Metrication in the United States There are no U.S. customary units for electric current, potential difference, or charge since these concepts were developed after the international adoption of metric in science. The metric units ampere, volt, ohm and coulomb are the only units used. The SI term hertz has replaced the term "cycles per second" as a unit of frequency. Energy is often measured in watt hours, BTUs, therms or calories rather than the SI joule. Residential and commercial electrical energy use is metered and billed in kilowatt hours, kW·h, as in most metric countries. Force measurements regularly use the pound instead of the SI
Consumer unit trips out. Another way to protect circuits under the 17th Edition IET Wiring Regulations is by fitting Residual Current Circuit Breaker With Overload (RCBOs) to every circuit although this can be a very costly method. Some older systems such as those that use MK or old MEM Consumer Units that had one fuse per spur, so for instance: etc.. Consumer unit A consumer unit is a type of distribution board (a component of an electrical power system within which an electrical power feed provides supply to subsidiary circuits). The IET defines a Consumer Unit, also known as a consumer control