Do you have intimate knowledge of this product? I've worked with other devices which appear to be similar and are actually tiny contactors (relay really) where the buttons control the contactor. My first encounter was on a saw table where A1 was connected via a faulty cover interlock and pushing the green button did nothing.
NVR Switch - What is this terminal?
- Thread starter diyer56
- Start date
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Guards switches are a safety function. Machine compartment door switches can be a safety function. A foot switch can be a safety function.
All usually fitted to mitigate specific hazards.
An emergency stop is usually a complementary safety function, generally not fitted to meet a specific risk.
Emergency Stopping a machine can be a sequence of actions that are necessary to bring the machine to a safe standstill.
An example is bringing a flywheel to a halt by a sequence of controlled braking. Hitting the brakes hard on could cause the machine's frame to break up
Quite extensive experience, from simple motor control, DC PWM boards, VFD’s, multi axis servo and stepper CNC, computer controlled pneumatics etc etc. Design, build, even control software. VFD’s and up will have a separate low voltage Estop so the device knows what to do in an emergency. The purpose of an EStop is to stop the machine in an emergency safely, isolate the controls and require a conscious interaction to reset. So in the case of CNC, many things may need to happen in a specific sequence to safely stop. With pneumatics, EStop may need to depressurise cylinders .. or ... maintain pressure .. pneumatic and or solenoid brake may need to remain pressurised/powered to allow machine components to be moved by hand ... which ever is safer. If you cut power to a servo driven ball screw, it can be moved by hand, a large stepper will just lock .. not very good if it's trapped your hand? Cut power to a VFD and there can be damage .. so a controlled stop is required etc etc hence a low voltage EStop signal to the VFD, and nothing to do with the diagram we are discussing. So the safe stop sequence (the fly wheel example is an excellent one) and final resting state is important depending on the machine you are dealing with and does not necessary mean just cutting the power, it can be very complex. With a simple power tool though, it is a lot simpler. The NVR ensures that, if there is, for example, a power cut, blown fuse, overload trip ... the machine will not randomly restart on it's own when the power is restored, it's in a SAFE state (while you are trying to figure out why it has stopped with your fingers in dangerous places). Our Dyson has removable brushes for cleaning, there is no interlock on the mechanism and it has no NVR, so if someone accidentality plugs it back in while you are cleaning it .. it might just start and take your fingers off. It can be on or off even when disconnected for the sake of an £8 switch. The CNC machine in my garage has little NEMA 17's on 4mm pitch ball screws and I can't stop it moving ... or move it when powered down without mole grips on the motor spindles. The EStop leaves it in a state where the axes can still be moved manually using cursor keys.
But here we have a very simple switch (a very very simple cheap switch) either connected directly to a low current motor or through a AC to DC PWM board to a motor (more common these days providing 180V DC to a brushed motor with PWM speed control (constant torque)). The OP is asking specifically about the KJD17 which is typically used to either cut or apply mains single phase from a wall outlet to a motor / pwm board. Not used to control low voltage TTL signals to controller boards or VFD's. In the original diagram … the Estop as drawn, will still leave the start button live and functional. If it is pressed, current will still flow to the motor and the machine will operate as long as it remains pressed. It's possible that this may be a desirable safe state, so the machine can still be "jogged", I doubt it, but I can foresee circumstances where this may be desirable ... to allow a press that happens to stop at BDC to complete it's cycle to TDC for example? The KJD17 is a very simple cheap on off switch with only two contacts, it looks like a proper start switch but isn’t ... this is important. It has a circuit diagram on the side for a reason. The contact is made mechanically when the green button is pressed, the circuit is made, power can then flow to the motor and the coil and the contacts are locked by the coil until power to the coil is interrupted (what the red NC button does). However, the mechanical connection is made REGARDLESS of power to the coil and contact (and hence power) will be maintained as long as the green button remains pressed, the motor will still operate even if the Estop as drawn is latched and isolating the coil. A more expensive switch will have a third set of contacts to specifically power the coil on pressing start. It is the coil in the more expensive switches that makes and completes the circuit, and without power to the coil, nothing will happen, in which case you can have an EStop placed in the coil feed. KJD17’s do not operate like that, the coil only maintains the circuit, it does not initiate or complete the circuit and there is no separate isolated coil contactor. This type of switch requires an EStop wired to isolate the actual feed to the switch.
Why not try it? Go test it? Go get a KJD17, completely disconnected from anything, put a continuity meter across 13/14 and/or 23/24 and press the green button ... mechanical contactors make continuity regardless of any power to supplied A1. Go try it for yourselves. But do what you want, it's not my fingers / arms / neck. BTW, a typical 1200W (1-1.5 hp) hobbyish lathe / pillar drill / mill with a DC PWM controlled motor has plenty of spare torque to pull your arm in, twist it into a little tight circle and tear it off. Take care.
Edit: I also suspect that off red button on this switch mechanically forces the contacts apart rather than cuts the feed to the coil. I suspect this because if you gently press the red button, the contacts buzz and chatter. Never had one apart, but will next time I get a failed one... My mates has just failed so we will see.
But here we have a very simple switch (a very very simple cheap switch) either connected directly to a low current motor or through a AC to DC PWM board to a motor (more common these days providing 180V DC to a brushed motor with PWM speed control (constant torque)). The OP is asking specifically about the KJD17 which is typically used to either cut or apply mains single phase from a wall outlet to a motor / pwm board. Not used to control low voltage TTL signals to controller boards or VFD's. In the original diagram … the Estop as drawn, will still leave the start button live and functional. If it is pressed, current will still flow to the motor and the machine will operate as long as it remains pressed. It's possible that this may be a desirable safe state, so the machine can still be "jogged", I doubt it, but I can foresee circumstances where this may be desirable ... to allow a press that happens to stop at BDC to complete it's cycle to TDC for example? The KJD17 is a very simple cheap on off switch with only two contacts, it looks like a proper start switch but isn’t ... this is important. It has a circuit diagram on the side for a reason. The contact is made mechanically when the green button is pressed, the circuit is made, power can then flow to the motor and the coil and the contacts are locked by the coil until power to the coil is interrupted (what the red NC button does). However, the mechanical connection is made REGARDLESS of power to the coil and contact (and hence power) will be maintained as long as the green button remains pressed, the motor will still operate even if the Estop as drawn is latched and isolating the coil. A more expensive switch will have a third set of contacts to specifically power the coil on pressing start. It is the coil in the more expensive switches that makes and completes the circuit, and without power to the coil, nothing will happen, in which case you can have an EStop placed in the coil feed. KJD17’s do not operate like that, the coil only maintains the circuit, it does not initiate or complete the circuit and there is no separate isolated coil contactor. This type of switch requires an EStop wired to isolate the actual feed to the switch.
Why not try it? Go test it? Go get a KJD17, completely disconnected from anything, put a continuity meter across 13/14 and/or 23/24 and press the green button ... mechanical contactors make continuity regardless of any power to supplied A1. Go try it for yourselves. But do what you want, it's not my fingers / arms / neck. BTW, a typical 1200W (1-1.5 hp) hobbyish lathe / pillar drill / mill with a DC PWM controlled motor has plenty of spare torque to pull your arm in, twist it into a little tight circle and tear it off. Take care.
Edit: I also suspect that off red button on this switch mechanically forces the contacts apart rather than cuts the feed to the coil. I suspect this because if you gently press the red button, the contacts buzz and chatter. Never had one apart, but will next time I get a failed one... My mates has just failed so we will see.
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Thank you for a comprehensive post. I too can quote some of the same experiences but certainly not all.
I have encountered products which look similar to the OP but to date they have been electrically operated contactors and no amout of pushing the green button has had any effect with the A1 terminal disconnected. One such machine was a belt sander and 2 of those units fitted, first operated the the dust extractor and second was reliant on the current switch on the extractor (transformer style) before the sander could be started. Both units were also connected via contacts on the m/c E stops and the w/s E stop contactor system.
I believe all of the m/c's I encountered with a jog facility are usually executed by holding the red button in and jogging with the green or a specific jog button, usually blue or orange quite often using a passing NO contact or electronic timer. I am of course referring to basic DOL/YΔ controls systems here.
My recollections of "safe" jogging are that in most cases two buttons needed to be pressed for the machinery to move. In most cases the buttons were far enough apart that both hands were needed, not just two fingers.
I absolutely and totally agree, on reflection my jogging example was far too simplistic and not meant to comply with any regs. Tom
I am a bit of a rebel and put common sense decisions before decisions based on blind compliance with regulations.
Totally agree and I believe you. The moral I suppose is to understand the switch function before you wire it. Again, my jog example on reflection is over simplified, apologies, it should be a specific function rather than a consequence of wiring. I just looked up the KJD17 spec sheet and it says
“Electromagnet provides automatic safety against power outages and automatic restarts” ... that's all it's meant to do.
If interested I'm here because my mates has blown and he was asking how to wire in a new one and sent some YT links which I found astonishing ... giving (wrong) advice but no disclaimer!
So he has exactly the same lathe as me, same model, same make, supplied a year apart. Single phase, DC PWM controller, 1200W. My A1 is wired through the guard switch, a little low current switch. I also have a handy EStop within easy reach which cuts power to the sockets which are on their own ring main breaker and RCD, the machine itself doesn't have a self contained EStop. His machine ... when we took it apart ... has different wiring and the guard switch is wired directly through the mains feed to isolate the KJD17 ... which now has a melted coil. The guard switch is definitely not capable switching 1200W on a regular basis and is only single pole. So we are still trying to figure out the actual cause .... the feed to the KJD17 has definitely cooked at some point as the wires are burnt. I don't lift my guard to stop the machine, but I could, its only low current to the coil. His is trying to switch 1200W (if he did that, I don't know). Another moral, just because the machine has a CE mark etc?
A multimeter across the switch will quickly indicate how it operates and that determines the wiring. I have a couple of old proper made in England starters somewhere, big clunky things about 1lb that still work and I will fit one day. KJD17s are rated to 16A @ 240V .... but I suspect there is still a big difference between a £8 one vs a £20 one and different manufacturers, quality of the contact alloys etc.
Hope all has been helpful.
Tom
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You know I was going to say something similar but I thought better of it for fear of starting an argument. It is absolutely about common sense. The young have moulded plugs now ... they are not taught how to wire a plug any more like it's a secret, they are let out with no comprehension or understanding at all of how dangerous that socket in the wall can be, devoid of the ability to think.. and that's safe apparently.
Totally on your side!
Tom (in Northamptonshire
Is it not forbidden to switch just the Neutral wire in the Uk
I tried to help my 15YO grandson with his physics revision and while sat there I put a new plug on one of his device chargers, i casually asked which colours went on which pins. Not an iota of recognition that there were even different colours in cables. Whereas from third year of senior school (age 13-14) onwards I was adding more tails to the school stage lighting circuits, building additional lighting switchboard, building SCR dimmers, altering the hall lights wiring to add dimming, adding sockets to the ring final etc.You know I was going to say something similar but I thought better of it for fear of starting an argument. It is absolutely about common sense. The young have moulded plugs now ... they are not taught how to wire a plug any more like it's a secret, they are let out with no comprehension or understanding at all of how dangerous that socket in the wall can be, devoid of the ability to think.. and that's safe apparently.
Totally on your side!
Tom (in Northamptonshire
And the interlocks:
I'd forgotten there was a router linked to the extractor too, all told there were 4 E stops, one stopped all 3 machines, the other 3 stopped only 2. There was also a workshop Estop.
I didn't take a note of the switch part number They had the same appearance as OP but I see they have A1 & B1 terminals which needed to be linked to enable it.
It seems the sander was wired for 3ph but a single phase motor and switch fitted.
Terminals designations S (in the sander), V (in the extractor) and numbers were mine, and were bits of choc bloc added in. The CT switch and relay were also extras.
All of the interlock wiring was done with flex, 5C or 3C
I'd forgotten there was a router linked to the extractor too, all told there were 4 E stops, one stopped all 3 machines, the other 3 stopped only 2. There was also a workshop Estop.
I didn't take a note of the switch part number They had the same appearance as OP but I see they have A1 & B1 terminals which needed to be linked to enable it.
It seems the sander was wired for 3ph but a single phase motor and switch fitted.
Terminals designations S (in the sander), V (in the extractor) and numbers were mine, and were bits of choc bloc added in. The CT switch and relay were also extras.
All of the interlock wiring was done with flex, 5C or 3C
Care is needed to ensure a short circuit in the cabling does not by pass any of the E-Stop switches.
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