# Industrial Control Cabinet Motor Protection



## GatorIE (Mar 22, 2020)

Just figured out the overload/circuit breaker units are the AB 140-MN series, but not the newer white version with the red and green start/stop buttons. They are (what I believe to be) one series older.


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## Wirenuting (Sep 12, 2010)

Like this? 
If so its fine because it's just a manual starter.


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## GatorIE (Mar 22, 2020)

Wirenuting said:


> Like this?
> If so its fine because it's just a manual starter.


Yep, that's pretty much the layout with the exception that the connection between the OL and starter is made with a set of 14AWG jumpers. I'm assuming that the 14AWG wiring to the PDB does not require OCP as long as long as the length complies with the tap rules?


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## Wirenuting (Sep 12, 2010)

GatorIE said:


> Yep, that's pretty much the layout with the exception that the connection between the OL and starter is made with a set of 14AWG jumpers. I'm assuming that the 14AWG wiring to the PDB does not require OCP as long as long as the length complies with the tap rules?


If it’s a factory design an engineer can spec just about anything they want. 
They could spec zip cord and it would pass as far as the NEC is concerned. 

Your installing or repairing a listed device.


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## JRaef (Mar 23, 2009)

So that device is referred to as a Motor Protection Circuit Breaker (MPCB) and performs the Short Circuit plus the OL protection of the motor, plus it provides a meas of disconnecting it separate from the Main. Totally legit and legal so long as the "conditions of use" provided by the mfr are adhered to. Generally, that usually means there is a maximum limit to the Main device used upstream of it. But in many cases, that might be as much as 1200A, so it rarely gets in the way, it just means you MUST have that Main breaker (or Fused Disconnect), you often cannot use those MPCBs stand alone (although there are some brands / models where you can).


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## John Valdes (May 17, 2007)

Telemecanique made a plate that went over the IEC overload relay so it could be mounted anywhere you wanted.
It covered the pins sticking up ( pins that went in the bottom of the starter) and left you with three screw terminals that tightened the pins and the wire.
I installed many many in drawing machines at Michelin 25-30 years ago. Same place they used ferrels that needed no tool. The pressure plate was all that was needed.


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## GatorIE (Mar 22, 2020)

Wirenuting said:


> If it’s a factory design an engineer can spec just about anything they want.
> They could spec zip cord and it would pass as far as the NEC is concerned.
> 
> Your installing or repairing a listed device.





JRaef said:


> So that device is referred to as a Motor Protection Circuit Breaker (MPCB) and performs the Short Circuit plus the OL protection of the motor, plus it provides a meas of disconnecting it separate from the Main. Totally legit and legal so long as the "conditions of use" provided by the mfr are adhered to. Generally, that usually means there is a maximum limit to the Main device used upstream of it. But in many cases, that might be as much as 1200A, so it rarely gets in the way, it just means you MUST have that Main breaker (or Fused Disconnect), you often cannot use those MPCBs stand alone (although there are some brands / models where you can).


Got it, thanks guys! I'll leave everything as-is, just wanted to make sure that there was no issue here as the situation seemed odd to me. 



John Valdes said:


> Telemecanique made a plate that went over the IEC overload relay so it could be mounted anywhere you wanted.
> It covered the pins sticking up ( pins that went in the bottom of the starter) and left you with three screw terminals that tightened the pins and the wire.
> I installed many many in drawing machines at Michelin 25-30 years ago. Same place they used ferrels that needed no tool. The pressure plate was all that was needed.


Interesting device, I've never had to use one (or ever installed anything from Telemecanique IIRC), but I'm sure they'd be useful in a lot of situations. Just don't ever find myself installing an overload in that manner.


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## TechyWalla (Apr 6, 2020)

On the question of contactor O/L, I still see the O/L contact placed on the RH side of the coil in a ladder diag. 
AFAIK it is now a no-no, evidently it is a left over from contactor stations where it made for ease/saving of wiring, I believe it is also not allowed in IEC 
If the control circuit is from 2 phases then technically it does not matter, but I see it where the RH rail is the N.
Personally I don't really see any reason for this prolonged tendency to use it the old way.

See the IEC version for being correct.
I could not add a link due to insufficient posts so add Https 
//studylib.net/doc/18040687/nema-and-iec-terminal-markings


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## BillyMac59 (Sep 12, 2019)

Your question appears to be: does the overload contact come before or after the coil?
The "old" stuff you mention is what I cut my teeth on. Some people wired starters as they are shown in the schematics....the OLs before the coil. Electrically, they both work: the tripped OL drops out the coil thereby opening the motor power circuit. I don't know if a code rule applies....


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## JRaef (Mar 23, 2009)

There is no rule in North America dictating where the OL relay contact should be placed in the circuit, either location is fine. The IEC convention (maybe a regulation, not sure) of it being on the left side of the coil has been accepted here. It was begrudgingly at first when I worked for an IEC company in the late 1970s, but eventually the NEMA people came to accept that it doesn't matter.


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## TechyWalla (Apr 6, 2020)

ValeoBill said:


> Your question appears to be: does the overload contact come before or after the coil?
> The "old" stuff you mention is what I cut my teeth on. Some people wired starters as they are shown in the schematics....the OLs before the coil. Electrically, they both work: the tripped OL drops out the coil thereby opening the motor power circuit. I don't know if a code rule applies....


The way that I heard it was when wiring the self contained motor starter P.B. stations, it saved one extra wire etc in the hookup, but I saw a (NEMA?) paper that mentioned a concern that when the O/L was between the coil and the N, any ground on the coil to O/L side, would by pass the O/L.
In any case, I don not see any purpose any longer to do it that way, and also the EU reg's do not allow it also.
You would never configure a PLC rung like that.
But it is shown repeatedly in modern prints for some reason?
T.W.


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## paulengr (Oct 8, 2017)

TechyWalla said:


> The way that I heard it was when wiring the self contained motor starter P.B. stations, it saved one extra wire etc in the hookup, but I saw a (NEMA?) paper that mentioned a concern that when the O/L was between the coil and the N, any ground on the coil to O/L side, would by pass the O/L.
> In any case, I don not see any purpose any longer to do it that way, and also the EU reg's do not allow it also.
> You would never configure a PLC rung like that.
> But it is shown repeatedly in modern prints for some reason?
> T.W.



It is safer to have the O/L after the coil in 480 V control circuits that don’t have a control power transformer.


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## TechyWalla (Apr 6, 2020)

paulengr said:


> It is safer to have the O/L after the coil in 480 V control circuits that don’t have a control power transformer.


Explain?
I assume you mean 480v derived from two phases? If so how is it safer?
I can't remember ever coming across any 480v control circuits, if there are, they must be pretty rare.
All the examples I see out there on web based tutorials or Youtube etc, seem to include it because of the 'Tradition', not for any logical reason.
T.W.


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## JRaef (Mar 23, 2009)

The reason it was on the right side was basically just because of how early motor OL relay were built. Originally each pole had its own OL relay with it's own separate OL contact. So to make them function to drop out the coil if any one OL tripped, the contacts had to be wired in series. That's a PITA to do in the field, so starter mfrs did it for you at the factory as they assembled the starter, connecting from the coil, then weaving the little red wired into the tight spaces between the OL relays, ending with only one connection to make in the field. In the assembly process, because people read from left to right, the final connection ended up on the far right, so that's how it was depicted in the drawings. 










By the 80s, most mfrs had switched to having all 3 OL relays operate the same single OL trip contact, so it became irrelevant, but the practice persisted because that's how it was taught.


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## gpop (May 14, 2018)

TechyWalla said:


> The way that I heard it was when wiring the self contained motor starter P.B. stations, it saved one extra wire etc in the hookup, but I saw a (NEMA?) paper that mentioned a concern that when the O/L was between the coil and the N, any ground on the coil to O/L side, would by pass the O/L.
> In any case, I don not see any purpose any longer to do it that way, and also the EU reg's do not allow it also.
> You would never configure a PLC rung like that.
> But it is shown repeatedly in modern prints for some reason?
> T.W.


years ago it wasn't that un-common to have the load on the left and all the relay logic on the right (switching neutrals). I always thought this was a dumb idea as it made troubleshooting harder then i came across a lot of american 208v/480v controls where there really was no left or right.


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