NO Emergency stop points

[Karl Atkins]

Hi All,

I've been asked by a client to fit 10 NO Emergency stops points in a training facility. My question is has anyone fitted these before (I'm guessing the answer is yes) why would a switch like this be used for emergency stop?

he request is also to fit 10 NO fused spurs too.

Am I being naive here or has it just been too long of a week.... Please help!

 

[Deleted member 26818]

If you use NO switches, you will need a controller of some kind.
Does the client mean switched FCUs?

 

[westward10]

What are the stops going to control. How is it going to be reset. What is a N/O fused spur.

 

[rapparee]

They won't be emergency stops, they'll be off buttons. An emergency stop circuit is always monitored.

 

[Pete999]

What are the stops going to control. How is it going to be reset. What is a N/O fused spur.

10 number I hope

 

[Karl Atkins]

Not sure he knows what he means tbh, they are a smart meter installation company, they will in some way control the training boards that the apprentices will be taught the job on, trouble is the big boss man who has specified these was far too busy to meet with the likes of me so lack of detail here to say the least. No idea what a NO fused spur is either????

 

[Karl Atkins]

10 number I hope

Yes 10 x No Fused Spurs

 

[Pete999]

Oh dear

 

[Deleted member 26818]

10 number I hope

You think perhaps the client wrote NO instead of No?

 

[Darkwood]

A request is one thing, knowing the strict regulations around such a requirement is another, do not dig yourself into a hole here that would see you liable for any accidents resulting in a failure of such a system due to poor design and/or breach of regulations.
This requires a monitored circuit design, it will normally require a key holder to power up and/or reset after a E-stop operation and be designed in a fail-safe manner... this means N/O E-stops will not be in the design... I believe the spurs will require to be energised via a contactor which will be N/O when it is not energised.

It seems that the cart is leading the horse here, if you have no experience of such safety circuits then walk away, I would if I was asked this be notifying them that their requests would not meet regulations and then offer them a alternative design that satisfies how they want it to work but does so to requirements following a risk assessment to establish what level of protection is required.

 

[Pete999]

You think perhaps the client wrote NO instead of No?

Yes probably, but in all honesty I don't know what I think, neither does the client.

 

[Karl Atkins]

Yeah maybe, that was my first thought but after speaking with a friend in the game he suggested it could mean "Normally Open", I believe from some research I've done on this notion that there is such a thing but these are more commonly used in PLC environments to control machinery

 

[Pete999]

What are the 'emergency stop' points doing, and a request is one thing, knowing the strict regulations around such a requirement is another, do not dig yourself into a hole here that would see you liable for any accidents resulting in a failure of such a system due to poor design and/or breach of regulations.
This requires a monitored circuit design, it will normally require a key holder to power up and/or reset after a E-stop operation and be designed in a fail-safe manner... this means N/O E-stops will not be in the design... I believe the spurs will require to be energised via a contactor which will be N/O when it is not energised.

Very well put darkwood, yes indeed.

 

[Darkwood]

I added a little on there as an Edit too.. @Pete999

 

[Pete999]

Yeah maybe, that was my first thought but after speaking with a friend in the game he suggested it could mean "Normally Open", I believe from some research I've done on this notion that there is such a thing but these are more commonly used in PLC environments to control machinery

A contactor suitably sized to control, via an E/M key opperated Stop button a radial circuit consisting of 10 fused spur units, a simple job really, if you know what you are doing.

 

[westward10]

Probably a rudimentary system with a contactor controlled dist bd with the control circuit run through N/C key controlled push stops with one at the board for overall control.

 

[Karl Atkins]

Very well put darkwood, yes indeed.

Thanks Pete999, so I'm clear are you saying that "NO" does stand for normally open and that if one of these was used in the scenario i'm describing without an estop then this would be unsafe?

 

[suffolkspark]

think I'm thinking the same as pete here, you sure he doesn't just mean 10 NO as in a quantity of 10

 

[Pete999]

Thanks Pete999, so I'm clear are you saying that "NO" does stand for normally open and that if one of these was used in the scenario i'm describing without an estop then this would be unsafe?

No I'm saying the "NO" stands for NUMBER OF, as in No.

 

[westward10]

Thanks Pete999, so I'm clear are you saying that "NO" does stand for normally open and that if one of these was used in the scenario i'm describing without an estop then this would be unsafe?

Yes the NO should probably be No (Number of) and the stop buttons would be N/C (Normally Closed).

 

[Darkwood]

You also have to consider a failure of the contactor IE it jams closed, it isn't always as simple as making a functional circuit, the fail safe aspect is usually what adds the costs up, I would tend to have a master contactor that feeds radial contactors thus a E-stop operation drops out 2 contactors in series of any power out to the desks, a failure of a contactor thus does not on it's own create a hazard.

 

[Deleted member 26818]

Many stop buttons come with two contacts.
One NO and the other NC.

 

[sevuk]

Normally Open and Normally Closed is quite a simple principle, Normally Open for if you want something to be only on a closed or on circuit when it's in use, like a relay controlling a fan. Then Normally Closed would be something you would want always on unless you deliberately want to break the circuit, a principle that may be used in emergency lighting for periodic battery drain tests.

 

[Karl Atkins]

Thanks for the replies, I think I'll insist on speaking with the organ grinder before submitting any quote.

 

[Pete999]

Thanks for the replies, I think I'll insist on speaking with the organ grinder before submitting any quote.

Good idea