Iec 60364 Part 551 Pdf [Easy — 2024]
Understanding IEC 60364 Part 551: Low-Voltage Electrical Installations – The Complete Guide to the PDF Standard
1. What is IEC 60364-5-551?
IEC 60364 is the international standard for electrical installations in buildings. Part 5-551 specifically addresses "Selection and erection of electrical equipment – Low-voltage generating sets."
While earlier parts of the standard deal with general protection against electric shock, Part 551 focuses on the specific hazards and operational requirements introduced when a building has its own power source. It covers generating sets that are: iec 60364 part 551 pdf
- Internal combustion engines (Diesel/Gas Generators).
- Photovoltaic (PV) systems.
- Fuel cells.
- Electrochemical accumulators (Batteries).
5. Overcurrent Protection
Generators are limited sources of fault current. Unlike transformers, they cannot deliver tens of kiloamps for long. Therefore: Internal combustion engines (Diesel/Gas Generators)
- Overcurrent devices (breakers, fuses) must be selected to operate within the generator’s decrement curve.
- Selectivity between generator main breaker and downstream breakers must be verified.
- For inverter-based generators (e.g., battery storage or solar hybrid), the short-circuit current may be very low – requiring electronic protection (e.g., overcurrent relays).
Clause 551 refers to IEC 60364-4-43 for overcurrent protection, but with the note that generator impedance must be considered. including the neutral
3. Switching and Isolation (Clause 551.4)
A common cause of accidents is backfeed—energizing a supposedly dead circuit. Clause 551 requires:
- A manual or automatic changeover switch (transfer switch) that breaks all live conductors, including the neutral, unless the neutral is solidly earthed at both sources.
- Mechanical interlocking to prevent parallel connection of two asynchronous sources (e.g., grid and generator) unless intentional and properly synchronized.
- A visible break or a reliable means of isolation on the generator side.
When you study the IEC 60364 part 551 pdf diagrams, pay close attention to the four-pole transfer switch arrangements—these are mandatory for most TT and TN-S systems.