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Safety circuit

David Slate

Hi all,

With more of a renewables background ive not done much in the way of safety circuits, but im trying to design a small lab set up as follows for solar PV training

main incoming supply split to 5 separate bays each with their own TP DB for various circuits, each having their own E stop

Id like to have a contactor that would either isolate all bays when ever an E stop is pressed or simply isolates the bay concerned.

From a simple perspective i thought a N/O E-stop with a NC contactor. but most E stops seem to be N/C (and have read better suited in safety systems?) but this would mean the contactor would require to be N/O. which is fine.... i assume, but that it will likely (fingers crossed) never be utilised so that it will be being held in unless their is a safety issue. Is it Ok to have a N/O contactor constantly engaged or is that bad design?

Id like the contactor/s to be needed to be reset perhaps by key or some other manual means any advice here?

thinking again im not sure how a single contactor could work as the load would need to be split into the 5 bays which would mean further OCPD's downstream of it, 

so perhaps 5 separate contactors all linked from the Estops to A1 (or not linked if we are only isolating each bay individually) 

anyway thanks in advance!! Image below shows just a single contactor 

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    The one in our centre is held on, perhaps considered fail safe, so coil always energised. Re-set from a remote key switch at tutors desk. 

  • 0

    Should say it’s only on when needed!

  • 0

    NC stops and NO contactors are perfectly normal, and often preferred as it is then easy to  ensure a clear disconnection and deliberate restart is required if there is a power cut or voltage droops for any reason.

    (The more likely failure is a wire to a stop button falling out, not shorting, and contactor coils rarely fail in a way that they are permanently pulled in against the spring.) A rather souped up version of the self-latching relay.

    If you are doing this as a real safety interlock, you'd probably have dual redundant force guided contacts on the stop buttons and some sort of fault detection, so if the relay contacts were shut but the coils had no power then an alarm would light or buzz.

    Mike

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    As Lyle says, this is the kind of system you need.

    The most relevant standard for a training environment is probably BS 4163 Health and safety for design and technology in educational and similar establishments. Code of practice

    The e-stop system requirements are in Clause 7.2.5 of the standard, which refers directly to BS EN 60204-1 and BS EN ISO 13850 for the e-stop system, and leads to what Lyle has discussed.

    You might also consider BS EN 50191 for helping assess and manage other risks.

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