Hi
I've recently been carrying some work out on a friends house. I've rewired a radial circuit & lights in the garage back to the existing CU. This could do with replacing as it is an old unit with rewireable fuses, one of the carriers cannot be fastened back properly exposing the busbar if the fuse is pulled What I'm trying to confirm is whether the existing supply cable is up to the job. I'd rather not replace unless its not up to standard as it means lifting concrete. I've done the calc from the 17th but could do with the heads up whether I'm correct. Details as follows:
- House supply - TNC-S
- Protective device for the garage (in house CU) - Type 2 20A BS3871 MCB.
- Design current - Full 16A for the garage radial plus 4 x 58w fluorescent fittings (4 x 58 x 1.8 / 230 = 1.82A) 18 Amps.
- Cable - 2.5mm FT&E (1.5mm CPC) first 20 metres beneath thermal insulation not exceeding 100mm. Last 10 metres 1.5mm 2 core SWA 70 degree direct in ground.
- Current carrying capacity of existing 2.5 FT&E 21 Amps for method
- Current carrying capacity of existing 1.5mm SWA 21 Amps for method
- Volt drop 6.48v for 2.5 & 5.22v for SWA. Total 11.7V/230V x 100 = 5.08%. OK for 6% max (Table 4Ab Low voltage installation from private LV supply)
- Table B6 in the on site guide states I need to meet max measured Zs of 1.32 ohms for compliance on disconnection times.
Any help appreciated. I am 17th edition & have C&G 236 (from way back)
Many thanks
I've recently been carrying some work out on a friends house. I've rewired a radial circuit & lights in the garage back to the existing CU. This could do with replacing as it is an old unit with rewireable fuses, one of the carriers cannot be fastened back properly exposing the busbar if the fuse is pulled What I'm trying to confirm is whether the existing supply cable is up to the job. I'd rather not replace unless its not up to standard as it means lifting concrete. I've done the calc from the 17th but could do with the heads up whether I'm correct. Details as follows:
- House supply - TNC-S
- Protective device for the garage (in house CU) - Type 2 20A BS3871 MCB.
- Design current - Full 16A for the garage radial plus 4 x 58w fluorescent fittings (4 x 58 x 1.8 / 230 = 1.82A) 18 Amps.
- Cable - 2.5mm FT&E (1.5mm CPC) first 20 metres beneath thermal insulation not exceeding 100mm. Last 10 metres 1.5mm 2 core SWA 70 degree direct in ground.
- Current carrying capacity of existing 2.5 FT&E 21 Amps for method
- Current carrying capacity of existing 1.5mm SWA 21 Amps for method
- Volt drop 6.48v for 2.5 & 5.22v for SWA. Total 11.7V/230V x 100 = 5.08%. OK for 6% max (Table 4Ab Low voltage installation from private LV supply)
- Table B6 in the on site guide states I need to meet max measured Zs of 1.32 ohms for compliance on disconnection times.
Any help appreciated. I am 17th edition & have C&G 236 (from way back)
Many thanks