All fed from the three phase supply, no?
Momentary e-stop and square D mechanically latched contactor
- Thread starter Caleb907
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fmtjfw
Senior Member
- Location
- Fairmont, WV, USA
Original post:
According to the original post it is SAFETY, maybe not LIFE SAFETY, but probably one required by the School's Insurance Carrier.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
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.
From the OP:
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.....
Typically, the main egress door.
Which would be readily accessible.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
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
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
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?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
One could, but the daily, maybe even hourly, operation and reset can make it a real hassle.
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
Member
- Location
- Anchorage, AK, USA
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.
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
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
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.
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