shower

[gooner1984]

im about to change a cu for a friend for my assessment with napit, the only thing worrying me is a 7.5kw shower is on a 32a CB and is wired in 4mm2 twin and earth i no it ant right, but not sure what to do do i take it out of use, or do i tel my friend that its best to run say 6mm or 10mm, some advice would be great

 

[topquark]

I would suggest a little due diligence may be in order and would ring the manufacturer. When you will probably find that the indicated load of 7.5KW is a peak load (on shower startup) and that the normal running load, as has been suggested, is considerably less.

If you do the calculations based on the length of run (and how much is in the wall etc) you may well find that the cable is adequate anyway. There is a safety margin built into the guide. The cable run length may affect the power disipation due to any voltage drop if it's a long run.

I'd agree that this is a borderline case, however Gooner has neither installed the cable nor shower. I'm sure he would have selected a 6mm cable if he had.

 

[nickblake]

im going to back rocker and Tel on this one they are correct ,as i stated in my first post nothing wrong with this depending on the installation method used, if its C clipped direct then there is no problem as the current carrying capacity will be 36 amps Ref Table 4D2A, also depends on the cable run , i would prefer 6 or 10 mm and in sure rocker and Tel would agree with that and if the shower was upgraded then yes the cable will require upgrading but as the shower is 7.5kw then this cable is fine it also depends on your supply voltage , yes for design purposes we use 230volts but in real terms its higher or lower if you are running on a 238v supply the the current will reduce so that will be aound 30 amps little thing to remember is higher the voltage lower the current lower the voltage higher the current

 

[nickblake]

I would suggest a little due diligence may be in order and would ring the manufacturer. When you will probably find that the indicated load of 7.5KW is a peak load (on shower startup) and that the normal running load, as has been suggested, is considerably less.

If you do the calculations based on the length of run (and how much is in the wall etc) you may well find that the cable is adequate anyway. There is a safety margin built into the guide. The cable run length may affect the power disipation due to any voltage drop if it's a long run.


I'd agree that this is a borderline case, however Gooner has neither installed the cable nor shower. I'm sure he would have selected a 6mm cable if he had.

well said , im off to see the wizard for a brain arghh i cant get away from it even on here lol were doing wizard of oz in the am drams group in in starting tomorrow lol

 

[RWJ]

The problem will be when the shower dies and someone goes to a shed and buys a new 10.5Kw and sticks that in on the 4mm cable.
OK not really your problem as your changing the CU, just make sure you've got the correct MCB. I'd be inclined to NOT put in a 40a spare if the board came with one.. Just in case!! Maybe someone wouldn't?

 

[Geoffsd]

We know this may be alright in the real world but this is for an assessment.

It has been stated that the cable is installed in conduit and for such the rating is 30A.
As it is a CU change I would assume - I may be wrong - that it was on 3036 30A fuse - 30A rating, 30A fuse.

It will now be on 32A mcb and so no longer complies - 30A rating, 32A cpd.
As you know this is actually better protected but the numbers don't match.

I'm not arguing with or disputing what anyone has said, merely stating that it will not be acceptable for the assessor and gooner will be left saying "Well, yes I knew that but..."

This is exactly the sort of thing he will be looking for. If I am wrong then what is the point of the BRB.

 

[gooner1984]

thanks all for your post, its border line, so im going to take it out that way if she wants it il run say 6mm or 10mm, just wanted to hear what you guys say, and you all have good points, it was said the shower might stop working and someone puts a new 10,5kw so best to take it out, and replace,

 

[nickblake]

If it was a 3036 fuse then it would be to small a 4mm sorry i hadnt realised it was but 3036 fuses have a correction factor of .725 so if you take that into the equation the yes it was too small because the breaking capacity for the fuse would be around 40 amps , sorry for the confusion here as i assumed it was a 60898 breaker , having said that if it is in conduit then the current rating does drop to 30 amps as liad out in the burb , now if you are going to change the cable then put a 10mm cable in or we may well be having the same conversation if you upgrade the shower to a 10.8 kw lol

 

[Geoffsd]

It was only me assuming it was 3036 before because the board has been changed. If it was it was wrong then. 3036s have a fusing factor of 2 therefore it would be 60A.
It is 60898 now.

This is just confusing matters as the only thing wrong with the circuit (now) is that it is in conduit - reducing the ccc to 30A.

 

[gooner1984]

its on a bs 60898 cb and its partly in conduit, when you work it out its ok,(i think) just getting confused, but 4mm just wrong so im going to change it if she wants,

 

[Geoffsd]

That's the best way.

Tell the assessor that you had to replace the cable for all the above reasons even though it was only just too small because of the conduit. Show him you understand and know what you're talking about.

Remember, the top priority for him looking at your work is safety, safety, safety.

Again, good luck.

 

[needasparks]

As the 4mm T&E has a 1.5 cpc does that comply to thermal constraints (S)