Estop motor contactor monitoring

rev667 · Mar 9, 2009

Hi folks,

Currently, I am working on a machine estop circuit. It has a string of estops and guard switches linked to a safety relay, the outputs of the relay drive a pair of contactors that remove all 3 phase power from the machine, there is a NC contact from each of these in the reset loop of the relay.

The machine has a number of DOL motors, and I was wondering if these contactors should also be monitored via the reset/monitor loop on the safety relay.

What are your suggestions?

Thanks

Rev

Lancie1 · Mar 9, 2009

Rev,

Pardon my American ignorance, but what is a DOL motor?

hd_coop · Mar 9, 2009

Lancie1 said:
Rev,

Pardon my American ignorance, but what is a DOL motor?

I believe Direct On Line.

tragically1969 · Mar 9, 2009

rev667 said:
Hi folks,

Currently, I am working on a machine estop circuit. It has a string of estops and guard switches linked to a safety relay, the outputs of the relay drive a pair of contactors that remove all 3 phase power from the machine, there is a NC contact from each of these in the reset loop of the relay.

The machine has a number of DOL motors, and I was wondering if these contactors should also be monitored via the reset/monitor loop on the safety relay.

What are your suggestions?

Thanks

Rev

Bit difficult to say really, a lot will depend on your risk assesment and the category of safety you are heading for, if you are trying to achieve above a certain level you will HAVE to monitor them no matter if you like it on not to satisfy the standards

Personally i would do it anyway, you know for sure then that the starterd are working correctly and are all in a safe to restart condition

leitmotif · Mar 9, 2009

rev667 said:
Hi folks,

Currently, I am working on a machine estop circuit. It has a string of estops and guard switches linked to a safety relay, the outputs of the relay drive a pair of contactors that remove all 3 phase power from the machine, there is a NC contact from each of these in the reset loop of the relay.

The machine has a number of DOL motors, and I was wondering if these contactors should also be monitored via the reset/monitor loop on the safety relay.

What are your suggestions? Thanks Rev

Reading between the lines a bit.
I would not allow restart of anything just by the action of resetting an e stop. Each motor or function should be individually started by a separate operator action.

Yes I know the Production God will be upset over the supposed huge time demand but that is too damn bad.
Safety God should be able to override Production God.
I have been around enough equipment that restarted everything when an E stop is reset - I am surprised still there were no injuries.

Dan Bentler

montech · Mar 9, 2009

I have wired these reset circuits into both AB MSR127 and Sick relays to a reset button on the front panel.So when the operator punches any estop,he will not engage the contactor untill the Safety relay used is reset by pushing the momentary reset button.I think this does 2 things.It will stop a issue with a frozen contatctor,and also adds a 2nd safety step in the reset.Not sure if this is required for CE?

Lancie1 · Mar 9, 2009

...the outputs of the relay drive a pair of contactors that remove all 3 phase power from the machine...

The machine has a number of DOL motors, and I was wondering if these contactors should also be monitored via the reset/monitor loop on the safety relay

Are you saying that the safety relay/pair of contactors actually DO NOT remove all power from the machine, and that the "DOL motors" are on separate circuits? If so, that certainly degrades the safety level, and would not be acceptable for many applications.

CB_182 · Mar 9, 2009

By Including the DOL's in the circuit then you could possibly prevent the circuit being reset should one of the starters be welded in, if not resetting the circuit (restoring the 3 phase) could result in one of the motors starting straight away.
But has been already said, will depend on your risk assesment.

Ned_Flanders · Mar 9, 2009

My 2d worth: For me, it would depend on what the drives did. If it were a main machine drive, I would include it but if was a contactor for a conveyor belt, I would not. From what you say, everything is guarded anyway.

I work with German machinery, and they use seperate pilz relays for guard and estop. Opening the guard crash stops the machine, requiring a "Fault reset" then "Start". An estop kills all the 415 and 240v circuits requiring "Machine on" to be pressed before Fault reset and start.

rev667 · Mar 9, 2009

Thanks for the replies.

The direct-on-line motors are subservient to the main pair of contactors.

Once an estop is performed, the operator has to release the estop or close the guard, then press 'estop reset' (which lights up blue if it resets). This brings in the 2 main contactors. Then the machine has to be started by pressing 'start'

The only motor that actually moves anything mechanical is the conveyor, the rest are low pressure water pumps and air blowers.

Hope that clears up any questions.

Previous machines did not monitor the motor control contactors, just the main power contactors, I was wondering if I should monitor the conveyor drive contactor.

Rev

Alan Case · Mar 9, 2009

The answer is no, you do not have to monitor and probably should not monitor the DOL auxillary contacts.
What you describe is a cat 3 or 4 E Stop system where there are 2 monitored breaks of the 3 phase power. (the cat 3 or 4 rating will come from how the Estops are wired)
When an EStop is active the safety relay will look for the NC aux circuit to be on. If it doesnt see this (ie 1 safety contactor welded in) then the system will not allow a re-enable of the safety circuit.

What you do with your DOL contactors after that is up to you.

Regards Alan Case

bhattnileshr · Mar 10, 2009

hi man

u w'd like to wire up the overload relays on devicenet to control it from remote location???? if so let me know....

Estop motor contactor monitoring

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