It just happens I am well aware of the situation this will be installed it, it is a college environment, where the power D/B with 100 amp contactor supplying sockets outlets, 13 16 32A, gas valves ect are controlled via the emergency stops around the workshop.
Explain how it won't comply with statutory requirements, it is not a peice of machinery, I am aware that additional stops should not be run at 230v but it will all be in the same containment system and in steel conduit, therefor it cannot be at extra low voltage.
There are accepted standards for basic design irrespective of the safety level required, a risk assessment will also include the consequences of component failure ie 'is it fail safe' and what measure have been undertaken or what extra components have been put into the design to give the required level of fail safety, you also mention using the Start button to do 2 functions, first as just a start then also as a reset if an E-stop is operated, this would not be a good design, you should incorporate a seperate device be it a key, button or similar to reset the system usually by a deliberate action, your reset should not energise the circuit at the same time, this must be by the use of another device again be it a P/B or K/S etc, even colour coding of indicator lamps, buttons etc have guidelines, if the red stop is on the same station as an E-stop then a red button would not be permitted, some of these points are not statutory but a written agreement and risk assessment with the customer must be drawn up say if the customer wanted a non standard button colour or indicator, this may be because of existing systems say on workshop machinery follow an older code, it reduces the chance of confusion if everything is the same.
Given the limited info I would as a basic have all the E-stop buttons as key release only, this way the students cannot mess about with the E-stops then quickly twist and release and then deny all knowledge, another way around this is to have an indicator system to identify the operated E-Stop...all this would be discussed on-site, I have seen so many poor designs when I worked through the schools and comments about this issues they have with them such as the one I just hi-lighted should be avoided in the design stage.
I also ask the question why you cannot change the voltage, you are allowed to run different voltages in the same containment as long as all cables are sufficiently insulated to that of the circuit and or controls of the highest voltage.
Yes I know it is not a machine but you have to consider what may be plugged in will be energised when power is restored so there is no real relaxing away from standards that cover machinery control, it is still a safety system and by the fact it is controlling power to gas valves, possible extraction fans etc it would fall within the realms of the standards required for machinery thus the system should be design to meet it as such, even if you don't actually fall under the BS60204, you will fall under other standards and given they are all derived from the same blueprint it would most likely follow the same basic design requirements, if you have any knowledge of the BS60204-1 you will see many standards are actually repeated in the BS7671 especially that of O/L protection of motors etc... you will find this overlapping of regulations very common across the many different areas of British Standards.
