One way voltage

[Lua]

Hi everyone, I have a question. I have two machines one is table saw and another extractor. To run a saw I need to turn on the extraction unit which is about 50m away and this procedure is repeated 40 times a day (20 ON and 20 OFF). My plan was to connect the switches together by a wire, so that with only one switch I could turn on both machines and with another one turn them off. When I turn on table saw at the same time extraction unit turns on as well, which is ok and it's working. My problem is that if I click to turn on the extraction unit for any other reason my table saw activates as well, which is very bad. So my question is how I can control voltage to go only one way ( I know that diodes do that but in my case I have 240 v. Thanks

 

[Evans Electric]

The saw should NOT be  switching ON  without warning / unattended   , its dangerous .      

You could have a  circuit that prevents the  saw working without   extraction  but you can't have machines starting up like that . 

 

[Lua]

So this is my issue, I do want the saw to turn on the extraction, but not vice versa . Thanks

 

[ProDave]

You need a relay and a bit of thinking, not difficult.

 

[Evans Electric]

   You need to alter the existing wiring  so each machine is separate .

If you are creating dangerous dust ..say...  you  could wire an air flow detector  in the extract flue  that prevents the saw from  being started  with the extract . 

 

[Lua]

So the machines are actually separate, the connection between them is only in my head at this moment. I just done some tests and it's working, the problem is that It needs to work only one way. Thanks

 

[Evans Electric]

I don't know how your machines are wired up ... it sounds like  they are wired  as one machine  , which is not good .  

Just noticed the extract is 50m away  so you need  remote stop / start  buttons  for the extract  unit  mounted by the saw , to save  all the walking   and a link in the control circuit  to prevent the saw from starting  without the extract.  

Or if its  not a big deal  with the extract ,  you could simply have a sign saying "  Do not use  saw without  extract "  .    

 

[Sidewinder]

Hello Lua,

Welcome to the forum.

Is this in the UK?

 

[Doc Hudson]

Hello Lua,

Welcome to the forum.

Is this in the UK?

The OP's location states "Basingstoke"

Doc H. 

 

[Andy™]

sounds like the SL from both machines are connected to each other so either switch will power both...

 

[binky]

just needs a relay operated by saw start button that by passes the switch for the fan, and some warning labels about dual start / isolation for the fan. Alternatively you could just extend the cabling for the fan switch to position start button at the saw. Could possibly manage this with wireless controls if cabling is diffficult?

 

[Sidewinder]

just needs a relay operated by saw start button that by passes the switch for the fan, and some warning labels about dual start / isolation for the fan. Alternatively you could just extend the cabling for the fan switch to position start button at the saw. Could possibly manage this with wireless controls if cabling is diffficult?

No you can't because that would not meet the safety requirements.

Unless you are going to ignore the harmonised standards which, if you follow guarantee compliance with the legal requirements, which BS 7671 does not, but, compliance with BS 7671 seems sacrosanct.

This falls under the supply of machinery safety regulations as it becomes an assembly of linked machines, thus the full legal requirements of that law apply.

Hence why I asked if it was in the UK, though, if it's in the EU the same applies as it falls under the Machinery Directive.

 

[binky]

OK, so can we move the start button for the fan?

 

[Sidewinder]

Yes the LEV controls can be moved.

They can be linked, if, it is done correctly, and the way the OP seems to be going about this would not meet the EHSR's of the SMSR, and would thus breach both the SMSR & PUWER, so would be a criminal offence.

 

[binky]

The OPs method is simple but deadly, as has been mentioned above, so how would you manage to link and be compliant

 

[Sidewinder]

The OPs method is simple but deadly, as has been mentioned above, so how would you manage to link and be compliant

How long have we got?  :slap

Firstly it starts with an assessment of any safety requirements, then the PLr for the safety circuits and goes on from there basically following the requirements of EN 60204-1 & ISO 13849-1, then once designed, validating the safety in accordance with ISO 13849-2, if it passes validation, then you build it, and test and inspect in accordance with 60204 & 13849, voila.

That's like 800 pages of standards to reference.

 

[Evans Electric]

Blimey  !    How about a big sign that says  ..(in  10 languages)     ....."DO NOT USE SAW WITHOUT THE EXTRACT UNIT "  

 

[binky]

so 3 relays, 2 powered from the individual machines that if powered off do not allow the third interlink relay to start both machines - simples 

 

[Sidewinder]

so 3 relays, 2 powered from the individual machines that if powered off do not allow the third interlink relay to start both machines - simples 

Not quite, how do you deal with the emergency stop, this is a safety function, and in the absence of a C-Type standard requires PLc under ISO 13849-1, a simple relay solution may not meet PLc, and anything less would not meet the legal requirements under SMSR & PUWER.

Machinery is no longer as simple as BS 7671 stuff as the standards are in place and they actually do offer compliance and this is stated in the legislation as a means for compliance, not like BS 7671, whilst the masses believe that BS 7671 must be followed, it is only an industry guide.  On the machinery side the standards are backed up by law, and if it goes wrong and you have not followed the standards, then you must have good reason for not doing so, and it must be documented with proof that it was just as safe, which, it quite possibly wasn't because it went wrong in the first place.

 

[SPECIAL LOCATION]

The logic of what you want to do is no different to the old bathroom without a window, but a fan and light...

Where customer wants to have single switch that can turn on both light & fan for when having a shower...

But another switch to turn on just the light for when only using the loo...

(in this case the light is equivalent to the dust extractor...

and the bathroom fan the equivalent to the saw..)

So if the light is wired via 2-way switch sort of arse about face..

Perm Supply to L1,

Lamp to Common

Switched supply from fan to L2...

So if the light is switched on its perm live via L1 and Common  (but NO feed to the fan).

if the light is switched off it will also become live if the fan switch is turned on.

e.g.  light switch will ONLY turn on light

Fan switch with turn on fan and also light even if light switch is turned off...

Done it for a bathroom with a double gang switch, one marked Light other marked Light+Fan…

Not sure if this concept is adaptable for this scenario though... especially 50m apart!

Guinness   But the logic is do-able.