Brian

Both of my inverters have the E Stop wired into the low voltage ‘Control’ side of the inverter. The lathe has a pendant with Forward, Reverse, Jog and E stop switches, wired to the inverter using alarm type multicore cable.

Simple factual answer to the question as stated – "could the e stop be wired into the single phase supply" is "Yes!"

But the question deserves some more thought than that, and the pro's and con's of putting an E Stop in the supply need a bit more consideration.

Firstly, my apologies if I've missed the relevant post, but I don't think I've seen what sort of machine this is. This arises because I think the proper answer to your question needs a rudimentary risk analysis to inform the design decisions. If the machine is something nasty and dangerous, then the risk of injury is offset (controlled) by being able to stop the machine quickly, and switching off the mains supply won't necessarily give you the optimum control. If your arm is in the mangle then having an active machine braking function activated by the emergency stop would probably be a good idea.

If the hazard is of the machine going berserk because of the inverter losing control then shutting the mains off is your only option. For the milling machines and lathes I have in my shed I think this is a very unlikely that a modern good quality inverter is going to go doolally, so I have the E Stop function as a stop signal to bring the inverter to zero frequency and with DC braking if appropriate. The inverter stays energised so it can do what it needs to do to effect a rapid stop pf the offending machine.

So the short and simple answer to your question is "Yes" – you can connect some sort of E Stop functionality to remove the mains supply from the machine motor, but my preference is to use the extra control facilities of the inverter to give me a quick stop function and for this I leave the supply on the inverter but tell the inverter to stop the machine. There's a big red latching button on the machine within reach, and if I bang it the machine comes to a stop whichever way it is configured.

Horses, as they say, for courses.

Hope this helps Simon

An Estop you wire into the control circuit, otherwise it's not and Estop it's a power disconnect, and not even a good one as it'll invariably leave neutral connected. if you desperately want the VFD to be instantly disconnect-able then feed it via a NVR.

Stopping in an emergency you want maximum braking and you won't get that by killing the VFD power.

An "emergency stop button" wired in series with the regular stop button is just another stop button. I normally stop my machines with the stop button and the VFD ramps down to standstill. I have emergency stops on my machines, they isolate power from the VFD. Fortunately I have not had to use them, but if I do I know the machine will stop even if the VFD control has failed.

Grid power failures must be accommodated by these VFDs, so switching them off while powering a motor is clearly permissible. Not necessarily the recommended route, of course. But a brake on a lathe with screwed chuck might not be such a clever idea, either.

Pete and the NVR is likely the better alternative, if the VFD control circuitry is not empowered.

Solar power inverters are very similar – they disconnect and reconnect automatically with no problems, but they will not tolerate switching the DC input while powered up.

This is from the 16th edition of the Wiring Regulations, since I don't intend to upgrade my house further (Feel free to purchase and work to later versions). Subject to the effects of beer it is an exact copy (Oxford commas included).

This actually constitutes the law in the United kingdom. It is, however, up to you to decide if it applies to your shed. In my case an NVR contactor operated by a button by the door of the shed would allow SWMBO to rescue me in the case of any electrically related emergency.

Turning of a lathe or bandsaw in normal use does not constitute an emergency stop, so NVR switches with silly clip on red buttons over the main controls get modified with extreme prejudice.

537-04 Devices for emergency switching

537-04-01 A means of interrupting the supply for the purpose of emergency switching shall be capable of cutting off the full load current of the relevant part of the installation. Where appropriate, due account shall be taken of stalled motor conditions.

537-04-02 Means for emergency stitching shall consist of:-

(i) a single switching device directly cutting off the incoming supply, or

(ii) a combination of several items of equipment operated by a single action and resulting in the removal of the hazard by cutting off the appropriative supply: emergency stopping may include the retention of supply for electric braking facilities.

A plug and socket-outlet or similar device shall not be selected as a device for emergency switching.

537-04-03 Where practicable a device for emergency switching shall be manually operated directly interrupting the main circuit. A device such as a circuit breaker or a contactor operated by remote control shall open on de-energisation of the coil, r another technique of suitable reliability shall be employed.

537-04-04 The operating means (such as a handle or pushbutton) for a device for emergency switchig shall be clearly identifiable and preferable coloured red. It shall be installed in a readily accessible position where the hazard might occur and, where appropriate, further devices shall be provided where additional emergency switching may be needed.

537-04-05 The operating means of the device for emergency switching shall be of th latching type or capable of being restrained in the OFF or STOP position. The resetting of the emergency switching device shall not re-energise the equipment concerned. A device in which the operating means automatically resets is permitted where both that operating means and the means of re-energising are under the control of one and the same person.

The wiring regulation (BS7671) are not applicable to this (or the law, you can in theory show alternative means of compliance, but good luck trying). The quoted text applies to electrical isolation, not machine E-Stops. The mention of machines is to allow the input to motor drive to NOT be isolated from the supply so it can stop the machine more quickly.

If using a VFD (inverter) with a separate E-Stop input (and you should be if the machine needs an E-Stop) that is what you should use for the E-Stop as it stops the machine in the shortest possible time (loose chucks are a separate hazard and should be dealt with accordingly). Use the Stop / Start inputs of the VFD for just that and connect a proper isolator switch (Rotary red and yellow with provision for a padlock in the OFF position) at the VFD supply input.

A No Volt Release (NVR) should not be required with a VFD because you should set it up not to power the motor on power up or when the E-Stop is released. (This is normally the default but can be bypassed when the drive is used under automatic control)

E-stops should not be used for routine stopping of the machine but should be tested regularly.

If you want to get legal, then there are a host of assessments to do and all safety components must be designed and approved for the application. Most Hobby machine tool safety provisions, though CE marked, would not pass a through assessment. The NVRs with flip-over E-Stops are a particular example.

Any E-stop is better than none and you should NEVER EVER use the mains plug as the only means to start or stop any machine.

Robert G8RPI.
(CEng and have done this stuff for a living on machines to CE / UL & C-Tick).

At work we have numerous items of high-powered portable/pedestrian operated plant, probably a couple of hundred different machines from 1kw to 35kw nearly all 'high risk'. Many of them have three Estops but not one single one of them is fitted with an Estop that disconnects the incoming supply. All of them stop the motor and serve as a control interlock so that no control can be used until the Estop is released.

BTW I wasn't suggesting than someone SHOULD power a VFD with a NVR. It was just a suggestion for someone who was so paranoid about the above that they find it a distraction. I wouldn't find it necessary myself, at all.

It's a long time ago, but I set my inverter up so that the e-stop button gives a rapid DC braked stop, and the 'stop' button gives a ramped down stop.

The inverter (and all inverters) should be programmed to be full stop when powered on, the instructions for mine say that this should only be over-ridden when essential e.g. remotely situated pumps or fans where no-one is likely to be available tor restart after a power cut.

Neil

3-phase-conversion-and-other-alternative-methods-of-powering-a-mini-lathe

There is a STOP for normal use, and EStop for emergency use, hopefully never ! One uses the inverter to brake, the other doesn't, just in case it is the inverter at fault.

You don't need a larger inverter than you would have specified anyway since you are not looking to ever have to use the EStop. As said above I'd rather buy a new inverter than lose an arm !

Chris