1. Introduction
In the power supply and distribution system of data centers, zero ground voltage is an important parameter that cannot be ignored. It is not only related to the stable operation of equipment, but also directly affects the reliability and security of the data center.
2. Definition and reasons for the formation of zero ground voltage
Zero ground voltage, simply put, is the potential difference between the neutral wire and the ground wire (N wire and PE wire). The main reasons for its formation include:
1. The three-phase load is unbalanced
In the data center power supply and distribution system, due to the different power needs of various equipment, it is more due to the fact that there are many single-phase equipment in the data center, and the three-phase load distribution is uneven.
For example:
1) A large number or power of one connected device is large, while other connected devices are less or less powerful.
2) When adding or removing equipment, the phase sequence of its access is not reasonably planned, resulting in uneven dynamic changes in the three-phase load.
2. The influence of harmonics
A large number of nonlinear loads in a data center room generate harmonic currents. These harmonic currents are superimposed on the neutral line, causing the zero (N) line current to increase, resulting in a zero-ground voltage.
For example:
1) Nonlinear loads such as UPS (uninterruptible power supply), inverter air conditioners, and switching power supplies generate harmonic currents. These harmonic currents are superimposed on the neutral wire, causing the neutral current to increase, resulting in a zero-ground voltage.
2) The high harmonics generated by the high-frequency switching power supply will complicate the current on the neutral line and increase the value.
3. Grounding system problems
If the grounding resistance is too large, the ground wire contact is poor, or the grounding system is not properly designed, it will cause the ground wire potential to be unstable, resulting in zero ground voltage.
For example:
1) The ground resistance is too large, so that the ground wire cannot effectively direct the current to the earth, resulting in an increase in the ground wire potential and the zero ground voltage.
2) The grounding wire connection is not firm, poor contact or rust, etc., which increases the impedance of the grounding loop.
4. The neutral impedance is too large
In the power distribution system of the data center, the cross-sectional area of the neutral wire (N) and ground wire (PE) of the equipment is not reasonably designed, which will generate or increase the zero ground voltage.
For example:
1) The wire diameter of the neutral wire is too small, resulting in a large resistance and a large voltage drop when the current passes through, forming a zero ground voltage.
2) The neutral wire is too long or the wiring is unreasonable, which increases the impedance of the line.
5. Electromagnetic interference
Electromagnetic interference within a data center can cause fluctuations in current and voltage in circuits. On the neutral line, if electromagnetic interference causes additional current fluctuations, it can cause a voltage drop on the neutral line, resulting in a zero-ground voltage.
For example:
This can be triggered by electromagnetic coupling between strong and weak lines. During wiring, if the strong power cable and the weak current communication cable are not effectively isolated and shielded, the electromagnetic field generated by the strong power line may be coupled to the weak current line. When the induced current in the weak current line flows back through the neutral wire, it may lead to the emergence of zero ground voltage. In this case, in order to reduce the impact of electromagnetic coupling, measures such as increasing line spacing, using shielded cables, and rational wiring are usually taken.
6. Transformer neutral point drift
In a three-phase circuit, transformer neutral drift refers to a change in the potential of the neutral point that no longer remains zero. The neutral point of the transformer is poorly grounded or drifting, which will lead to the occurrence of zero ground voltage.
For example:
In the TN-S system, the front-end N-wire has poor contact or disconnection, and when the three-phase load is unbalanced, the neutral potential will drift, resulting in an imbalance in the voltage of each phase. In extreme cases, if only one phase is loaded, the neutral voltage after the breakpoint may rise to the phase voltage, reducing the voltage of the other phases. This situation will not only cause high ground zero voltage, but also lead to equipment damage and electric shock accidents.
3. The impact of zero ground voltage on data centers
The impact of zero ground voltage on data centers is significant, mainly reflected in the following key aspects:
1. Equipment failure
Excessive zero ground voltage may cause damage to electronic components such as chips and capacitors on the motherboard of critical equipment such as servers and storage devices, affecting the normal operation of the equipment and increasing the failure rate of the equipment.

For example, a data center burned out a number of server motherboards due to high ground zero voltage, resulting in business interruptions.
2. Data error
Affect the accuracy and integrity of data, causing data loss or errors.
For example, during large-scale data backup or migration, voltage fluctuations at ground zero may cause some data to be unable to be fully transmitted.
3. System stability declines
Excessive zero ground voltage may cause frequent crashes or automatic restarts of servers and network equipment, seriously affecting business continuity.
Excessive zero ground voltage may reduce equipment operating efficiency, slow down data processing speed, and affect the service quality of the entire data center.
4. Reduce power efficiency
It increases the energy loss of the power supply and distribution system, reduces the efficiency of power supply, and increases the operating cost of the data center.
Taking the UPS system as an example, too high ground voltage will reduce its work efficiency and increase energy consumption.
5. Safety risks
Excessive zero ground voltage may cause the equipment shell to become electrified, increasing the risk of electric shock accidents for O&M personnel.
Excessive zero ground voltage can cause electrical short circuits, increasing the likelihood of fires and posing a significant threat to the physical facilities and data assets of the data center.
4. Data center requirements for zero ground voltage
In the data center industry, many experts, scholars, power and server suppliers, on-site operation and maintenance personnel, etc. have different opinions on the requirements (views) of zero ground voltage in data centers, which is a controversial issue in the data center room.
On the one hand, there is a view that the zero ground voltage has a significant impact on the normal operation of the equipment in the computer room, and it needs to be controlled below 2V or even 1V. This view is usually based on case studies, believing that when the zero ground voltage is high, the server is prone to crashing and the communication equipment runs slowly, and these phenomena will be improved after the zero ground voltage is reduced. On the other hand, some power supply equipment suppliers and experts believe that the zero ground voltage has no direct impact on the equipment in the computer room, as long as the zero ground voltage is below 10V. They reasoned through circuit logic that there was no influence path for the zero ground voltage to the load. But the general consensus is that it should be kept low.
In the data center design code (GB 50174-2008), it is required that the zero ground voltage of the computer room should be controlled within 2V. However, in the GB 50174-2017 specification, the technical requirement that the zero ground voltage should be less than 2V is deleted, and the numerical parameters of the zero ground voltage are not limited, but opinions are put forward in the explanation of the provisions.
[8·1·10 The potential difference between the neutral wire and the PE wire is called the "zero ground voltage", and when the "zero ground voltage" is higher than the allowable value of the electronic information equipment, it will cause hardware failure and burn the equipment; Triggering a malfunction of the control signal; Affect the quality of communication, delay or prevent the normal progress of communication. Therefore, when the "zero ground voltage" does not meet the requirements of the load (generally the "zero ground voltage" should be less than 2V), measures should be taken to reduce the "zero ground voltage". For TN system, equipping an isolation transformer at the output of the UPS is an effective way to reduce the "zero ground voltage". 】
GB 50174-2008
[8.1.10 The potential difference between the neutral wire and the PE wire is called the "zero ground voltage", and when the "zero ground voltage" does not meet the requirements of some electronic information equipment, measures should be taken to reduce the "zero ground voltage". For TN-S systems, equipping the UPS with an isolation transformer at the output is an effective way to reduce the "zero ground voltage". When choosing a protection switch for an isolation transformer, the excitation inrush current when the isolation transformer is put into operation should be considered. 】
GB 50174-2017
In the past, IBM's server equipment required that the zero ground voltage in the computer room should be less than 2V, but it was later clarified that this measure was used to check whether the N line was connected.
Later, China Telecom and Huawei jointly conducted the "Analysis of the Impact of Zero Ground Voltage on Data Communication Equipment". In the test, the simulated production of adjustable zero ground voltage difference, and the rack server, blade server, DTU and other equipment were tested respectively.
Through the test, in the test of rack server and blade server, when the zero ground voltage is below 22V, there is no effect on both servers. In the test of DTU, the zero ground voltage difference below 10V has no effect on the DTU data communication equipment, but in the case of scattered communication systems, the zero ground voltage difference will have an impact on the data communication (the reason is that the ground potential difference between the device ports of the data communication line will cause the ground potential difference). Finally, the conclusion of the report is that it is recommended that the zero ground potential difference of data communication equipment should be less than 10V.