Wiring compressor

[dave63]

Hi Guys,
I’m new to the forum though I’ve been here a few times in the past.
I'm wiring a single phase 240v compressor and could use a little help.
I'm using the following components:
240v 1ph motor 3hp
240v furnas pressure switch 69ha1z
Rockwell Allen Bradley magnetic contactor 509 bod wired for 240V 1ph with a 120v coil
Rockwell Allen Bradley 800s-2as push button NO NC on/off switch.
When I look at the bottom diagram on the following link. I have to read L2 as the ground for the pilot device (on off switch) right? I’ll be using one leg on the 240v supply to power the 120v coil.

http://www.ab.com/en/epub/catalogs/12768/229240/229248/10521726/10525386/10539953/tab5.html
Since the contactor coil is 120v I must interpret the meaning of L1 and L2 in the schematics as power and ground using the 240v ground throughout ie box to box.

Any pointers or comments regarding wiring this thing would be appreciated.
Dave

 

[nehog]

L2 is neutral not ground. L1 and L3 are power (hot). Ground is not shown in the diagram.

But...

That diagram doesn't look right at all to me. There is something wrong with it. (Where is there a connection from T2 to L3?)

 

[dave63]

Hi Peter, These things are a little different than what I'm used to. Let me give you a short explanation.
The contactor is designed as a three phase or single phase unit. To operate it as a single phase contactor they use the 2 legs of the 240v L1 arrives at T1, L2 arrives at T2 is looped bac to L3 and arrives at T3 as the second leg of the 240v.
I'm struggling with a 120v coil that pulls the contactor in and the diagram does give info on this. There is no neutral cause it's 240v so is it OK to use a single leg of the 240 to power the 120v coil and then ground the circuit to the box?
It appears there are two legs of 240v going to the contactor in the diagram. If that where true then both sides of the coil as depicted wound be 120v, it can't happen. the control circuit it 120v and must have a ground though I am looking for a neutral I must have to use the 240v ground. Since I've never done this before I wanted to know if that wiring is acceptable practise. It would seem to be acceptable as I don't see another alternative. I'm sure these units are not wired with a 240v and 120v line.

 

[PT Doc]

My recommendation is to call Furnas tomorrow and chat with someone in the tech department. If you wire it incorrectly then the problem is all yours. Easier to be doubly sure to get it right.

 

[Aceman]

You need a 240v coil or else you need a neutral. Using the ground IS NOT acceptable.

 

[OccupantRJ]

The diagram referenced is a 3 phase setup. The contractor can still be used for single phase setup by using only two of the three L connections, leaving the other one empty. There is no neutral in that drawing. One would be run to one side of a 120 coil. So the wires entering would be L1, L2, and a neutral. There seems to be four poles on that starter. One is used as a holding circuit when the on button is pushed. When stop is pushed, the holding circuit is broken, and the contractor "drops out".

 

[dave63]

The diagram referenced is a 3 phase setup. The contractor can still be used for single phase setup by using only two of the three L connections, leaving the other one empty. There is no neutral in that drawing. One would be run to one side of a 120 coil. So the wires entering would be L1, L2, and a neutral. There seems to be four poles on that starter. One is used as a holding circuit when the on button is pushed. When stop is pushed, the holding circuit is broken, and the contractor "drops out".

Your looking at the top schematic, wired for 3Ph. scroll down to the single phase schem

 

[dave63]

The diagram referenced is a 3 phase setup. The contractor can still be used for single phase setup by using only two of the three L connections, leaving the other one empty. There is no neutral in that drawing. One would be run to one side of a 120 coil. So the wires entering would be L1, L2, and a neutral. There seems to be four poles on that starter. One is used as a holding circuit when the on button is pushed. When stop is pushed, the holding circuit is broken, and the contractor "drops out".

OK I get it, 4 wire 240v and I can keep the 120v coil using 1 leg of 240v the neutral, and ground the system. all legit. I understand the pilot circuit. Two momentary switches, 1-NO, green: pulls the contactor in and it stays in until broken by the 1-NC, red: breaks the circuit contact drops out by spring action. This is just like my dryer circuit then 4 wire only 30 amp. The pressure switch is last in line after the contactor and is 240v pressure. Thanks for the help Occupant RJ. I realllly appreciate it.

 

[dave63]

You need a 240v coil or else you need a neutral. Using the ground IS NOT acceptable.

Thanks for helping me get out of the box I only had two legs and a ground and needed your help to get the neutral. You and Occupant RJ I appreciate the help and the rest of you that took to time to get involved.
Dave

 

[71flh]

As others have said, you need a neutral since 240V will fry the coil and the ground isn't supposed to be used as a neutral.

Since its impractical to use the on/off switch combo, replace it with an ordinary switch. If you use it, you have to press start every time the compressor tank gets low on pressure.

Replace one set of contacts on the P-switch for the on/off push buttons in the 2nd drawing, the 2-3 NO holding contact won't be used.

As you've probably figured out, the circle with the 2 small circles is the coil that engages the mag. starter.

The NC contact is to shut things off when overloaded.

L1, SPST switch, P-switch, coil, NC contact, Neutral

The above is my opinion on how to wire it, not what I consider absolute truth. If I'm wrong hopefully the experts will correct my errors.

 

[dave63]

As others have said, you need a neutral since 240V will fry the coil and the ground isn't supposed to be used as a neutral.

Since its impractical to use the on/off switch combo, replace it with an ordinary switch. If you use it, you have to press start every time the compressor tank gets low on pressure.

Replace one set of contacts on the P-switch for the on/off push buttons in the 2nd drawing, the 2-3 NO holding contact won't be used.

As you've probably figured out, the circle with the 2 small circles is the coil that engages the mag. starter.

The NC contact is to shut things off when overloaded.

L1, SPST switch, P-switch, coil, NC contact, Neutral

The above is my opinion on how to wire it, not what I consider absolute truth. If I'm wrong hopefully the experts will correct my errors.

Thanks I appreciate your response.

 

[SgtRauksauff]

This is the diagram I ended up using for my 5hp single-phase compressor install. It came with the Siemens box that I got a good deal on:

--sarge