Back feed breaker.

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relbas

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If the breaker is feed from the load side ,will it trip at the rated trip current?
Scenario : The generator became motorized.
 

Dennis Alwon

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Location
Chapel Hill, NC
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If the breaker is feed from the load side ,will it trip at the rated trip current?
Scenario : The generator became motorized.

Article 408.36(D) allows back fed breakers

(D) Back-Fed Devices. Plug-in-type overcurrent protection
devices or plug-in type main lug assemblies that are
backfed and used to terminate field-installed ungrounded
supply conductors shall be secured in place by an additional
fastener that requires other than a pull to release the
device from the mounting means on the panel.
 

iwire

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Location
Massachusetts
If a breaker is marked line and load you must follow those markings. Without those markings they will operate fine in either direction.

Typically line and load is found on beakers that have electronic components in them such as AFCIs, GFCIs and GFP type breakers.
 

GoldDigger

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If a breaker is marked line and load you must follow those markings. Without those markings they will operate fine in either direction.

Typically line and load is found on beakers that have electronic components in them such as AFCIs, GFCIs and GFP type breakers.
It makes a difference with shunt trips too.
 

petersonra

Senior Member
Location
Northern illinois
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engineer
If a breaker is marked line and load you must follow those markings. Without those markings they will operate fine in either direction.

Typically line and load is found on beakers that have electronic components in them such as AFCIs, GFCIs and GFP type breakers.

As best I can tell the primary difference between at least larger MCCB that can or cannot be backfed is whether they have changeable trip elements. If you can change the trip unit, it is not reverse feedable. No idea why.

The AFCI/GFCI/GFP stuff may also apply. Don't use much of it.
 

GoldDigger

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Location
Placerville, CA, USA
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Some or all shunt trips? Most I have been involved with probably doesn't matter as they are still a standard breaker with the shunt coil added and it has it's own separate terminals.
As long as the shunt coil is isolated and you connect it on the load side it should be fine.
But if the breaker is under high current load would the polarity of the shunt coil matter? Or does it have a totally separate magnetic trip mechanism?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Shunt trips are completely isolated from the electrical power of the CB. The shunt trip mechanically trips the CB when it is activated. AFAIK, the CB does not even need power applied for the shunt trip to work.
 

kwired

Electron manager
Location
NE Nebraska
Shunt trips are completely isolated from the electrical power of the CB. The shunt trip mechanically trips the CB when it is activated. AFAIK, the CB does not even need power applied for the shunt trip to work.
That has been my experience - I suppose there could be something different out there.

I think there are shunt coils that can take being continuously powered and some that is recommended they have control circuit supplied by the load side of the breaker they control or other provisions to ensure the coil doesn't remain energized for extended periods of time. Some could even have an internal switch that opens the control circuit if the breaker is open to keep coil from extended load time.

If shunt coil is not same voltage as the power circuit - then your control voltage is going to be a separate voltage source, but could possibly still be supplied from the same circuit and through a transformer.
 

jim dungar

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Location
Wisconsin
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PE (Retired) - Power Systems
As best I can tell the primary difference between at least larger MCCB that can or cannot be backfed is whether they have changeable trip elements. If you can change the trip unit, it is not reverse feedable. No idea why.

Among other issues
When you open the breaker to change the trip unit they want it to be de-energized, which would not be the case if it was reverse fed.
 
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