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Thread: Relay question to NC or to NO, that is the question...

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    Weapons Grade Moaner Silly Car's Avatar
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    Question Relay question to NC or to NO, that is the question...


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    I have a quick electrical control question that will probably set the forum into mingmong melt down over whether it should be done, how it should be done, whether I need Part P sign off or whether electrics is voodoo.

    But considering all of that, I am looking to add zoning to the central heating via thermostats on each floor controlling a motorised two port valve with the option to switch on the boiler with a boost / timer button.

    Which would be better practice in respect of a relay to determine the control of a motorised valve?

    A or B below?

    20181204_123802.jpg


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    Should Get Out More Big Pete's Avatar
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    Default Re: Relay question to NC or to NO, that is the question...

    personally, I would use the upper layout. If the relay fails it drops back to timer, rather than running constantly.

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    Default Re: Relay question to NC or to NO, that is the question...

    Lower one makes no sense. Upper one does, a bit, but not much.

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    Default Re: Relay question to NC or to NO, that is the question...

    Quote Originally Posted by Big Pete View Post
    personally, I would use the upper layout. If the relay fails it drops back to timer, rather than running constantly.
    That makes sense although, in the event of failure, the system wouldn't run constantly as the boost button is a 2hr timer switch.

    However, in reality, I will probably use the lower layout as it will put less load on the Central Heating timer as it will potentially be firing 4 valve motors at the same time. Unless anyone expresses an opinion that it really isn't a good idea.

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    Should Get Out More Big Pete's Avatar
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    Default Re: Relay question to NC or to NO, that is the question...

    if you're worried abaout the timer load you could relay up the valves as well, you're already assembling a control box, so you might as well do the job properly.

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    Default Re: Relay question to NC or to NO, that is the question...

    Quote Originally Posted by Big Pete View Post
    if you're worried abaout the timer load you could relay up the valves as well, you're already assembling a control box, so you might as well do the job properly.
    Yeah, that. Get a PLC in there whilst you are at it for full over engineering.

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    Should Get Out More Big Pete's Avatar
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    Default Re: Relay question to NC or to NO, that is the question...

    Quote Originally Posted by go_slow View Post
    Yeah, that. Get a PLC in there whilst you are at it for full over engineering.
    I prefer to call it "user proofing"

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    Should Get Out More Ant's Avatar
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    Default Re: Relay question to NC or to NO, that is the question...

    I've got an Allen Bradley SLC500 in a box here plus loads of I/O boards that a client didn't want.

    Maybe we could come up with some cool heating cotroller from that.

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    Should Get Out More go_slow's Avatar
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    Default Re: Relay question to NC or to NO, that is the question...

    Quote Originally Posted by Big Pete View Post
    I prefer to call it "user proofing"
    You'll never make something foolproof since fools get smarter every day

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    Default Re: Relay question to NC or to NO, that is the question...

    Quote Originally Posted by go_slow View Post
    You'll never make something foolproof since fools get smarter every day
    Word. OTOH, I'm a mech eng, so it's easier to make stuff harder to break than for sparky types.

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