Emergency stop wiring... placement in circuit
When installing an Emergency Stop, I have a few questions:
*Is it ONLY to be wired on the control circuit of a magnetic motor starter? In other words, can it be installed directly in line between incoming live power and those lines which connect to the motor?
*If used with a VFD, do you install it before the VFD input power or between the VFD and motor?
Estops are connected to the mains. When you hit it it kills motive power to the system.
Estop goes between the wall and the VFD. Nothing ever goes between the vfd and motor unless otherwise noted in the manual.
Some VFDs also have a e-stop input that will bring the motor to a controlled stop with dynamic braking.
Why are they all rated so low then? For example, looking through McMaster's listings for Emergency Stops, the highest rating is "Rated 6 amps @ 120 volts AC and 2.5 amps @ 24 volts DC with a maximum voltage of 600 AC and DC" Yet, the breaker specified for the VFD input on my 2HP TECO unit is 20A. What am I missing?
E-stop switches are wired into the control circuit only. In the case of an across the line motor starter the e-stop switch is wired in series with the coil of the contactor. When the switch is pressed the contactor drops out stopping the motor. Now in the case of a vfd the e-stop switch is wired in series with the run switch. Now when the e-stop switch is pressed the vfd goes into the stop mode. In both cases a service disconnect will be provided to isolate the device from the source of power. also to lock out the power with a pad lock that only you have the key.
They are intended to interrupt power to a contactors coil. There are higher current rated Estop switches available too.
True e-stops use twin contact maintained mushroom head buttons wired to at least one (or more in series depending on level of security) safety relay. this relay is then used as the control voltage source for the magnetic starter circuit, ahead of the stop button. The link below is a simple safety relay, one that we use quite often at our plant.
I just used two of them in the control scheme to shut down the hot rails to two five ton overhead cranes in our carbon rodding plant. I wired six Allen Bradley 800T E-Stop buttons in series as per the drawing in the link.
Note also the manual reset button that resets the relay. No push reset- no control voltage.
For the average home shop this might be considered overkill, but then again, if you are thinking about an e-stop in your circuit, there must be a reason. And therefore, maybe it's not so overkill for you. These relays are around a hundred bucks a pop. Without it, you are only essentially installing another stop button, and they are subject to fail much easier than the relay scheme.
Okay... So is this a valid diagram? Listed numbers are McMaster item numbers. I already have the fuse block 7688K42, E-Stop switch 9235K3, the drive and motor. The drive is already mounted on a 35mm DIN rail, so it would be real easy to just add the relay 70255K623 on Monday. As mentioned, this is all really overkill for a one-man home shop. I just really don't like the idea of a remote mounted keypad with a full host of buttons if there is trouble. I don't bother with my other machines---they all use a nice big lever for the main on/off. No real thought is needed to switch those.
always wire EM stops normally closed!
You are effectively using the EPO switch as an "off-on" button. IMO... Restoring the EPO should not automatically restore the power. I wouldn't wire it like that - I'd have a separate "start button" that is bridged by the relay aux contact, and the EPO NC contact in series with that. My way does not need a "maintained" switch (although you may desire this "lock" feature). If you do it your way, make sure the vfd is set to not restart on power fail. Of course, that will only be true if your vfd is working correctly which is why the EPO alone should not restore power in a critical application.
As a rule I also don't like using 240vac control voltages. Why? The EPO should be placed where you can hit it in a hurry, which isn't necessarily on the VFD box. For example, On a lathe.. that would often be near the tail stop (you don't want to reach past the problem to kill the power). Now you'd be running high volts all over the place. You can have more than one EPO - one on a magnet placed where needed can work. My choice of control voltage is 24vac. You'd need a small transformer with separate input fuse.
Instead of McMaster (to save $$) consider Ebay for EPO, indusrial control switches and motor starter contactor (you only need two poles, not three). For industrial switches ,search on " bradley 800t " (no quotes) then refine your search from there.
What you are about to pay over $100 (switch) you can get for $28 on ebay, and better quality : http://www.ebay.com/itm/Allen-Bradle...item1e68898d76
or $20 : http://www.ebay.com/itm/ALLEN-BRADLE...item3f0fb2c1d9
or brand new : http://www.ebay.com/itm/Allen-Bradle...item5199ee71ea
Over the years I've accumulated quite a few of the first two link types for $10-20.
If you just use two push buttons (on, stop) - like this (many many variantion, colors etc on ebay) : http://www.ebay.com/itm/800T-A-Allen...item3ca93cd106
Last edited by lakeside53; 12-03-2011 at 03:36 AM.
What you have posted is necessary but not sufficient. All it does when you hit the E-stop is to kill the power to the VFD. You need to read the VFD manual to see what effect this will have.
Originally Posted by Arthur.Marks
If the desired outcome is a near-instantaneous, controlled stop, this may not be achieved with your circuit. As someone said above, you need a second connection between the big red button and the VFD control circuit (this is possible on your VFD using the multifunctional terminal - see inter alia p. 4-30 of the manual). When this is triggered, the VFD will stop the motor as fast as possible. Depending on which user-defined parameters in the VFD are set, this will include coasting to a stop (useful if an independent external emergency brake is used such as would be needed for a high inertia load) or braking to a stop in a set time.
You should only use the E-stop to stop the machine in an emergency. Use another method for standard stops.