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# Contactor Relay Coil Current Requirements

04/05/2017 5:35 PM

Trying to calculate the current requirements although it seems to easy which usually means i did something wrong.

Siemens contactor

I have a pdf of the data sheet but my apologies i dont know how to upload it here to make it easier. Here is a screen shot of the important stuff

So i know its a 230V control and im given an S of 61VA

Its a 3 phase contactor but the control is single phase 230

I want to calculate the current that the control coil will draw

Im tempted to say 61VA/230V = I = .26A

Obviously from S = V*I Magnitude

but it seems to easy and im sure im forgetting something.

Anyone want to double check this simple task?

I know it seems ridiculous but if we could keep the laughter to a minimum that would be great.

Thanks

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Anonymous Poster #1
#1

### Re: Contactor relay coil current requirments

04/05/2017 5:42 PM

Image is rather fuzzy. Could you add the part number as text.

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#2

### Re: Contactor relay coil current requirments

04/05/2017 6:00 PM

sure thing

here it is

3RT1024-1AP00

3
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#3

### Re: Contactor Relay Coil Current Requirments

04/05/2017 7:06 PM

There's actually two different current draws, the pickup current and the holding current. Since the pickup is very short time, the holding current is usually the one that governs. However, you must look at the duty cycle to determine the size of the control transformer as well as the size of the wiring, although the only circumstances in which it may matter is if there are clusters of relays all being simultaneously powered from the same source.

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#4

### Re: Contactor Relay Coil Current Requirments

04/05/2017 8:59 PM

Thanks

That is what I was gathering. Im assuming the holding current is the one that will wold the contacts closed and the pickup current is the initial current to get them to close

Is this a simple S = V*I or is it more complicated?

I know so far in industry most field engineers take the VA needed for the closing and just some them all together and make sure the supply transformer is at least that many VA but what if you want a more precise answer then that?

For say wire sizing ?

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#5

### Re: Contactor Relay Coil Current Requirments

04/05/2017 9:45 PM
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#6

### Re: Contactor Relay Coil Current Requirments

04/05/2017 11:24 PM

looks like that is mostly concerned with VA ratings

which I think is common. I need to give that doc a second look tho

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#7

### Re: Contactor Relay Coil Current Requirments

04/05/2017 11:44 PM

You size the transformers according to the contactor current requirement, those calculations detail the current requirements of the contactors, which I believe was what your question was about....

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#8

### Re: Contactor Relay Coil Current Requirments

04/05/2017 11:53 PM

That is true but as Ram mentioned, if you have a cluster of relays power by the same transformer then you have size the transformer accordingly.

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#9

### Re: Contactor Relay Coil Current Requirments

04/06/2017 12:33 AM

Yes the document is titled "PROPER SELECTION OF CONTROL CIRCUIT TRANSFORMERS" in which all parameters are taken into consideration, be it one contactor or a dozen...Determining the current requirements for control circuits is determining the individual current requirements for every device and is covered in NEMA Standard ICS 2-110...

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#11

### Re: Contactor Relay Coil Current Requirments

04/06/2017 8:07 AM

Now, if we've moved on to wire sizing then that's a different game, because it is all given by your local national electrical codes. Don't forget that circuit protection devices go in here too.

Wire sizing for 7.8VA, though?

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#13

### Re: Contactor Relay Coil Current Requirments

04/06/2017 8:31 PM

I see. Rscott9399 and wannabecontroller, are one and the same person.

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#14

### Re: Contactor Relay Coil Current Requirments

04/06/2017 11:36 PM

Good catch! Tell me you're not playing left outfield? Not'n worse than being overhead and not able to swim!

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#16

### Re: Contactor Relay Coil Current Requirments

04/07/2017 10:29 AM

I already suspected as much during this thread, where Rscott9399 was defending wannabecontroller. Highlighting by me:

wannabecontroller in post 35: "sitting on their thrown"

Rscott9399 in post 46: "Just like you are entitled to sit on your thrown"

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#17

### Re: Contactor Relay Coil Current Requirments

04/07/2017 11:28 AM

Abuse/Attack: This post was deleted because it was an attack on another user. Please review the Site FAQ and the Rules of Conduct.

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#18

### Re: Contactor Relay Coil Current Requirments

04/07/2017 3:00 PM

thats it, account deleted

this site is rediculous

anyone can be attacke and harassed but no one can defend themselves

typical!

im out good riddins

sorry to the op that is just trying to get help early in his career

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#19

### Re: Contactor Relay Coil Current Requirments

04/07/2017 3:18 PM

Sorry you are getting a bunch of crap for trying to defend me

This forum is ridiculous i may leave as well. Every time i make a post im ridiculed for asking damn near anything.

How vile of me to ask a question on a forum and its not just me. Other people get abused repeatedly for doing nothing but asking a question yet admins do nothing to maintain the integrity of the forum.

truly disgusting

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#15

### Re: Contactor Relay Coil Current Requirments

04/07/2017 10:29 AM

What are you talking about? The OP has not made a single comment since asking the question. I was thanking the guy above for a good reply to a topic that i was also interested in.

So someone chimes in and thanks someone for posting and we are now the same person?

How this forum never fails to amaze me. This place is often worse then a first grade playground

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#10

### Re: Contactor Relay Coil Current Requirments

04/06/2017 4:53 AM

In induction motors, it is called "LRC" locked rotor current which is a little lower than the IN-RUSH or starting current but its the one that is considered in sizing transformer for an assembly of contactors in a control circuit. If you want to add up fuses for safety not to burn up coils or the neighbouring circuit element in your contactor later on in life which ants mostly preferred to infest on coils and contacts, refer it to the IN-RUSH current.

Some crazy ants infestation

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#12

### Re: Contactor Relay Coil Current Requirments

04/06/2017 8:09 AM

0.26A on energising, or around 1/8 of that continuously, from that information.

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