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Forum topic by , posted 04-22-2015 02:02 AM 941 views 0 times favorited 10 replies Add to Favorites Watch
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2387 posts in 2965 days

04-22-2015 02:02 AM

Today I attempted what should have been very simple. My edgebander needs air to run, but there is no fail safe on the machine so if it runs without air it just damages the EB.

The EB is 220 single phase. The solution was very simple. I bought a pressure switch that utilizes NC and NO when air pressure is applied. There is a setting range that I set at around 40 psi, so when it detects 40 psi it sends a 110v to my 220v contactor which has a 110 coil, then the contactor allows 220 to pass through to my machine.

So my issue is this. I have really no idea how to wire the switch and I fear I may have burned the 70.00 switch out in my failed attempts.

The switch has a ground terminal, a Common terminal, a NC “nominally closed” terminal and a NO “nominally open” terminal. So coming from my power source, I have a hot, common or neutral, and a ground. I only had 1 terminal for the common and one terminal for the ground. I thought I needed the common to carry through to the coil and the ground to carry through and ground out with the contactor. But with just one terminal for ground and one for common, I just combine 2 wires on each of those terminals, basically 2 neutrals on the common terminal, 2 grounds on the ground. This allowed me to bring a ground and neutral to the contactor/coil.

Then I brought the live hot wire to the NC terminal and then connected and black wire from NO to the coil. I also brought the white wire that I had connected to the common on the switch down to the coil.

Well it never worked. In fact I tripped my breaker. Thinking that I had the black wires wrong, I swapped them. That Was much worse as the pressure switch sparkled for a quick second before I unplugged it. Might have just wasted 70.00. Chalk that money up to education.

Maybe someone has some knowledge about this. I have wired a lot of machines, single and 3 phase, have wired contactors, done my fair share, but this little 110 switch has me stumped.

-- .

10 replies so far

View Madsteve's profile


3 posts in 556 days

#1 posted 04-22-2015 03:04 AM

The common terminal is the other side of the N.O. And the N.C. Contacts. One of you 120 volt lines needs to connect to this common. This is the one you switch. The other 120 volt goes to the motor. Then take the N.C. To the coil. The neutral wire by passes everything and goes to the other side to the coil. All grounds tie together. Just check the contacts on the pressure switch to be sure they are not welded together from the spark

-- Too much wood and not enough time.

View TopamaxSurvivor's profile


17573 posts in 3094 days

#2 posted 04-22-2015 03:33 AM

The switch may or may not be toast, depending on the brand of breaker and a few other factors. Forget about the neutral and NC terminal. Connect the equipment ground to ground. Wire your EB so it works as it did before. The neutral does not go to this switch. Take the hot coil wire off and run it to the common terminal in the switch. Run a wire from the NO to the coil where you just took off the wire you ran to the common terminal. When you have pressure, the motor starter should pull in and start the motor. Without pressure, it should stop. If this doesn’t work, the pressure switch contacts are probably burned off or welded shut.

Edit: The NC contact will be closed without air pressure applied. That will allow the motor to run without air pressure and stop it from running with air pressure.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View MrUnix's profile


4023 posts in 1617 days

#3 posted 04-22-2015 03:38 AM

It should be pretty easy to test the pressure switch… just slap a continuity meter on it (one wire to common, other to NO) and apply pressure. Doesn’t make much sense to hook everything up until you verify it’s not fried.


-- Brad in FL - To be old and wise, you must first be young and stupid

View TopamaxSurvivor's profile


17573 posts in 3094 days

#4 posted 04-22-2015 03:53 AM

Unfortunately, a meter operating on a few volts, it may or may not tell you if that switch will work or not. Considering the trauma it may have experienced, I would just try it in the circuit.

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View klassenl's profile


167 posts in 2077 days

#5 posted 04-22-2015 04:19 AM

Phone an electrician. I will likely cost you double the $70 again but it will be done right.

-- When questioned about using glue on a garbage bin I responded, "Wood working is about good technique and lots of glue........I have the glue part down."

View TopamaxSurvivor's profile


17573 posts in 3094 days

#6 posted 04-22-2015 07:03 AM

Yeah, fly me down. I could see the Alamo while I’m there ;-))

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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2387 posts in 2965 days

#7 posted 04-22-2015 01:12 PM

Hey guys, thanks a ton.

I would love to fly you down here TopamaxSurvivor :)

That common terminal confused me some. I did not think the neutrals should go through the switch. Well I hope I did not burn the switch. It only sizzled for a fraction of a second and there was no flames or smoke so that has to be a good sign :)

The bright side is the switch is only a 70.00 part and not some 500 or 1000 dollar part. Worst case is ordering another pressure switch. And the EB runs fine without this pressure switch, as long as the operator remembers to turn on the air pressure. In fact, new Holzher EB would not even turn on without air pressure to the machine.

I have done a fair amount of wiring on our own shop and have wired contactors for both my DC and my 10 hp 3 phase Becker pump. In fact, the pump is loud so I put it outside in a shed and wired it with a 3 pole contactor with 110 coil that is activated with a light switch right next to my CNC control center.

I guess I just figured a simple little switch would be no big deal but it did confuse me.

Thanks again.

-- .

View TopamaxSurvivor's profile


17573 posts in 3094 days

#8 posted 04-25-2015 04:03 AM

Jerry, did you get it to work?

-- Bob in WW ~ "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

View bonesbr549's profile (online now)


1137 posts in 2485 days

#9 posted 04-25-2015 12:18 PM

Yea, I was hoping to learn that myself. Did you figure it out?

-- Sooner or later Liberals run out of other people's money.

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2387 posts in 2965 days

#10 posted 04-26-2015 01:15 PM

Hey guys, thanks for the interest. Yes I did try to rewire the switch but I think I may have burned the switch out as it seems dead and does nothing now. I have been extremely busy with misc things in the shop as we went from one very large job to another very large job back to back.

Then my EB blinked on me and threw me for about a 10 hour repair. It did not cost me any money and the actual issue was a simple adjustment that a technician with knowledge would have repaired in about 30 minutes. But my repair involved tearing my EB down and removing the glue system and thoroughly cleaning out everything and putting it all back together again. As it turned out there was an alignment issue with the Dozing rod. All in all I believe these things are the price of education because in the future I will be much more prepared to work on it.

In any case, with being as busy as I have been I have not been able to order a new switch. I should get the new switch ordered in the next couple of weeks and get it installed. No doubt that it will work armed with the correct knowledge you all have given me.

Thanks again… Jerry

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