P
Phoenix
Hi, not been here for a few months and my first visit back is asking for advice, sorry but I need my sanity back!...
This is in relation to installing a new CU. As well as the CU and a couple of other jobs I have to sort out the supply cable to the shed & garden. The supply is a TNC-S. The shed is currently supplied through 6mm SWA from the house, that is in turn supplied by 2x2.5mm cables
whatchutalkingabout) from the existing CU and a 32A MCB. The total cable run is 25m. The EXISTING Zs in the shed sockets is 0.31 and the RCD in the CU trips well within time (don't have the exact times to hand, sorry). In the shed itself is a 3036 board with 5A for lights and 32A for sockets.
I am proposing to run T+E from the new CU to a JB on the outside wall then pick up the existing SWA. There is no way SWA will be entertained inside the house and even if it was some of the bends needed to reach the CU may not be achievable with it. In the shed itself I will install a 20A power circuit and 6A lighting. From the JB I will also run external sockets through a 13A FCU. As there is a lighting circuit in the shed I am intending to use 10mm T+E (10m) to the JB, then 15m of 6mm SWA giving a voltage drop of 4.57v so within the 3% (I have ignored diversity as there could be a few things drawing current at the same time so using worst case). Installation method will be Clipped Direct (possibly buried for SWA). I am protecting this with a 40A 30mA RCBO in the main CU, and will change the CU in the shed to MCB's.
Now to the part when my brain kicked in and I started getting all hyperthetical so I'm throwing this out there...to maintain safety the shed lights and sockets should, ideally, be on a split load CU but that seems massive over-kill. My worry is that if the RCBO trips at night, there is potential danger in trying to get out of a cluttered shed in darkness and stagger back up to the house to re-set the RCBO. So now we are left with necessity for discrimination if we are to install RCD's in the shed...can you get time delayed RCBO's? Would that still comply in protecting the 10mm T+E inside the house (buried cables)??? How would you achieve diversity with RCD's?
My solution - unless I hear differently on here - is to utilise the RCBO for protection and just install a simple 4-way CU in the shed with a main switch and MCB's; if the RCBO trips then it will have to be a short walk! To maintain safety I will add a non-maintained LED emergency light; they're cheap enough!
Over to to you all and I'm off to my bunker!
This is in relation to installing a new CU. As well as the CU and a couple of other jobs I have to sort out the supply cable to the shed & garden. The supply is a TNC-S. The shed is currently supplied through 6mm SWA from the house, that is in turn supplied by 2x2.5mm cables
whatchutalkingabout) from the existing CU and a 32A MCB. The total cable run is 25m. The EXISTING Zs in the shed sockets is 0.31 and the RCD in the CU trips well within time (don't have the exact times to hand, sorry). In the shed itself is a 3036 board with 5A for lights and 32A for sockets.I am proposing to run T+E from the new CU to a JB on the outside wall then pick up the existing SWA. There is no way SWA will be entertained inside the house and even if it was some of the bends needed to reach the CU may not be achievable with it. In the shed itself I will install a 20A power circuit and 6A lighting. From the JB I will also run external sockets through a 13A FCU. As there is a lighting circuit in the shed I am intending to use 10mm T+E (10m) to the JB, then 15m of 6mm SWA giving a voltage drop of 4.57v so within the 3% (I have ignored diversity as there could be a few things drawing current at the same time so using worst case). Installation method will be Clipped Direct (possibly buried for SWA). I am protecting this with a 40A 30mA RCBO in the main CU, and will change the CU in the shed to MCB's.
Now to the part when my brain kicked in and I started getting all hyperthetical so I'm throwing this out there...to maintain safety the shed lights and sockets should, ideally, be on a split load CU but that seems massive over-kill. My worry is that if the RCBO trips at night, there is potential danger in trying to get out of a cluttered shed in darkness and stagger back up to the house to re-set the RCBO. So now we are left with necessity for discrimination if we are to install RCD's in the shed...can you get time delayed RCBO's? Would that still comply in protecting the 10mm T+E inside the house (buried cables)??? How would you achieve diversity with RCD's?
My solution - unless I hear differently on here - is to utilise the RCBO for protection and just install a simple 4-way CU in the shed with a main switch and MCB's; if the RCBO trips then it will have to be a short walk! To maintain safety I will add a non-maintained LED emergency light; they're cheap enough!
Over to to you all and I'm off to my bunker!
