How To Choose Uc And Up Of The Surge Protector Of The Distribution Box?
This is a true story about a tunnel lighting project. The customer consulted us last month. They were facing a problem: the tunnel lights were powered off many times after being struck by lightning, which caused a lot of trouble for their project. They were confused by this problem because the complete surge protector and surge protector had been installed in the distribution box on site, and the grounding on site also met the requirements. The question is, there are lightning protection measures on site, why do some tunnel lights still lose power?
In order to find out the problem, we fully communicated with the customer and understood the situation on site. The customer also provided photos of the on-site distribution box for our reference. After careful observation, we found that the surge protector in the distribution box was intact, but the switch behind it jumped. This situation shows that the surge protector did not play a protective role. Our technicians conducted further investigations and finally concluded that this was because the Uc selection of the surge protector was too high, which caused it to fail to start the protection action and could not effectively discharge the surge current. It was a typical surge selection error.
Therefore, we recommend that customers replace the surge protection device with a suitable Uc value and choose an SPD with a Uc value of 275V to improve the stability and safety of the tunnel lighting system.
The story tells us that correctly selecting a suitable surge protective device and ensuring that its Uc value meets actual needs is a key step in ensuring the safe and stable operation of the equipment.
According to Article 5.4.3 of GB 50343-2012, the maximum continuous working voltage Uc of the surge protector should not be lower than the value specified in Table 5.4.3-2
In a three-phase four-wire distribution system with a neutral line, the line voltage is √3 times the phase voltage. In a three-phase three-wire distribution system without a neutral line, the line voltage is the same as the phase voltage. Common rated voltages of low-voltage distribution systems are 220/380 (phase voltage is 220V, line voltage is 380V), 230/400 (phase voltage is 230V, line voltage is 400V). If the system voltage of the TN-S system is 220/380V, Uc≥1.15*220V can be selected, and then according to the national standard preferred value, 255V and 275V can be selected.
