Workshop RCD, Radial circuit

[brunoo]

My first post here so a big Hi to everyone!

I am planning on adding a 32A+6A RCD into my workshop. I use very high powered tools in excess of 4-5KW for a few hours at a time.

Now, My old shower still has cable intact and is quite close to my workshop, The shower is no longer used.

The shower is on a 40A RCD in the main CU with 6MM T&E direct to the shower, I will be disconnecting this and using a 2-way 100A junction box, Then continuing with 6mm T&E to the workshop RCD unit.

The total cable length from main CU to workshop RCD is about 25 meters, Then from workshop RCD to first socket in workshop is about 8 meters, Then another socket 2 meters away, Total length from CU is about 35M.

I will run the cable in some trunking, For about 10 meters length, Will this de-rate the cable a lot? the conduit will be about 25x15mm.

Can anyone spot any possible issues?

 

[Iggifer]

by 2 way 100a junction box I assume you mean a Henley Block?

If so these are not intended for extending twin and earth cable, you can use something like this
http://www.tlc-direct.co.uk/Products/AAJB60.html
but it must remain accessible.

Adding a consumer unit is notifiable btw

 

[Taylortwocities]

Please detail the route that the cable will take from the house to the workshop.

Will it be buried, draped along a fence, hung from catenary wire or what?

 

[riveralt]

Is the workshop separate from your house and its CU?

 

[JohnW2]

Adding a consumer unit is notifiable btw

In Wales, it still is, but in England the only related thing which remains notifiable is replacing a CU. If the proposed work constituted installation of 'a new circuit', then it would obviously still be notifiable, even in England, but it sounds as if what the OP is proposing is extending an existing circuit (that originally used for a shower). These are obviously rather contentious issues, on which views will probably differ (quite possibly strongly) but I don't think it's a foregone conclusion that what the OP is proposing would be notifiable (in England).

Kind Regards, John

 

[Iggifer]

but then, by definition, the new cu becomes a submain and any cables connected to that, are new circuits and are definitely notifiable.

However, I see where you're coming from and I don't want to start the notification argument again, which I have managed to avoid thus far

 

[brunoo]

by 2 way 100a junction box I assume you mean a Henley Block?

If so these are not intended for extending twin and earth cable, you can use something like this
http://www.tlc-direct.co.uk/Products/AAJB60.html
but it must remain accessible.

Adding a consumer unit is notifiable btw

Thanks.

Please detail the route that the cable will take from the house to the workshop.

Will it be buried, draped along a fence, hung from catenary wire or what?

Sorry I think I explained myself quite badly in the OP.

The workshop is just a room within the house but because a lot of the house is on 1 32a 2.5mm ring-main, 3 floors inc kitchen (ex cooker),

I feel the loads are near exceeding 32A when I'm in the workshop and my wife boils the kettle or other in the kitchen, No trips yet but better safe than sorry as I'm buying more tools shortly.

The disused shower cable is below the floorboards, Next door to the workshop, Just an interior (brick wall) separating the rooms, So I plan to bring the 6MM T&E cable from the shower up through the floor, then inside 25x25mm trunking up the wall to the Garage RCD http://www.screwfix.com/p/bg-garage-kit-enclosure-5-module-ip55-40a-rcd-dual-6a-32a-mcb/68849

From the garage RCD unit, Through the interior wall to the workshop sockets, On a radial circuit, 2 double MK sockets a couple meters apart.

The shower has its own 40A RCD in the main CU, With 6MM t&E going up 1 floor ( in 50x50mm conduit) about 20m in length and then under floor to shower about 5m in length, Then onto garage RCD -> workshop sockets.

 

[JohnW2]

but then, by definition, the new cu becomes a submain and any cables connected to that, are new circuits and are definitely notifiable.

Like you, I don't want to repeat the whole of the 'notification debate', but I don't think it's as straightforward or as 'definite' as you suggest. Your argument is presumably that the feed to the new CU is a 'submain', and the 'final circuits' eminating from that new CU are 'new circuits', because of the existence of OPD(s) in the CU. However, what if, for example, the existing shower circuit were extended to the garage, where it fed two or more FCUs which supplied lighting and sockets? That is functionally effectively the same as having a mini CU, but if you believe that approach (with FCUs) would be notifiable, then the same argument would apply to, say, fused spurs from existing ring finals - which were explicitly non-notifiable even before the April 'relaxations'.

As I said, it's not straightforward!

Kind Regards, John

 

[ban-all-sheds]

What is straightforward is that the OP should be asking how and where he can learn so that he can answer his own questions (and the ones he's not yet realised he needs to ask himself), not try to palm off his responsibilities as designer to people on an internet forum.

BTW - re the replacing/providing a CU Q, I've been corresponding with people @communities.gsi.gov.uk on the topic - I'll report back when (if ) we reach a conclusion....

 

[JohnW2]

BTW - re the replacing/providing a CU Q, I've been corresponding with people @communities.gsi.gov.uk on the topic - I'll report back when (if ) we reach a conclusion....

I'll be interested to hear about that 'conclusion' - but, as you are always saying, the words of the law are extremely clear, so I don't think there is really any room for debate. I would say that the more relevant (and important) discussion is about the definition of a 'new circuit' (and preferably a definition which doesn't make fused spurs notifiable!).

In terms of these garage/shed issues, even if it were 'decided' that fitting a new CU was notifiable, it would usually be possible to get around that with a collection of FCUs, RCDs and even switch-fuses - but the issue about possible 'new circuits' would remain.

Kind Regards, John

 

[securespark]

IIRC, 6 milli in trunking is 38A.

 

[ericmark]

Reading I am looking at around 35 meters of 6mm cable at 7.3 mV/A/m at 5kW or 22A so around a 5.6 volt drop so that seems OK.

However I would want to use a loop impedance meter as rather hard to measure cable around a house. Although 11.5 volt is allowed should there be any hidden faults the loop impedance will likely highlight them.

Where I find it hard is the use of BS EN 60309-2 sockets in a domestic premises 553.1.4 would seem to say they should not be used. I would want the type with a linked isolator so power can only be turned on once the plug is in the socket.

When the 32 amp RCD is referred to I would hope there is also some automatic over current device as well. The amp rating on a RCD refers to what it can handle not what current it will trip at. With a RCBO (RCD and MCB combined) it will be marked with B32, C32, or D32 which shows the magnetic and thermal ratings of the trip. With the B32 you may find large equipment will trip it but before selecting B, C, or D you need the loop impedance readings.

Since Part P does not define a circuit the same way as BS7671 it is hard to work out if it requires notifying.

 

[ban-all-sheds]

I would say that the more relevant (and important) discussion is about the definition of a 'new circuit' (and preferably a definition which doesn't make fused spurs notifiable!).

We've got that far, and their view is that a circuit is as defined in BS 7671.

Nothing back from them since I pointed out that that would make installing an FCU notifiable.

 

[JohnW2]

I would say that the more relevant (and important) discussion is about the definition of a 'new circuit' (and preferably a definition which doesn't make fused spurs notifiable!).

We've got that far, and their view is that a circuit is as defined in BS 7671. Nothing back from them since I pointed out that that would make installing an FCU notifiable.

That's obviously the problem. If one sticks precisely to the BS7671 definition of a circuit, then I don't think there's any escaping the fact that anything 'new' downstream of an FCU would be a 'new circuit', and hence notifiable. I don't think that (m)any of us believe that was 'intended' - let's face it, even prior to the 'relaxations' in April, extending circuits with fused spurs was explicitly non-notifiable.

Kind Regards, John

 

[ericmark]

If a circuit is defined as a "Final circuit" (A circuit connected directly to current - using equipment, or to a socket-outlet or socket-outlets or other outlet points for the connection of such equipment.) then how can it feed any other circuit?

It is like saying very end. Clearly very is not required as end is the end. Final is in the same way the last circuit you can't have the very final circuit in same way as can't have very end or very last.

So with an old shower supply if it feeds a socket and a consumer unit then it's not forming a new circuit because it is by definition a final circuit but if it feeds just the consumer unit then it not a final circuit so all circuits from consumer unit are new circuits.

Yes I know it's daft and no one is going to pay the LABC if by including a socket you can get around it even if you later remove the socket. Or at least say that's what you did. In fact since it once "connected directly to current - using equipment" it has already been defined as a "final circuit" so to take any one to task would really be hard any lawyer worth his salt would argue it complied and so no LABC would be likely to push the point for fear of losing and setting a president.