Nicely put mate. Could be 6mm cable, would 6mm cable be enough for 8.5kw?
I love simple jobs, I will be getting my sparkie mate to come over like but would like to know what he would be up against
Electric shower and RCD
- Thread starter newbuildinstaller
- Start date
Nicely put mate. Could be 6mm cable, would 6mm cable be enough for 8.5kw?
I love simple jobs, I will be getting my sparkie mate to come over like but would like to know what he would be up against
No I was interested in your interpretation of (iv)You missed 314.1 (i)
Also 314.2 if you like.
But as you have already pointed out/hinted that the installation is not to current standards but that does not deem it unsafe, just maybe inconvenient at times, providing the lights don't go out at a critical moment, but that could happen even if you had dual or multiple RCD protection.
If it is 6.0mm² then depending on installation methods, such as the length of run, and none of the cable is in thermal insulation, plus a few other bits, then normally yes, you can use 6.0mm² for a 40A circuit.
Having said that it's not unknown for 4.0mm² to bue used on old shower circuits, which can't handle 40A. It needs a sparks on site to give you a definate yay or nay.
That would depend on other factors, such as cable routes and method of installation.
route is 3m to pull switch then 3m to shower
Yes - Mira Showers on 8.5kw require min of 6mm ² and a 40Amp MCB.
6m of cable clipped direct will not affect the rating - might be an issue if it goes through any insulation though.
No I was interested in your interpretation of (iv)You missed 314.1 (i)
Also 314.2 if you like.
But as you have already pointed out/hinted that the installation is not to current standards but that does not deem it unsafe, just maybe inconvenient at times, providing the lights don't go out at a critical moment, but that could happen even if you had dual or multiple RCD protection.
(iv) is not really a huge issue, but I have seen problems with home offices and RCDs. With an installation like this, I'd personally leave it be unless the RCD started to nusiance trip, or 'major' electrical work is carried out.
6.0mm T&E can carry a maximum of 47A, your shower at 8500w would require no more than 37A.
But cable routing, method of installation and voltage drop can derate the cables current carrying capacity. So things such as thermal insulation within walls and ceilings where cable is run, routing within containment such as conduit and trunking will decrease the rating of the cable.
But cable routing, method of installation and voltage drop can derate the cables current carrying capacity. So things such as thermal insulation within walls and ceilings where cable is run, routing within containment such as conduit and trunking will decrease the rating of the cable.
In this case would you not be more concerned that the rating of the RCCB is 63A.
Not really. I'm sure it'll be fine after diversity. Most domestic cutouts round my way are 60A, with plenty of 30A cutouts around, and it's very rare indeed to hear of one operating due to overload.
I have no doubt it will be fine, but simple diversity calcs could already put the system above 90A load plus the extra load of new shower and there is a possibility that the spare could be used to increase load.
So I would personally think that that would be more an issue, than single RCD covering all circuits.
So I would personally think that that would be more an issue, than single RCD covering all circuits.
I'm tempted to suggest that 'prohibited' is perhaps a bit strong - 314.1 is written in very general terms/
What about a TT installation like mine which has an up-front RCD to protect the long distribution circuit? Would you say that was non-compliant with 314.1, even though 411.3.2.4 effectively requires the RCD to be present. [admittedly, since I have 3 phases, each with its's own up-front RCD, that could be argued to comply with 314.1. However, if I had a single-phase supply with a long distribution circuit, that would not be the case]. If you did an EICR, would you code the presence of this RCD as being in violation of 314.1?
Kind Regards, John
Not allowed, prohibited, non compliant, take your pick.
I'm assuming you have a time delayed up front RCD probably 100mA too, and then more than one 30mA RCD at the final CU. So that discrimination would mean that only a fault on the submains would take out the upfront RCD, and a final circuit fault would take out the local RCD. That seems ok to me.
In the OPs installation, I would give it code 3, and in your installation, assuming the criterea I mention are met then no issue, so no code.
Indeed, that is the situation - and it seems OK to me (since I can't really see any alternative), too, in common sense terms. However, given that some people seem to be thinking about strict compliance with 314.1, that regulation talks about a requirement for division into circuits "to avoid danger and minimise inconvenience in the event of A fault", without making any exception of a fault in the distribution circuit.
Again, very sensible (and I who hope/expect you to be sensible and exercise that discretion) - but, in view of what I say above, do you believe that my installation is strictly compliant with the word of 314.1? A fault (albeit only if it were in one particular location) could take out the whole submain.
In passing, in addition to having 'one or more 30mA RCDs at the final CUs', I confess that in two or three cases I have final circuits in those CUs protected only by a SP RCBO. Since a N-E fault on one of those circuits would take out the up-front Type S 100mA RCD, would you code that as non-compliant (with 314.1)?
Kind Regards, John
It's no different to any other installation, which is supplied via a submains, or to go to the extremes, every single phase installation which has a cutout fuse a single point of failure.
The difference between these situations and that of the OP, is that an earth fault on any circuit will also render every other circuit inoperable.
In your case, discrimination will allow at least some of the installation to remain operable. The only time the upfront device will (should) operate is if there is a fault with the actual submain, in which case it has to be disconnected, but the amount of wiring is limited, and the likelyhood of faults is much less than the combination of all your final circuit wiring.
You have taken steps to minimise (not eliminte!) inconvenience in the event of a fault.
Yes I would! As mentioned above, a fault on one circuit would render the entire installation inoperable, due to inproper design. This could be remidied bt the use of the correct RCBOs, so inconvienience in the event of a fault has not been minimised.
I would code 3 this as it's more of a recommendation, and doesn't effect electrical safety.
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