Wrong usage of overloads.

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
19,006
You can still find control examples posted regarding the use of contactor control wiring implementing the O/L in the wrong part of the circuit.
For many decades the O/L in ladder circuitry has been inserted on the common or Neutral side of the coil.
This has been a no-no for some time now, but the practice still seems to exist.
It is considered a dangerous practice, especially where the common side is a ground-referenced conductor.
The diagrams shown, the O/L should be on the Left of the coil.
Max.
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SamR

Joined Mar 19, 2019
1,136
Yeah but some of the starters we had probably dated back to maybe the 40s and certainly the 50s and the overloads were part of the internal starter wiring weren't they? The electrical supply houses used to give away a pretty good Square D booklet on ladder logic diagrams and control wiring for starters. ~30-50 pages I probably still have one around here somewhere. We had to build into and around a lot of "grandfathered" electrical equipment designs. It was always a pleasure to raze and build from scratch with new gear. I was told to salvage some motor control centers from an abandoned area of the plant and had to tell the Project Manager the gear was not up to code and we could either buy new or surplus code compliant but could not use the scrap gear. If it was in place it could be grandfathered, but not to relocate to reuse for new construction. Plant was 75 years old 25 years ago and still some of it in operation today.
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
19,006
I have the Groupe Schneider/Square D in PDF if needed, and yes, even they have made the error if showing it on the wrong side still.
I had heard that it was originally did to save a little time and wire on motor P.B. stations.
On most it is easy to correct it.
 

THICKO

Joined Jun 10, 2016
14
If you look at the physical overload it's designed to switch the 0v side as the control wiring is
routed through the attached device directly to the contactor coil in many instances.
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
19,006
But the drawing method is still generally applied to All types of O/L's in many example prints, and it is not safe, or necessary.
The old style that originated this method are rare now and can easily be modified, anyway.
I have yet to come across a modern one where the now, electronic type of O/L is prevalent, that cannot be wired by the current recommended method.
Max.
 

strantor

Joined Oct 3, 2010
5,025
You can still find control examples posted regarding the use of contactor control wiring implementing the O/L in the wrong part of the circuit.
For many decades the O/L in ladder circuitry has been inserted on the common or Neutral side of the coil.
This has been a no-no for some time now, but the practice still seems to exist.
It is considered a dangerous practice, especially where the common side is a ground-referenced conductor.
The diagrams shown, the O/L should be on the Left of the coil.
Max.
What regulatory guidance are you citing? I believe you're correct per IEC but here in the wild west I'm not aware of anything expressly prohibiting it. I received UL panels just last year with OLs on the right side of the coil. Also I think calling it dangerous might be a little extreme. The only thing that could happen is a short to ground between the coil and the contact which, upon overload condition, does not allow the overload to do its jobs, and the result is a burnt motor. And the chances of that are (est.) one in [an unfathomably big number].
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
19,006
I read a paper on it a few years back, unfortunately I did not keep a copy.
I believe it was a recommendation by NEC, I see no real reason for doing it now, and it seems to be a left over from an old practice just to save on wiring.
One concern was that if any part of a controlled device had a circuit on the neutral side, it was open to fault by way of a possible short to ground and in the process, bypassing the O/L.
Now for the typical DIN style contactors with electronic O/L's there does not seem to be a point as it is just as easy to place the O/L on the coil supply side, but wiring diagrams still insist on showing it this way.
Oddly this is the only coil control device that still tends to be shown wired on the Neutral side.
I would be interested to hear of any other reason why this old method should still be insisted on?
Max.
 

strantor

Joined Oct 3, 2010
5,025
I read a paper on it a few years back, unfortunately I did not keep a copy.
I believe it was a recommendation by NEC, I see no real reason for doing it now, and it seems to be a left over from an old practice just to save on wiring.
One concern was that if any part of a controlled device had a circuit on the neutral side, it was open to fault by way of a possible short to ground and in the process, bypassing the O/L.
Now for the typical DIN style contactors with electronic O/L's there does not seem to be a point as it is just as easy to place the O/L on the coil supply side, but wiring diagrams still insist on showing it this way.
Oddly this is the only coil control device that still tends to be shown wired on the Neutral side.
I would be interested to hear of any other reason why this old method should still be insisted on?
Max.
I'm not advocating for putting the OL on the neutral side. I think best practice is to put it on the live side, as you suggest.
I don't think there's any reason other than "but this is how we've always done it," which isn't a good reason.
My only point is that, while not best practice, I do not believe it is a no-no, or dangerous.
 
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Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
19,006
Well there is a caution and a rule that there should be no disconnection of any grounded conductor.
NFPA79 I am pleased to see, show schematic examples of all disconnect means O/L's etc, in the 'live' conductor side.

"Such overcurrent protection (fuse or overcurrent trip device) shall be placed in an ungrounded conductor"
Max.
 

strantor

Joined Oct 3, 2010
5,025
Well there is a caution and a rule that there should be no disconnection of any grounded conductor.
NFPA79 I am pleased to see, show schematic examples of all disconnect means O/L's etc, in the 'live' conductor side.

"Such overcurrent protection (fuse or overcurrent trip device) shall be placed in an ungrounded conductor"
Max.
Sorry I don't have NFPA79 in front of me. Is that quote referring to the overcurrent device (starter) of the actual equipment (motor) or the overcurrent device (fuse) of the low voltage control circuit switching the equipment? Because overcurrent typically speaks to wire ampacity, which in either case seems the requirement is satisfied with an OL "downstream" of the starter coil. The starter contacts are "upstream" of the motor and the fuse is "upstream" of the starter coil (and the O/L is not even an overcurrent device for the control circuit).

For example, if a starter were used to control a resistive heater instead of a motor, it should be Line>starter>heater>ground, not Line>heater>starter>ground. The case of the latter would be a violation of what you quoted. I'm not sure a downtream OL contact is though.
 

strantor

Joined Oct 3, 2010
5,025
This comes from the 2007 edition. Maybe things have changed:
8.3 Control Circuits. Control circuits shall be permitted to be grounded or ungrounded. Where grounding is provided, that side of the circuit common to the coils shall be grounded at the secondary winding of the control transformer if alternating current or at the power supply terminal if direct current. Exception No. 1: Exposed control circuits as permitted by Section 6.4 shall be grounded. Exception No. 2: Overload relay contacts shall be permitted to be connected between the coil and the grounded conductor where the conductors between such contacts and coils of magnetic devices do not extend beyond the control enclosure.
And I found someone with a pretty good reason to have the contact downstream:

The core issue is consistency. If you have a standard FVNR starter, it really doesn't matter which side of the coil you put the OL relay aux contact on, it works either way. But what if you have a FVR (Reversing) starter, where you have two coils, but only one OL relay, and that OL relay has only one set of contacts? If your standard was to have the OL aux contact on the "hot" side of the coil, you would have to have it VERY far ahead of all of the reversing starter control circuits where it is still common with everything. In the case of a stand-alone enclosed starter with a remote push button station, that means you must run your circuit from the control power source to the OL aux, out to the control station, feed the pilot devices, then back to the starter for the Seal-In, then back out to the control station, then back to the starter for the coils. LOTs of places for an error to happen or a wire to rub up against something and short to ground. If you just put the OL aux contact on the common side of both coils, it stays INSIDE of the control enclosure with very low risk of shorting to ground, fewer wires in the field, fewer errors, fewer problems later. So for an FVR starter, and a Wye-Delta starter and an RVAT starter etc., where there are multiple coils used in the same unit, it makes sense for the OL aux contact to be on a common connection side of all of the coils. Then for consistency, do it that way on the FVNR starter as well, so no matter where you look, it's always in the same place. Hence, it became the standard for industry.
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
19,006
The way I read it, and have always understood, even from my electrical training in the UK, that you never interrupt grounded nuetral.
In this case, the the O/L opens the control circuit for the contactor so I don't see how it is not an over current device?
Like I said, NFPA79 specifically show the O/L's on the live supply side of the coil.
From my perspective, I will always carry on wiring it the same way.
Max.
 
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THICKO

Joined Jun 10, 2016
14
Well anyone who builds control panels without isolating transformers or low voltage isolated supplies
is contravening regs anyway. So in that case placing the OL contact in the 0v side is not a huge misdemeanor.
Going back to the days of Earthed centre taps, then yes, fault finding becomes a pain but under normal
circumstances the OL contact is ok in the 0v side. I draw it in the 'live' side but if using a conventional
device the wiring shop would often 'Flag' it and it would be changed.
 

strantor

Joined Oct 3, 2010
5,025
But the drawing method is still generally applied to All types of O/L's in many example prints
but wiring diagrams still insist on showing it this way.
I draw it in the 'live' side
Just to clarify, we are talking about the actual wiring, correct? The quotes above leave room for a theme of drawing things one way and physically wiring them another way. If that's the actual beef here, then I totally agree. Panels and circuits should always be drawn equivalent to how they are wired. But if a circuit shows the OL on the neutral side and it's physically wired that way, then per the NEC*, that's OK.

*that is, until someone finds something more recent than 2007, contradicting section 8.3 as quoted in post #11.
 

Thread Starter

MaxHeadRoom

Joined Jul 18, 2013
19,006
But if a circuit shows the OL on the neutral side and it's physically wired that way, then per the NEC*, that's OK.
Whether it is legal or not, my main beef is why anyone still insists on wiring it the 'old' way, especially when using modern DIN style contactors with electronic O/L's, instead of wiring it the now logical way as outlined in the examples in NFPA79.
Is this another case of 'Well we have always done it that way'? !:( ;)
Max.
 

strantor

Joined Oct 3, 2010
5,025
Whether it is legal or not, my main beef is why anyone still insists on wiring it the 'old' way, especially when using modern DIN style contactors with electronic O/L's, instead of wiring it the now logical way as outlined in the examples in NFPA79.
Is this another case of 'Well we have always done it that way'? !:( ;)
Max.
At first I didn't know of a reason other than "Well we have always done it that way," which as it turns out was only half the story.
My 2nd quote in post #11 is the origin story, the reason behind it, which is the other half of the story.
The reason in that quote is (or was) a pretty good reason. It could be just as good a reason today as it was "in the beginning," especially for simpler systems.
If we start with that reason and then mix in equal parts [common sense standardization] and ["because we've always done it that way"] then it's not surprising to me that we are still seeing this today even with better methods available.
 
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