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#39810 07/01/04 11:59 PM
Joined: Jan 2004
Posts: 171
Merlin Offline OP
I have a scenario that I am trying to figure out. I believe this is right,but want to make sure.

I am still working on our pump station at work. I have Benshaw soft starts in a control house with 110 volt "local" controls. Then approx. 500 foot away I have a 250 HP pump and a 300 HP pump. At this pump station, I have "remote" controls. These are 480 volt. (due to the distance and voltage drop for 110 volt) I have four 480 volt power relays that are to tie these two together. ( by the way, this is a 3 wire control situation )

This is where I am in a brain feeze. I have a 480 Volt circuit at this pump station. How do I utilize these relays to switch this 480 "remote" circuit back to 110 at the "local" controls.

This was all drawn up by my engineer and supposed to work, but I have no prints. I know there is a way and am sure I know how,but I don't want to screw this up.

Thanks to all!!


#39811 07/02/04 12:05 PM
Joined: Jan 2003
Posts: 73

I am a little confused with the concern regarding voltage drop on the 110 Volt, 3 wire control circuit.

I'm sure if you did a voltage drop calulation based on the In-Rush VA of the contactors and Pilot Lights you will find that maybe all you have to do is increase the wire size to #12 or #10 AWG wire to make up for the potential voltage drop.

From what you have described this sounds like it would be much easier, the fewer relays and such the less chance for breakdowns and eaisier to trouble shoot breakdowns.

I know this did not directly answer your question but....

#39812 07/03/04 01:35 AM
Joined: Apr 2002
Posts: 2,527
Salient discussion at..
Also.. e4f84/114f29214c232a6a852568390055a15d/

Be very careful expecting high reliability from 480V pilot circuits, particularly if the control-voltage source is ungrounded; runs are long or any wet conditions occur. Unanticipated/unreliable operation can be especially expensive, particularly with listed motor sizes.

[This message has been edited by Bjarney (edited 07-03-2004).]

#39813 07/04/04 07:35 PM
Joined: Jan 2004
Posts: 171
Merlin Offline OP

I know this sounds very confusing. But this is what was determined to be the "best" way to go by my engineer. Now I just have to make it work. My original suggestion was 120 volt controls. But he says that it is to far to run 120 due to voltage drop. I don't know exactly, but it is between 500-700 foot.

It is set up "local" at 120 volts in a Benshaw softstart. The reason for this is for float controls. I guess I will have him draw this circuit out how he wants it, so I am not as responsible if it doesn't work.

Thanks for the input gentlemen.

#39814 07/05/04 10:56 AM
Joined: Jan 2003
Posts: 73

Sorry, but I disagree with your Eng.

I ran some calculations using 120 Volt, 1 Amp load with 3% allowable voltage drop(this is probably high for a Starter or Control Relay coil, Pilot light or PLC I/O situation).

Results with 75 degree C operating temp:
#12 = 750 feet
#10 = 1250 feet

Note: If your operating temp or load (Amp's)is less the length increases.

I agree with Bjarney, using High Voltage for control is not a recommended practice!!!

#39815 07/05/04 02:04 PM
Joined: Apr 2001
Posts: 507
We do a lot of grain elevators. Always 480v motors w/120v controls. I agree with the others that 120v controls would work fine for your application. Anything else is more complicated, less reliable, and mainly, not as safe.


#39816 07/06/04 09:34 AM
Joined: Jul 2001
Posts: 599
JBD Offline
For this to work, you bring your 480V control circuit back to the soft-starter. At the soft-starter you install your 480V coil relay(s). You use the relay contacts in your 120V control circuit just like you would any other contact or pushbutton.

I do not know why you are using 2 relays for a remote 3-wire control scheme. My thought is that one relay is for the Stop function, which would be a "normally" open (when de-energized) contact wired in series with your local stop button. the other relay would be for the Start function which would be a normally open contact in parallel with your local start button. My suggestion would be to use a single 480V relay wired with a standard 3-wire scheme. A normally open contact from this relay would be wired in series with the local 120V circuit.

You need to (should) place identification of your foreign voltage control circuit (most people use yellow wiring). A local disconnect of the 480V circuit would also be helpful.

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