Start/Stop Circuit - Overloads wiring position

[leverboi]

Hi Mike,
I ran into a situation where I found a simple start/stop circuit had been wired with the overload not in series with the coil and not on the neutral side of the circuit. The designer claims that the overloads can be wired anywhere in the circuit as long as in stops the motor on overload. Until this situation I have never seen the overloads wired in a different place. Is there a standard, code or regulation that I can reference that can tell me whether or not the designers way of wiring is acceptable or not.
Thank you Mike and all the best, David

 

[kwired]

Hi Mike,
I ran into a situation where I found a simple start/stop circuit had been wired with the overload not in series with the coil and not on the neutral side of the circuit. The designer claims that the overloads can be wired anywhere in the circuit as long as in stops the motor on overload. Until this situation I have never seen the overloads wired in a different place. Is there a standard, code or regulation that I can reference that can tell me whether or not the designers way of wiring is acceptable or not.
Thank you Mike and all the best, David

If the opening of the overload contact opens the circuit to the coil being controlled how is it not in series with the coil? I also believe it can be anywhere in the circuit as long as it's operation interrupts power to the coil. Having another contact in parallel in a particular segment of the circuit could be a problem - but really need to know the intent of the other contact as there could be some cases where that may still be acceptable. Manual vs automatic reset is also another issue sometimes, but in general all that is needed is for the overload condition to remove power to the coil of the contactor so that the overloaded motor will stop. Nothing wrong with it stopping other associated equipment as well, though that is typically done with interlocking contacts on the contactor.

 

[don_resqcapt19]

There are a number of designers that specify that the overload contact be on the left side of the first rung of the ladder diagram. I think I read somewhere that GM requires that for all of the motor starters in their factories. I have worked on a few jobs where the electrical engineer has required that design.

 

[texie]

Hi Mike,
I ran into a situation where I found a simple start/stop circuit had been wired with the overload not in series with the coil and not on the neutral side of the circuit. The designer claims that the overloads can be wired anywhere in the circuit as long as in stops the motor on overload. Until this situation I have never seen the overloads wired in a different place. Is there a standard, code or regulation that I can reference that can tell me whether or not the designers way of wiring is acceptable or not.
Thank you Mike and all the best, David

As mentioned the coil is still in series. This is fine from what you describe and very common. You maybe thinking of 430.74 which does have requirements when the control circuit has a grounded conductor. But from your description I don't think this applies to you.

 

[don_resqcapt19]

430.74 really has to do with an installation where the overload is in the grounded conductor side of the circuit and where you bring the wire that is connected between the overload contact and the coil out of the starter enclosure. In that case a ground fault on the conductor that you have extended outside of the starter enclosure would prevent the overload relay from opening the circuit to the contactor coil.

Sometimes this rule is the very reason that you put the overload contact on the hot side of the circuit, but there are potential issues there too as a short circuit on the control circuit could weld the OL relay contacts closed preventing them from shutting down the motor if it would become overloaded.

 

[ptonsparky]

430.74 really has to do with an installation where the overload is in the grounded conductor side of the circuit and where you bring the wire that is connected between the overload contact and the coil out of the starter enclosure. In that case a ground fault on the conductor that you have extended outside of the starter enclosure would prevent the overload relay from opening the circuit to the contactor coil.

Sometimes this rule is the very reason that you put the overload contact on the hot side of the circuit, but there are potential issues there too as a short circuit on the control circuit could weld the OL relay contacts closed preventing them from shutting down the motor if it would become overloaded.

How the heck are we going to stop that from happening?:roll:

 

[texie]

430.74 really has to do with an installation where the overload is in the grounded conductor side of the circuit and where you bring the wire that is connected between the overload contact and the coil out of the starter enclosure. In that case a ground fault on the conductor that you have extended outside of the starter enclosure would prevent the overload relay from opening the circuit to the contactor coil.

Sometimes this rule is the very reason that you put the overload contact on the hot side of the circuit, but there are potential issues there too as a short circuit on the control circuit could weld the OL relay contacts closed preventing them from shutting down the motor if it would become overloaded.

I mentioned 430.74 just to clarify that the grounded conductor is fine to use to open the coil circuit as long as it does not leave the enclosure. You could still have the overload in series on the grounded conductor and have a remote start/stop or other contacts in the ungrounded conductor.

 

[don_resqcapt19]

How the heck are we going to stop that from happening?:roll:

By keeping the overload contact in the traditional location...on the grounded side of the circuit and the wire between the coil and the OL relay contact not leaving the enclosure.

 

[kwired]

430.74 really has to do with an installation where the overload is in the grounded conductor side of the circuit and where you bring the wire that is connected between the overload contact and the coil out of the starter enclosure. In that case a ground fault on the conductor that you have extended outside of the starter enclosure would prevent the overload relay from opening the circuit to the contactor coil.

Sometimes this rule is the very reason that you put the overload contact on the hot side of the circuit, but there are potential issues there too as a short circuit on the control circuit could weld the OL relay contacts closed preventing them from shutting down the motor if it would become overloaded.

How the heck are we going to stop that from happening?:roll:

What if both sides of the control circuit are ungrounded?hmy:

better put in a back up contact in case the first one fails, and a back up for the back up and so forth

 

[Jraef]

By keeping the overload contact in the traditional location...on the grounded side of the circuit and the wire between the coil and the OL relay contact not leaving the enclosure.

Years ago I went to work for a German company, and learned that there is an IEC standard that REQUIRES the OL contact to be on the left side of a ladder rung. I got into several arguments about this issue because I had learned here in the US, under the original JIC standards from which we get most of the conventions still in use, to put it on the Right side of the coil for the exact reason Don mentions. It has little to do with whether the coil circuit is grounded or not, in fact "full voltage" (meaning line voltage) coil circuits used to be very common in industrial systems 25 years ago. The reasoning was that of NOT having that side of the circuit EVER leave the starter enclosure, thus reducing the risk to practically nil of a short circuit that might weld the OL contacts closed. In fact, it was ALSO considered a bad practice to run any OTHER circuit elements out on that side of the circuit for the same reasons.

 

[don_resqcapt19]

What seems weird to me is the way an Eaton MCC, that I installed about 2 years ago was wired. The control power was 120v from a CPT in the bucket and the overload contact was on the grounded side, but they brought the wire between the OL contact and the coil out to the field terminal block. I have never seen that on any other starter and have no idea why they would do that because connecting a field wire to that terminal would result in a code violation.

 

[kwired]

What seems weird to me is the way an Eaton MCC, that I installed about 2 years ago was wired. The control power was 120v from a CPT in the bucket and the overload contact was on the grounded side, but they brought the wire between the OL contact and the coil out to the field terminal block. I have never seen that on any other starter and have no idea why they would do that because connecting a field wire to that terminal would result in a code violation.

IAEI paid them to do it so they could have their inspector members write up anyone that did connect anything to that terminal:happyyes:

 

[Jraef]

What seems weird to me is the way an Eaton MCC, that I installed about 2 years ago was wired. The control power was 120v from a CPT in the bucket and the overload contact was on the grounded side, but they brought the wire between the OL contact and the coil out to the field terminal block. I have never seen that on any other starter and have no idea why they would do that because connecting a field wire to that terminal would result in a code violation.

I doubt that is their standard, but I have seen specifications from CEs that say something to the effect of "All control circuits shall terminate on a terminal block..." and someone at the Eaton plant may have taken that a bit too far. Or maybe a CE reviewed the submittals and REQUIRED them to add it. I always review specs for crap like that and tell the factory what to ignore, then if the CE bounces it back as "not compliant to the specification", I'll take them to task on it (unless it's just superfluous BS like nameplate material). I get them asking for things that would violate UL 845 rules ALL the time, they don't know and often don't care. A common one is someone insisting on putting MCP (Mag-only) breakers in buckets by themselves as feeders.

On several occasions I have asked them to sign a letter stating that they understand that the inclusion of their insisted-upon design will result in the MCC UL labels being removed and that they accept responsibility for the consequences, which usually shuts them up.

 

[don_resqcapt19]

There were only two of us involved in writing the order, myself and the electrical engineer for the plant, and there was nothing non-standard in our specs. The drawing showing the wiring that way was a standard drawing with no revisions or custom changes.

 

[ptonsparky]

By keeping the overload contact in the traditional location...on the grounded side of the circuit and the wire between the coil and the OL relay contact not leaving the enclosure.

Maybe a fuse or two?

 

[don_resqcapt19]

Maybe a fuse or two?

You might be able to protect the contacts that way, but I am not sure.

 

[ritelec]

better put in a back up contact in case the first one fails, and a back up for the back up and so forth

and so on and so on and so on ......

 

[kwired]

and so on and so on and so on ......

Cloning yourself some girlfriends??

 

[Jraef]

There were only two of us involved in writing the order, myself and the electrical engineer for the plant, and there was nothing non-standard in our specs. The drawing showing the wiring that way was a standard drawing with no revisions or custom changes.

Wow, that is odd then. I've never notice that before, but then again I've never looked. I have a friend over at Eaton, I'll see if he has anything showing that or knows why they do it.