NO Emergency stop points

[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

 

[Darkwood]

As it has been brought up it does seem rereading it that the NO is probably 'Number Of' but the lack of punctuation ie No. or N/O made the post very ambiguous, this could be a mistake by the OP or simply that he has passed on the info' as given, either way I think it matters not to the end advice given.

I would also be implementing RCD cover for said circuits too in addition to my previous postings, this may not be required under the BS7671 depending on install methods but a risk assessment would probably implement them into the design as I assume they are training to wire up smart meters and energising them, probably a very expensive 4hrs of training for a crap wage.

 

[Karl Atkins]

this is the email I received.

I have had a chance to speak to my Operations Director and found a list of the work that needs doing in the training room.


Please see below quoted work:


Test Bay Work to be carried out under mezzanine floor.

• All other existing power to be altered or removed and made safe.
• TEST BAY to supply and install 2 dado trunking to house 10 no emergency stop points.
• 10 no switch fused spurs.
• 1 no emergency lock off with key lock to control the whole room (near the entrance)
• Boiler switch spur to be swapped to an unswitched spur.
• To supply and install A/M 3 consumer unit to power all new installs (This will be fed from DB1)

 

[Darkwood]

So no active safety control monitoring circuit mentioned by the looks of it, totally relying on a very basic arrangement that probably falls far short of requirements, who is requesting this and what knowledge do they have of the relevant safety requirements?

I would be asking them who designed this installation you are been asked to quote and what relevant guidelines/regs it follows as you have your concerns about the design. Tell them you will be happy to quote said work if someone else signs of the design of the safety system.

 

[davesparks]

Pretty clear that it means 10 number, not 10 normally open

 

[Darkwood]

Not to someone that builds panel daily .. a full top or forward slash make a big difference

 

[telectrix]

why did the donkey who prepared that request not say 10 x switched fused spurs ( or switched fused connection units). clearasdaythen.

 

[Pete999]

why did the donkey who prepared that request not say 10 x switched fused spurs ( or switched fused connection units). clearasdaythen.

Probably picked up the "switched fused spur" without having the faintest idea what it is and thought he would drop the phrase in a specification, Smartarse.

 

[davesparks]

Not to someone that builds panel daily .. a full top or forward slash make a big difference

Why, do panels often use normally open switched fused Spurs?

 

[Spoon]

I can't remember the last time NO contact were used for an Emergency Stop. We use 'one NO and one NC contact' on lots of functions, so to monitor it correctly.

Test Bay Work to be carried out under mezzanine floor.

• All other existing power to be altered or removed and made safe.
• TEST BAY to supply and install 2 dado trunking to house 10 no emergency stop points.
• 10 no switch fused spurs.
• 1 no emergency lock off with key lock to control the whole room (near the entrance)
• Boiler switch spur to be swapped to an unswitched spur.
• To supply and install A/M 3 consumer unit to power all new installs (This will be fed from DB1)

Correct me if I'm wrong but isn't this just power for a 'training room'?
Does the guy mean "Isolation points" rather than "Emergency Stops"?

 

[Darkwood]

Why, do panels often use normally open switched fused Spurs?

You missed my previous post suggesting NO was probably relating to 'number', also of it did indeed mean normally open then it would suggest that the spurs have no power until the tutor uses his key, N/O will not mean the actual spurs are normally open due to the fact you cannot get such a thing, if a spur has a switch on then it cannot be called N/O or N/C.

 

[Darkwood]

@Spoon
This is a training room and students will be dealing with wiring and energising smart meters, there will be a requirement for the students safety so it will mean E-stop but an E-stop is only as good as the method it is wired in and a full risk assessment should be carried out to ensure it is fail safe and fully under the control of a responsible person (tutor in this case), wiring a very basic system that is not self monitoring would not be suitable in my opinion especially if they intend to just run the live wire through all the stops first and then to the spurs... this is how I read their request.

 

[Pete999]

Why, do panels often use normally open switched fused Spurs?

Only if they are switched OFF Dave

 

[Spoon]

... if they intend to just run the live wire through all the stops first and then to the spurs... this is how I read their request.

Is this the intention OP? I don't like it if it is.
Wouldn't it be better to have a contact that switches the power for the whole room and the 11 E-Stops are wired to this, via a safety relay.
Then if one of the students see someone else in trouble they can hit their E-Stop and that will cut the power, rather than someone running over to whoever is in trouble and hitting their E-Stop.

 

[Darkwood]

You misinterpreted my post @Spoon I meant through all the E-stops first before then going to each spur, that way any E-stop is in series with all the spurs thus cuts power.

 

[Spoon]

You misinterpreted my post @Spoon I meant through all the E-stops first before then going to each spur, that way any E-stop is in series with all the spurs thus cuts power.

Yes I did misinterpret your post mate. Soz.