Earthing woodworking machine question

[Woodworker]

Hi, I am replacing a “fizzing” start /stop switch on a metal framed woodworking machine , with an NVR switch with emergency stop. The machine itself is mounted on nylon castors which presumably insulate the machine electrically from ground. My question is therefore, where do I attach the earth wire - to the frame or elsewhere? The machine has a 1hp electric motor. Thanks!

 

[Lucien Nunes]

There's no one-size-fits-all answer to that. It depends on how the cabling is run through the frame, how that is insulated, how continuity is maintained between the frame and the motor. Why are you not connecting it to where it was before?

Note also that changing the spec of any safety-critical control element such as a stop button could make you responsible for the design and safety of the finished job. I won't bang on about the ramifications of this but others here might.

 

[Wilko]

Hi - are you saying there is no earth connection at present?

 

[Woodworker]

Thanks for your reply. The machine is about 35 years old - the previous start/stop switch was contained in an exterior metal box attached to the frame and fed directly with power cable and motor connection cables with separate earth connection within and attached to the box.
The new NVR and Emergency stop switch is all plastic and YouTubers suggest earth cables should be attached to the frame. However as the machine on its integral frame has now been mounted on nylon wheels for ease of movement, I believe this will insulate the machine from the ground. Would the earth be effective if the earth wires are attached to the frame and a separate earth cable run from the frame to a copper pipe cemented into the floor - or is there a neater solution? The machine is only for my own use.

 

[davesparks]

Th

The new NVR and Emergency stop switch is all plastic and YouTubers suggest earth cables should be attached to the frame. However as the machine on its integral frame has now been mounted on nylon wheels for ease of movement, I believe this will insulate the machine from the ground. Would the earth be effective if the earth wires are attached to the frame and a separate earth cable run from the frame to a copper pipe cemented into the floor - or is there a neater solution? The machine is only for my own use.

I strongly recommend that you don't carry out this work yourself, it is clear that you have no understanding of the basics of electrical safety and you could easily put your life at risk by making a simple mistake.

You need someone who is competent to do the work and also competent to carry out testing to ensure that the machine is safe to use.

Watching YouTube is not a substitute for training and experience.

 

[Wilko]

Hi - the machine must be earthed effectively for your safety. As the earth point will now be changed an assessment is required as to the most effective location(s). That’s why fault fixing with a like for like part approved by the original manufacturer is preferred. From what you’ve described, I too think you should get an experienced person in to take responsibility for the new design, installation and testing.

 

[Woodworker]

I get your justifiable concerns with my electrical experience which is certainly limited- and therefore I will only undertake straightforward electrical tasks -I also note the careful advice to get a qualified electrician on to the job. However this is basically a straightforward replacement of a vintage on/off machine switch with a modern safety switch. There are two cables coming into the switch, each of 3 wires. The new switch comes with wiring diagram for live and neutral but no mention of earth. I am told by an authority on these vintage woodworking machines that it is sufficient to join the two earth wires together using a mini-block within the new plastic switch box. Besides the cautionary advice already given, would you agree this is the correct procedure?
Thanks for your attention.

 

[davesparks]

owever this is basically a straightforward replacement of a vintage on/off machine switch with a modern safety switch.

I am told by an authority on these vintage woodworking machines that it is sufficient to join the two earth wires together using a mini-block within the new plastic switch box.

What exactly is the 'safety' feature of the new switch that the old switch doesn't have?

It is impossible to say how the earth should be connected without seeing the machine itself and being able to make that judgement, this may also require some testing.

All exposed metalwork of the machine which could become live during an electrical fault should be connected to the earth of the supply cable.

If you have been told by an 'authority in vintage machines' that this is the correct thing to do, and they are accepting liability for this advice should it prove to be wrong then carry on.

 

[Woodworker]

Thanks Dave - pictures of machine and switches old and new attached

 

[Lucien Nunes]

If I am seeing this right, you are intending to replace a starter comprising a contactor and overload relay, with a ZVR and a pair of buttons. What are you using for overload protection?

 

[Woodworker]

Thanks for your question Lucien - Ignorantly I thought i could do without but from reading up , inspired by your question, it’s evident I need to replace it with similar- in fact I understand I could use the opportunity to source a unit that will also be able to reverse the motor which would be occasionally useful. It’s clear to me now that I have the wrong replacement switch unit and must change it. Thanks

 

[Lucien Nunes]

Had you not mentioned adding reverse, I'd have suggested fixing the existing starter. Your 'fizzing' might be just the contactor not closing fully due to dirt or corrosion - you get a characteristic buzzy / fizzy / chattery noise if the pole faces don't sit snugly together, or a poor connection. It takes heavy industrial use to wear one out completely.

For reversing, you will need to bring the two windings out of the motor separately to the starter. The terminal board may or may not be accommodating of that. Be prepared for the winding leadouts and capacitor flylead to have rather frail insulation. Also beware of doing too many starts per hour on that original start cap; some of the caps on these Gryphons are getting beyond their anticipated lifespan.

 

[Vortigern]

As you will be hands on with the machinery, if you do get the earthing wrong, you will become the earth in a fault situation. I don't imagine that would be too pleasant, proceed with caution!