Momentary e-stop and square D mechanically latched contactor

[Besoeker]

You are comparing this to a contactor used in a drive, so maybe up to 4 poles, which would not be a problem being energized all the time. But what is done with these contactors is not to kill ALL of the 3 phase power, it kills ONLY the circuits feeding the bench power tool outlets, and there may be 10 of them in the classroom, so 20 poles.

All fed from the three phase supply, no?

 

[fmtjfw]

It is not a safety device.
It is a master enable relay, maybe. There is no life safety intended to be directly involved in it operation or lack thereof.

Its purpose to do turn off a large area of power at one time just like a lighting circuit.

Automatic restart of the power tools is handled, per OSHA, at each power tool cord.
These have been in use for school shops for maybe 60 years or more.
The function could be achieved with a shunt trip breaker installed (as mentioned by Jraef)fmtjfw, other than the hassle of having to turn a breaker on and off versus simply pushing a button.

Original post:

The e-stop is mounted next to the door so that a teacher can shutdown all of the power in case of an emergency

According to the original post it is SAFETY, maybe not LIFE SAFETY, but probably one required by the School's Insurance Carrier.

 

[jim dungar]

Original post:

According to the original post it is SAFETY, maybe not LIFE SAFETY, but probably one required by the School's Insurance Carrier.

Or, this may be the OP's wording.
Regardless, it is definitely a slang practice to call these circuits 'Emergency Power Off', even though they are primarily and routinely used in non-emergency situations (such as at the end of every class period or school day).

We do not know how many Off pushbuttons are being installed.
We do not know where the pushbuttons are being installed and if there is ready access to them.
The supplied wiring diagram will automatically reapply power as soon the pushbutton is no longer operated.
If the insurance company required this, I am sure the plans and specs would have included a detailed wiring diagram that must be followed.

FWIW, I was in a school two weeks ago, the contactor had been bypassed by removing the wiring to the unlatch coil sometime in the past 25 years (no one could remember when), so I would guess their insurance carrier was not worried about it.

 

[Besoeker]

We do not know how many Off pushbuttons are being installed.
We do not know where the pushbuttons are being installed and if there is ready access to them.

From the OP:

The e-stop is mounted next to the door so that a teacher can shutdown all of the power in case of an emergency

How many.....
"The e-stop......." would make it one

Where.....
"next to the door" answers the where.

Ready access.....
"next to the door"..........would seem to infer ready access unless, of course, there isn't ready access to the door in question.....

 

[Smart $]

...

Ready access.....
"next to the door"..........would seem to infer ready access unless, of course, there isn't ready access to the door in question.....

Typically, the main egress door.

 

[Besoeker]

Typically, the main egress door.

Which would be readily accessible.

 

[jim dungar]

Typically, the main egress door.

Not in the school district I am presently working in.
All of the power off buttons are a flush mounted style button (not a mushroom or extended head) none are located near any egress door.

Actually the welding and auto shop both share 1 button for the two separate shops, it is inside of the locked instructor's office.
The wood working shop has the button close nippled to the power panel, located in the front of the room near the instructor's station.
Some day I will ask someone where the 'Off' button is in the chemistry labs.

Our industry casually uses the term 'emergency', to the point where it is all but meaningless as an adjective.
NFPA79 has a pretty good description of Stopping and E-stopping functions.
These 'room power off' buttons do nothing to actually E-stop equipment. The individual pieces of equipment need to be protected just like on any jobsite or factory, typically to OSHA standards.

Regardless, the wiring diagram supplied by the OP is unlikely to provide the type of control we all concur is likely desired.

 

[kwired]

I guess it depends somewhat on what the intended function of this control is for, but why couldn't one use a shunt trip breaker to feed a panel with all the equipment involved supplied from that panel, and this "E stop" connected to power the shunt trip coil when pressed?

 

[jim dungar]

I guess it depends somewhat on what the intended function of this control is for, but why couldn't one use a shunt trip breaker to feed a panel with all the equipment involved supplied from that panel, and this "E stop" connected to power the shunt trip coil when pressed?

One could, but the daily, maybe even hourly, operation and reset can make it a real hassle.

 

[Besoeker]

Our industry casually uses the term 'emergency', to the point where it is all but meaningless as an adjective.
NFPA79 has a pretty good description of Stopping and E-stopping functions.
These 'room power off' buttons do nothing to actually E-stop equipment. The individual pieces of equipment need to be protected just like on any jobsite or factory, typically to OSHA standards.

Fair points. Power off in the situation you mention describes it.
In our works we have various test and production areas. Some of the equipment has elevated voltages and the potential to pose personal risk to the operators. It would need a combination of failures for that to to be the case but to cover that eventuality or the kit going in fire we have e-stop buttons in conspicuous locations. Emergency power off would maybe describe them better. They are stay-put key release.

Any incident that initiates their operation gets investigated before an authorised person will release it.

 

[Caleb907]

Basically got my awnser

Basically got my awnser

Thank you for all the input. From what I've been reading of the responses, it's not a simple solution with the equipment that I have here on site. I thought I could simply wire my push button (e-stop) thru the NO contact and each time the button was pressed it would latch/unlatch. Not the case, the auxiliary relay that powers the two coils just returns back to the default state when I release the button which is the unlatch position. I will be writing a RFI to see what they want for a button.

 

[kwired]

One could, but the daily, maybe even hourly, operation and reset can make it a real hassle.

Like I said, it depends on the intent, if it is used for routine control the shunt trip probably not a good idea, if for emergency stop purposes only, it may work great.