- Reaction score
- 7
Excuse how long winded this is but want peoples opinion: :angel_smile::frown2:
Doing a basic shed install but would just like people to check my calculations and thinking as I am using it as an assessment piece with Elecsa.
House has an old TNS supply where the supply head has been upgraded to TNC-S (for whatever reason) and the TNS earthing has been bonded to TNC-S earth. I am assuming that rules following TNC-S supply would apply in this case.
The run to the shed is approx 12m however the shed itself is only about 3m from the building. The ground between the two is mainly flagged although there is a concrete 'apron' at the side of the shed. There is no soil, grass or whatever between the house and the shed. The shed is brick built with no extraneous conductive parts. Am I safe to export the earth from the house?
The dist board in the house is an old wylex split unit with type 2 mcbs. The house has an upstairs and downstairs ring for the sockets fed from the RCD side of the board. Everything else is run from the unprotected side.
My intention is to run a 30A Type2 MCB from the unprotected side, 6mm T&E through the back of the consumer unit, out the wall into an adaptable box. Gland my 4mm 3 core SWA (extra core to use to export earth just to be safe in case armour/gland joint deteriorates over time) into that buried under the flags (at the appropriate depth of course) over to the shed. Up the wall and into an adaptable box again.
At this point is it necessary to convert back into 6mm T&E or can I leave the SWA 'tails' long enough to go through the wall into a shed CU?
Gutted that 2.5mm SWA is rated at 29A buried direct, just less than the 30A I need to be within lb<ln<lz.
In the shed itself I'm just running a shed/garage CU with RCD main switch. Then going to have 6A circuit for lights supplying one light fitting in the shed itself and a security light to be fitted to the outside of the shed. Then going to have a 16A radial feeding one double socket outlet. This is just going to be used to power a tumble dryer and then a spare socket.
The lighting circuit will be 1mm T&E and the radial socket will be 2.5mm T&E. Everything inside the shed will be surface mounted within trunking.
My calcs for those who haven't fallen asleep yet:
lb = 16+6 = 22A
ln = 30A Type 2 (in house)
lz = 37A (4mm SWA buried direct)
Volt Drop =
(22*11*12)/1000 = 2.904V to Shed CU
(6*44*8)/1000 = 2.112V Lighting Circuit from Shed CU
(16*18*2)/1000 = 0.576V Socket Circuit from Shed CU
Total Drop Lights = (5.016/230)*100 = 2.18%
Total Drop Sockets = (3.48/230)*100 = 1.51%
Thanks in advance and apologies for boring you all to death with something thats really simple just worried come assessment time!
Doing a basic shed install but would just like people to check my calculations and thinking as I am using it as an assessment piece with Elecsa.
House has an old TNS supply where the supply head has been upgraded to TNC-S (for whatever reason) and the TNS earthing has been bonded to TNC-S earth. I am assuming that rules following TNC-S supply would apply in this case.
The run to the shed is approx 12m however the shed itself is only about 3m from the building. The ground between the two is mainly flagged although there is a concrete 'apron' at the side of the shed. There is no soil, grass or whatever between the house and the shed. The shed is brick built with no extraneous conductive parts. Am I safe to export the earth from the house?
The dist board in the house is an old wylex split unit with type 2 mcbs. The house has an upstairs and downstairs ring for the sockets fed from the RCD side of the board. Everything else is run from the unprotected side.
My intention is to run a 30A Type2 MCB from the unprotected side, 6mm T&E through the back of the consumer unit, out the wall into an adaptable box. Gland my 4mm 3 core SWA (extra core to use to export earth just to be safe in case armour/gland joint deteriorates over time) into that buried under the flags (at the appropriate depth of course) over to the shed. Up the wall and into an adaptable box again.
At this point is it necessary to convert back into 6mm T&E or can I leave the SWA 'tails' long enough to go through the wall into a shed CU?
Gutted that 2.5mm SWA is rated at 29A buried direct, just less than the 30A I need to be within lb<ln<lz.
In the shed itself I'm just running a shed/garage CU with RCD main switch. Then going to have 6A circuit for lights supplying one light fitting in the shed itself and a security light to be fitted to the outside of the shed. Then going to have a 16A radial feeding one double socket outlet. This is just going to be used to power a tumble dryer and then a spare socket.
The lighting circuit will be 1mm T&E and the radial socket will be 2.5mm T&E. Everything inside the shed will be surface mounted within trunking.
My calcs for those who haven't fallen asleep yet:
lb = 16+6 = 22A
ln = 30A Type 2 (in house)
lz = 37A (4mm SWA buried direct)
Volt Drop =
(22*11*12)/1000 = 2.904V to Shed CU
(6*44*8)/1000 = 2.112V Lighting Circuit from Shed CU
(16*18*2)/1000 = 0.576V Socket Circuit from Shed CU
Total Drop Lights = (5.016/230)*100 = 2.18%
Total Drop Sockets = (3.48/230)*100 = 1.51%
Thanks in advance and apologies for boring you all to death with something thats really simple just worried come assessment time!
