Prolonged or gradual heating is the most dangerous for conductors. For this, of course, a special bimetallic release is installed in the circuit breakers, but 2 regulatory documents have all the data to maximize the protection of the home network from unwanted heating. These are GOSTs: R 50571.9-94 and R 50571.7-94.
Change of sections, material, laying method
The connection of a large conductor with a small conductor leads to the fact that the place itself connections will heat up, since the number of electrons per 1 mm2 in a wire with a small cross-section there will be more. Clause 473.1.1.1 states that in such places a protective device must be installed - an automatic or differential switch.
Addition: this rule works if it does not contradict clauses 473.1.1.2 and 473.1.2. The machine can be installed behind the connection if:
- Further to the consumer there are no branches.
- Protective devices are already installed up to the connection point.
It is not necessary to put the machine on working neutral, if the sections of the "phase" and "zero" are equal
Transparent and clear point 473.3.2.1, namely, its subparagraphs "a" and "b". The first says that the residual current device is not necessary on the working neutral conductors, if their cross-section is equal to phase. And the second one says that if the "phase" is protected, then it is not necessary to set the machine to "zero".
Correct disconnection of "zero"
It is also very important to disconnect the line correctly, for example, if repair work is required. DOST R 50571.9-94, paragraph 473.3.2.2: the working zero is turned off only after the phase conductor is turned off, and is activated - simultaneously with it.
When "zeroing", the neutral conductor does not require disconnection
In old multi-storey buildings very often the working "zero" is connected to the protective one. This allows you to compensate for the grounding line, which is simply not provided in such buildings. GOST R 50571.7-94. cancels the installation of protective devices on two combined neutral conductors. This is detailed in paragraph 461.2.
The machine is not set to zero even in rooms with a high probability of electric shock
Installation of circuit breakers or differential switches is not necessary even in rooms such as bathrooms. Many experts can cite as an example paragraph 464.2, which states that in places with high the risk of electric shock, protection must be provided for all current carrying lines. But at the end of the paragraph there is a small amendment: except for those specified in clause 461.2. The features of which were indicated in the previous chapter.
You can not set single-pole machines to "zero"
If there is a need to protect the zero line, then in this case it is necessary to mount a two-pole circuit breaker, where the phase wire is connected to the first pole, and to the second - "zero".