help me understand this

[Designer69]

I think this question will help me understand circuits

In the sketch below if switch SW1 is open as shown, will the R1 relay coil be energized to close contact R1 or will it be De-energized with R1 staying open?

I say De-energized

 

[LarryFine]

I say De-energized

You are correct. The contacts are shown as normally open (NO) while deenergized, without the slash that indicates normally closed (NC) while deenergized.

Added: By the way, the zig-zag line is traditionally used to indicate a resistor. A coil is usually shown in a schematic as a circle with the designation (R1 in this case) inside the circle.

 

[charlie b]

I agree with deenergized. But I have seen the zig zag used as the symbol for a coil.

What I object to (knowing well that I will continue to lose this argument) is the use of ?normally open? and ?normally closed.? If the design calls for a coil to be energized for 99.99% of its operating life, isn?t ?energized? the ?normal? state for that coil? It is just an opportunity for mis-communication that can be easily avoided. The standard convention is to show contacts in the state they would be in with the coil deenergized (?shelf state?), regardless of whether the coil is ?normally kept energized.? I prefer the use of the a/b nomenclature: An ?a contact? will be open with the coil in its shelf state, and a ?b contact? will be closed in that same state.

 

[charlie b]

In the sketch below . . . .

I don't like the design here. I would put the switch between the "hot conductor" ("L") and the coil. As shown, the coil is at line potential, even with the switch open. Or is that the reason for your question? Is this really a discussion of terms, as opposed to a discussion of circuit operations? The word "energized" can be used in two different senses here.

With the switch open, no current will flow, so the coil will not act as an electromagnet, will not move the contacts in opposition to the springs that hold them in their shelf state, and the "a contact" will remain open. That condition is commonly called the "deenergized state." However, the coil really is "energized," in the sense that if you were to touch its termination point, you would get a shock.

 

[LarryFine]

The standard convention is to show contacts in the state they would be in with the coil deenergized (?shelf state?), regardless of whether the coil is ?normally kept energized.?

I approve of that method of ID. To me, "normally" has always implied deenergized.

 

[LarryFine]

However, the coil really is "energized," in the sense that if you were to touch its termination point, you would get a shock.

No, that's when the observer has become energized.

 

[Designer69]

Or is that the reason for your question?

yes exactly. I wasn't sure since the relay is at line potential it would energize the coil.

but you explained it perfectly. i understand the other parts to this. Thanks!

 

[steve66]

I've seen the zig-zag shown for a coil also, but I think its usually used more for a solenoid, where the output is something mechanical.

For a coil, the symbol is always a single zig-zag (like its shown in the diagram) while a resistor always has more than one zig zag.

 

[ronaldrc]

I say de energized, but that switch being on the grounded or common side is a NEC violation
should be on the hot side.

 

[ZinskI/E]

I agree with Charlie that the switch should be on the ungrounded side of the circuit, but is doing otherwise an NEC violation? What if the switch is an output from a PLC? I can't say it's common, but I have definitely come across switching the neutral in the field, usually on start permissive circuits.

 

[ATSman]

Control Theory Semantics

Control Theory Semantics

By definition I have always thought of "energized" as meaning current passing thru the coil to operate the device (change contact state as in this case.), not voltage applied to one side. If you think of it this way then it may become less confusing.

TT

 

[G._S._Ohm]

By definition I have always thought of "energized" as meaning current passing thru the coil to operate the device (change contact state as in this case.), not voltage applied to one side. If you think of it this way then it may become less confusing.

TT

Yes.
Magneto Motive Force is supplied by amps times the number of coil turns.
The voltage across the coil to give those amp-turns is determined by the wire resistance so current is a more basic factor in coils.

 

[Dennis Alwon]

I agree with Charlie that the switch should be on the ungrounded side of the circuit, but is doing otherwise an NEC violation? What if the switch is an output from a PLC? I can't say it's common, but I have definitely come across switching the neutral in the field, usually on start permissive circuits.

Article 404.2(B) seems to say so.

404.2(B) Grounded Conductors. Switches or circuit breakers shall not disconnect the grounded conductor of a circuit.
Exception: A switch or circuit breaker shall be permitted to disconnect a grounded circuit conductor where all circuit conductors are disconnected simultaneously, or where the device is arranged so that the grounded conductor cannot be disconnected until all the ungrounded conductors of the circuit have been disconnected.

 

[hillbilly1]

I agree with Charlie that the switch should be on the ungrounded side of the circuit, but is doing otherwise an NEC violation? What if the switch is an output from a PLC? I can't say it's common, but I have definitely come across switching the neutral in the field, usually on start permissive circuits.

Though technically you might not consider it a switch in the context we are discussing, but most motor starters that have 120 volt coils, have the overload contact on the neutral, or common side of the coil.

 

[kwired]

I say de energized, but that switch being on the grounded or common side is a NEC violation
should be on the hot side.

I agree with Charlie that the switch should be on the ungrounded side of the circuit, but is doing otherwise an NEC violation? What if the switch is an output from a PLC? I can't say it's common, but I have definitely come across switching the neutral in the field, usually on start permissive circuits.

By definition I have always thought of "energized" as meaning current passing thru the coil to operate the device (change contact state as in this case.), not voltage applied to one side. If you think of it this way then it may become less confusing.

TT

Think of it as energized, but open circuit vs energized with complete circuit. A solenoid coil does not care about whether either conductor supplying it is grounded or non grounded or which one has any control switches in it. All that matters is that enough voltage is applied when intended to create enough magnetism to operate the armature. Change the line marked 'N' to read 'L2' and there is nothing to criticize in the drawing, and it will function regardless of what the voltage is or which line (if any) is grounded or not.

Though technically you might not consider it a switch in the context we are discussing, but most motor starters that have 120 volt coils, have the overload contact on the neutral, or common side of the coil.

I was going to mention that when I selected the first two quotes but you beat me to it.

 

[BJ Conner]

"Shelf position"

"Shelf position"

I think this question will help me understand circuits

In the sketch below if switch SW1 is open as shown, will the R1 relay coil be energized to close contact R1 or will it be De-energized with R1 staying open?

I say De-energized

It's customary to draw things in their "shelf" position. That is how it would be in the box on the shelf before it was installed.
The switch shoud be connected to the L1 side of the the circuit. Any ground fault down stream of the coil as drawn will energize the coil. Not so apparent in this simple circuit but the more componets in the circuit the more probable a circuit somewhere could energize the coil. The closing contact could start a motor or something else dangerous.

 

[kwired]

Any ground fault down stream of the coil as drawn will energize the coil.

To be more specific - which is sort of what this thread is about, maybe you should have said something like 'any ground fault down stream of the coil as drawn will complete a circuit - allowing the coil to operate in an unintended condition'.