My house was built in 1950. The electrical wiring has a few fixable problems (no GFCIs, outdoor outlets using indoor receptacles, no grounding, switches in inconvenient places, circuits no longer to code, too few outlets, etc.) but the main problem is that some of the breakers trip due to too much load. I guess in the 1950's they didn't have PCs, flat screen TVs, pot lights, microwaves, etc. So I have a big job of correcting and upgrading the wiring but I am going about it slowly in priority order (safety first then convenience).

My problem now is that I have reached the point where I need to upgrade a 15A circuit to 20A but I am finding it difficult to run my cable the last 1-2 feet to the breakers (is this called an MCB?). The MCB is located in the garage, the cables run down the wall under the house and enter the basement. I can see the cables as they go into the garage floor and again when they enter the basement - the bit inbetween is not visible.

What I am trying to find out is what happens inbetween. Does anyone know when the MCB is in the garage how the cables are brought into the house? Should I be able to run new cable through this area? Or should I create a new channel into the garage (if that is possible)? I will be replacing several cables eventually. I have disconnected the 15A circuit from the breaker and thought I could use this to pull a new 20A cable through but although I have removed all the cable clips that I can see there must be one or two in the area I can't access/see.