Boy – there are so many answers to this question, but the best is “It depends.” What it depends on primarily is the design of the electrical line – a high-tension power line is going to carry much more current than will the feeder line to an office (or apartment) building, and that feeder line will carry more juice than the line that runs to your home is going to carry. So the best answer, again, is “It depends.” But more important is that you have got to keep your electrical loads comfortably within the carrying capacity of your electrical lines, whether that’s the line feeding your home, your business, your shop, or whatever it is that you’re wiring up. In fact, you really shouldn’t exceed about 80% of the rated capacity of any electrical line, just to be safe. Also – and this is important – you should never try to push an electrical line (or fuse box or breaker box) beyond its rated capacity.