relay
- Thread starter fireryan
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zog
Senior Member
- Location
- Charlotte, NC
They are usually shown in thier normal state, that could be energized or denergized, open or closed, etc...what ever is the normal state.
Thanks for the replys. The reason I ask is because i dont have much motor control experience so i am taking a motor control class and there is a few things I dont understand. When you feed the relay with your 120v does that have to be constant or do you switch that 120v on and off to control the relay? I can see where pin 5 and 6 are used for actuating so that makes me think that the 120v should be constant comin in on terminal 2
steelersman
Senior Member
- Location
- Lake Ridge, VA
whatever powers the coil is what turns it on and off. So if your relay coil is 120 volts then you wouldn't want it constantly on or else there wouldn't be much need for the relay. When the coil is energized then the N.O. contacts close and the N.C. contacts open and when the coil is de-energized then the contacts do the opposite or return to their normal state.
- Location
- Illinois
- Occupation
- retired electrician
Unless you are working with a time delay relay you turn the power to the coil on and off to operate the relay contacts. Some time delay relays require constant power and a trigger signal.
thats what had me confused. This is a time delay relay. I have my 120v feeding my relay and my trigger switch. I also have constant 120v feeding one side of my NO contacts and the other side goes to my contactor to provide a off delay for the contactor when the relay is closed. My question is does the other side of my trigger switch need to jump to anything else or do i have this right?
steelersman
Senior Member
- Location
- Lake Ridge, VA
I'm not quite following what you say.thats what had me confused. This is a time delay relay. I have my 120v feeding my relay and my trigger switch. I also have constant 120v feeding one side of my NO contacts and the other side goes to my contactor to provide a off delay for the contactor when the relay is closed. My question is does the other side of my trigger switch need to jump to anything else or do i have this right?
- Location
- Illinois
- Occupation
- retired electrician
If it is the time delay relay that I am thinking of, you close a contact between terminals 5 and 6 to trigger the timer.
yeah I know. I wish I could post a daigram to show you
yeah we are on the same page. thanks
zog
Senior Member
- Location
- Charlotte, NC
That is why I didnt say always. And I agree with you about the de-energized being the norm, nut what about a UV coil for example?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Every diagram I have worked with has shown the shelf (de-energized) state of all relays (UV coils not excepted). It does not matter whether the relay, when in its "usual" (note that I did not say "normal") operating condition, has power all the time.
I tend to cringe, when I hear the terms "normally open" or "normally closed," both in the context of switches and in the context of relay contacts. These phrases provide such great opportunities for mis-interpretation. I prefer the convention that in the shelf state of a relay, its "a contacts" are open and its "b contacts" are closed. Thus, when I look at a control diagram, and I see an "a contact," and if I determine that that relay will have power most of its operating life, I will infer that that "a contact" will be closed for most of its operating life. That is the mind set I have when study such diagrams.
I tend to cringe, when I hear the terms "normally open" or "normally closed," both in the context of switches and in the context of relay contacts. These phrases provide such great opportunities for mis-interpretation. I prefer the convention that in the shelf state of a relay, its "a contacts" are open and its "b contacts" are closed. Thus, when I look at a control diagram, and I see an "a contact," and if I determine that that relay will have power most of its operating life, I will infer that that "a contact" will be closed for most of its operating life. That is the mind set I have when study such diagrams.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I especially hate "a 3-position switch with (1) normally open and (1) normally closed contacts.
weressl
Esteemed Member
Looking at a relay on th3e drawing can not determine it's state. You have to look at the entire rung of the ladder to determine its state.
Ladder diagrams are depicting the state of the devices in the off-shelf conditions with power ON.
So if you have a NC contact energizing the relay, then the relay would be energized. The associated contacts would be shown in the off-shelf condition.
The big argument comes about when showing various process connected devices, such as flow or temperature switches when the off-shelf NO open contacts used, but for the steady state operations flow or temperature is necessary to achieve the normal operating state. Some people argue that these should be shown in the operational state, eg. NC. I disagree.
weressl
Esteemed Member
thats what had me confused. This is a time delay relay. I have my 120v feeding my relay and my trigger switch. I also have constant 120v feeding one side of my NO contacts and the other side goes to my contactor to provide a off delay for the contactor when the relay is closed. My question is does the other side of my trigger switch need to jump to anything else or do i have this right?
Depend on the type of TD. We use true-off-delay timer to overcome power dips and short outages, so the TD energizes when the control power is turned on and the contact instantly closes and remains closed while the the power is of. (It remains closed for the time-set duration.) This is an undervoltage/loss of power off-TD finction.
weressl
Esteemed Member
That is why it important to define that the NO and NC states mean off-the-shelf condition. Ladder 101.
weressl
Esteemed Member
3 position switches should indicate the status of the contacts in each position. This is done with showing the contacts in both position together with the 3 handle positons. Whatever you decide to be the NORMAL postion of the switch if there is not OFF position, you would draw a solid veritical line and dashed lines for the other positions. The position of each contact is determined. The OFF position of each contact is solid and the other postions are indicated by small corsses at the intersections of the two other positions and the alternate postions of the contacts.
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