Electrical Service Boxes
Wiring safety codes are intended to protect people and property from electrical shock and fire hazards. Regulations may be established by city, county, provincial/state or national legislation, usually by adopting a model code (with or without local amendments) produced by a technical standards-setting organisation, or by a national standard electrical code.
First Electrical codes arose in the 1880’s with the commercial introduction of electrical power. Many conflicting standards existed for the selection of wire sizes and other design rules for electrical installations.
The first electrical codes in the United States originated in New York in 1881 to regulate installations of electric lighting. Since 1897 the US National Fire Protection Association, a private non-profit association formed by insurance companies, has published the National Electrical Code (NEC). States, counties or cities often include the NEC in their local building codes by reference along with local differences. The NEC is modified every three years. It is a consensus code considering suggestions from interested parties. The proposals are studied by committees of engineers, tradesmen, manufacturer representatives, fire fighters and other invitees.
Since 1927, the Canadian Standards Association (CSA) has produced the Canadian Safety Standard for Electrical Installations, which is the basis for provincial electrical codes. The CSA also produces the Canadian Electrical Code, the 2006 edition of which references IEC 60364 (Electrical Installations for Buildings) and states that the code addresses the fundamental principles of electrical protection in Section 131. The Canadian code reprints Chapter 13 of IEC 60364, but there are no numerical criteria listed in that chapter to assess the adequacy of any electrical installation.
Although the US and Canadian national standards deal with the same physical phenomena and broadly similar objectives, they differ occasionally in technical detail. As part of the North American Free Trade Agreement(NAFTA) program, US and Canadian standards are slowly converging toward each other, in a process known as harmonization.
The service box includes a circuit breaker which can be used to shut off all the power in the house, or a switch with a handle located on the outside, and the service fuses inside. The cover on the service box is often sealed by the utility.
The service box may stand alone, although in modern homes, the service breaker is often incorporated into the service panel. In either case, it is important that the rating on the box itself, is at least as large as the service entrance cables and fuses or breakers inside. For example, if a house has service entrance wire and fuses rated for 100-amps, a box rated for only 60-amps is not acceptable. More than 60- amps flowing through this box may lead to overheating.
Every home should have a disconnect means so the system can be shut off. Working on a live electrical system is very dangerous. In the U.S. (and in some Canadian situations) it is permitted on existing installations to have up to six switches to disconnect all the house power.
To enable wires to be easily and safely identified, all common wiring safety codes mandate a colour scheme for the insulation on power conductors. In a typical electrical code, some colour-coding is mandatory, while some may be optional.
Service Boxes and Panels
In a conventional 60-amp service with circuit breakers, the breakers will trip when the current in either leg reaches 60-amps. Where fuses are used in the main service box, each fuse works independently. If more than 60-amps flows through one fuse it will blow. This leaves roughly half the house without power, including part of the electric stove, for example. If more than 60-amps flows through the other fuse, it too will blow, leaving the entire house without power.