from an 8kw shower to a 10.5.

[Phenz]

thats what i thought, what is the most powerful shower i could run on this circuit then?

could i get away with a 9.5, or something similar or would i have to stick with an 8kw?

 

[Spark123]

They must operate within 0.4s or 5s depending on the circuit. As this is a shower and the lower body resistance that would be intorduced by being immersed in a water stream, any protective device must operate to disconnect the circuit in the event of a fault within 0.4s.

I thought fixed equipment in a bathroom is now 5s disconnection with greater emphasis has been put on local supplementary bonding? However if he is using MCBs then the efli should be such that the maximum amount of current required to operate the magnetic trip is achieved, hence in reality a 0.1s disconnection should be achieved.

 

[Spark123]

It is almost impossible for us to tell over the internet, a 6mm will be almost flat out at 45A, this isn't taking into account any correction factors such as ambient temp, grouping and thermal insulation. The cable length effects the volt drop and also the earth fault loop impedance which needs considering when selecting the circuit breaker. Without being there with the appropriate testers it is impossible for us to give the correct and most importantly, the safest advice.

 

[Phenz]

so what would you suggest i do?

how would i go about testing the cabling myself? Its copper wire, there is a 45A mcb and it doens't go anywhere near any hot pipes or anything.

if you were to recommend something to me from what i've said in the previous posts, what would it be?

should i install a 9.5kw, 8.5kw, or an 8kw shower?

 

[Spark123]

I'm not entirely convinced a 45A MCB is correct to be used with the 6mm cable. Along with length and efli, the cable runs in a loftspace hence ambient temperature will also be a factor on its current carrying capacity.
Has it been run from an old cooker circuit or something?
I think the best advice it to get an electrician to take a look, they should have the necessary test equipment and experience to check the installation is up to spec. Remembering your body has a decreased resistance when using a shower it is essential that all work in a bathroom including the equipotential bonding is up to scratch. Unless you own an insulation resistance, a low resistance ohm meter and an efli tester which cost hundreds of pounds, it is impossible to say if it is safe or not, regardless of the shower size.

 

[Phenz]

i'm really not sure, the house is about 20 years old. i bought it about 3 years ago and it has just had a new kitchen put in. Its got a built in electrical cooker.

it definetly looks like the shower circuit has been added at a later stage, i'll get some pics of the fuse box so you can see what i mean...

 

[Firkin]

Phenz, try CEF (City Electrical Factors) and see what they are charging for 10 mm cable they gave me a great price for what I needed (15 metres = £26:00) If nothing else, the cost cannot be balanced against personal safety - just buy the right size cable.
Firkin

 

[Phenz]

camera doesn't really take good pics cause its too close/dark

knocked up this diagram to show you what i mean...

 

[Phenz]

its not really the cost of the cable thats a problem, its the hastle of having to install it though the house, goes inside the wall, down two floors, behind kitchen tiles/units, underneath floorboards/laminate, two different sets there of. just for a better shower i don't think its worth stringing the 10mm cable at this stage, i need to put in a new shower cause the old one broke - just trying to work out what the most powerful shower i could fit with the current cabling would be.

 

[Stulz]

They must operate within 0.4s or 5s depending on the circuit. As this is a shower and the lower body resistance that would be intorduced by being immersed in a water stream, any protective device must operate to disconnect the circuit in the event of a fault within 0.4s.

I thought fixed equipment in a bathroom is now 5s disconnection with greater emphasis has been put on local supplementary bonding? However if he is using MCBs then the efli should be such that the maximum amount of current required to operate the magnetic trip is achieved, hence in reality a 0.1s disconnection should be achieved.

Spark, you may be right there. I do not work in the domestic market and so my memory may be out of date on the disconnection time.

Regarding putting 6mm² T&E on a 45A breaker, I would urge against such a move. Even if you utilise good quality BASEC rated cable and take into account all environmental factors, your still on the fringe of acceptable loading capabilities for the cable. If, on the other hand, you buy the cheaper quality, non-BASEC approved cable, then you have no idea of the quality of the copper used, the insulation or the quality control utilised to maintain conductor size and quality. This may seem a trivial point, but are your really willing to risk your life, and that of your family for the sake of a few pounds and some effort to install the correct size cable?

 

[Phenz]

erm, its not a case of changing the wiring any more.

i'm assuming that the 8kw shower i had in there for 3 years was OK to be run of the 6mm wiring?

all i really would like to know is that can i safely install a shower with a wattage of 8kw? would an 8.5kw shower be okay for example?

the way its starting to sound is that for *any* shower i need to have 10mm cable if i want to be able to sleep at night knowing my house isn't going to burn down...

 

[C&GStudent]

If I were you Phenz, I would either replace the shower like for like, or replace the cable.

That is probably the safest option if you don't want to call a pro.

 

[Adam_151]

They must operate within 0.4s or 5s depending on the circuit. As this is a shower and the lower body resistance that would be intorduced by being immersed in a water stream, any protective device must operate to disconnect the circuit in the event of a fault within 0.4s.

I thought fixed equipment in a bathroom is now 5s disconnection with greater emphasis has been put on local supplementary bonding? However if he is using MCBs then the efli should be such that the maximum amount of current required to operate the magnetic trip is achieved, hence in reality a 0.1s disconnection should be achieved.

Spark, you may be right there. I do not work in the domestic market and so my memory may be out of date on the disconnection time.

I reckon thats probably right going strictly by what BS7671 says, I'm not sure it treats it much differently to anyother fixed equipment, but maybe going upto 5s in this case isn't strictly within the spirit in which BS7671 was written, I've heard it said that the 5s disconnection time value wasn't really intended for use in houses (and while there is nothing that says you can't use it) it would probably be better practice to design to 0.4 or faster.

You could use two 2.5 cables parrelleled up at both ends and running the same route, for your shower in all likelyhood, but no one is saying its good design practice...

Regarding putting 6mm² T&E on a 45A breaker, I would urge against such a move. Even if you utilise good quality BASEC rated cable and take into account all environmental factors, your still on the fringe of acceptable loading capabilities for the cable. If, on the other hand, you buy the cheaper quality, non-BASEC approved cable, then you have no idea of the quality of the copper used, the insulation or the quality control utilised to maintain conductor size and quality. This may seem a trivial point, but are your really willing to risk your life, and that of your family for the sake of a few pounds and some effort to install the correct size cable?

All cable from reputable suppliers will meet the relevant british standards, if you then install as per BS7671 then all will be tip top, BS7671 will take account of the range of copper grades and the allowed deviation from the stated CSA allowed within the BS for cable, etc, etc

EDIT: Though likewise to my point a paragraph above, I suppose you could say its probably not azmazing design practice to be pushing your cables to the limits in BS7671, and I guess I'd kinda go along with that

(and FWIW a cable thats slightly overloaded tends just run a bit hot and loose a few years off its lifespan rather than bursting into flames, I suspect if this wasn't the case then ring final circuits would at least be a lot rarer than they are, thats if they would be allowed at all, due to it being difficult to ensure that ring inbalence *never* occurs enough to overload one side for a length of time)

Not that I'm saying its acceptable to overload cables, its just that I suspect poor terminations present a much bigger menace in the real world than cables a size too small

 

[cb9002]

Phenz, I'm not a pro but I would say 25m is a long run even for an 8kw shower. I wouldn't recommend going any higher at all. If you look through the archive you'll see links to online calculators that will give you the maximum power for your particular run without exceeding the permitted votage drop.

PS Just becuase it is there already doesn't mean it was done right (or safely) to begin with!