Underlying the benefits of its 10 Mbps speed and bandwidth, and its 200 m cabling distance, Ethernet-APL’s main attraction is that its communications run at safe voltage levels that can’t ignite fires or explosions in hazardous areas. The four power classes defined in its 120-page “Ethernet-APL Engineering Guide” include:
- Power Class A source ports have a maximum voltage of 15 VDC and minimum output power of 0.54 W, with an S-spur permitted segment class, and permitted Power Class A for load ports;
- Power Class C source ports have a maximum voltage of 15 VDC and minimum output power of 1.1 W, with an S-spur permitted segment class, and permitted Power Class A and C for load ports;
- Power Class 3 source ports have a maximum voltage of 50 VDC and minimum output power of 57.5 W, with a T-trunk permitted segment class, and permitted Power Class 3 for load ports; and
- Power Class 4 source ports have a maximum voltage of 50 VDC and minimum output power of 92 W, with an T-trunk permitted segment class, and permitted Power Class 3 and 4 for load ports.
“By the time it reaches 200 meters, Power Class A is only 540 milliwatts, or about half a watt. This is part of Ethernet-APL’s section of the two-wire IEC 60079-47 technical document published in February 2021, while Power Class B is expected to be added soon,” says Arnold Offner, strategic marketing manager for process automation at Phoenix Contact. “It’s also OK if only one APL device is running because each has to operate within its own envelope, so users don’t have to worry about inductance or resistance.”
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Because these and other upcoming power classes are part of Ethernet-APL’s operating profiles, Offner reports that devices connected to a Power Class A switch must fulfill the same requirements, just the point and end devices in an Ex-ia system must also be certified as intrinsically safe.
“Besides running at reduced voltages and currents, Ethernet-APL also relies on ‘engineered power,’ which requires that all the electricity used by each network and its devices always stay within a diligence-designed range or envelope. It also makes sure that no port operations go outside the perimeter of the same operating range,” explains Offner. “Range A is 0.5 W or less, and is a subset of the larger Range B that’s 0.5 W to 1.17 W, with both in Zone 1. Meanwhile, Range C is up to 1.1 W in Zone 2. Reducing APL’s distance compared to regular Ethernet is what allowed is what allows it to run at reduced and safer power levels.”
