Figure 4: Using multiple redundancy modules (right) can eliminate the single point of failure and enhance reliability. (Image source: Siemens)
industrial installations. As defined in the U.S. NEC, Class 2 power supplies have an output limited to less than 100 VA. Class 2 power is also required or recommended with some industrial devices outside of the U.S. Limiting the power reduces the risks of electric shock and fire. As a result, Class 2 installations do not require the power cables to be routed through conduits or ducts, simplifying installation and reducing costs. In addition, simpler inspections are required
multiple redundancy modules can be employed to eliminate the possibility of a single point of failure (Figure 4). For example, Omron’s S8VK-C12024 AC/DC power supply can support 24 V loads up to 120 W. Two of those power supplies can be connected using the S8VK-R10 redundancy module to create a 120 W 1+1 redundant power system.
for Class 2 installations, further reducing costs. There are two ways to achieve a Class 2 power rating. Power supplies that internally limit the output power to under 100 VA are available. Or, a higher wattage power supply like the 480 W (24 V DC and 20 A) 6EP15663AA00 from Siemens can be used with redundancy modules like Siemens’ s that limit the output power as well as providing redundancy for multiple loads (Figure 5).
Class 2 and redundant Class 2 power can be an important safety factor in
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