This is the 4th part of the questions and answers for electrical engineering. Let me remind you that in a series of publications here on the Zen channel, I publish the questions that were asked on my site asutpp.ru, as well as the answers that readers received on them.
The answers to the questions published in parts 1, 2, 3 you can find on the links that are posted after this publication.
Question N1. Asked by markus. The question itself sounded like this:
Good evening. I got a new electric stove. When you plug it into an outlet, the light starts blinking, sometimes the TV even turns off. The wiring in the house is old, the wires are aluminum, I can't give an exact answer about the cross-section. Why is this happening? There were no such problems before. I would be grateful for your answer.
I gave the following answer:
Hello. What is the power of the electric stove? It is possible that there is a voltage drop. This could be due to your old wiring. Namely, the cross-section of the wires does not withstand this load. I advise you to replace the wiring in the house, the wires must be copper, and the cross-section of the conductors for sockets is at least 2.5 mm2, and for lighting 1.5 mm2.
Alternatively, there may be poor contact in the wire connection, and this in turn leads to an increase in the voltage drop. To prevent a voltage drop that can lead to equipment failure, I advise you to use voltage stabilizers.
Question N2. Asked stolar. The question itself sounded like this:
Good day, I bought an apartment - before the owners did not have any automatic machines, the wiring is old, so I have already changed it. At the entrance there is a coupled 25A. Now I don’t know which of the machines you can install in your apartment and do you need to install several for different rooms?
The reader received the following response:
If a 25A circuit breaker is already installed at the entrance, then it makes no sense to install more than this rating in the apartment. It is more advisable to install circuit breakers of a lower rating - 16 or 20A.
If you connect a large number of powerful devices in your apartment that can be simultaneously included in the electrical circuit, and their load significantly exceeds or approaches the rating of 16 - 20A, you can use the same 25A, but with greater sensitivity than installed in the entrance. For example, if there is a C25 in the entrance, you can put a B25 in the apartment.
Regarding the installation of separate circuit breakers for each room or any consumers, this is not a mandatory measure, but convenient enough to quickly find the place of damage and eliminate malfunction. For example, if the bathroom is closed, the rest of the apartment will receive power while you troubleshoot.
Question N3. Arsen asked. The question itself is literally:
Hello!
The house is connected to the network 3 x 5 kW (total 15 kW). Single-phase water heater 8 kW. According to the specification, the cable is 4 mm2 in cross section.
The electrician connected the C40 to the machine. The wire was very hot and the device gave an error "abnormal input power voltage". I changed the wire to 6 mm2 in cross section, it became less heated, but it continues to heat up and the power error still occurs.
Why?
Note: I admit that one phase of 5 kW connected to the machine is simply not enough, and it is necessary to connect the 2nd phase to this machine.
I gave Arsen the following answer:
Good day!
If you have set a power limit for each phase of 5 kW, then connecting a single-phase water heater with a consumption rating of 8 kW is a clear excess of the permissible network parameters. If this is true, then an increase in power consumption in excess of the permissible can cause a drawdown voltage, which, possibly, displays the error of the water heater “abnormal input voltage power ". But, this is just an assumption, I would like to see the model of your water heater and the factory list of errors for it (this information is given in the device passport). Perhaps there are errors in connecting the boiler, but this can be determined on the spot, based on the actual connection diagram and recommended by the manufacturer.
I will immediately refute your assumption about connecting two phases to the machine. If you receive a supply voltage of 220 V from one phase and a neutral wire on a two-pole machine, then bringing two phase wires to the same two-pole machine for connecting a water heater, you will get 380 IN. As a result of this method of power supply, the boiler will simply burn out due to the supply of too high a voltage.
According to the cross-section of the supply cable, 4 mm2 of copper is enough for normal operation of a load of 8.3 kW, which is right next to it for your boiler. However, under the condition of a voltage drop, the current load could significantly exceed this limit. Why the cable heats up even with a cross-section of 6 mm2, it is worth disassembling on the spot with a multimeter, since the new cable must freely withstand 10 kW of load.
P.S. Previous parts of the answers to the questions:
Part 1, Part 2, Part 3