djedesign1 (Customer) asked a question.
Surge Suppress on Safety Circuits
I have a little confusion about these requirements.
If I use a 24VDC safety interlock circuit - perhaps using a Mosaic safety controller, some other brand, or just a relay - does the 24VDC Class 2 power supply count as my Surge Protection? Do I need 24VDC Surge Protection in addition? Do I need Surge Protection on the 120VAC Primary to the power supply? Do I need 480VAC Surge Protection if I'm opening Motor Starters (24VDC Coils)?
You should use surge suppression on coils; relays, motor starters, definite purpose contactors, pneumatic solenoids, etc. I have never heard of a power supply being a surge suppression device. Surges are the flyback voltage that come from a coil and into your control circuit when said coil is powered off. You want a device to choke that off, otherwise you can destroy solid state outputs, like those found on a PLC.
You misunderstand. There is a surge protection requirement for safety circuits now in effect. This includes solid state devices such as ADC's Mosaic Safety Controller, Light Curtains, etc.. There may not be a coil anywhere in some (admittedly rate) cases. The concern is surges (or voltage impulses) damaging the devices you rely on for safety - such as the 24VDC power to the solid state device.
ADC provides Mersen UL Type 1 Surge Protective Devices. But, as an example, does the 480VAC device cover the 120VAC from the control transformer, and the 24VDC from the DC power supply? Can I get away with just a 120VAC device on the control transformer secondary? Is a Class 2 DC Power Supply considered "good enough" that I can do without additional Surge Protection either before or after?
I'm trying to find the full extent of how and where Surge Protection Devices are fully required to meet safety circuit requirements
It's a good question. You might try posting over on the Reddit PLC sub. I'd like to know what the answer is as well. By the way, the Mersen surge traps that AD sells are very large and not DIN mountable. You might be better served with the DIN mountable ones.
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