Most of differences in the layout and design of low-voltage networks are dictated by the mains voltage rating. In Europe and most of the world 220–240 V is the dominant choice, while in North America 120 V is the standard.[5]ANSI standard C84.1 recommends a +5%, −2.5% tolerance for the voltage range at a service point.[6] North American LV networks feature much shorter secondary connections, up to 250 feet (80 m), while in European design they can reach up to 1 mile (1,600 m). North American distribution transformers must be therefore placed much closer to consumers, and are smaller (25–50 kVA), while European ones can cover larger areas and thus have higher ratings (300–1000 kVA); only the remote rural areas in European design are served by single-phase transformers.[5]As the low-voltage distribute the electric power to the widest class of end users, another main design concern is safety of consumers who use the electric appliances and their protection against electric shocks. An earthing system, in combination with protective devices such as fuses and residual current devices, must ultimately ensure that a person must not come into touch with a metallic object whose potential relative to the person's potential (which is, in turn, equal to the ground potential unless insulating mats are used) exceeds a "safe" threshold, typically set at about 50 V.