electricbeaver
Member
I have been working with motor controls for the last 5 years. and have yet to find anyone to tell why we open the neutral on a overload condition.
breaking the neutral in a motor starter
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I have been working with motor controls for the last 5 years. and have yet to find anyone to tell why we open the neutral on a overload condition.
Re: breaking the neutral in a motor starter
It's hard to answer your question if you don't describe the motor starter application. You just indicated "overload condition" and made not mention of how the motor was actually controlled.
But....this is a guess.
On a single phase 120v motor where you have a line and neutral it is quite common to use a 2p starter, either manual or magnetic where both the line and neutral are opened and closed simultaneously to control the motor. The overload will also open both line and neutral contacts in response to an overload condition.
Their's nothing wrong with this as long as the neutral is opened and closed at the same time as the line is. However, the neutral does not need to be broken as a single pole would do.
It's hard to answer your question if you don't describe the motor starter application. You just indicated "overload condition" and made not mention of how the motor was actually controlled.
But....this is a guess.
On a single phase 120v motor where you have a line and neutral it is quite common to use a 2p starter, either manual or magnetic where both the line and neutral are opened and closed simultaneously to control the motor. The overload will also open both line and neutral contacts in response to an overload condition.
Their's nothing wrong with this as long as the neutral is opened and closed at the same time as the line is. However, the neutral does not need to be broken as a single pole would do.
electricbeaver
Member
Re: breaking the neutral in a motor starter
ok a little clairifcation on the application...lets say 480 vac with a 120 volt control you wire the "neutral" in series with the n/c contact on the overload block...why is this done instead in series with the "hot" control wire.......
ok a little clairifcation on the application...lets say 480 vac with a 120 volt control you wire the "neutral" in series with the n/c contact on the overload block...why is this done instead in series with the "hot" control wire.......
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- PE (Retired) - Power Systems
Re: breaking the neutral in a motor starter
It is more tradition than anything else. The old Joint Industry Council (JIC) and the Automotive industry required this placement. NEMA also recommends this arrangement.
Advantages of placing the overload relay (OLR) contact on the load side of the starter coil include:
1. Less risk of a short circuit in the control circuit causing the OLR contact to weld. This is particularly true of the standard NEMA starter with their direct connected OLR.
2. The wiring of multi-coil starters (i.e. reversing and reduced voltage) is easier and the resulting schematic is simplified.
[ December 02, 2003, 02:42 PM: Message edited by: jim dungar ]
It is more tradition than anything else. The old Joint Industry Council (JIC) and the Automotive industry required this placement. NEMA also recommends this arrangement.
Advantages of placing the overload relay (OLR) contact on the load side of the starter coil include:
1. Less risk of a short circuit in the control circuit causing the OLR contact to weld. This is particularly true of the standard NEMA starter with their direct connected OLR.
2. The wiring of multi-coil starters (i.e. reversing and reduced voltage) is easier and the resulting schematic is simplified.
[ December 02, 2003, 02:42 PM: Message edited by: jim dungar ]
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