You may be rewiring your house for one of several reasons. Your old, outdated wiring may be insufficient for your present needs, you may have hazardous aluminium wiring or you may simply be updating your circuitry as part of a comprehensive renovation. Whatever the reason, you need to plan ahead to get the most from your retrofitted electrical system. Not only will planning help you size your panel correctly, it will also make the maintenance and repair of your circuitry easier.
Calculate your energy needs on a room-by-room basis. Add up the sockets and light in each room and the amount of current they will draw if they are all in use at the same time. This will help you determine how many circuit breakers you will need for each room, and the amperage rating for each breaker. If it is practical, consider having one auxiliary lighting circuit on a separate breaker that services all the rooms in your house. This way, if a breaker controlling a room trips, you can still have light in that room.
Count up the number of 230-volt appliances that need to be powered, including water heaters, stoves, air conditioners and dryers. You will have to connect each of these to a separate circuit that will require two breakers in the panel.
Add up the number of circuit breakers you need and verify that you have enough room for all of them in your old panel. If you don't, plan on investing in a new one that will give you the number of breaker slots you need, plus a few extra so you have room for more circuits in the future. If your old panel is ungrounded, plan on replacing it with a groundable residential service panel.
Size the cable for each circuit according to the amperage rating of the breaker controlling it. You can use #14/2 cable for 15-amp breakers, but you need #12/2 cable, which is thicker, for 20-amp ones, #10/3 cable for 30-amp ones and #8/3 cable for 50-amp ones. Appliances requiring 30 and 50 amps will be on 230-volt circuits, so the cables will have an extra conductor, which will make them harder to pull.
Measure each run of cable and add them up, then plan on buying 20 per cent more. You will need the extra to make connections, to allow for slack in long runs and to get around corners and through tight spaces.
Plan on replacing all your existing ungrounded sockets with grounded ones if your house has older, two-conductor wiring. You may also have to change some light fixtures, if they have no way to be grounded. Replace sockets in the bathroom, kitchen, laundry room and outside with ground fault interrupting (GFI) sockets.
Make a diagram of all the circuits in the house, showing all the outlets, lights and switches. Check it with an electrician, who will be able to pinpoint any standards violations or possible hazards.
If the walls of the house are already covered over, plan on routing as many wires as possible back to the panel through the attic, basement or crawlspace to minimise the number of wires you have to pull through the walls.
The electrical code has many requirements, and some of them can be confusing. You will rest easier, and save yourself possible problems in the future, by consulting a professional who understands it.