Regulations with I/O cards


Thread Starter


I am faced with up-dating an ancient PLC system (see q below), with a comparatively new system. The old system dig i/o is 100v AC. Are there any regulations in force today that stipulates low voltage to be used for I/O card connections. No-one so far seems entirely sure. Thank you.
We have plants in the US and UK. Anything we ship to Europe must meet "CE" requirements. This is true for any equipment to be used in manufacturing plants that is being shipped there. CE is the European equivalent of UL but much more comprehensive. Much, much more than I/O voltages are covered by this standard. We are in the beginning stages of getting the automation equipment we build here in the USA CE certified. I wish I knew more about it at this time but I do not. We have hired a consultant to bring us up to speed. Your best bet is to get a copy of the CE standards or find an organization that provides CE approvals to speak to.


I am currently working on projects for the UK and CE certification. Any voltage above 50 Volts is considered to be a high voltage and therefore considered a critical component for CE approval for safety. Any device that is considered
to be a critical device must have a declaration of conformity, which makes your job tougher.
Regulations do not require you to use low voltage devices, but they make it a much tougher job to get CE approval and to meet the Health and Safety standards. All connections internal to a cabinet
must be fist safe and any connections that an operator may come in contact with must be finger
I hope this helps. If you need further info, just E-Mail me or contact the BSI.


Mark Hellyer

Are you talking about retrofitting PLC's in a control cabinet?

If so..

From a safety point of view you have to ensure that 'Low Voltage'(50 to 1000Vac/120 to 1500Vdc) is segregated from lower voltages such as 24Vac/dc. I have seen PLC systems where the 120Vac output modules have been either at one end of a rack or on a totally seperate rack with respect to other i/o modules.

Less than 50Vac is considered safer(not safe!) for the majority of people in terms of preventing cardiac problems when in contact. 50Vac and above is considered a level at which the risk of danger is too high for the majority of people and so given more respect.

We use 120Vac in control panels. Some of our customers demand 24Vac/dc - but not many.

With 24Vac/dc you can sometimes eliminate panel door interlocked isolators (disconnectors if you prefer) which makes fault finding easy.