Hi, a while ago we did some landscaping in the garden and laid a single length of 6mm 3 core SWA cable underground in pea gravel from the house CU to an outhouse in the center of the garden (20 metres). Then 4mm 3 core swa another 20 metres from there to the end of the garden (40m total from house). We never got round to having an electrician come to terminate or connect anything. We're currently deliberating over building a summerhouse at the end of the garden with a shower room, in there, I'm thinking about an 8.5kw one of these: http://www.ukhps.co.uk/products/Zip-Instantaneous-ILX009-
for the shower and sink and I'm trying to decide whether the 4mm cable can supply the load for this. At the house CU would be an 60a RCD with 50amp MCB to the outhouse where the 6mm terminates in a CU with a 15amp MCB for a couple sockets and 6amp for light. OK there, now, what I'm not sure about, is, can I put one core of the 4mm swa to summerhouse on 40amp MCB for the water heater and a 20a MCB to supply the other 4mm phase for a few sockets (lights on 5amp FCU).
I've checked what the TLC cable calculator says, and it recommends 4mm for an 8.5kw load over 20metres with 3.2% voltage drop at 37amps, but not sure if it is possible to have 2 phases on 3 core swa with a shared neutral? Does the combined load need to be less than 40amps, or can the shared neutral handle, say 50amps? Is there a lower current option for heating water-would a small tanked heater work for this setup, in which case it would only be 5kw
The summerhouse would be used only when guests stay, so it's not like it would be in frequent use, but would have a 13amp heated towel rail with frost protection thermostat
If it helps, the house has 25mm meter tails, 100a lead-paper supply and an 18 way split-load board with 2x60a RCD's, so I'd have a separate RCD unit fitted for the garden with separate tails from henley block.
apologies, that's a bit waffly.
thanks, and just to clarify, I would be getting an electrician to be doing this, just want to know what's possible first.
for the shower and sink and I'm trying to decide whether the 4mm cable can supply the load for this. At the house CU would be an 60a RCD with 50amp MCB to the outhouse where the 6mm terminates in a CU with a 15amp MCB for a couple sockets and 6amp for light. OK there, now, what I'm not sure about, is, can I put one core of the 4mm swa to summerhouse on 40amp MCB for the water heater and a 20a MCB to supply the other 4mm phase for a few sockets (lights on 5amp FCU).
I've checked what the TLC cable calculator says, and it recommends 4mm for an 8.5kw load over 20metres with 3.2% voltage drop at 37amps, but not sure if it is possible to have 2 phases on 3 core swa with a shared neutral? Does the combined load need to be less than 40amps, or can the shared neutral handle, say 50amps? Is there a lower current option for heating water-would a small tanked heater work for this setup, in which case it would only be 5kw
The summerhouse would be used only when guests stay, so it's not like it would be in frequent use, but would have a 13amp heated towel rail with frost protection thermostat
If it helps, the house has 25mm meter tails, 100a lead-paper supply and an 18 way split-load board with 2x60a RCD's, so I'd have a separate RCD unit fitted for the garden with separate tails from henley block.
apologies, that's a bit waffly.
thanks, and just to clarify, I would be getting an electrician to be doing this, just want to know what's possible first.