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I am going to do a CU change for part of my scheme provider assessment, so I want to get this right. Currently the old CU (Wylex bs3036 rewirable fuses) is fed with 16mm tails & 10mm earthing conductor. The CU is positioned against the ceiling on an outside wall in the kitchen and the meter cutout is on the other side of that wall. It is TNC-S supply with 100amp bs1361 fuse. The customer has elected for RCBO's in the new CU.
I'm going to replace the tails to 25mm & 16mm EC. However the old tails are run in the cavity, for about one meter. Now my understanding is that the tails do not need rcd protection, because they are more than 50mm from the surface, they will not be excessively strained because of they short length. I'm not changing whats already there with anything that could be conceived worse. But what about protection from cavity insulation, not currently installed, dampness migration and anything else I might have missed?
Another slight issue, is from the cutout the current tails leave via the bottom of the cutout and run to the left of the cutout and then up to the CU. Routing the new tails will be difficult. Is it acceptable to make a hole in the top of the cutout box to fish the new cables (terminating via the original hole at the bottom), as long as this is properly resealed afterwards?
I'm going to replace the tails to 25mm & 16mm EC. However the old tails are run in the cavity, for about one meter. Now my understanding is that the tails do not need rcd protection, because they are more than 50mm from the surface, they will not be excessively strained because of they short length. I'm not changing whats already there with anything that could be conceived worse. But what about protection from cavity insulation, not currently installed, dampness migration and anything else I might have missed?
Another slight issue, is from the cutout the current tails leave via the bottom of the cutout and run to the left of the cutout and then up to the CU. Routing the new tails will be difficult. Is it acceptable to make a hole in the top of the cutout box to fish the new cables (terminating via the original hole at the bottom), as long as this is properly resealed afterwards?