Hehe, I still think you're thinking of another model? Perhaps the 1766-L32
AWA (AC IN RLY OUT)?
The 1766-L32BWA has 20 x 24VDC inputs (12 Fast / 8 Normal).
The 1766-L32AWA has 20 x 120VAC inputs...
jraef said:
...Not a problem here in North America because if you have 240VAC single phase, it's never more than 120V L-N. But I've had people fry them using the 208V "stinger leg" on a 240V 3 phase delta source. The PLC itself doesn't care because it can take it, but the Inputs can't. The same would hold true overseas as well; they have 230V L-N.
For the models that sport 120VAC inputs, I hear you. In Ireland we have 230VAC 50Hz single phase (L-N) which is standard for domestic, commercial and industrial outlet supplies. We also use 120VAC industrial outlets for power tools as it's a safer voltage. You'll also see shaver sockets in Hotels rated at 120VAC.
Of course, many industrial devices are still supplied with these voltages (110/120/230/240VAC), but for automation control voltages, 120/240VAC are seen or used far less nowadays on the plant floor. It's mostly all 24VDC as I'm sure is the same for many other regions. But, you'll always have the existing older installations and certain newer equipment that will require these voltages. The fear I often have is the younger Engineers starting out who have little or no experience with these potentially more dangerous voltages. They assume everything is nice, touch-friendly 24VDC. Their test meters are often on DC (default at ON) when they land their probes and I have to prompt them to switch to AC if it's necessary or when they don't know what there measuring for - test for both.
Because Relay outputs are just dry contacts which switch whatever voltage and current they are rated for, they are often rated 110/120VAC up to 240/250VAC to facilitate our common single phase voltages. The biggest misconception I've found is that "AC outputs" are often understood to be all the same and can all handle this voltage range. There is often no knowledge of or distinction between relay contact and electronic triac outputs, for instance. So you could find someone who has wired a 240VAC device from a 120VAC triac output and is experiencing "weird happenings".
It can then be misunderstood that "AC inputs" are likewise all the same. So it's though OK to wire either 120VAC or 240VAC signals to say a 120VAC rated input. Again, we know the input channel is not simply a leg on an internal AC relay coil, but an electronic circuit, often bridge rectified and then switching an optical isolator to signal the module and PLC at typically 5VDC i.e they are specifically designed and rated for the intended voltage and current.
These mix ups are happening less and less as we move mostly toward all DC control, but I feel it's still important to teach these differences for the foreseeable.
Regards,
George
