Broken common neutral wire in the access electrical panel: danger of overvoltage

Last year, in our hostel, refrigerators, televisions, and other appliances began to burn in people. I immediately checked the tester with a voltage in the socket - 280 volts, after an hour it was already 190 volts. So it constantly jumped. Light bulbs shone on the floor, then burned out. The hostel electrician was looking for damage for 2 days. Then it turned out - there was no contact of the zero wire in the switchboard. So everything that is written in this article is very real and is not a rare case. It’s just that the hostel is very old, the wiring in it, too, and at the time when it was designed there was no such powerful equipment in each room, the power spread across the phases was small and the current passed through the zero wire. Now, through the neutral wire, the current is decent, since through zero the spread of currents in individual phases is compensated. Therefore, the probability of zero burning in houses with old wiring made by wires in small sections is very real. In my Khrushchev’s father, my aluminum wire lies in a 1.5 mm cross section. In any case, you need to somehow try to defend yourself against the possibility of a zero wire break.

To protect lighting devices and household appliances from overvoltage and voltage dips, you can use the voltage control relay, which sets the maximum and minimum voltage thresholds and delay time, in the event of a break in the neutral wire, the voltage can increase very sharply, in this case you can install a relay, it It has an output switchable group, which can be used to switch a contactor, etc.

I once conducted a demonstration experiment for fellow electricians who could not understand what happens when a zero break ... I connected three lampholders with an incandescent lamp in a “star” with a common zero point, with the same lamp power and turning off the zero, the lamps did not glow changed, and if the lamp was placed on one of the beams of lower power, then it burned out with a bang ...

That is, everything is as you described ...

The presence of a neutral wire does not play a role only with a completely symmetrical load, for example, when a three-phase asynchronous motor is connected to the network. In the TOE course there is such a laboratory work. The load (bulbs on the stand) is collected in a star (6 bulbs in each phase), the phase voltage is measured, and then in one of the phases you need to turn off 2-3 bulbs. In a less loaded phase, the voltage increases, in the remaining phases it decreases. If the circuit contains a neutral wire, then no manipulation of the bulbs does not cause a voltage change.

and if you connect the zero terminal block to the shield body, that is, ground it?

Itself got on this malfunction - the equipment burned out, and then the refrigerator! I recommend using overvoltage protection in the apartment UZM-50M, UZM-51M.

In April 2013 in the suburbs of Kiev Vishnevoy burned out a zero in the substation that feeds a bunch of apartment buildings. About 1,000 apartments were affected.

Ruslan,
An individual (apartment) zero block, in the absence of a generator zero point (break), is not in itself fraught with danger. Household appliances if they fail, but not because of increased voltage. True, there are times when another apartment "sits" on your shred, which is fraught with a number of consequences. The main neutral conductor, one way or another, is connected to the ground, but the state of the grounding armature (if any) laid in the ground decades ago is a big question.