Test Question for Students (level - medium)

[kme]

Since Canoeboy`s excellent question has piqued interest, I thought I`d add another, maybe slightly easier one.....

Here`s the scenario:

You`ve installed a ring final into a room which is to be used as a practical classroom. The specification has called for emergency stop buttons to be fitted to the circuit.

You can either post a diagram or drawing; or describe how you`d wire such a circuit.

Be aware of the following stipulation: The circuit must NOT re-energise on release of the emergency stop. A separate "reset" switch must be used.

Please provide diagrammatic or descriptive schematic, and list the materials needed to complete the project.

1. You need to provide 4 no. emergency stop buttons.

2. The wiring is to be installed in 20mm PVC conduit - the same conduit the ring final wiring is installed within.

3. The ring final feeds six double socket outlets; is wired in 6491X 2.5mm throughout. Ring length & tests are not part of the exercise.

4. The OCPD is a B32 BSEN60898.

5. The distance from the DB to the final emergency stop is 16 metres.

6. The reset switch must be key-operated.

Good luck

KME

 

[Mr T]

Since Canoeboy`s excellent question has piqued interest, I thought I`d add another, maybe slightly easier one.....Here`s the scenario:

You`ve installed a ring final into a room which is to be used as a practical classroom. The specification has called for emergency stop buttons to be fitted to the circuit.

You can either post a diagram or drawing; or describe how you`d wire such a circuit.

Be aware of the following stipulation: The circuit must NOT re-energise on release of the emergency stop. A separate "reset" switch must be used.

Please provide diagrammatic or descriptive schematic, and list the materials needed to complete the project.

1. You need to provide 4 no. emergency stop buttons.

2. The wiring is to be installed in 20mm PVC conduit - the same conduit the ring final wiring is installed within.

3. The ring final feeds six double socket outlets; is wired in 6491X 2.5mm throughout. Ring length & tests are not part of the exercise.

4. The OCPD is a B32 BSEN60898.

5. The distance from the DB to the final emergency stop is 16 metres.

6. The reset switch must be key-operated.

Good luck

KME

Here goes...

t&e from a 32 amp MCB to feed the supply side of the contactor - then from the load side of the contactor to each socket.. then a t&e from a 6 amp MCB to feed each em stop finishing at a key reset switch and back to A1 on the contactor...

I believe the key has a contactor in which means in the event the em stop button is pressed and then pressed again then the circuit wouldnt re energise until the key is operated and the contacts are closed again.. When an em stop is pressed then this breaks the circuit and the coil is deactivated...

 

[philbas]

I think they are stuck on my question at the moment :slap

Even you are stuck on your question, you asked Sidey to provide the answer

 

[Sidewinder]

There does seem to be a low uptake!

BTW I still have not had chance to pick up that other info for you, perhaps tomorrow!

Honest Guv!

 

[Apache]

There does seem to be a low uptake!

If I can be brutally honest, to have even a stab at the answer required a lot of work, instantly putting most people off.

Personally, I think this question is far more accessible!

 

[steptoe]

have a go then Apache,

I have one too, but mine will be in the easy peasy category, :|

 

[kme]

To mrT:

As canoey says, can we have a diagram please?

Check what a keyswitch does

There are a couple of other points I would raise; but I`m not going to say anything yet.

`Pache - :x

 

[Apache]

have a go then Apache,

I'm working on it now!

 

[Manator]

Do you know something, these questions really make you retest your knowledge. It is so easy doing what you do, day in and day out, but being asked to design and take some responsibility for your design is like doing homework that you enjoy. Its keeps you on your toes, and whilst its good for students, it is also extremely good for those who have forgotten how to do all those calcs that made us what we are.

 

[steptoe]

I agree, I even got a pen and done a quick sketch of how I would do it, so I have some comparison with anyone that loads something up,

just so Im not just in my head with it all, and can see other possible options that may, or may not work, but see the reasoning behind the ideas.

 

[Apache]

The only way I can see is using a 4 pole 'normally open' contactor fed from the 4 em stops, which in turn feeds the over-ride. When an em stop is pushed then the 'key over ride''s power would be removed, that in itself has an integral contactor and requires a key to reset. The phase would then go from the over-ride switch to the ring. There has to be a separate 'stop' circuit like the other chap says. I am just having trouble drawing it without confusing superimposition! Art never was my thing.

I'd use this as the key over-ride

Crabtree 1-Way A-Lock Mushroom Head Stop Push Button & Key Reset | Screwfix.com

This for the contactor

25 Amp 4 Pole Contactor - 2 Module

And 4 of these for the EM stops

Crabtree 1-Way Mushroom Head Stop Push Button | Screwfix.com

Anywhere near?

 

[steptoe]

Apache,

myself, without wanting to give too much away,

would, at a basic level, employ 2 contactors,

as you suggest, so you are obviously, IMHO, going along the correct route.

 

[M107]

Contactor rating patch

 

[Apache]

Contactor rating patch

40 Amp 4 Pole Contactor - 3 Module

 

[Sidewinder]

Steps,

You don't actually "NEED" 2 contactors.

 

[M107]

I was going to go with one & possibly not a seperate circuit for the switching of the coil.

 

[kme]

May be my fault - I did pose the question to point to this, but maybe it needs to be specified.

The question started by saying "you`ve installed a ring final"; and you`re now having to fit an e-stop circuit to it.

In other words - you don`t need to list the materials specific to the ring circuit; but you do have to interrupt the ring with your stop controls.

Sorry if I wasn`t specific enough......so you`ve actually got less work to do now opcorn

 

[steptoe]

Steps,You don't actually "NEED" 2 contactors.

correct,

it would make it a lot easier for patch though , without a specific knowledge of electrics,

the simpler wiring method would be latching interrupt.

 

[Apache]

What about muddying the water and using logic control? I remember from my GCSE physics AND/OR/NOT gates.

If we had 2 AND gates each with a pair of em stop buttons with their output to another AND gate, then if any button was pushed we'd lose one of the AND signals, the first gate would close, causing the second AND gate to close and the key 'over-ride' to trip.

Not sure how that works in real life.

Can you just buy this stuff?

 

[kme]

Ooh - now that`s "thinking outside the box" for you

Logic control is used in some situations - but iirc not for e-stop, due to the implications of circuit failure.

KME