DIYIdoits's shower cable question.

[JohnW2]

Winston made a statement without mentioning / considering the method of installation. Maybe the cable is clipped direct to a wall and doesn't have any section of it laying horizontally across a ceiling ....

I think it does lay horizontally across ceilings, but that is still 'Method C' (aka 'clipped direct').

... in which case 4 mm² might be OK But dropping almost 5 volts at 37 amps is 180 watts about 2 % of the power measured by the meter and thus paid for is being wasted in heating the cable..

No-one has suggested 4mm² cable - the OP already has 6mm², and that is almost certainly quite adequate.

Are you seriously suggesting that anyone would go to the tremendous hassle of wiring an 8.5kW shower with 16mm² cable, just to avoid a small amount of energy loss in a cable for a few minutes per day?

Kind Regards, John

 

[EFLImpudence]

The 230/240 is irrelevant for your questions.

 

[JohnW2]

In the CU there is the main red switch followed by one RCD 80A/30mA/240v with 3 MCB's 32/240, 16/240 and 6/240. Then there is a 2nd RCD 80A/100mA/230v with 2MCB's 40/240 (unused and off) and 32/240 (shower). Should the 240 MCB's be with the 230v RDC?

No, the 230v vs. 240V is essentially arbitrary labelling. There is no difference.

Kind Regards, John

 

[bernardgreen]

The voltage rating on the RCDs and the MCBs is the nominal voltage they are designed to cope with and has little relevance to how they operate. Nominal UK supply is 230 volt but can be 10% higher ( 253 volts ) or 6 % lower ( 216 volts )

 

[bernardgreen]

Are you seriously suggesting that anyone would go to the tremendous hassle of wiring an 8.5kW shower with 16mm² cable, just to avoid a small amount of energy loss in a cable for a few minutes per day?

Are we not being badgered into using low energy lighting to reduce the waste of electricity in heating up the area around the lamp. ?

 

[JohnW2]

Are you seriously suggesting that anyone would go to the tremendous hassle of wiring an 8.5kW shower with 16mm² cable, just to avoid a small amount of energy loss in a cable for a few minutes per day?

Are we not being badgered into using low energy lighting to reduce the waste of electricity in heating up the area around the lamp. ?

That's not really the reason for encouraging the use of low-energy lighting and, in any event (a) much of the 'lost energy' is not wasted in winter, and (b) I doubt that there would be much 'badgering' if lights were only used for 10 minutes per day.

I've only rarely wired with 16mm² T&E, but it's not an experience I would particularly want to repeat any time soon - and some would probably have something to say about the use of 3 or 4 times more copper than was actually 'necessary'!

Kind Regards, John

 

[DIYIdoit]

Thanks for the voltage clarification, but I'm still confused about the cable.

8.5kw Shower-6mm cable-18"plastic conduit-through ceiling-5 metre loft (assume buried in insulation as I can't easily get to it)-through ceiling-2 metre plastic conduit-through floor-1 metre plastic conduit-through wall-CU-80A/100mA RCD-32A MCB.

The MCB trips when shower is on high.
Can I change the 32A MCB to a 40A MCB (which is unused on the same RCD) keeping the 6mm cable?
If yes, can the MCB's be pulled out and swapped or do the need to be wired?

Please forgive the laymans terms.

 

[JohnW2]

Thanks for the voltage clarification, but I'm still confused about the cable. ... 8.5kw Shower-6mm cable-18"plastic conduit-through ceiling-5 metre loft (assume buried in insulation as I can't easily get to it)-through ceiling-2 metre plastic conduit-through floor-1 metre plastic conduit-through wall-CU-80A/100mA RCD-32A MCB.

The goalposts seem to be moving quite a bit! IF some of it were 'buried in insulation', then 6mm² cable would not be adequate. The sections in conduit might also render 6mm² inadequate - what sort of conduit is it, and is it buried in a wall (if so, what type of wall), on the surface of a wall or what?

Kind Regards, John

 

[EFLImpudence]

What has happened to the thread?
My posts seem to have been split into a new thread.
Edit - all correct again. ???



Anyway, the 32A MCB should not trip with a 8.5kW shower drawing a nominal 34A.

In view of the unknown characteristics of the cable routing, I would replace the 32A MCB with a new 32A one.
Not ideal but at least it will remain 'safe.

 

[GaryGarden]

Thanks for the voltage clarification, but I'm still confused about the cable.

8.5kw Shower-6mm cable-18"plastic conduit-through ceiling-5 metre loft (assume buried in insulation as I can't easily get to it)-through ceiling-2 metre plastic conduit-through floor-1 metre plastic conduit-through wall-CU-80A/100mA RCD-32A MCB.

That 100ma RCD needs swopping for a 30ma RCD like the other that you have.

 

[JohnW2]

Anyway, the 32A MCB should not trip with a 8.5kW shower drawing a nominal 34A. ... In view of the unknown characteristics of the cable routing, I would replace the 32A MCB with a new 32A one. Not ideal but at least it will remain 'safe.

What initially appeared to be a simple questioin has got more complicated. The problem with what you say above is that there is now a suggestion that some of the 6mm² cable may be 'buried in insulation', in which case protecting it with a 32A MCB might not be 'safe' (and any MCB <32A would obviously be inadequate for the shower).

I think that the OP really needs to ascertain with some degree of certainty exactly how this cable is routed/installed before any of us can give any proper advice.

Kind Regards, John

 

[DIYIdoit]

Yes my fuddled explanation of the situation hasn't helped John, I'll check it out properly. However, it has been this way for 10 years and the only issue I've had is the tripping out MCB. I did change the shower a few years ago but as far as I remember it was like for like. I changed it due to blackening of the area around the cables inside the shower itself...

...err maybe I've just answered my own question! God I can be thick sometimes.

 

[DIYIdoit]

Thanks for the voltage clarification, but I'm still confused about the cable.

8.5kw Shower-6mm cable-18"plastic conduit-through ceiling-5 metre loft (assume buried in insulation as I can't easily get to it)-through ceiling-2 metre plastic conduit-through floor-1 metre plastic conduit-through wall-CU-80A/100mA RCD-32A MCB.

That 100ma RCD needs swopping for a 30ma RCD like the other that you have.

Thanks Gary, is this absolutely necessary?

 

[JohnW2]

Yes my fuddled explanation of the situation hasn't helped John, I'll check it out properly. However, it has been this way for 10 years and the only issue I've had is the tripping out MCB. I did change the shower a few years ago but as far as I remember it was like for like. I changed it due to blackening of the area around the cables inside the shower itself... ...err maybe I've just answered my own question! God I can be thick sometimes.

I don't think so. If it transpires that some of the cable is 'buried in insulation', any overheating of the cable would happen there (within the insulation), not elsewhere - although I doubt that any great harm would come to the cable given the brief duration of normal use of a shower.

However, if you did find that some of the 6mm² cable is buried in thermal insulation, something ought to be done about that. Since replacing the whole cable with a larger one would presumably be a pain, the simplest solution, if practicable, would be to 'get it out of the insulation'.

Kind Regards, John

 

[GaryGarden]

Thanks for the voltage clarification, but I'm still confused about the cable.

8.5kw Shower-6mm cable-18"plastic conduit-through ceiling-5 metre loft (assume buried in insulation as I can't easily get to it)-through ceiling-2 metre plastic conduit-through floor-1 metre plastic conduit-through wall-CU-80A/100mA RCD-32A MCB.

That 100ma RCD needs swopping for a 30ma RCD like the other that you have.

Thanks Gary, is this absolutely necessary?

Only if you are creating a new circuit, this thread was so mixed up earlier that was the the impression I got of your intention, but now reviewing the thread in a more complete aspect that I understand is not what you are doing. If any new socket or bathroom circuits were to be connected to the RCD on this side of the board then it would need changing to 30ma.