Multiple control stations for one three phase compressor. Best practice?

[brianmoooore]

Any particular requirements for the isolating Tx, other than it is an isolating type, with the windings on separate legs or an earthed screen between them?
Does it need to reduce the voltage or is 230:230 OK?
Shouldn't be to expensive to make this compliant. Tx will only need to be 10s of watts.

 

[netblindpaul]

Emergency stops, if originally fitted to the equipment, will need to be re-implemented, otherwise the person modifying the control system, will become the manufacturer of the equipment in law.
Any control circuit modifications will need to comply with the relevant requirements of the law, PUWER & SMSR.
They require compliance with the relevant designated standards.
As has already been mentioned BS EN 60204-1, additionally BS EN ISO 13850 for emergency stop functions.
BS EN ISO 13849-1, with validation by an independent person (not the circuit designer) in accordance with BS EN ISO 13849-2.
These are far from obscure standards, they are the underpinnings of machinery safety legislation.
You can forget BS 7671, clause 110.2, xi, excludes machinery controls.
The Designated Standards have a much closer and stronger link to the relevant legislation than for example the statement by HSE in the front of BS7671 because both the standards and legislation are designed and enacted to support and reference each other.
The other thing is the insurance aspect, both for the work on the controls and the insurance for the location where the machinery is being used, business or home.
Finally, the law is constructed or modified such that machinery for the use within a business undertaking even when the machinery is designed and manufactured or modified by the user falls within the requirements of the law.

 

[Lister1987]

Emergency stops, if originally fitted to the equipment, will need to be re-implemented, otherwise the person modifying the control system, will become the manufacturer of the equipment in law.
Any control circuit modifications will need to comply with the relevant requirements of the law, PUWER & SMSR.
They require compliance with the relevant designated standards.
As has already been mentioned BS EN 60204-1, additionally BS EN ISO 13850 for emergency stop functions.
BS EN ISO 13849-1, with validation by an independent person (not the circuit designer) in accordance with BS EN ISO 13849-2.
These are far from obscure standards, they are the underpinnings of machinery safety legislation.
You can forget BS 7671, clause 110.2, xi, excludes machinery controls.
The Designated Standards have a much closer and stronger link to the relevant legislation than for example the statement by HSE in the front of BS7671 because both the standards and legislation are designed and enacted to support and reference each other.
The other thing is the insurance aspect, both for the work on the controls and the insurance for the location where the machinery is being used, business or home.
Finally, the law is constructed or modified such that machinery for the use within a business undertaking even when the machinery is designed and manufactured or modified by the user falls within the requirements of the law.

Fancy seeing you here Mr S ? it's bad when you read a post and think, I know exactly who would write like that ?

 

[Mark42]

This is getting silly.

If all I'm supposed to do is to use an isolating transformer, or ELV circuit, for the remote controls (when there are more than two switch positions) that’s trivial to implement.

But why do it? If two directly-connected mains voltage control stations are safe, why aren’t three? Or a hundred and three? Genuine question.

Maybe I’ve introduced complexity by using the term ‘emergency stop’, which I accept may have an unintended meaning in law. What I really mean is a simple off switch. Ignoring semantic argument, in general language the latter can act as the former.

The most-used machine is a simple chip extractor. (Pic below). This is not some industrial production line with entrapment dangers, exposed mechanisms and rotating parts. It’s a bloody vacuum cleaner: sold widely for commercial and hobby use.

I'm struggling to understand what hazards such a machine could present.

If the regulations prevent me from adding remote switches next to the saws, drills etc where the vacuum ducting ends, it would be necessary to walk into the next room - and sometime the next building - every time an operator wants to cut even one small piece of wood, then return again to switch the extractor off. This obviously means sometimes an operator wouldn’t bother, creating a dust hazard. Any plan which does not include human factors is an incomplete plan.

Also I’d have though it better planning to have a way of turning the vacuum off immediately if something big gets sucked up and jams the pipes or fan. Not particularly dangerous, but it could damage the machine.

These machines are sometimes provided with cheap remote controls of the type used for garage doors, sold without limit to number, for hanging on rusty nails driven into the wall next to each machine. How is that different (or better/more compliant) than what I propose?

 

[Darkwood]

Let's first get things right here, regulation is not preventing you doing what you want to do in this case, it is merely stating the preferred method you originally wanted to take would not comply and you need to implement certain design features to do the work and comply so you can achieve what you wanted to do simply not the way you intended.
Yes on the preface of it it does sound a crazy regulation but you have to look at this the opposite way around in that the regulation is applicably the normal but your approaching this from an exemption to this regulation.
I would also like you to give citation of any 'machinery' like the one you exampled above that has this remote accessory you make claim to, I find no option on Charnwood site for this.

To give you incite to the regulation and why they are applied you need to understand the environments this equipment is designed to be used in, these are he likes of workshops, factories etc, these are areas where risk of damage, contaminants, accidents are perceivable high and thus regulations are brought in to try keep operators safer, consider a 3KW motor connected directly to a start/stop DOL contactor in a contained enclosure similar to the one mounted on the picture you posted -
The control has no fusing down protection
The control has no isolating TX
The control is low voltage and not SELF
The exemption that is put on this set-up is basically because the risk assessment of the fully all in one enclosed system does not raise the risk to operators even in fault conditions, however the moment you start to adding external control points, limits, start/stop station you are creating added potential for damage, abuse, misuse etc and this exponentially increases the risk to users so that is where certain regulations kick in, the one I mentioned is one of many you would need to comply with here.
Let's look at this another way, if you had a workbench and a grinder on it you could have it on a flex and 13amp plug plugged into an adjacent socket the risks of damage although not omitted are small, if however the socket was three benches across and you wanted to add a local socket for convenience then that socket, it cabling etc would need to comply for installation practices for its environment and the risks it poses, IE you couldn't simply run a flex across the 3 benches and fix a socket locally, it is likely if you adhere to even the BS7671 on this matter you would house the extended circuit in impact resistant enclosure like conduit or trunking.
Regulations are based around real world risks, real accidents and historical data gathered over the period of the existence of regulations, you may have the most obedient and respected employees who look after the equipment and are class A safe and thus never damage anything, never operate a machine with wet hands and never trip up and grab what might be a wire connected to a control system and yes your install may never see issue in its entire life of operation but that unfortunately isn't how regulations work, they are designed on risk assessment and averages.

We are merely the messengers here so try not to get frustrated with us, I build machine controls for a living, I repair them and upgrade them and I fully understand why these regulations exist and I could show you many examples of damaged control stations that could have been a serious safety hazard had the regulations not been followed so I struggle to understand your position when you call it silly, although I empathise slightly because when I started in this side of the trade it too was a learning curve and wasn't until I saw many occasions the regulations kept operators safe that I lent them more respect and understanding.

 

[netblindpaul]

I know exactly what a “chip extractor” is.
You might consider it silly, but it’s the law.
Emergency stop functions are no longer considered a primary means if safeguarding.
They are primarily for the protection of the equipment and prevention of “collateral” damage.
The regulations prevent nothing.
They merely require that the modifications are done in a suitable manner.
This is absolutely no difference to what is required by Building Regulations, BS7671 & the competent person schemes.
It is merely the requirements differ because the hazards are different and the requirements of the legislation and standards differ.
The term “emergency stop” is a specific term which invokes the requirements of a safety function.
If the machinery doesn’t have any emergency stops then you will not have to implement them. However if it does then you need to continue that with the modifications.
A simple off switch cannot act as an emergency stop or means of emergency isolation unless it meets the requirements for such.
The standards are very clear on that.

This discussion would not be happening if the work was covered BS 7671, everyone would be supporting compliant work. Just because there is additional legislation and different standards, it is thought to be nonsense.

I believe that if the HSE enforcement archive is checked, then many more actions regarding PUWER and machinery legislation will be found than BS7671/EAWR/Building Regulations.
If you are unsure of the hazards posed then please look up the Essential Health and Safety Requirements in the SMSR, and then refer to the product standard for the chip extraction here:

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shop.bsigroup.com

 

[netblindpaul]

One last point I missed.
Just because fob remote control units are available, perhaps from well known online marketplaces, does not mean that they are compliant.
Nothing is guaranteed to be compliant, hence why the law requires that the end users have to get the compliance checked before they use the equipment.
PUWER Reg 10.
Real Regulations, real law, the breach of which is a criminal offence.