Got a question for you guys - we have a motor starter in which all of the auxiliary contacts have been used, but we want to add 'Running indication' back to our DCS system. I was wanting to add an additional set of wires to one of the NO aux contacts, so when the starter closes the aux contacts close, which completes a circuit back to our DCS telling it that the motor is running. The question I have is will this disrupt or affect any of the other circuits that are attaced to the same set of aux contacts? Has anyone tried of had any experience in doing this? Thanks
Starter Auxiliary Contact Usage
- Thread starter adamscb
- Start date
- Status
- Location
- Massachusetts
You want to use the same aux switch to control circuits from two different sources?
If so no, do not do that.
In most cases you can order additional aux contacts to install on motor starters.
ATSman
ATSman
- Location
- San Francisco Bay Area
- Occupation
- Electrical Engineer/ Electrical Testing & Controls
As iwire stated, you cannot mix circuits.
If all of the aux contact spaces are used you can install an Idec or any
cube relay in the bucket or panel and wire the coil in parallel with the contactor coil. Make sure you match the voltage.Then wire the DCS wires to the NO contact of this aux relay.
If all of the aux contact spaces are used you can install an Idec or any
cube relay in the bucket or panel and wire the coil in parallel with the contactor coil. Make sure you match the voltage.Then wire the DCS wires to the NO contact of this aux relay.
Tony S
Senior Member
- Location
- Resting under the Major Oak UK
Many contactors have the facility to add extra contact blocks or you could add an auxiliary relay to the contactor coil supply.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
A relay in parallel to the coil does not tell you that the contractor closed. It only tells you rant the coil circuit was energized. If the contactor coil fails, the relay tells your DCS that the contactor closed when it did not. To do it right, you remove one circuit that is using an aux contact now and use that aux contact to pull in the slave relay, then move that circuit to your slave relay plus the new one you need for the DCS.
That is IF you cannot add any more aux contacts. How many do you have now and what's the make and model of the contactor?
That is IF you cannot add any more aux contacts. How many do you have now and what's the make and model of the contactor?
I noticed that you told us what type of contactor that you had. Not.
The contactors that I'm familiar with can accommodate up to 4 contact blocks each, each block can have:
(1)NO(1)NC, or (2)NC,or{2)NO. It is difficult to help you find a solution we without knowing what you have. And how many different manufacturer contactors are there?
ATSman
ATSman
- Location
- San Francisco Bay Area
- Occupation
- Electrical Engineer/ Electrical Testing & Controls
Your suggestion of a better design? Possibly. But it all depends on have far your want to take this risk analysis.
What if the signal to the DCS fails because: 1. The aux contact fails to close (dirty contact) when energized
2. The contact on the slave relay fails to close 3. There is an earthquake, flood, tornado and the panel is destroyed 4. What if........... What if.................!!!!!!!! But in the end, maybe either suggestion is the simplest way out.
Saturn_Europa
Senior Member
- Location
- Fishing Industry
- Occupation
- Electrician Limited License NC, QMED Electrician
+1
The overloads switch X2. So if you wire in parallel to the X1 on the starter coil you still show running during overloads.
Saturn_Europa
Senior Member
- Location
- Fishing Industry
- Occupation
- Electrician Limited License NC, QMED Electrician
Do you have an open set of NC contacts? You can use them instead of an NO. Just reverse your logic in the DCS from ----| |--- to a ----|\|----
- Location
- Massachusetts
In many cases the NO and NC share a common so that could be an issue.
- Location
- Massachusetts
We have used these self powered current sensors to do this sort of thing.
http://www.veris.com/Item/H609.aspx
http://www.veris.com/Item/H609.aspx
Good point. What you have described are form"C" contacts which are commonly found which aux, contacts on breakers. But I would immagine the some control manufactures may use them on contactors.
With all due respect, I don't think that is true. If the contactor coil fails, then the holding contacts open, which de-energizes the holding circuit.
If the slave relay you mention above requires 120v to pull in, then that scheme won't work. The way I understand auxiliary contacts is that they are dry, and do not supply any voltage.
Saturn_Europa
Senior Member
- Location
- Fishing Industry
- Occupation
- Electrician Limited License NC, QMED Electrician
This is why controls are fun, because if you want to make it work you can usually sit down and figure out in a few minutes. In this case you would use 120 v as the wetted voltage to one side of your dry contacts. Its definitely possible and there are multiple correct ways to do it.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
He was explaining that if you add an additional relay in parallel to the contactor coil that the additional relay will operate even if the contactor relay has failed, giving you false signal that it pulled in. If you power a slave relay first then drive the contactor from it - the contactor never pulls in if the slave relay fails to operate. You still have contacts that operate while others don't but you need to select which ones are more important to the control scheme and connect accordingly.
Add: and if knowing a motor is actually running a current monitoring relay may be necessary as has been mentioned. Otherwise contactor might be pulled in but maybe a fuse or breaker is blown and the motor is not running, or a belt is broken and motor is running but at a current level below what you have set in the current monitor.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
It's the way I was taught; better to be more sure than less, especially if it costs you nothing. You are adding a relay anyway, the only difference is in how you wire it. Why not add the assurance? Sure, you can go hyperbolic on anything, but it's not like I am saying "go out and spend more money needlessly". I don't understand the objection.
Modern trend is probabilistic thinking. Had you also stated your proposal how reliable it is ie with a measure of probability, no voice might have raised against it.
I guess your clients are really that rich and have deep pockets for them to entertain such 'probabilistic" idea of yours! My mentor always tell me: KEEP IT STUPIDLY SIMPLE! (though, there's another way of saying those):lol:
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
For a manually /locally controlled starter you are right. But this discussion is regarding an automated system, by virtue of the DCS. When someone spends six to seven figures on a control system, they do not rely on a local Start-Stop push button for control (other than maybe a manual override). The DCS will be using 2 wire control, in which case there is no seal in contact. Reliable control system design philosophy dictates eliminating as many errors as is reasonably possible. If for example this is a chemical feed pump as part of a process to make a product, having the pump not run, but the DCS getting an indication that it is running, can result in major losses and clean out costs. A simple extra wire prevents that false reporting.
Now, all that said, the reality is that MOST starters can accept at least 4 aux contacts, many larger ones and most NEMA contactors can accept as much as 8. The likelihood that the OP's DCS controlled starter is using 4 aux contacts already is fairly low. You typically do not need a lot of aux contact interlocking in a DCS controlled system because that would be done in the DCS for a variety of other safety issues. So most likely the reason the OP is silent on this is because after reading iwire's first response, he figured that out.
Last edited:
- Status