Hi all, first post here. I own around 25 properties and normally do the maintenance myself and also the work for new developments I buy. I'm registered so I can notify myself when I do the refurbs etc. My latest project is converting a large terraced house into 7 bedsit rooms with ensuite shower rooms and communal kitchen and living. The set up im looking at is a three phase supply to the property, one main meter for the property. Each bedsit will have it owns supply consisting of a prepayment card meter, distribution board (RCD, 40A for shower, 20A for small socket radial and electric heater, 6A for lighting). It was suggestedto me that from the three phase board to each of the rooms DB's the supply cable would need to be armoured (to prevent persons from putting nails in the walls and therefore the supply cables) however they are tenants of their rooms and so not allowed to do anything like that (although I'm not there permenantly to keep an eye on this so accept it's a possibility). I was considering if I put in a 3 pole RCD at the three phase board, this would make all the supply cables RCD protected and therefore would I still need to make the supply cables to the rooms armoured. I could then use normal cable to feed the individual rooms DB's and therefore save a huge amount on cable cost. Is anyone able to help me if this is permitted or not or able to make a better suggestion instead of having 7 lots of armoured to run around the property. Thank you
It is a very poor idea to put a triple pole RCD at the front end. It is not only doubling up on RCDs, if there are any faults in any one of the flats it would potentially knock out the entire supply and you wouldn't enjoy calling out to angry tenants regularly. If I were you I would plan the routes of the supply to each flat very carefully and see if you can provide a dedicated duct and riser to distribute the supply to each flat. As you are converting the house it shouldn't be too difficult to do. I don't know who suggested that armoured cables are required to prevent nails being knocked through, its 50mm depth rule that is relevant. If you can keep the cables more than 50mm from the surface of the wall (ie in a purpose made duct and riser), there is no need for mechanical protection of the cable. Will you be having a communal meter cupboard? I don't see the point in having a main meter and sub-meters. Just create one room where the electricity supply comes in, divide it in to each meter for each flat then run tails from them to cu's in each flat.
Thanks for your reply. The idea was to still have rcds on the rooms DBs. That way a fault in the room would cut the supply to the room. Then a time delay 3 pole rcd on the three phase board. So only a fault on the supply cables to the rooms would cause the whole building to go, very unlikely. The idea of armoured was because of the requirement for mechanical protection as a dedicated ducting is going to be very troublesome to install. The building conversion as it stands is very easy to do with no major structure changes. I thought by installing an rcd at the three phase board it would negate the need for armoured and could just run the supply cables. (Forgive my lack of correct lingo, supply cables/ tails) There is no room for a communal meter cupboard, as it stands the supply will come in the room under the stairs. Hence having the prepaid card meters in the rooms. (Main meter paid for by me, prepaid card meters topped up by buying cards from me, the idea being everything is run on the electric which they prepay for). If I install a meter cupboard for all the prepaid meters do I need an isolator switch after every meter in the cupboard before it leaves to run to the rooms?
I definately agree with unphased regarding the RCD being a nuisance when a fault on any of your Distribution Circuits causes it to trip. Lots of upset people! Not so bad with one tenant/occupier, but much worse when there are multiple, especially if access to the RCD might also be an issue? An aside comment on the prepaid meters, you might also cause problems there too, as many tenants will want to know how the bills are derived. Many of my customers use standard meters out of reach of the tenants (or at least installed to avoid tampering!), and then when the bill comes in, their bill will be that ratio of their consumption of the total (on the main meter).
If it was me I would use armoured. Tbh I think your making a rod for your own back trying to build/route conduit/ducking to run t+e cable < 50mm from the surface. I think it a false economy.
SWA is certainly quicker to install, and ticks the boxes for requirements (again making assumptions here and not knowing your job inside out) And the isolation question - obviously you need to ensure that safe isolation is possible, but if also have a practical requirement to be able to isolate individual circuits (which I guess you will if a problem develops on any one of them), then it would make sense to fit individual isolators.
Yes mate I agree, also if you use twin your gonna have all sorts of problems terminating etc at either end, much easier to use a gland + swa.
Hi all, thanks for all your replies. The reason behind installing an RCD over SWA was for ease of installation. I've only installed it once before and seemed like it would take me a lot longer. Having said that once the cable is run it would only be 14 connections. The only other option I suppose is metal conduit. But that seems like even more work to install. With regards to the meters. Basically everything in their room is run off the electric, so they pay for whatever they use. Water is included in the rent for the room. They will have prepaid meters so there is no problem with not paying or being wasteful with the electricity. Also it saves having 7 different meters installed by EDF and them having to arrange bills in their name (done it once before in another building and the tenants seemed to prefer it as they only had to move in, no hassle with utilities etc). They pay for the exact cost of the electricity so no issues there. THen we pay the full bill which also would include the communal areas. Once again thanks for all your input
In regard to the flat supplies your not really going to be able to put the supplies on an RCD, If you do it will need to be a 30mA RCD so you will have no discrimination between the flat supply RCD and the Rcd's in the flat. You cant really have one RCD for each flat at the source as you cant expect the tenants to go down to the mains cupboard to reset the supply, you would also need to let tenants have access to the mains which could cause problems. You really have 3 options. 1, Install the cables at a depth greater then 50mm which can be hard to achieve 2, Install standard PVC cable on the surface in Trunking / clipped / Ducts 3, Install SWA - But then trying to install 10 or 16mm SWA chased into the wall is not going to be easy. My choice would be to install PVC cables surface / in Trunking. You would also need some sort of switch fuse to supply each flat at the mains position.
Dunno really, no difference I guess. Just would use swa and glands myself, just a lot easier from my pov.
Caddy, The plan was to have a DB in each bedsit room. On that would be a main switch, an rcd, and then a 40, 20, and 6a mcb. So the tenant would have access to his own DB and therefore could reset the rcd himself if need be. Then in the main meter cupboard would be a 3 pole rcd, this would cover the cabling running to each bedsit (basically in the communal area), negating the need for mechanical protection. In the highly unlikely event that main rcd has tripped then yes they would need access to the rcd but I'm thinking this is likely to be so unlikely it wouldn't be a problem. Am I right in thinking that fitting a time delay 3 pole rcd to the main supply would mean that if the rcd tripped in a bedsit room, due to the time delay it wouldn't trip the 3 pole main rcd at the three phase board as the supply would be cut prior to this activating, thus allowing the electricity to remain on in the other bedsits (where there is no fault), or have I misunderstood this? Think it might be easiest to install PVC cables in trunking, but it won't look pretty.
Mate if you conceal cables >50mm from the surface you need a 30ma rcd protection, ie NOT time delayed. So this design will not work as what your proposing is not allowed. And no you can't have two 30ma rcd's in series. Your only options are either to run the cables in such a way as they are <50mm from any surface (very hard to do imo) or surface mounted (also quite hard given your situration imo) OR, best of all, use swa.
JB5, why are you trying to avoid use of SWA? It is sometimes much more difficult to find other ways than to use the obvious? Just asking, not a criticism.
Also a couple of other points - if you use swa you could (potentially) use the steel as an cpc which will probably also give you a better Zs for a 5s second disconetion time (than twin) (to save a few $$$) on whatever fuse you use at the start of the run. Also what's troubling me is that you say you are registered yet you are posting up ideas and designs which would suggest you don't really have the knowledge to tackle problems like this. I'm not having a go, I just think it would be better for you if you where a honest with us
One other point, you obviously still need to run the SWA (if you go that route) in allowed zones and not willy nilly up communal hall walls. and to be honest Twin in surface trunking in corners would be a while lot easier.
It's good to hear you can notify yourself when doing refurbs etc.......... I'm often the last to know when I've started a job.
I'd go twin in trunking, no rcd on the main DB (CU), rcd in each flats CU and yes i'd put an isolator switch on every flats CU between meter and CU.
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