Good practice for lathe circuit design

[RainbowsParticipant @rainbows]

My Wilfin lathe currently has a wiring circuit of

Plug -> Fused switch box -> Motor

While it does work and I could take test cuts I'd rather not have this be the long term wiring plan.

New one, as far as I can think would be

Plug -> Isolator -> NVR switch w/ E stop -> Motor

But also I want in the future to add lighting (240V AC), tachometer (??) , pedal E stop (not sure where it wires in), electronic leadscrew (12V DC? 24-48V DC??), DRO (230V AC), VFD (230V AC), maybe some more stuff.

Ideally I want all electronics stuck in the cast iron cabinet under the headstock of the lathe.

So my questions are

Is my Isolator -> NVR switch w/ E stop enough safety for the immediate task of just controlling the motor?

Also I don't want to have to rip everything out to rewire each time I add a component. I can wire a plug but 7+ circuits in a small space is not something I'm used to making or making look neat. Does anyone have tips on how to make things modular and keep wiring organised?

Also is there a chance that electrical noise from the VFD would affect the electronics in the tachometer or DRO?

Also also (last one now) should an E stop cut power to all parts of the lathe or only cut power to the spindle motor?

[RainbowsParticipant @rainbows]

[David JuppParticipant @davidjupp51506]

On your last point – the E-Stop should stop anything that might cause harm to people, or cause damage to equipment.

On that basis it should power off the motor, and probably the ELS.

It's probably advantageous to leave lights and DRO powered during an E-stop event – those circuits aren't going to move anything, but should be fused, or have equivalent electrical protection.

If you progress to a VFD you might want to consider if injection braking with delayed power off would be preferable to a simple power off – though it is harder to provide this.

Low voltage lighting would be preferable to mains (hurts less when you poke a screwdriver through the lamp), lots of good LED lamps around these days.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Rainbows, as far as your E-stop goes, it should stop anything that can automatically start again after a power cut or when the E-stop is released, i.e. anything that moves, things like DRO's should be OK unless a sudden return of power would cause a surge into any electronics etc. and do them damage.

Regards Nick.

P.S. More or less what David has said.

Edited By Nicholas Farr on 04/10/2019 15:04:23

[Clive FosterParticipant @clivefoster55965]

Rainbows

Your suggested Plug -> Isolator -> NVR switch w/ E stop -> Motor layout is functionally equivalent to standard industrial practice although the machine will usually be hardwired into the supply. The normal electromagnetic contactor does the NVR thing and there will usually be a switch wired in series with the contactor coil to do the E-Stop. Most modern lathes will have a stamp on bar across the front to operate the switch. Common practice is to put extra switches in series to ensure the lathe cannot be started if anything is unsafe.

E-Stop or equivalent usually operates on the spindle and coolant pump motor only.

If you have a VFD normal practice is to wire all the main motor control switches to the VFD. Isolator swithc comes first then sort out the other power feeds as seems logical. Quite common to have more than one swithc on a single button / lever or whatever to interrupt multiple power feeds at the same time. On a machine tool its good practice to run pretty much everything via NVR switches so you know that its all fully powered down in emergency and know where to start from when bringing it back up.

Given the choice I prefer to wire the light direct to the isolator to clearly indicate that the machine has power and can run.

Clive

[Speedy Builder5Participant @speedybuilder5]

RCD ??

[BazyleParticipant @bazyle]

There are plenty of NVR switches around like this one. However notice that it has 4 terminals. 2 in and 2 out. Seems fine but there are some with one or two extra terminals and a connection between two , or a wire coming out to one terminal. The extra wire / terminals are bringing out the connections to the electromagnet that holds the switch on. This is intended to allow you to wire in an additional safety switch that breaks the supply to the internal relay.

However larger lathes get a bit more complex by having a 24v supply and creating a NVR switch (and reverse relays) and allowing the safety interlocks to be at a lower voltage. 24v is a hangover from having it available for lights. You might be better to use 12v as you can get more options for LED lighting etc using car parts.

[Pete RimmerParticipant @peterimmer30576]

I see no good reason for needing an isolator switch where there's a plug and a NVR switch. The NVR switch will turn the machine off, and not allow it to turn on automatically should there be a supply interruption. The plug is the isolator.

[old martParticipant @oldmart]

When we rewired the museums single phase 1 1/2 hp drill mill, we didn't bother with reverse, but kept the pulley lid safety microswitch, added a NVR switch, and added a standard emergency stop switch. The emergency stop switch is in the live incoming wire.

 Other things like DRO would benefit from their own separate power supply. Our lathe has a microswitch in the chuck guard which is linked to the stop button, which gets used all the time rather than bending down to reach the regular stop button.

Edited By old mart on 05/10/2019 21:20:41

Edited By old mart on 05/10/2019 21:25:17

[EmgeeParticipant @emgee]

If you have the Emergency stop and the pulley lid micro switch in the incoming live conductor then they are switching the motor current, not good practise, such switches should be in the starter control circuit.

Emgee

[AJAXParticipant @ajax]

Posted by Rainbows on 04/10/2019 13:51:20:

Is my Isolator -> NVR switch w/ E stop enough safety for the immediate task of just controlling the motor?

Also I don't want to have to rip everything out to rewire each time I add a component. I can wire a plug but 7+ circuits in a small space is not something I'm used to making or making look neat. Does anyone have tips on how to make things modular and keep wiring organised?

Also is there a chance that electrical noise from the VFD would affect the electronics in the tachometer or DRO?

Most NVR switches (or DOL – direct online starters) will not include overload protection. In the event the motor stalls, the motor could overheat before the plug fuse trips. Typically, a higher fuse rating is chosen (e.g. 13A) than the motor rating (e.g. 2A) to accommodate high startup current. Smaller value fuses are likely to blow regularly.

To get around this problem it is common practice to include a manually resettable thermal overload in the supply circuit. This can be set at just above the typical motor run current and will not trip for the short duration of inrush current at startup. The overload protects the motor in the event that it stalls.

To keep things modular you could consider using a short length of DIN rail and DIN connectors. Some VFDs are DIN rail mountable. I use this and it works well.

Noise is a potential problem with motors and VFDs. Check your VFD manual – mine suggests using shielded (e.g. SY cable) between the VFD and motor. It is important to ground the shielding – you can do this by making a pigtail. Control cabling should also be shielded and grounded. My local electrical wholesaler stocks 1.5mm 4 core SY cable (3 phase + earth) for about 70p + VAT per metre.

[EmgeeParticipant @emgee]

Posted by AJAX on 02/11/2019 13:34:54:

Posted by Rainbows on 04/10/2019 13:51:20:

Is my Isolator -> NVR switch w/ E stop enough safety for the immediate task of just controlling the motor?

Also I don't want to have to rip everything out to rewire each time I add a component. I can wire a plug but 7+ circuits in a small space is not something I'm used to making or making look neat. Does anyone have tips on how to make things modular and keep wiring organised?

Also is there a chance that electrical noise from the VFD would affect the electronics in the tachometer or DRO?

Most NVR switches (or DOL – direct online starters) will not include overload protection. In the event the motor stalls, the motor could overheat before the plug fuse trips.

Your statement is partly correct as you can buy a DOL starter without an overload unit fitted, it is usual though to purchase the DOL starter complete with an overload unit sized to the motor FLC .

Emgee

[Neil WyattModerator @neilwyatt]

Use a kettle plug strip for the accessories?

You would need to fit the opposite of 'kettle lead' connectors to each appliance, but much neater than 13A plugs and provides twin and earth.

kenable-iec-10a-250v-c14-6-way-pdu-with-overload-switch

Neil

[Guy LambParticipant @guylamb68056]

Also something to look at is the rating of the kettle leads (proper name IEC lead) as the same configuration can be used on computers etc and these are only rated 5 Amp. The danger being you put a higher rated fuse in the plug than the rated value of the lead. It's possible that a 5A rated lead would go pop before the 13A fuse has time to blow. Proper kettle leads are only 0.5 M long and have a half moon cut away to stop under rated leads being connected but this doesn't stop a kettle lead fused at 10A-13A being used to supply a computer and thereby over rating the fuse.

Having said all that most of the rest of the world does not use plug top fuses!

Guy

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