The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!

Featured:
   

2017 NEC and Related
2017 NEC
Now Available!

   
Recent Posts
Locked rotor, no burnout
by andey
Yesterday at 04:48 AM
Temporarily feeding a panel...
by Potseal
09/29/16 11:05 PM
Massive power outage South Australia
by Meadow
09/29/16 06:46 AM
short circuit??
by Meadow
09/29/16 06:43 AM
Norwegian power?
by Meadow
09/29/16 06:36 AM
New in the Gallery:
12.5A through 0.75mm˛ flex (just out of curiosity)
Shout Box

Top Posters (30 Days)
HotLine1 12
sparky 10
gfretwell 8
Potseal 7
sparky66wv 6
Who's Online
0 registered (), 281 Guests and 4 Spiders online.
Key: Admin, Global Mod, Mod
Page 1 of 2 1 2 >
Topic Options
Rate This Topic
#182578 - 12/02/08 09:26 PM motor starter
Sandro Offline
Member

Registered: 12/30/01
Posts: 449
Loc: Stoney Creek, ON, Canada
Ever get those jobs where you think you "know" something can be done, but due to brain cramp, can't figure it out??

With a push button motor starter (1 stop, 1 start. Not a manual button starter but one controlled with coil), connected to a compressor with pressure switch. When the pressure switch opens the circuit and breaks the coil contact, it takes the operator to push the start button again once the pressure drops to get the motor going again.

Argh! the holding contact, I believe there is a way around this..... and can't quite remember how to do this. Wire the pressure switch into the aux contacts?

Top
Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#182579 - 12/02/08 09:31 PM Re: motor starter [Re: Sandro]
twh Offline
Member

Registered: 03/11/04
Posts: 892
Loc: Regina, Sask.
I think a compressor needs an off-auto switch.


Edited by twh (12/02/08 09:34 PM)
Edit Reason: changed switch type

Top
#182580 - 12/02/08 09:45 PM Re: motor starter [Re: twh]
wire_twister Offline
Member

Registered: 07/25/07
Posts: 265
Loc: Georgia USA
You need an off-auto switch, or a locking run push button
_________________________
Jimmy

Life is tough, Life is tougher when you are stupid

Top
#182581 - 12/02/08 10:31 PM Re: motor starter [Re: wire_twister]
JoeTestingEngr Offline
Member

Registered: 11/04/05
Posts: 786
Loc: Chicago, Il.
I don't think I would leave it that way. I would fill the holes with a press-to-test indicator and a momentary-off-on rotary selector switch. The pressure switch should have a pressure and deadband or differential adjustment. The Off position breaks path to N.C. opens on P increase, switch terminals. The momentary, "Hand" position, parallels P-switch, to check operation without bleeding the tank. The N.O. aux switch would be used to drive your indicator. Do you have any E-stops in the mix? You wouldn't need any holding contacts unless you were going to use 2 separate pressure switches in series. In that case, the holding contact is in parallel with the low pressure switch. It helps to think of one as "closes on low pressure", and the other as, "opens on high pressure"
Joe

Top
#182582 - 12/02/08 10:58 PM Re: motor starter [Re: JoeTestingEngr]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5300
Loc: Blue Collar Country
Seems like someone is trying to defeat a safety device ... to me. If there's a high-pressure cut off switch, it's there for a reason. I'm not about to give advice on defeating it.

If you want the compressor to automatically re-start when the pressure has dropped ... well, that's a normal control problem, and would be solved by adding a pressure switch - not by bypassing an existing one.

I'm real close to locking this thread. Did I understand the request correctly?

Top
#182583 - 12/03/08 12:59 AM Re: motor starter [Re: renosteinke]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9012
Loc: Estero,Fl,usa
I didn't read this as an over pressure switch, just the one that establishes proper tank pressure.
_________________________
Greg Fretwell

Top
#182584 - 12/03/08 06:09 AM Re: motor starter [Re: gfretwell]
Sandro Offline
Member

Registered: 12/30/01
Posts: 449
Loc: Stoney Creek, ON, Canada
BINGO!!!

Top
#182585 - 12/03/08 06:10 AM Re: motor starter [Re: gfretwell]
Sandro Offline
Member

Registered: 12/30/01
Posts: 449
Loc: Stoney Creek, ON, Canada
Originally Posted By: gfretwell
I didn't read this as an over pressure switch, just the one that establishes proper tank pressure.


BINGO!

Top
#182589 - 12/03/08 09:35 AM Re: motor starter [Re: Sandro]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5300
Loc: Blue Collar Country
Thanks for the clarification.

Top
#182590 - 12/03/08 10:27 AM Re: motor starter [Re: renosteinke]
electure Offline

Member

Registered: 12/24/00
Posts: 4225
Loc: Fullerton, CA USA
Quote:
Argh! the holding contact, I believe there is a way around this.....


Forget the holding contact

You need to bypass the holding contact entirely, and run the coil directly from the pressure differential switch.

A MAINTAINED contact switch can be inserted anywhere in the control circuit to turn it off.



Top
Page 1 of 2 1 2 >



ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals