motor controll

[savage1]

So I've been building a couple of motor controllers and the go button closes 3 double pole relays which have the LV controll lines from six motors which basically means that there is 6 standard pickle circuits in a box.

 

The e-stop button cuts power to the motors thanks to a pair of big 3 pole contactors.

 

 

However somebody I work with told me that I could skip the relays on the go button and just tie all the motor controll lines together? Is that possible, I mean I'd worry about certain motors having different controll voltages.

[david.elsbury]

If I were you I'd be stopping what I was doing, and talking to an electrician who is experienced in such matters.

Considering you clearly have some gaps in your knowledge, would you want the responsibility if something were to go wrong? :)

[dbuckley]

The e-stop button cuts power to the motors thanks to a pair of big 3 pole contactors.

 

yeah, how does that work?

[AdrianW]

However somebody I work with told me that I could skip the relays on the go button and just tie all the motor controll lines together? Is that possible, I mean I'd worry about certain motors having different controll voltages.

 

 

That would work... provided that the control supply from each motor is not referenced to earth or anywhere else. Using a separate contact for each control line is a better solution. I have seen the control transformers in lodestars burntout by using such a commoning arrangement ... the problem was that one transformer was phase revered with respect to the others.

 

Using the E-stop button to remove the power from the coil of a contactor whose main contacts supply the motor power is the most common way of achieving this.... you just need to make sure that those main contacts cannot weld closed......

[savage1]

the pair of contactors have a total switching capacity more than twice what the mcb is rated at.. I did reduce the design to 4 channels to make sure I could have a big margin in switching capacity, each pair of motors also go through an rcd.

 

It would be very simple to have the e-stop trip the rcds but in the few controllers I've had a look inside cutting power to the contactor coils has been the chosen approach. I know there are other options but I had assumed that the combination of excessive switching capacity and appriate protection would be safe?

[dbuckley]

When you say a pair of contractors, are they in series, so you can survive one contactor failing (or welding) and still be assured that power will be ceased?

 

With the right pair of series contractors, mirror contacts, and a contactor integrity monitoring arrangement, you would be at category 3, which should satisfy most nit-pickers, and give good confidence of a system that will estop when instructed so to do.

 

I do not think tripping RCDs as an estop is a smart thing to do, it would require the making of a circuit or shunt trips, both of which do not fail safe.

[savage1]

Yes the main contactors are in series, the e-stop also cuts the power to the controll relays. I've got myself the relevant literature to read. It wont go in to service until it has been inspected by the spark.

[sturgjoh]

So I've been building a couple of motor controllers and the go button closes 3 double pole relays which have the LV controll lines from six motors which basically means that there is 6 standard pickle circuits in a box.

 

The e-stop button cuts power to the motors thanks to a pair of big 3 pole contactors.

 

 

However somebody I work with told me that I could skip the relays on the go button and just tie all the motor controll lines together? Is that possible, I mean I'd worry about certain motors having different controll voltages.

 

So, without wanting to jump in too deep, and this applies to others who build machinery and operate it... here's my thoughts....

 

Where I work, (which is a manufacturing company), when we design a new machine or control system we have to do a machinery risk assessment, determine any SRCF's (Safety related control functions) like the E-Stop function, then define the PL (performance level) that the SRCF's need to meet, and then the electrical design can be started. Once the design is built there also need to be a verification to ensure that the safety design has been met. Then you'll need a test procedure to be carried out on a frequent (test interval to be determined based on t he risk) basis. This all falls under standards.

The EN 954-1 standard. (categories) is being phased out and replaced by EN ISO. 13849-1 (PL, Performance Level) and EN 62061 (SIL, Safety. Integrity Level).

Everyone: please ensure that whatever you build has been risk assessed properly. Your actions or omissions, that may or may not contribute to personal injury, could put you up in front of a judge or jury, asking you to prove you were competent to do the work you've done, and asking you to prove it was safe.

E-Stop contactors are generally wired to a safety relay with cross monitoring and a dual channel safety circuit to the safety inputs (eg e-stop button)

Please ensure you take care people... to be safe and follow legislation.

oh, and btw, just noticed that you didn't mention what your machine was doing, so perhaps none of this applies to you....(sorry). rant over.