TonyE Posted February 6 Share Posted February 6 Hi everyone, I’m doing a self build and I’m planning/prepping to install the main feed for the house. When we got to site I had a new connection from SSE and this was taken from the pole into a temporary box which houses a mini CU, meter and 100 Amp fuse etc. I then use this supply to power my site/caravan. when SSE installed the connection the chap advised that when we build the house that we could then just run an SWA from this temporary box straight into our new house and its proper CU. This was explained as being much cheaper than getting them to come back out to move the meter and install a new electric cable/feed directly from pole to the house. So I have 2 options, as per my picture below…. It’s a long run from the temp box and both options require a fair trench digging (trench: 450mm deep, 110mm twin wall conduit, bedded on sand and with marker tape). Taking into account the voltage drop and wanting to get the max out of the Single Phase supply (I have GSHP etc) I see a 100 amp fuse in the temp box; the SWA calcs say either a 35MM SWA for one option (shorter run) or a 50MM SWA for the other option…. Can anyone offer advice on this intended setup, the size of SWA and also the amount of cores required? I think I need 5 core so I can re-use the earthing rod that’s already installed… but am I right? Or is it better with 4 cores and then I need a new earthing around the house? Advice appreciated! Link to comment Share on other sites More sharing options...
ProDave Posted February 6 Share Posted February 6 I would not put a 100A fuse in your switch fuse as you have no discrimination from the DNO's 100A fuse. I have mine fused at 80A and have never had any problem with lack of power. If you re run the calcs at 80A you might get better cable size options. You mention 5 core so you are talking 3 phase neutral and earth, so no way will you ever require anything like 100A per phase if you have a 3 phase supply. Link to comment Share on other sites More sharing options...
TonyE Posted February 6 Author Share Posted February 6 Thanks for the advice. 80 AMP switch fuse, I assume that will be installed inside the temp box? I’ll re-run the SWA calcs based on this load. Regards the cores of the SWA, I have a single phase supply…. From your reply, as it’s not 3 phase, you say I don’t need 5 core. But what amount of cores is required. Thanks Link to comment Share on other sites More sharing options...
TonyE Posted February 6 Author Share Posted February 6 I’ve also recalculated the SWA using 80AMP and it still requires either 50MM for the longer run and 35MM for the shorter run…… ho-hum. On similar posts on this forum, I see that using 50MM inside the CU can be very tight…. IMHO I’d like to route the cable on the 65m run (alongside a road) instead of having to go off-road (steep-incline) with the shorter run. So in summary I think the advice is: 80Amp Fuse Switch, 50MM SWA, 3 core? Link to comment Share on other sites More sharing options...
FarmerN Posted February 6 Share Posted February 6 I've just had connection in a temrorary box moved into the house by SPNetworks. They cut the temporary supply cable put an underground joint in and ran it to house, so the box is now completly redundant. I am no electrician and my school boy electrics is now clearly redundant. The cable used is single core + the armoured sleve, so two stands only !! I have no idea how that works. We have a large all electric range cooker, 3 to12 Kw GSHP, ( seems to use under 1 Kw when running) MVHR and a car charger is a condition of my planning. I wait to see what happens when we finally live there. The bit that will make it really interesting is SPNetworks keep telling me I have a 25 KV transformer, even though the plate on it says 15 KV. ! It also supplies one other house Link to comment Share on other sites More sharing options...
ProDave Posted February 6 Share Posted February 6 46 minutes ago, TonyE said: Regards the cores of the SWA, I have a single phase supply…. From your reply, as it’s not 3 phase, you say I don’t need 5 core. But what amount of cores is required. 3 core, Live Neutral and Earth. You also clamp the armour of the SWA in the correct type of gland as an additional earth. Link to comment Share on other sites More sharing options...
ProDave Posted February 6 Share Posted February 6 32 minutes ago, FarmerN said: I am no electrician and my school boy electrics is now clearly redundant. The cable used is single core + the armoured sleve, so two stands only !! I have no idea how that works. the DNO use a combine Earth an Neutral core, the outer core of a concentric cable. After the supply head the earth and neutral remain separate so we can't use 2 core concentric cable from the supply box to the house. Link to comment Share on other sites More sharing options...
kandgmitchell Posted February 20 Share Posted February 20 I'm at a similar stage, new supply goes to a cabinet with the meter. It's a three phase supply (because it was only £300 more) but only one phase is being used at present The kit company want me to run the cable from the cabinet via the duct I've laid through the insulated raft. That distance is about 20m. The house will have a 7kW ASHP, a car charger and then the usual induction hob, ovens etc. As far as I am aware the house will be wired onto that phase but I want to keep the flexibility of having the second phase available. So am I looking at a 5 core cable with the spare ends just made safe or is that too simple? Link to comment Share on other sites More sharing options...
Alan Ambrose Posted February 20 Share Posted February 20 Something like this? What rating are the main fuses? 63A? https://www.superlecdirect.com/cables/steel-wire-armoured-cables-bs5467-pvc/?&conductor[]=10mm²&conductor[]=16mm²&conductor[]=25mm²&cores[]=5 Link to comment Share on other sites More sharing options...
kandgmitchell Posted February 20 Share Posted February 20 2 hours ago, Alan Ambrose said: Something like this? What rating are the main fuses? 63A? Not sure - I'll have a look when it stops raining! (again!!)...... Link to comment Share on other sites More sharing options...
kandgmitchell Posted February 22 Share Posted February 22 Well it's stopped briefly, drain trenches flooded and the clay is just Somme like! Those fuses are 80A. Sparks suggests 25mm 4 core for 3 phase 100A. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now