Why does zero burn out more often under load, and not the phase?
Perhaps many have heard of such a problem, when, under loads, the wire with zero in the contact zone begins to overheat, and not the phases themselves.
There is a joke on the Internet that an overload is signaled by a harsh Russian LED. But why does zero overheat in the place of weak contact (which indicates high currents)? After all, all loads consume current from the phase wires!
As a rule, this situation occurs at substations in areas with apartment buildings, or in private houses, where the load is not correctly distributed across the phases.
The wiring entering the entrance consists of three phases and a neutral wire. And each phase is evenly distributed across the apartments. Let's say three apartments are the first phase, the next three are the second, then the third and then this is repeated. For private power consumption, a three-phase star-shaped circuit is used, where all apartments are connected to one neutral wire.
The sinusoid of currents in each phase is shifted by 120 degrees. With symmetrical loads in each phase, currents flow from phase to phase without loading the neutral wire. And when the so-called asymmetric load appears, then there is also a current through the zero wire. But, as a rule, such a current through the neutral wire is less than the phase one. Why is the neutral wire overloaded?
With linear loads (heating elements, incandescent lamps), there is no significant current imbalance between the phases. But due to the presence of a large number of switching power supplies in digital devices, uneven current consumption appears in the phase wires. Current consumption occurs in pulses. Harmonics of the current appear in the network, which are not compensated for in the neutral wire, but are added.
Another, simpler explanation: each apartment has a single-phase wiring. And the current flows from the load to zero. Zero common at the entrance. And with significant total loads from each apartment, this zero core of the wire is loaded more than phase. As some say, zero is even more hard worker than phases.
Sometimes the neutral wire burns out (it's correct to say - an open circuit). And this already leads to disastrous consequences if there are no protection systems. Phase imbalance or complete zero break occurs.
I think everyone has heard that at the same time, 380V may appear in the sockets in a 220 V single-phase network. The fact is that a second phase appears in the outlet instead of zero.
How can you avoid this? In order not to overload zero, all electronics must be with a power factor corrector in the circuitry of switching power supplies. This is a question for manufacturers.
It is necessary to choose the cross-section of wires not according to the phase current, but according to GOST R 50571.5.52-2011 (P. 523.6.2) - selection of the cross-section for the most loaded wire.
And the simplest thing for a consumer in a private house is to install a voltage relay.
Cost from 3000 rubles. up to 7000 rubles. All sorts of RCDs or difavtomats with zero break control will also help.