combo disconnect /motor starter
- Thread starter beardley
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Re: combo disconnect /motor starter
There's not a lot of information here. But, no you don't need to fuse the neutral and to be honest you don't need to run the neutral through an overload either. As long as the motor is protected from any overload condition then you are okay.
My only confusion comes from the thought that it sounds like you are wiring a 120 volt motor (of unknown H.P.) Most fractional HP motors have internal overload protection and does not need a "starter". If your looking for "control" capability that a starter provides then a HP rated relay would be cheaper.
There's not a lot of information here. But, no you don't need to fuse the neutral and to be honest you don't need to run the neutral through an overload either. As long as the motor is protected from any overload condition then you are okay.
My only confusion comes from the thought that it sounds like you are wiring a 120 volt motor (of unknown H.P.) Most fractional HP motors have internal overload protection and does not need a "starter". If your looking for "control" capability that a starter provides then a HP rated relay would be cheaper.
Re: combo disconnect /motor starter
On a 120 volt magnetic motor starter the ground/neutral is switched through the overload heater switches.
This is about the only place a neutral is permitted to be switched by itself.
The neutral to the motor is normally not switched, but can be.
On a 120 volt magnetic motor starter the ground/neutral is switched through the overload heater switches.
This is about the only place a neutral is permitted to be switched by itself.
The neutral to the motor is normally not switched, but can be.
Ed MacLaren
Senior Member
Re: combo disconnect /motor starter
I thought a control or protective device can only switch the grounded conductor as long as all ungrounded conductors are opened at the same time.
BTW, in the interests of accuracy, there is no "neutral" in a 120 volt circuit.
Ed
Is there an exception in the NEC for this?
I thought a control or protective device can only switch the grounded conductor as long as all ungrounded conductors are opened at the same time.
BTW, in the interests of accuracy, there is no "neutral" in a 120 volt circuit.
Ed
- Location
- Illinois
- Occupation
- retired electrician
Re: combo disconnect /motor starter
Ed,
It is a common practice that the grounded conductor to the starter coil is switched by the starter overload realy. I know of no exception in the code that permits this, but almost all magnetic starters come factory wired in this manner.
Don
Ed,
It is a common practice that the grounded conductor to the starter coil is switched by the starter overload realy. I know of no exception in the code that permits this, but almost all magnetic starters come factory wired in this manner.
Don
Ed MacLaren
Senior Member
Re: combo disconnect /motor starter
Sorry Bennie, I didn't realize you were referring to the control (coil) circuit.
The original post referred to the load conductors, and I thought you were too.
Ed
Sorry Bennie, I didn't realize you were referring to the control (coil) circuit.
The original post referred to the load conductors, and I thought you were too.
Ed
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: combo disconnect /motor starter
In my opinion:
A listed magnetic motor starter (combination of a contactor and an overload relay) is a factory wired device and not subject to the NEC. The NEC does not cover the integral parts of electrical utilization equipment. The NEC only covers the installation of equipment.
See NEC 2002
90.2(A)
110.3(B)
725.1
Also the overload relay (OLR) contact does not meet the NEC definitions of a switch, particularly in regards to Article 404 and therefore 404.2(B).
This rational/interpretation is only for directly connected contators and relays, seperatly mounted devices would required the OLR contact to be mounted in an ungrounded conductor.
In my opinion:
A listed magnetic motor starter (combination of a contactor and an overload relay) is a factory wired device and not subject to the NEC. The NEC does not cover the integral parts of electrical utilization equipment. The NEC only covers the installation of equipment.
See NEC 2002
90.2(A)
110.3(B)
725.1
Also the overload relay (OLR) contact does not meet the NEC definitions of a switch, particularly in regards to Article 404 and therefore 404.2(B).
This rational/interpretation is only for directly connected contators and relays, seperatly mounted devices would required the OLR contact to be mounted in an ungrounded conductor.
- Location
- Illinois
- Occupation
- retired electrician
Re: combo disconnect /motor starter
Jim,
I don't see how an overload relay is not within the scope of Article 404. It is a "switching device". If you are installing IEC type starter from components is a control panel the overload relay is not "factory wired".
Don
Jim,
I don't see how an overload relay is not within the scope of Article 404. It is a "switching device". If you are installing IEC type starter from components is a control panel the overload relay is not "factory wired".
Don
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: combo disconnect /motor starter
Don,
I think the following parts of NEC Art 404 do not apply to the overload relay contact.
404.1 - none of the Switch, definitions in Art 100 apply
404.3(A) - these are not externally operable in both directions
404.5 - energized parts are not barriered
404.6 - these are not knife style
404.9 - these are not general use snap style
404.15 - these contacts are not marked with ratings
Also these contacts are typically not UL Listed however they are UL Recognized which means they are to be used as a component in a listed assembly which takes us back to 110.3(B).
Don,
I think the following parts of NEC Art 404 do not apply to the overload relay contact.
404.1 - none of the Switch, definitions in Art 100 apply
404.3(A) - these are not externally operable in both directions
404.5 - energized parts are not barriered
404.6 - these are not knife style
404.9 - these are not general use snap style
404.15 - these contacts are not marked with ratings
Also these contacts are typically not UL Listed however they are UL Recognized which means they are to be used as a component in a listed assembly which takes us back to 110.3(B).
- Location
- Illinois
- Occupation
- retired electrician
Re: combo disconnect /motor starter
Jim,
So if I want to wire a circuit with a contactor or relay that switches the grounded conductor, but not the hot, there is no code section that says I can't?
Don
Jim,
So if I want to wire a circuit with a contactor or relay that switches the grounded conductor, but not the hot, there is no code section that says I can't?
Don
Re: combo disconnect /motor starter
I didn't think it was a good idea to switch the neutral especially a motor starter because if you have a fault to ground it will start the motor.That wouldn't be a good thing.I think there is a code that says you can't switch the neutral on a motor starter.
My code books are out dated you know so I want quote from it. :roll:
Don't mean to mislead you. I'm not talking about overload contact switches here they work fine in the neutral or common side as long as your start stop are on the hot side of the coil I was refering to a regular switch with a maintained contact.
[ July 11, 2003, 10:53 PM: Message edited by: ronaldrc ]
I didn't think it was a good idea to switch the neutral especially a motor starter because if you have a fault to ground it will start the motor.That wouldn't be a good thing.I think there is a code that says you can't switch the neutral on a motor starter.
My code books are out dated you know so I want quote from it. :roll:
Don't mean to mislead you. I'm not talking about overload contact switches here they work fine in the neutral or common side as long as your start stop are on the hot side of the coil I was refering to a regular switch with a maintained contact.
[ July 11, 2003, 10:53 PM: Message edited by: ronaldrc ]
Re: combo disconnect /motor starter
The 120 is usually from a small control transformer, in the starter enclosure. One side may be grounded, but can be ungrounded. The grounded conductor is not supplying anything else.
It is not a power wire for premises systems.
A ground on the ground side will not turn on the starter.
The 120 is usually from a small control transformer, in the starter enclosure. One side may be grounded, but can be ungrounded. The grounded conductor is not supplying anything else.
It is not a power wire for premises systems.
A ground on the ground side will not turn on the starter.
Re: combo disconnect /motor starter
Did I miss something here? I don't thing I'm being redundant to what somewhat else has said. When the subject of fusing the neutral was brought up which we understand the reason why you can't. However, you could apply a 2-pole circuit breaker if you selected that type of an OCPD.
Keeping with that train of thought a multipole contactor that controls the grounded neutral conductor simultaneously with the line conductor would be allowed. Since a 2-pole OLR monitors both the grounded neutral and line conductor current an overload current sensed in either conductor by the OLR will cause the OLR N/C contact to open which in turn causes the 2-pole contactor to drop out and open both the grounded neutral and line conductors to the motor.
The OLR really does nothing but control the 2-pole contactor.
Did I miss something here? I don't thing I'm being redundant to what somewhat else has said. When the subject of fusing the neutral was brought up which we understand the reason why you can't. However, you could apply a 2-pole circuit breaker if you selected that type of an OCPD.
Keeping with that train of thought a multipole contactor that controls the grounded neutral conductor simultaneously with the line conductor would be allowed. Since a 2-pole OLR monitors both the grounded neutral and line conductor current an overload current sensed in either conductor by the OLR will cause the OLR N/C contact to open which in turn causes the 2-pole contactor to drop out and open both the grounded neutral and line conductors to the motor.
The OLR really does nothing but control the 2-pole contactor.
Re: combo disconnect /motor starter
Not always the case though is it Bennie?
Some one reading these post could wire a regular 120 volt motor and put the Toggle on the neutral side and have a very dangerous situation.
Just because some here say it doesn't matter.
If you wire a 120/240 volt single phase w/ 120 coil magnetic starter and put the start, stop and the overloads on the neutral side don't you think that wouldn't be a dangerous situation?
If the motor has a fault to ground on the neutral side of the coil the motor will start!
Not always the case though is it Bennie?
Some one reading these post could wire a regular 120 volt motor and put the Toggle on the neutral side and have a very dangerous situation.
Just because some here say it doesn't matter.
If you wire a 120/240 volt single phase w/ 120 coil magnetic starter and put the start, stop and the overloads on the neutral side don't you think that wouldn't be a dangerous situation?
If the motor has a fault to ground on the neutral side of the coil the motor will start!
Re: combo disconnect /motor starter
Side ways and upside down.Didn't mean to change the subject.:-S
I rewired a wood mill machine for a company that rebuilds old ones and resales them.
The electrician that wired the one before me got the company sited for having his start stop push buttons on the common side of the coil. The control transformer was a .5 KVA x1 was 120 hot x2 was the grounded conductor and grounded to the equipment body. Don't know why? But he put the controls on the grounded side this was very dangerous.They give the NEC. article and par. but its been a few years.
Ronald
[ July 12, 2003, 01:06 AM: Message edited by: ronaldrc ]
Side ways and upside down.Didn't mean to change the subject.:-S
I rewired a wood mill machine for a company that rebuilds old ones and resales them.
The electrician that wired the one before me got the company sited for having his start stop push buttons on the common side of the coil. The control transformer was a .5 KVA x1 was 120 hot x2 was the grounded conductor and grounded to the equipment body. Don't know why? But he put the controls on the grounded side this was very dangerous.They give the NEC. article and par. but its been a few years.
Ronald
[ July 12, 2003, 01:06 AM: Message edited by: ronaldrc ]
Re: combo disconnect /motor starter
It appears to me as if there wouldn't be a problem should a qualified person wire the 2-pole starter and control correctly. The problems appear to be as a result of incorrect wiring by unqualified individuals such as "put the start, stop and the overloads on the neutral side", "fusing the neutral" , "put the Toggle on the neutral side" etc.
It appears to me as if there wouldn't be a problem should a qualified person wire the 2-pole starter and control correctly. The problems appear to be as a result of incorrect wiring by unqualified individuals such as "put the start, stop and the overloads on the neutral side", "fusing the neutral" , "put the Toggle on the neutral side" etc.
- Location
- Illinois
- Occupation
- retired electrician
Re: combo disconnect /motor starter
430.73 prohibits the start buttons from being in the grounded conductor if they are remote from the controller. While a ground fault on the grounded conductor between the overload realy and the contactor coil will not cause the motor to start, it will prvent the overload relay from doing its job.
Don
430.73 prohibits the start buttons from being in the grounded conductor if they are remote from the controller. While a ground fault on the grounded conductor between the overload realy and the contactor coil will not cause the motor to start, it will prvent the overload relay from doing its job.
Don
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