The service panel is the central distribution point for electricity after it enters the house. In new construction or in houses that have been built fairly recently, the service entrance will in all likelihood be a circuit-breaker-protected 150-amp to 200-amp 240-volt service. But older houses often still have fuse boxes with either round or cartridge-type fuses protecting the circuits. There are plenty of houses with 60-amp 120-volt services, knob and tube wiring, and only four 15-amp circuits. This type of system isn't inherently unsafe-in fact, fuses are more reliable than circuit breakers-but it is inadequate for most modern households and can mean that a bathroom upgrade will require that the electrical system be upgraded as well, a potentially costly and likely unanticipated add-on. A 100-amp 240-volt service will likely have little room for additional circuits, though piggyback breakers (two breakers that fit in a single slot) may provide the additional circuitry needed for a bathroom upgrade. Panels with 150 amps or 200 amps usually have enough room for additional breakers.
Branch circuits, protected by either circuit breakers or fuses, distribute electricity to different parts of the house. Circuits are sized according to the electrical demand of the particular branch. For example, a lighting and general purpose household circuit might have a 20-amp circuit breaker and be wired with #12 type NM (or Romex nonmetallic sheathed) cable. Individual appliances-a jetted tub, for example-usually require an individual circuit. Sizing circuit breakers and wiring is governed by local building codes, which in turn are based on the National Electric Code (NEC), published by the National Fire Protection Association. Local codes may also allow only certain types of wiring.
All fixtures and appliances that use electricity are rated for the amount of current they use. This figure is measured in amps (the rate of flow of electricity) and should be available with the appliance's technical literature, as well as right on the appliance itself. This information is essential for planning bathroom wiring because it determines how many circuits will be needed and their size. So it's important to know exactly what is going into the bathroom and to either have the fixture's technical literature or the fixture(s) itself in hand before planning the electrical layout. For example, there are a few low-flow toilets that require an electrical outlet, and any sauna, steam unit, or whirlpool tub is going to require additional electrical capacity and usually its own circuit.
Another code requirement is that light switches be no closer than 5 ft. from any type of tub or shower. This is to keep switches out of the reach of someone standing in a pool of water. Outlets of course also aren't allowed in tub or shower spaces (NEC 410-57), but bathrooms are required to have at least one GFCI (ground-fault circuit interrupter)-protected 20-amp wall receptacle outlet adjacent to each sink (NEC 210-8). A GFCI continually compares the flow of electricity through the hot and neutral sides of a circuit and will shut off almost instantly (in less than 5/iooo of a second) if the difference becomes greater than 5 milliamps. All bathroom outlets and jetted tubs need to be protected by GFCIs (NEC 680-70), which can be installed in the service panel as a GFCI circuit breaker or in the bathroom itself as a GFCI outlet. GFCI circuit breakers are typically more expensive and less convenient to reset than outlet GFCIs if they trip, but they are less affected by the sometimes excessive humidity in a bathroom, which can cause false tripping of the circuit.
The code also requires that appropriately rated fixtures be used in damp or wet parts of the bathroom. Most codes prohibit track lighting above a tub. And any cord-connected fixtures-this includes hanging fixtures or ceiling fans-should not be located either directly above a tub or 3 ft. horizontally or 8 ft. vertically above the rim of a tub (NEC-410-4).
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