Alternating Current Distribution Board (ACDB)
AC Distribution Panels can be simply made using circuit breakers just as your home utilizes. However, critical loads that utilize UPS systems for protection from power outages and other types of power problems should use a different form of branch circuit protection for their protected loads. Larger UPS systems, typically 5 kVA and above, normally feed the output of the UPS system into a distribution panel that distributes power to the critical loads through it’s branch circuits. Should a fault or overload occur during a power outage, the UPS inverter must supply the power to clear the fault by opening a breaker or blowing a fuse within the output distribution panel.
Unlike most applications where the utility has infinite power to clear the fault, UPS systems are limited in the amount of current they can produce to clear a fault. When the UPS reaches beyond it’s overload rating and into the current limit point, the voltage begins to decay. Now the race is on to see how long it will take the available current of the UPS to open the branch circuit protector versus how long the devices being protected by the UPS can go without voltage and not be affected.
Most molded case circuit breakers used as branch breakers in Panel boards take 2-3 cycles (up to 50
milliseconds) before they will open under short circuit or fault conditions.
The solution is simple. Since your loads are important enough that they are being protected by a UPS, Make sure the rest of the UPS installation and ancillary equipment are designed and coordinated to Work together. Use fuses for your branch circuit protection to make your UPS system and installation as reliable as possible.
Fused Switch AC Panel boards are AC distribution panels that are designed for reliability by using a fuse for branch circuit protection and a molded case switch in line with the fuse so that an individual branch circuit can be isolated via a switch(ELCB). These types of panels can also be equipped with blown fuse indicators so that blown fuses can be spotted and replaced easily. Circuit breakers that provide overload protection can also be used in combination with the fuses, in place of a molded case switch.