Question about the need to connect neutral wire (N) through circuit breaker in a single-phase network 220V causes heated debate among both novice electricians and professionals. Some argue that this is a mandatory requirement PUE (Electrical Installation Rules), others - that it is enough to protect only phase wire (L). The disagreements are aggravated by the fact that in different circuits (lighting, sockets, electric motors) the approaches may differ.
In practice, errors in connecting the zero are fraught phase imbalance, electric shock when zero breaks or even fire due to overheating of the wiring. The topic is especially relevant for auto electricians working with on-board networks 12/24V, where the principles of protection are similar. In this article we will analyze regulatory requirements, typical connection diagrams, risks of incorrect installation and nuances for specific loads - from lamps to inverters.
Spoiler: answer to the question "Do I need to let the zero go through the machine" not clear. It depends on load type, wire sections, circuit destination and even regional amendments to the PUE. But there are clear rules that will help you avoid serious mistakes.
1. What the PUE says: standards for connecting zero via a machine
The main document regulating the installation of electrical networks in Russia is PUE (7th edition). It does not directly say that zero must pass through the machine, but there are key points that indirectly define the requirements:
✅ PUE 1.7.145 states that all conductors of the circuit, except PE (ground)must have overcurrent protection. This also applies to the neutral wire if it worker (N) and participates in load nutrition.
✅ PUE 3.1.18 requires that disconnecting devices tore apart all poles of the circuitexcept for grounding. This rule is relevant for three-phase networks (380V), but is often extrapolated to 220V.
However, there is a nuance: in single-phase networks (for example, in apartment wiring) the zero often doesn't break automatically, since it is considered common to several groups. But this doesn't mean you can always do this.
🔹 Exceptions to the PUE, when zero not necessary let through the machine:
- 🔌 Lighting circuits with incandescent lamps or LED drivers where leakage current is minimal.
- 🔋 Lines with low currents (up to 6A), if the cross-section of the neutral wire corresponds to the phase wire.
- 🔄 Circuits with RCD / automatic circuit breaker, where the protection is triggered when there is an imbalance of currents in phase and zero.
⚠️ Attention: B three-phase networks (380V) zero always must pass through a machine or switch, since its break leads to overvoltage on phases up to 380V and equipment failure.
2. When zero MUST be passed through the machine
There are situations where automatic zero break not just recommended, but required for safety. Here are the key cases:
🔧 1. Powerful single-phase loads (from 3.5 kW)
If you connect electric stove, boiler, inverter welding machine or car charger, zero must burst along with the phase. Reason: if the zero is broken, a phase voltage (220V), which will result in electric shock.
🔧 2. Circuits with electronic devices (switching power supplies)
Modern LED drivers, computer power supplies, battery chargers sensitive to the quality of the zero. If the zero is not broken, when break or poor contact The device may malfunction or cause interference.
🔧 3. Circuits with reverse start (for example, in garage doors)
If the zero is not broken, when incorrect commutation possible spontaneous start of mechanisms, which is dangerous for auto electricians.
🔧 4. Lines with RCD without difavtomat
If there is a chain only RCD, and the machine breaks only the phase, then when leakage to zero the protection will not work. Therefore zero must pass through a two-pole circuit breaker.
3. Typical mistakes and their consequences
Incorrect zero connection is one of the main reasons fires, equipment failure and electric shock. Let's consider top 5 mistakes and their consequences:
❌ Error 1: Zero is connected directly, bypassing the machine
🔥 Consequence: When short circuit or overload the phase circuit breaker will work, and the zero will remain energized. If at this moment someone touches the wire, considering it de-energized, he will receive an electric shock.
❌ Error 2: Using a single-pole circuit breaker in a circuit with a powerful load
🔥 Consequence: When zero break on the load (for example, in an electric stove) will appear phase voltage, which will lead to insulation breakdown and fire.
❌ Error 3: Connecting neutral and ground to one terminal
🔥 Consequence: This is a gross violation PUE 1.7.135. If the zero breaks, the device body will be energized, and RCD will not work, since the leakage current will flow through the “grounding”.
❌ Error 4: Using zero as ground (grounding without the correct circuit)
🔥 Consequence: If the zero in the shield breaks, all zeroed housings will be under phase voltage.
❌ Error 5: Mismatch between the cross-sections of the neutral and phase wires
🔥 Consequence: If the zero is finer than the phase, it will burn out first, which will lead to overvoltage on load.
What happens if the zero burns out in a three-phase network?
In a three-phase network (380V), when the zero is broken, phase imbalance: in one phase the voltage can rise to 380V, and on the other - drop to 120V. This will disable all connected equipment (from refrigerators to machine tools).
4. Connection diagrams: when zero goes through the machine, and when it doesn’t
Let's sort it out 4-part schemes zero connections in single-phase networks 220V and their features.
| Load type | Do I need to let the zero go through the machine? | Recommended scheme | Risks of error |
|---|---|---|---|
| Lighting (lamps, chandeliers) | ❌ No (phase is enough) | Single-pole circuit breaker per phase, zero per bus | Minimal (only risk of residual stress) |
| Household sockets (up to 16A) | ⚠️ Preferably (two-pole circuit breaker) | Two-pole circuit breaker or RCD + single-pole | Electric shock when zero breaks |
| Powerful appliances (stove, boiler, welder) | ✅ Required | Two-pole machine or difavtomat | Fire, insulation breakdown |
| Electric motors (pumps, fans) | ✅ Required | Two-pole circuit breaker + contactor | Spontaneous start, overheating of windings |
| Circuits with RCD / automatic circuit breaker | ✅ Required (for correct operation of the protection) | Two-pole circuit breaker in front of the RCD | False alarms or protection failure |
☑️ Checking the correct connection of the zero
5. Practical advice for auto electricians
B on-board networks of cars and garage equipment (for example, in chargers or inverters 12V→220V) the principles of protection are similar to household networks, but there are nuances:
🚗 1. Inverters 12V→220V
If you connect inverter to the battery for powering the tool, zero at the inverter output must break along with the phase. Otherwise, when zero break will appear on the instrument voltage 220V, which is life-threatening.
🚗 2. Battery chargers
In the charging circuit the neutral is often grounded to the bodybut if you use pulse memory, zero must pass through fuse or circuit breakerto avoid breakdown of power transformer.
🚗 3. Welding machines
B single-phase welders zero necessarily should break automatically, since when zero break the arc may go past the part being welded, which will lead to breakdown of cable insulation.
🚗 4. Lighting in the garage
For LED spotlights or halogen lamps enough to tear only phase, but if you use metal cases, better install two-pole circuit breaker for complete blackout.
When working with auto electricians, always check voltage between zero and ground multimeter. If it exceeds 2-3V, this is a sign bad contact or leaks.
6. How to choose a machine for zero: denomination and type
If you decide that zero must go through the machine, it is important to choose the right denomination and type devices.
🔹 Rated current of the machine for zero should be:
- 🔹 Equal to phase - if the cross-section of the wires is the same.
- 🔹 One step lower - if the zero is thinner than the phase (for example, the phase
2.5 mm², zero1.5 mm²).
🔹 Machine type:
- 🔹 Double pole (2P) - the best option for single-phase networks, it breaks both phase and neutral.
- 🔹 Single-pole + RCD - acceptable for sockets, but requires proper installation.
- 🔹 Difavtomat (AVDT) — optimal for wet rooms (garages, workshops).
⚠️ Important point: Never use single-pole circuit breaker to zero separately from the phase - this violates PUE 3.1.18 and creates a risk incomplete disconnection of the circuit.
If there is a chain RCD, zero necessarily must pass through it along with the phase. Otherwise, the leakage protection will not work.
7. Frequently asked questions and answers (FAQ)
❓ Is it possible to connect the zero directly to the bus if the phase goes through the machine?
✅ Possible, but only for low-power loads (lighting, sockets up to 10A). For powerful devices (stove, welder) zero must burst along with the phase.
⚠️ Risk: if the zero breaks, phase voltage will appear on the load, which is life-threatening.
❓ What happens if you put a machine with a lower denomination to zero than to the phase?
❌ You can't do that. The machine's nominal value for zero should be equal to or less phase, but wire cross section it must correspond to the current.
🔥 Consequence: the zero will burn out first, which will lead to overvoltage on the load.
❓ Is it necessary to break the zero in the circuit with an RCD?
✅ Yes, definitely. The RCD operates on the principle of comparing currents in phase and zero. If the zero is not broken, in case of leakage protection won't work.
🛠️ Correct scheme: Automatic 2P → RCD → Load.
❓ Is it possible to use zero as grounding?
❌ Strictly prohibited (PUE 1.7.135). It's called zeroing and it is dangerous because if the zero breaks, the housing will be energized.
⚡ Correct: there must be grounding separate conductor (PE).
❓ How to check if the zero is connected correctly?
🔧 Verification steps:
- Turn off the machine.
- Ring with a multimeter zero and phase - there must be resistance
∞(open). - Turn on the machine and check the voltage between phase and zero - it should be
220V ±10%. - Check the voltage between zero and ground - there should be
0V(or no more2-3V).