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Electric shower fuse question


 
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taosway

from United Kingdom

Joined: 20 Dec 2003
Posts: 4
Location: United Kingdom

PostPosted: Wed May 05, 2004 5:58 pm Reply with quote

We have an electric shower that has been installed for a few years. Recently the fuse blew. The fuse is housed in a seperate single fuse box rated at 30 amps (the wire thickness to the shower seems to measure approx 12mm). I replaced the fuse and it lasted for several weeks and has just blown again - it was extremely hot and had damaged the fuseholder with the heat.

From articles on the web I note that a 40 amp fuse rating is usually recommended. My question is, can I simply use a 40 amp fuse in the box or should I replace the box itself?
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breezer

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PostPosted: Wed May 05, 2004 6:05 pm Reply with quote

neither, a fuse is there to protect, putting in a bigger fuse will mean something else will "give" causing a fire, electric showers only last about 5 years, i should say its time for a new shower, but get the identical one that you have, it will be less hassle
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securespark

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PostPosted: Wed May 05, 2004 6:16 pm Reply with quote

What is your shower rating?

Often showers are replaced with a higher wattage model on the old circuit, and a small overload would not be detected by a 3036 rewireable fuse.

You need to make sure that the rating of the shower does not exceed the capabilities of the existing circuit. IE, cable size and fuse size etc...
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taosway

from United Kingdom

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PostPosted: Wed May 05, 2004 6:30 pm Reply with quote

Thanks for info.
I don't know the shower rating, but the model is an Aqua-tronic (Triton) W9500i.
What I'm unsure of is, has the fuse blown (and got very hot) because the fuse and box rating at 30 amps is too low?
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breezer

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PostPosted: Wed May 05, 2004 6:47 pm Reply with quote

taosway wrote:
has the fuse blown (and got very hot) because the fuse and box rating at 30 amps is too low?


no its as i said, your shower is on its way out. the fuse is doing its job
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plugwash

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PostPosted: Wed May 05, 2004 6:47 pm Reply with quote

for that shower in your present setup i would advise using a 45A mcb in a small CU with a rcd incomer

also you should make sure the cable is 10mm (cables are mesured by conductor area the outside demensions of 10mm twin and earth are 17.1mm x 10mm)

unfortunately few brands seem to do 45A breakers and do small CUs

you could use a mk modular enclosure with an rcd and mcb
bring the incomeing tails into the top of the rcd

connect the shower neutral to the neutral terminal on the bottom of the rcd

conenct the live on the bottom of the rcd to the bottom of the mcb with a short peice of tail

and connect the live from the shower to the top of the mcb

connect the earth from the shower and the earth from the main earth termina to the earth terminal in the box
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breezer

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PostPosted: Wed May 05, 2004 6:50 pm Reply with quote

plugwash how do you justify telling him to put in a bigger rated protective device, he has already said its not a 10mm cable, also his shower has workd for years, it is just a case of his shower is on its way out
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plugwash

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PostPosted: Wed May 05, 2004 6:56 pm Reply with quote

im pretty sure the model numbers of mira showers are ratings in watts 9500 is way too much for a 30A protective

it only worked for years because rewireables take a very long time to go at moderate overloads

if it's not 10mm or more then it needs to be rewired and i would honestly be putting in 16mm theese days with the way higher power showers are increasing in popularity
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BR

from Ireland

Joined: 31 Dec 2003
Posts: 334
Location: Ireland

PostPosted: Wed May 05, 2004 7:19 pm Reply with quote

IF this shower is 9.5KW then 6mmsq cable will suffice, although it will be running at it's limit of complience. I would reccomend that a 40A RCBO be fitted to the circuit at the board.
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securespark

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PostPosted: Wed May 05, 2004 9:11 pm Reply with quote

Breezer

It may not be a faulty unit.

It looks like a 9.5kW unit. IE 41.3A

A 3036 fuse (rewireable) will cope with this overload for quite a while, but will eventually blow.

If the unit has been changed recently, that may account for the fuse blowing. If not, is the shower being used for longer periods of time?

Whatever the reason, the circuit is not sufficient, and the unit and circuit need checking over to make sure it is safe and complies.

Br

My guess is with it having a 3036 in the board it is a wylex or proteus that is not adaptable to take rcbo's.
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BR

from Ireland

Joined: 31 Dec 2003
Posts: 334
Location: Ireland

PostPosted: Thu May 06, 2004 8:18 pm Reply with quote

I agree, but an RCBO could be fitted alongside the existing board in a 2-module enclosure
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