Control Wiring
- Thread starter rcaldwell
- Start date
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- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Control Wiring
The reference might be to 430.73, which concerns grounded conductors and unintentional starting (not stopping).
I know of no section of the NEC that is applicable to a factory assembled motor starter that would govern the placement of the overload relay contact. Motor control circuits, internal to enclosures, are not always governed by the same rules as general branch circuits.
NFPA79 (standard for industrial machinery) has 6 exceptions to 9.1.4.1, the rule prohibiting control circuit contacts between the coil and the "grounded conductor". Exception #1 specifically allows overload contacts where the wiring does not extend beyond the control enclosure.
The reference might be to 430.73, which concerns grounded conductors and unintentional starting (not stopping).
I know of no section of the NEC that is applicable to a factory assembled motor starter that would govern the placement of the overload relay contact. Motor control circuits, internal to enclosures, are not always governed by the same rules as general branch circuits.
NFPA79 (standard for industrial machinery) has 6 exceptions to 9.1.4.1, the rule prohibiting control circuit contacts between the coil and the "grounded conductor". Exception #1 specifically allows overload contacts where the wiring does not extend beyond the control enclosure.
Re: Control Wiring
rcaldwell,
I'm a may have missed something but, knowing control wiring as I do, I fail to see where an OLR contact would ever break a neutral. Where would there be a neutral in a control wiring scheme? If you a refering to the N/C OLR contact it is placed in series with the coil between the coil and the supply. The opposite side of the coin would be the pushbuttons.
Also, control voltage may be taken from the line side of the contector L-L through (2) fuses, from and external source, or from the L-L on the line side of the contactor through (2) fused feeding a CPT the secondary feeds the control of which one conductor is fused the other is grounded.
Dave
rcaldwell,
I'm a may have missed something but, knowing control wiring as I do, I fail to see where an OLR contact would ever break a neutral. Where would there be a neutral in a control wiring scheme? If you a refering to the N/C OLR contact it is placed in series with the coil between the coil and the supply. The opposite side of the coin would be the pushbuttons.
Also, control voltage may be taken from the line side of the contector L-L through (2) fuses, from and external source, or from the L-L on the line side of the contactor through (2) fused feeding a CPT the secondary feeds the control of which one conductor is fused the other is grounded.
Dave
bdarnell
Senior Member
- Location
- Indianapolis, IN
- Occupation
- Retired Engineer
Re: Control Wiring
The only instance where a control circuit breaks a neutral would be in the overload contacts on a motor starter that uses a 120 volt coil.
As Jim and Dave pointed out, this is permitted as long as the circuit does not extend beyond the enclosure of the starter.
The only instance where a control circuit breaks a neutral would be in the overload contacts on a motor starter that uses a 120 volt coil.
As Jim and Dave pointed out, this is permitted as long as the circuit does not extend beyond the enclosure of the starter.
B
bthielen
Guest
Re: Control Wiring
My understanding is that he was talking about circuits similar to motor starter circuits where the coil is supplied by the control circuit and by nature of the component assembly, the overload contact(s) are wired in series between the coil and the neutral or grounded conductor. In a motor starter thermal overload condition, the neutral side of the coil is opened, not the supply side.
Bob
My understanding is that he was talking about circuits similar to motor starter circuits where the coil is supplied by the control circuit and by nature of the component assembly, the overload contact(s) are wired in series between the coil and the neutral or grounded conductor. In a motor starter thermal overload condition, the neutral side of the coil is opened, not the supply side.
Bob
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