DIYIdoits's shower cable question.

[DIYIdoit]

Sorry to hijack the thread, we have an 8.5kw shower using 32A/240v at the MCB via 6mm cable. We had an electrician look into this as the RCD kept tripping when we used it on high (2 red dots) although it's fine on low (1 red dot). The electrician said the 32A was the problem and we needed a 40A but he couldn't fit one because of the 6mm cable, he said we needed 10mm.
What I'm getting from this thread is it's OK to put a 40A on to 6mm?
We have a spare 40A/240v in the MCB, I think it's the old cooker one, is it OK to just swap them over after switching the big red switch off?

 

[winston1]

Sorry to hijack the thread, we have an 8.5kw shower using 32A/240v at the MCB via 6mm cable. We had an electrician look into this as the RCD kept tripping when we used it on high (2 red dots) although it's fine on low (1 red dot). The electrician said the 32A was the problem and we needed a 40A but he couldn't fit one because of the 6mm cable, he said we needed 10mm.
What I'm getting from this thread is it's OK to put a 40A on to 6mm?
We have a spare 40A/240v in the MCB, I think it's the old cooker one, is it OK to just swap them over after switching the big red switch off?

Yes 6mm cable is OK on 40A, and yes you can swap them over.

 

[EFLImpudence]

The RCD tripping is nothing to do with the MCB being 32A.

 

[winston1]

The RCD tripping is nothing to do with the MCB being 32A.

True, bit I think he is confusing MCB and RCD.

 

[DIYIdoit]

Yes, sorry the RCD is 32A.

Thanks Winston, so why would he say I need a 10mm? What would I need 10mm for?

 

[EFLImpudence]

Yes, sorry the RCD is 32A.

It is a Miniature Circuit Breaker - MCB.


Is the cable in conduit or thermal insulation anywhere?

 

[winston1]

Yes, sorry the RCD is 32A.

Thanks Winston, so why would he say I need a 10mm? What would I need 10mm for?

Probably because he doesn't know what he is talking about, or maybe he wants to make some money doing unnecessary work.

 

[bernardgreen]

Probably because he doesn't know what he is talking about, or maybe he wants to make some money doing unnecessary work.

Do you ?

You can go to the site and change the values if you want to at https://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html

 

[JohnD]

where did the insulated stud wall and the 8.5kW at 230v come from?

The route the cable takes, whether it is buried, exposed or clipped makes all the difference.

 

[JohnW2]

Probably because he doesn't know what he is talking about, or maybe he wants to make some money doing unnecessary work.

Do you ? ... <TLC cable calculator screenshot

For some reason, you have selected the worst conceivable installation method ('buried in thermal insulation'), whereas the OP has indicated an installation method which sounds like Method C ('clipped direct'). If one feeds that into the TLC calculator, one gets a much more sensible answer (and that's assuming that it really is 8.5kW at 230V, which I doubt)! ...

Kind Regards, John

 

[OwainDIYer]

We have a spare 40A/240v in the MCB, I think it's the old cooker one, is it OK to just swap them over after switching the big red switch off?

If you are swapping the cable over, you will need to move both live and neutrals if the two MCBs are on different RCDs.

Even with the big red switch off the incoming terminals to the main switch are still live.

 

[JohnW2]

We have a spare 40A/240v in the MCB, I think it's the old cooker one, is it OK to just swap them over after switching the big red switch off?

If you are swapping the cable over, you will need to move both live and neutrals if the two MCBs are on different RCDs.

Indeed - and, before someone else says it, I would add, being pretty pedantic, that some/many would probably say that to do as the OP has suggested would result in the creation of a 'new circuit', which would thus become 'notifiable' work!

Kind Regards, John

 

[DIYIdoit]

OK, let me clarify as much as I can. I thought MCB was referring to the consumer unit (master consumer board).
So, in my consumer unit (where the fuses used to be) I have trip switches I'm assuming these are RCDs?
The shower is connected to the consumer unit to a 32A trip switch via 6mm cable and yes it does go through some conduit. It goes from the shower to the bathroom ceiling via about 18" of plastic conduit. It then goes the length of the house in the loft with no conduit. It then goes from top to bottom of the bedroom through plastic conduit, then through the floor/hall ceiling, then another couple of feet through plastic conduit, then through the wall into the meter cupboard and into a 32A trip switch in the consumer unit.

Is it OK the change the 32A trip switch for a 40A one.

 

[bernardgreen]

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 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..

 

[DIYIdoit]

Ah, now hang on, more info, I'm learning the terminology which will probably help a bit!

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?