Wiring a siren through a timer

[alanmcm]

Looking some advice on wiring a siren through a timer to alert everyone to the conveyor belt running. They don't want it to delay the belts starting (stupid idea) they just want it to sound when the belt starts up as it's unguarded. I'm wiring it off a n/o contact on the push button. I'm trying to figure out the rest of it. I will be with someone when doing it but I'd rather know in advance how to do it so I can learn it myself. Any advice appreciated. It's a 3 phase motor and contactor.

 

[Spoon]

Yes, you are probably not going to like me but:

What does the risk assessment say?
Is it safe to not give people prior warning of the conveyor starting up?

 

[alanmcm]

Yes, you are probably not going to like me but:

What does the risk assessment say?
Is it safe to not give people prior warning of the conveyor starting up?

Haven't seen the risk assessment yet. The job isn't to start for another few days yet so I'm just nerding up and trying to figure it myself, I don't agree with it not delaying the conveyor start as it seems a more sensible choice but I'm not the manager.

 

[Barry White]

I think you need to reappraise this. Employ someone to do a proper risk assessment and then go forward with the recommended modifications.
Altering a startup procedure of a manufacturers machine needs careful thought.You will become fully responsible for the safety of the system too. (Sometimes the machine manufacturer has an upgrade made to meet current standards so try contacting them for advice too)
Adding a siren once the belt starts is in my opinion is at best a nuisance at worst dangerous

 

[Spoon]

I don't agree with it not delaying the conveyor start as it seems a more sensible choice but I'm not the manager.

Is your manager going to do the risk assessment?
Who is taking responsibility for the safety of the design, you or your manager?
If its you then I would stay away from it. There is a lot to look into. Get someone who is up to date with all the necessary procedures to do it.

 

[Darkwood]

This as others have pointed out will need a risk assessment if the siren is providing an audible warning to stop people getting injured or worse in any way, if that is the case it is unlikely this solution is the correct one required to meet safety regulations, if however it is just a pre-empt for the workforce to ready themselves possibly if they are packers or pickers etc working directly with products passing along the conveyor then its not there for safety reasons and shouldn't be a problem.

A delay off relay, triggered by an input from the motor contactor auxillary N/O contact would be one solution but with limited info it's really hard to express the best solution here.

 

[alanmcm]

I think you need to reappraise this. Employ someone to do a proper risk assessment and then go forward with the recommended modifications.
Altering a startup procedure of a manufacturers machine needs careful thought.You will become fully responsible for the safety of the system too. (Sometimes the machine manufacturer has an upgrade made to meet current standards so try contacting them for advice too)
Adding a siren once the belt starts is in my opinion is at best a nuisance at worst dangerous

Someone proper is doing a risk assessment I'm only after some knowledge to help learn. I won't be doing the work unaided and without an assessment completed. Not once have I mentioned that the assessment isn't being completed either so I'm not sure where you gathered this information from. Sorry if I'm coming across as rude but I was only after a bit of a nudge in the right direction to help learn myself, but seems there is a fixation on risk assessment. I'm only assuming that delaying the conveyor would be the better option, in my mind it's the safer option but I'm not designing the work.

 

[Barry White]

Someone proper is doing a risk assessment I'm only after some knowledge to help learn. I won't be doing the work unaided and without an assessment completed. Not once have I mentioned that the assessment isn't being completed either so I'm not sure where you gathered this information from. Sorry if I'm coming across as rude but I was only after a bit of a nudge in the right direction to help learn myself, but seems there is a fixation on risk assessment. I'm only assuming that delaying the conveyor would be the better option, in my mind it's the safer option but I'm not designing the work.

You don't appear to have come across rude You have supplied extra information too. but this is what prompted my reply.

They don't want it to delay the belts starting (stupid idea) they just want it to sound when the belt starts up as it's unguarded

 

[Spoon]

The risk assessment it very important for the design, that is why we bleat on about it mate.
As @darkwood has asked in post #6, do you know the purpose for the siren?

 

[alanmcm]

Yeah the purpose of the siren is on a slew conveyor bringing sand and stone into bins. The alarm is to let everyone know the belt is running. I won't be doing the risk assessment or design for the work I've just been told what I'll be looking at at the end of the week.

I gathered materials for it today, 24v siren as there is a transformer in the panel. Another n/o contact for the push start button and a timer. Not sure if there's more to come but won't know until Thursday. I'm just swatting up to learn more so I can be self sufficient and asking on here was one of the ways I was hoping to learn.

 

[Darkwood]

A extra N/O contact block on the start button would work if your only able to start it at one point and it doesn't have any automatic start, I assume your workmate/boss is using a pulse triggered timer relay in this case that just needs a momentary signal and it will operate its outputs for a preset period which you set.
Like I said earlier, to give a definitive answer we would need alot more info, although these kind of conveyors are pretty robust and heavy duty and do pose a risk to operators getting too close, all modern versions of these are very well caged and protected, its not just about getting caught up in the mechanics but also falling debris, there should be a clear way around this conveyor when in use. If this is an old model and lacking modern guards etc then I would thus say the risk assessment has not been done or this is just a temp' measure put in place while a permanent solution can be sorted during the next available down time if a action plan has been drafted up.

I understand your just trying to get a heads up to how it all works but just pointing out a few things to look out for or even raise as a question during the job.

 

[David Prosser]

Is the alarm just to get people back to work or something like that, or part of a safety review ?

I would suggest an extra N.O. block on the contactor to a pulsed timer relay, or if there is a start relay you could put it through that first then a timer which could also delay the start this would also mean it comes on either in hand or auto.

 

[alanmcm]

Yeah sorry for the lack of info. Haven't seen the job yet so only going by what I've been told. The conveyor only starts up with the press of a button. And I've been told that the conveyor is fully guarded from top to bottom. The alarm is just to alert them that it's moving and that's what's been assessed and it's all that's needed, ive asked questions. I'll get the risk assessment as I'd like to see the layout and the information contained within.

So if it was wired through the n/o on the switch I would take my 24v through a n/o on the contactor through the timer and then onto the live side of the siren? Or am I missing a step?

 

[Darkwood]

It all depends on your control system as to how it is best done, the timer relay will normally have volts free contacts and you use these to run the siren from whatever power source you choose, this means the control wiring of the machine can be kept isolated from that of your siren if required, the regulations that cover this is not the BS7671 and will more than likely fall under the BS60204-1 ... so don't worry if you cannot pick it up fast as its pretty complex with the regulations that you need to follow although the job itself may seem simple.

 

[alanmcm]

It all depends on your control system as to how it is best done, the timer relay will normally have volts free contacts and you use these to run the siren from whatever power source you choose, this means the control wiring of the machine can be kept isolated from that of your siren if required, the regulations that cover this is not the BS7671 and will more than likely fall under the BS60204-1 ... so don't worry if you cannot pick it up fast as its pretty complex with the regulations that you need to follow although the job itself may seem simple.

Thanks it's a slow progress learning about control circuits at the minute. Just got through star delta starters and wiring in timers for lights, there handy enough to do. I don't like not knowing things and I always seek to try and learn as much as I can as fast as I can so I can be an asset to the company and be more self sufficient. Is their any examples of how it would be done, not necessarily specific to my case. It might give me a clearer outlook on what's involved. Thanks again for having patience with me.