Coil & NC Contacts

[Little Bill]

Is it common to run the 120V coil, A2 (neutral) through the NC contacts on an overload? Why would you not run the A1 through the NC contacts? Does it make a difference?

 

[TwoBlocked]

Is it common to run the 120V coil, A2 (neutral) through the NC contacts on an overload? Why would you not run the A1 through the NC contacts? Does it make a difference?

Yes, that is normal, and is how Ugly's shows starters are wired. The biggest difference is if the OL contacts were before the coil, that is not how you would expect it to be. It does seem odd to have a circuit designed that "opens the neutral."

I've seen motor overide circuits that will bypass the OL contacts in case a motor trips and you have a suspended load that HAS to be let down. Lifeboat winches are one application.

Have had this discussion with some graduates from a local tech school. They had an instructor that insisted that they wire the OL immediately after the control power fuse, even if it requires rewiring one that was wired the normal way from the factory. Imagine the confusion of trying to follow the schematic on the inside door of a combo starter and someone wired it differently!

If my boy goes there, I have already told him that I need to keep track of what he's being taught. He's a senior and is leaning toward lineman school, though.

 

[retirede]

My theory is that the OL contacts are on the “common” side from the factory so that people in the field won’t inadvertently mis-wire something in the control circuit (bypassing the OL contacts) since all of the control connections will be on the “hot” side.

 

[kwired]

My theory is that the OL contacts are on the “common” side from the factory so that people in the field won’t inadvertently mis-wire something in the control circuit (bypassing the OL contacts) since all of the control connections will be on the “hot” side.

This usually the case with NEMA motor starters that have the OL control contact and the aux holding contact control wires prewired from factory.

Most everything else has no prewiring from the factory. Some still wire them in similar fashion. I do if there is other controllers already in place just to keep the same way. If starting from scratch I usually put the OL contact in series as first item ahead of coil on the ungrounded conductor though.

I've seen motor overide circuits that will bypass the OL contacts in case a motor trips and you have a suspended load that HAS to be let down. Lifeboat winches are one application.

Bear in mind I have no idea what is common for lifeboat winch motors but I'd have to say that a lifeboat winch possibly could be an intermittent duty motor, and overload protection rules are not the same as for continuous duty motors, often you don't even need an overload protector in many I have been involved with. Vehicle hoists with hydraulic pump is one the more common ones I see.

 

[Tulsa Electrician]

I say no for 120 v ac
I teach A1/ A2 based on 1,2,3,4 which is left side of ladder moving right with the grounded conductor right side A2 through overloads. Code teaches us left to right top to bottom so this falls in line with the rest of the teaching.

1 ends at 1, 2 ends at 2
Makes trouble shooting a piece of cake


This also help them understand all stop in sieres. 1a,1b etc before 2.

It add meaning to the madness.



Commentary:
Now if it did not run (grounded conductor) though OL,NC you could run into an issue
The reason is In case the the grounded conductor get damaged and makes a ground contact.

The chances are lower for that one short piece of wire.

Another reason to use line to line with fuses on both lines when it really maters. Then it takes that short wire out of the hazard analysis.

Imagine an e- stop with a start stop using a grounded conductor for 1,2,3 with the ungrounded running thru OL, NC. Greater chance of the control circuit being out of control if a wire makes a ground connection.

Ugly was mentioned and ask your self why L-3 instead of L-2 for line to line control circuit in 3- phase.

 

[kwired]

I say no for 120 v ac
I teach A1/ A2 based on 1,2,3,4 which is left side of ladder moving right with the grounded conductor right side A2 through overloads. Code teaches us left to right top to bottom so this falls in line with the rest of the teaching.

1 ends at 1, 2 ends at 2
Makes trouble shooting a piece of cake


This also help them understand all stop in sieres. 1a,1b etc before 2.

It add meaning to the madness.



Commentary:
Now if it did not run (grounded conductor) though OL,NC you could run into an issue
The reason is In case the the grounded conductor get damaged and makes a ground contact.

The chances are lower for that one short piece of wire.

Another reason to use line to line with fuses on both lines when it really maters. Then it takes that short wire out of the hazard analysis.

Imagine an e- stop with a start stop using a grounded conductor for 1,2,3 with the ungrounded running thru OL, NC. Greater chance of the control circuit being out of control if a wire makes a ground connection.

Ugly was mentioned and ask your self why L-3 instead of L-2 for line to line control circuit in 3- phase.

Any two lines works. You know that as well.

L1 and L3 seems to be most common, though I have seen L1 and L2 used at times as well.

I think possibly L1 and L3 often are used as you sometimes find a 2 pole contactor build on a three pole frame, they just leave parts out of the middle pole space. Seemed to be more common in the past than it has been in more recent years. Now those two pole units are almost non existent and if you want a two pole application (at least for something over 30 amps) you buy a three pole contactor and just don't use one pole.

 

[TwoBlocked]

I say no for 120 v ac
I teach A1/ A2 based on 1,2,3,4 which is left side of ladder moving right with the grounded conductor right side A2 through overloads. Code teaches us left to right top to bottom so this falls in line with the rest of the teaching.

1 ends at 1, 2 ends at 2
Makes trouble shooting a piece of cake


This also help them understand all stop in sieres. 1a,1b etc before 2.

It add meaning to the madness.



Commentary:
Now if it did not run (grounded conductor) though OL,NC you could run into an issue
The reason is In case the the grounded conductor get damaged and makes a ground contact.

The chances are lower for that one short piece of wire.

Another reason to use line to line with fuses on both lines when it really maters. Then it takes that short wire out of the hazard analysis.

Imagine an e- stop with a start stop using a grounded conductor for 1,2,3 with the ungrounded running thru OL, NC. Greater chance of the control circuit being out of control if a wire makes a ground connection.

Ugly was mentioned and ask your self why L-3 instead of L-2 for line to line control circuit in 3- phase.

I do see your point. With the OL last, the coil is sourcing and the OL is sinking. The other way, the OL is sourcing and the coil is sinking. For those scratching their heads, consider what happens if the wire between them grounds out. In the first case the coil could pull in when the OL is actually tripped. In the second case, you get a blown fuse when there is a ground. Or would this all be an argument to have an ungrounded control circuit?

 

[Little Bill]

Look at this schematic and go down about half way. Start at the door safety LS-1 and over to the "wash/off/rinse switch.
How would you wire this through M1 and OL?

 

[don_resqcapt19]

Is it common to run the 120V coil, A2 (neutral) through the NC contacts on an overload? Why would you not run the A1 through the NC contacts? Does it make a difference?

All NEMA starters come wired that why unless you specify otherwise. I only did one project in my career when the engineer would not permit the overload relay contact to be in the grounded conductor side of the circuit.

Note that if for some reason, the conductor between the overload relay and the starter coil leaves the starter enclosure, you are not permitted to have the overload relay switch the grounded conductor. See 430.74.

One major MCC manufacturer provides a terminal point on their MMC buckets that permits you to make a connection to the conductor between the overload relay and the coil and extend it beyond the MCC enclosure, and I have no idea why they do that the code does not permit a connection to that terminal point.

 

[Tulsa Electrician]

It looks like the grounded conductor for M1 ( motor 1) coil runs through NC of O-1 ( over load 1)

Grounded conductor(X2) to 95. 96 to A2. 95/96 NC overload block.

2 to 2 right side of ladder.

My copy a little blurry hope I read it correctly.

 

[Little Bill]

It looks like the grounded conductor for M1 ( motor 1) coil runs through NC of O-1 ( over load 1)

Grounded conductor(X2) to 95. 96 to A2. 95/96 NC overload block.

2 to 2 right side of ladder.

My copy a little blurry hope I read it correctly.

That's correct and the way I see it. Most of the schematics that I have seen actually say A1 and A2, this one did not and I wanted to make sure.

 

[TwoBlocked]

Look at this schematic and go down about half way. Start at the door safety LS-1 and over to the "wash/off/rinse switch.
How would you wire this through M1 and OL?

It darn well better be wired like shown. I am the one that designed the thing and approved the drawing! (Just kidding). But yes, that is the normal way and what I would do with the motor control. But I would also include a lighted e-stop first thing after the fuse.

 

[kwired]

Look at this schematic and go down about half way. Start at the door safety LS-1 and over to the "wash/off/rinse switch.
How would you wire this through M1 and OL?

If I were designing it I either put the OL as first thing in the line or first thing before the coil.

I have worked on grain drying systems that have all the motor overloads in series as an input to the logic board. Any overload that trips shuts down and locks out everything in the system and gives a fault output/alarm. This system has methods of operating individual loads by hand, but nothing operates in any mode if any overloads are tripped. Main call I get nearly every year has to do with aux equipment that ties into this system. If said aux equipment is not in proper "ready mode" it's feed back to the main system is essentially tied into that overload circuit. Since they only operate this system a few weeks out of the year and sometimes don't operate at all if crops are dry enough, they forget how to run it and I end up coming out and find they just didn't follow proper sequence of operations. I don't always remember all the specifics either, and sometimes some component is having some sort of issue that complicates it even further.

 

[Tulsa Electrician]

It darn well better be wired like shown. I am the one that designed the thing and approved the drawing! (Just kidding). But yes, that is the normal way and what I would do with the motor control. But I would also include a lighted e-stop first thing after the fuse.

I would first do a risk analysis based on the operation of the machine.
An E- stop may cause more harm than just a stop.

Not to say a nice big maintained stop button would not be a good idea.

If an E- stop was used. What happens to the timer when the E- stop in enabled.

For an e- stop, when enabled would take another action before any thing can run. Would the trimmer rest with power loss to the static state with no run command.

Now you would need to add this to the operation protocols for that machine. This would be why I recommend a hazard risk analysis.

Basically a what if.

So maintained stop or an E- stop?
An E- stop with a start function may be required to have the yellow back ground and label versus a maintained stop red mushroom head button( no E- stop label or back ground).

May be a reason the cabinet does not have one on the front.