Contactor question - multiple inputs

[thegruf]

Any contactor specialists out there?

I have multiple machines that are connected via extraction ducting to a 2KVA 3 phase extraction fan on the external wall.

At the moment I rely on machine operators to switch the extraction fan on before using any of the machines (not all machines are used at the same time). Trouble is they forget sometimes and this causes problems.

I am thinking there ought to be a contactor out there to which you can just add additional input modules, so if I wire back a 230V signal from each machine to an input to the contactor from each of the machines, then if any machine is switched on the contactor will make to switch on the fan.
Then all I need is one last function to delay the off by say 30 minutes after the last machine has been switched off.

I know there is other ways of doing this, but wanted to explore what could be the simplest route if there is such a modular contactor.

 

[Martin Kerr]

There are no input modules on a basic contactor ,just a coil supplied with the relevant voltage, I remember a fault input module from way back, where you could have multiple fault inputs, which would switch a common fault output on a standard relay base
I think a basic PLC would be a much easier way to go , but would require some basic programming

 

[Spoon]

I'm with the idea above about using a basic PLC.

 

[ipf]

You could fit signs to the machine control points along the lines of 'Before using this machine, ensure extraction is in operation'....worth a try, maybe...and cheapest way out.

 

[sam400]

You need volt free aux contacts in each machine that needs to bring the extract on, take a supply from extract unit to each machine aux contact then back to the input on a delay off timer, which in turn pulls extract contactor in.
All the aux contacts are in parallel so any machine will activate
extraction. You can even daisy chain the machines for ease of wiring. Make sure you label machines for the additional voltage present.

 

[David Prosser]

Or you could wire the start controls for the machines to go through a simple normally open auxiliary block on the fan contactor. This would mean the machines couldn't start without the fan running.

 

[netblindpaul]

Remember that the LEV is a safety system.
The machine controls if they have an e-stop have safety functions.
Modifications to machinery must be carefully considered as they are covered by several pieces of legislation.
This integration is easy to do, but not easy to do in compliance with the laws in place, unless you follow the requirements of the harmonised standards.
The LEV being a safety system, and being required for the machines to operate, makes this part of a safety function.
A normal PLC is not acceptable for use within a safety function under any circumstances.
A programmable device forming part of a safety function must be failsafe from input, through processing to output, and the software must be independently validated by another person, not the writer to ensure that it is also fail safe.

 

[PEG]

Hi,you could make the fan switching,separate from the individual machine controls,by having it switched via independent,use-specific means.
This could by PIR,sensor-mat,or a machine induced switching signal,such as temperature or air flow. A simple timer relay,would cater for any post-running requirement.

A look in to the costings,for such a system,may encourage you to do as suggested above,and simply press home the training and signage.

Out of interest,is the fan providing cooling only,or extraction of material?

 

[Ffoeguk]

This might be an idea to investigate.

 

[thegruf]

Hey - a ton of ideas here.
Signs - well wouldn't be here if they worked 100% of the time, sadly it's the few percent I have to deal with.
We realised that most of the machines are not fully off when switched off so the current sensor idea is good but then we have to set it up to ignore the background current draw and all gets a bit messy even if cabling is simplified, also the DB is stuffed so not much chance of even finding space for current sensing coils.
The PLC is great idea and being in electronics we already thought of this but eliminated as there is a safety aspect to the extraction.
Locking out the start of the machines if the fan wasn't on gave me a laugh. The idea is sound but mucking about with the machine wiring creates other concerns.
We'll just put a few relays/delay timers together on a DIN rail for logic ahead of the contactor actuation along the lines of Sam400 post. Simple enough, extensible if required and cheap too.
Thanks all.

 

[James]

you can get a safety plc for around £300 that you can program to suit the application, search for SICK SAFE. you can then define what happens if certain inputs fail. for example, rather than just relying on volt free contacts for each machine, the plc will send a series of coded pulses to the machine and only react if the pulses returned are correct.
without going into lots of tec. details this is a suitable way to sort the problem without relying on signs that say before you switch on make sure this is switched on!!

 

[Darkwood]

Like has been mentioned already, there are several approaches to this but as mentioned it may be a minefield of regulation and safety aspects to be considered...

Noted here if you go down the aux' contact to each machine then you will still have to comply with machinery standards on how to implement it, yes it is a simply solution on the face of it but you will need to know the regulations that even determine the colour of the conductors used.(Diagrams would need to be updated & measures taken to ensure it is clear to any electrician/engineer you have external sourced supply in the machine even when the power to the machine is isolated, the method and nature of how you do this varies with the voltage used).
If however the workforce isolate the machines at a wall isolator then there is an option here to use the power source itself as a trigger and this then doesn't require you to step into the machinery side of things.

My last point is also to consider what happens in a fire situation, does the extraction system fall under any regulations that would require it is shut down in the event of a fire?.. I suspect it will already have such a setup if required but food for thought if you are altering the controls.