I am looking for proper location of overload contacts in the control circuit. The NEC book shows then on the neutral side of the coil. However I have all ways practiced not breaking the neutral and placed the overload contacts on the line side of the control circuit. The control voltage is 120vac or less.
Motor overload control contact
- Thread starter hughb3
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Ed MacLaren
Senior Member
Re: Motor overload control contact
The grounded conductor of the two-wire supply for the control circuit isn't a neutral by definition.
The overload relay contact can be connected in either location indicated in the sketch below. I have seen manufacturer's circuit diagrams showing both locations.
Ed
[ December 12, 2003, 06:00 PM: Message edited by: Ed MacLaren ]
The grounded conductor of the two-wire supply for the control circuit isn't a neutral by definition.
The overload relay contact can be connected in either location indicated in the sketch below. I have seen manufacturer's circuit diagrams showing both locations.
Ed
[ December 12, 2003, 06:00 PM: Message edited by: Ed MacLaren ]
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: Motor overload control contact
To: hughb3, and Ed MacLaren, If you look in a Square D, or an Allen-Bradley motor wiring diagrams you will see that they always have the three motor overloads on the grounded side of the Maintaining coil(potential coil).
I feel very strongly that you should do the same for consistency in all of your wiring diagrams.
For an added thought, we would always put any interlocking contacts in the motor control circuit before the stop button.
Again, we at Dupont did this world wide.
To: hughb3, and Ed MacLaren, If you look in a Square D, or an Allen-Bradley motor wiring diagrams you will see that they always have the three motor overloads on the grounded side of the Maintaining coil(potential coil).
I feel very strongly that you should do the same for consistency in all of your wiring diagrams.
For an added thought, we would always put any interlocking contacts in the motor control circuit before the stop button.
Again, we at Dupont did this world wide.
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: Motor overload control contact
To: hughb3 and Ed MacLaren, I forgot to add on my last post, that the control circuit that you show is not a two-wire control, it is a three-wire control circuit.
To: hughb3 and Ed MacLaren, I forgot to add on my last post, that the control circuit that you show is not a two-wire control, it is a three-wire control circuit.
Ed MacLaren
Senior Member
Re: Motor overload control contact
Sorry, I wasn't specific enough. I was referring to the supply as being two wire, in other words, the control transformer is not center-tapped, so the grounded conductor is not "technically" a neutral. I've edited the original statement.
Ed
[ December 12, 2003, 06:01 PM: Message edited by: Ed MacLaren ]
Sure is.
Sorry, I wasn't specific enough. I was referring to the supply as being two wire, in other words, the control transformer is not center-tapped, so the grounded conductor is not "technically" a neutral. I've edited the original statement.
Ed
[ December 12, 2003, 06:01 PM: Message edited by: Ed MacLaren ]
Re: Motor overload control contact
Just for the sake of discussion,
hughb3, I too wire the overloads on the hot side of the coil on 120 & 24vac controls just for the reason if an accidental ground develops between the coil & OL (if common is wired thru OL)then the OL would be bypassed, this is HIGHLY unlikely but the potential does exist.
Just for the sake of discussion,
hughb3, I too wire the overloads on the hot side of the coil on 120 & 24vac controls just for the reason if an accidental ground develops between the coil & OL (if common is wired thru OL)then the OL would be bypassed, this is HIGHLY unlikely but the potential does exist.
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: Motor overload control contact
To: harryg, and hughb3, I hear what you are saying about where you wire your overload contacts, and why, but my question to you is: Do you rewire the control circuit in the starters that you receive from a vendor? Because all combination starters, and starters in Motor Control Centers are wired with the overload contacts on the grounding side of the potential coil.
To: harryg, and hughb3, I hear what you are saying about where you wire your overload contacts, and why, but my question to you is: Do you rewire the control circuit in the starters that you receive from a vendor? Because all combination starters, and starters in Motor Control Centers are wired with the overload contacts on the grounding side of the potential coil.
Ed MacLaren
Senior Member
Re: Motor overload control contact
Ed
I'm wondering what that has to do with the question under posted by hughb3?
Ed
- Location
- Massachusetts
Re: Motor overload control contact
Does anyone know why all NEMA contactors come with the grounded conductor broken by the overloads?
I have always wondered about this but would never change it as the diagrams that come with the contactor show it that way.
I assume
NEMA has a reason for this method and knows why this is the best way to go.
I poked around the NEMA website but I could not find an answer.
Does anyone know why all NEMA contactors come with the grounded conductor broken by the overloads?
I have always wondered about this but would never change it as the diagrams that come with the contactor show it that way.
I assume
NEMA has a reason for this method and knows why this is the best way to go.I poked around the NEMA website but I could not find an answer.
- Location
- Illinois
- Occupation
- retired electrician
Re: Motor overload control contact
Don
While the standard wiring is with the overload relay on the grounded control circuit conductor, all of the stater manufacturers will supply the overload contact in the ungrounded conductor on request. I have done a few jobs where the engineers specs required the overload contact to be in the ungrounded conductor. We ordered the starters that way at not increase in cost, but a 3 to 4 week longer lead time.
Don
Ed MacLaren
Senior Member
Re: Motor overload control contact
With regard to my own code (CEC), all separately derived AC systems are required to be grounded, if the voltage to ground will not exceed 150. That would include most control transformers.
Also, if the transformer VA is 1000 or less, the secondary can be grounded to the enclosure EGC, instead of to an acceptable grounding electrode.
Are the NEC requirements similar?
You asked why. How about - to clear a winding-to-winding fault in the control transformer?
Ed
With regard to my own code (CEC), all separately derived AC systems are required to be grounded, if the voltage to ground will not exceed 150. That would include most control transformers.
Also, if the transformer VA is 1000 or less, the secondary can be grounded to the enclosure EGC, instead of to an acceptable grounding electrode.
Are the NEC requirements similar?
You asked why. How about - to clear a winding-to-winding fault in the control transformer?
Ed
Re: Motor overload control contact
I thought that the OL in the grounded conductor side ( coil - OL - ground ) was only to be permitted when the control circuit did not leave the motor controller enclosure.
When the Control Circuit left the motor controller enclosure for remote control(s), the chance of an un-intentional ground in the control circuit increases and the OL may not do it's intended duty to open the cicuit when under an OL condition.
An un-intentional ground between the coil "M" and the OL in Ed's diagram, the OL would not do it's duty.
gwz@
I thought that the OL in the grounded conductor side ( coil - OL - ground ) was only to be permitted when the control circuit did not leave the motor controller enclosure.
When the Control Circuit left the motor controller enclosure for remote control(s), the chance of an un-intentional ground in the control circuit increases and the OL may not do it's intended duty to open the cicuit when under an OL condition.
An un-intentional ground between the coil "M" and the OL in Ed's diagram, the OL would not do it's duty.
gwz@
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: Motor overload control contact
Glen. This is what I was taught too.
I have seen where a indicator light was placed across the Ol's to allow for faster trouble shooting the lights were installed in the main control console remote to the starter which was in the controller cabinet. We switch the wiring on the starter to put the OL's in series with the L1 side of the coil, the L2 side of the coil then just connect to L2 (common). switching of the wires easy to do as all the wires are terminated on clamp down screws.
Also on a few jobs we chose not to ground the control transformer because it would cause more danger to operators if the whole line went down. but we would always install two red monitor lights to show if a control circuit went to ground. This allowed for a repair on the next shut-down, with out causing the whole line to go down.
[ December 14, 2003, 08:44 PM: Message edited by: hurk27 ]
Glen. This is what I was taught too.
I have seen where a indicator light was placed across the Ol's to allow for faster trouble shooting the lights were installed in the main control console remote to the starter which was in the controller cabinet. We switch the wiring on the starter to put the OL's in series with the L1 side of the coil, the L2 side of the coil then just connect to L2 (common). switching of the wires easy to do as all the wires are terminated on clamp down screws.
Also on a few jobs we chose not to ground the control transformer because it would cause more danger to operators if the whole line went down. but we would always install two red monitor lights to show if a control circuit went to ground. This allowed for a repair on the next shut-down, with out causing the whole line to go down.
[ December 14, 2003, 08:44 PM: Message edited by: hurk27 ]
- Location
- Illinois
- Occupation
- retired electrician
Re: Motor overload control contact
Glenn,
I agree that if the grounded conductor between the overload relay contact and the coil were to leave the starter enclosure, there would be the potential for a ground fault to prevent the overload relay from dropping the coil out. In my opinion, this wire from the OL contact to the coil is rarely run external to the enclosure and an internal ground fault is not very likely.
Don
Glenn,
I agree that if the grounded conductor between the overload relay contact and the coil were to leave the starter enclosure, there would be the potential for a ground fault to prevent the overload relay from dropping the coil out. In my opinion, this wire from the OL contact to the coil is rarely run external to the enclosure and an internal ground fault is not very likely.
Don
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Motor overload control contact
NEMA publication ICS 2-2000 Part 2 section 7.3 specifies the location of the overload relay in a starter control circuit. The primary rational for the location on the "right" side of the coil is to minimize the possibilty of damage to the OLR contacts caused by a short circuit in the control circuit.
NEMA publication ICS 2-2000 Part 2 section 7.3 specifies the location of the overload relay in a starter control circuit. The primary rational for the location on the "right" side of the coil is to minimize the possibilty of damage to the OLR contacts caused by a short circuit in the control circuit.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Motor overload control contact
Hugh, I don't know how you are reading ICS2-2000 different than I am.
I went to this website: http://mywebpages.comcast.net/rsdoran/ICS2.pdf
and looked at page 30 of the PDF (page 2-10 of the standard). The title for section 7.3 is "Location of Overload Relay Contacts in Circuit".
I would never rewire a NEMA starter to relocate the OLR contacts. My feeling is the OLR should control the coil directly, for PLC annunciation a second contact should be used.
When I wire seperately purchased contactors and overload relays that are direct connected I wire them the same as a NEMA starter.
However, when I wire control panels using seperate contactors and overload blocks (i.e. an IEC style panel), I place the OLR contact on the L1 side of the coil after all other control contacts.
Hugh, I don't know how you are reading ICS2-2000 different than I am.
I went to this website: http://mywebpages.comcast.net/rsdoran/ICS2.pdf
and looked at page 30 of the PDF (page 2-10 of the standard). The title for section 7.3 is "Location of Overload Relay Contacts in Circuit".
I would never rewire a NEMA starter to relocate the OLR contacts. My feeling is the OLR should control the coil directly, for PLC annunciation a second contact should be used.
When I wire seperately purchased contactors and overload relays that are direct connected I wire them the same as a NEMA starter.
However, when I wire control panels using seperate contactors and overload blocks (i.e. an IEC style panel), I place the OLR contact on the L1 side of the coil after all other control contacts.
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