Special computer programs enable electricians much easier to plan where and how they will run the wire, where will be located branch and so on.
In this way, more and more electricians may remind us of specialists, because the design of electrical networks at the present time is done properly only through the computer.Special programs also allow control of parameters during operation of the installation.
The electric code makes a distinction between "high" voltages (100 volts and higher), and "low" voltages below that, and which have two different safety classifications and regulations.For circuits defined as low voltage, in some jurisdictions, there no requirement for licensing, training, or certification of installers, and no inspection of completed work is required, for either residential or commercial work.
Low voltage cabling run in the walls and ceilings of commercial buildings is also typically excluded from the requirements to be installed in protective conduit. The precise reasoning for the selection of 100 volts as the division between high and low is not clearly defined, but appears to be based on the idea that a person could touch the wires carrying low voltage with dry bare hands, and not be electrocuted, injured, or killed.
Telephones for example use low voltage cabling, but the ringing voltage from the central office is approximately 90 volts peak AC, and which has an RMS voltage of 63v. In more recent terms, the upper cutoff for what is considered low is approximately 50 volts, with most computer network equipment operating at 48 volts DC or lower, and not requiring special training to connect or use. Although low voltage cabling does not require inspection or training to install in some jurisdictions, it is still important for installers to be aware of specific electric code safety rules such as how to correctly penetrate building fire barriers and use firestop putty (intumescents) to prevent a low voltage cable from reducing building fire protection and increasing the risk of injury or death for building occupants.Access to such safety information is typically restricted and limited access by the electrical industry itself so as to only permit licensed professionals to learn the NEC rules and educate themselves.Źródło: https://en.wikipedia.org/wiki/National_Electrical_Code