity of at least 50A. Do I take it that you are sure that the cable really is 10mm²?

I take it this is a good thing and that it means that it can adequately carry more current than what is necessary for a 5 minute shower?

Indeed, again assuming it is 10mm² cable, adequate for a 5-hour shower

I was also thinking of downgrading to a 8.5kw shower which would mean only a 35A fuse required?

Assuming it's 8.5kW at 240V (which is what it usually means), that would be about 35.4A at 240V, around 33.9A at the nominal 230V - so a 35A fuse would just about be OK - although I'm not at all sure you'd find a 35A fuse! However, given that the cable is more than capable, a 40A fuse (assuming it would fit) would probably be more sensible, and probably easy to find.

Kind Regards, John

 

[summerisle]

I'm with you. In the garage it is in conduit clipped to the wall and then attached to rafters before disappearing into the wall - from there it probably goes between floor and ceiling clipped to the joists and into the shower room. There would be no insulation in the equation.

Fair enough. In that case, assuming it is 10mm² cable, it's likely to have a current-carrying capacity of at least 50A. Do I take it that you are sure that the cable really is 10mm²?

I take it this is a good thing and that it means that it can adequately carry more current than what is necessary for a 5 minute shower?

Indeed, again assuming it is 10mm² cable, adequate for a 5-hour shower

I was also thinking of downgrading to a 8.5kw shower which would mean only a 35A fuse required?

Assuming it's 8.5kW at 240V (which is what it usually means), that would be about 35.4A at 240V, around 33.9A at the nominal 230V - so a 35A fuse would just about be OK - although I'm not at all sure you'd find a 35A fuse! However, given that the cable is more than capable, a 40A fuse (assuming it would fit) would probably be more sensible, and probably easy to find.

Kind Regards, John

Thanks John

I have a spare bit of 10mm cable on a reel and it is the same size as that.

So fitting a 40A fuse into that Unit would not be a problem (other than getting it to fit!). I take it that its not a matter of putting a 40A fuse into the current 30A carrier but replacing the carrier - or is it?

 

[JohnW2]

Thanks John ... I have a spare bit of 10mm cable on a reel and it is the same size as that.

Fair enough.

So fitting a 40A fuse into that Unit would not be a problem (other than getting it to fit!). I take it that its not a matter of putting a 40A fuse into the current 30A carrier but replacing the carrier - or is it?

I don't know - but others here probably do! As BAS said, sometimes fuses of different rating have a different physical sizes, and therefore need different size carriers. Hopefully someone will know whether that is the case with yours.

Kind Regards, John

 

[flameport]

I take it that its not a matter of putting a 40A fuse into the current 30A carrier but replacing the carrier - or is it?

45A fuses are significantly larger both in diameter and length, so a new carrier will be required.

45A carriers were made for that consumer unit, but are no longer available. They are likely to be next to impossible to find, as 45A would be a seldom used size.

 

[ban-all-sheds]

What about an RCBO?

 

[flameport]

What about an RCBO?

The Memshield2 range might fit in there - some of them were interchangeable with the Memera ones, although some were not due to the busbar prongs being the wrong size.

Memshield2 is also obsolete, although can still be obtained for a price.

 

[JohnW2]

I take it that its not a matter of putting a 40A fuse into the current 30A carrier but replacing the carrier - or is it?

45A fuses are significantly larger both in diameter and length, so a new carrier will be required. ... 45A carriers were made for that consumer unit, but are no longer available. They are likely to be next to impossible to find, as 45A would be a seldom used size.

What about 40A ones, which it appears would be adequate for the OP? Do/did they exist, and what physical size?

Kind Regards, John

 

[flameport]

40A do exist, although probably not made for that board as 40A is not part of the BS1361 series of values.

40 and 45A are the same physical size, both are larger than the 30A.

 

[summerisle]

Thanks for all the help folks.

It may be easier to fit a new CU for the shower - what sort of price are we talking and what do you recommend?