line side/load side of circuit breaker

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AAEB

Member
Location
Southeast Asia
Good day!

what will happen if a load is connected to the line side (and vice versa )of a circuit breaker that is not listed as interchangeable? We have this recent proj. in where the contractor did this kind of connection and cause a wire burn-out. they are claiming that the CB is interchangeable. CB is square-d easy pact 100A.

thanks in advance
AAEB
 

tallgirl

Senior Member
They're wrong, unless the manufacturer indicates in some other location that the breaker can be backfed.

Some breakers can, some can't. The documentation I found for the EasyPact family seems to indicate they can be backfed. I'd double check for the exact CB you have.
 

iwire

Moderator
Staff member
Location
Massachusetts
ALL molded case breakers are suitable for back feed use UNLESS marked line and load.

From the UL white book.
CIRCUIT BREAKERS, MOLDED-CASE AND
CIRCUIT-BREAKER ENCLOSURES (DIVQ)
USE


This category covers circuit breakers and circuit-breaker enclosures
designed to provide service-entrance, feeder or branch-circuit protection in
accordance with ANSI/NFPA 70, ‘‘National Electrical Code’’ (NEC).

Listed circuit breakers may be mounted in any position unless marked to
indicate otherwise. If, however, the circuit breaker is mounted so that the
handle is operated vertically rather than rotationally or horizontally, the up
position of the handle should be in the ‘‘on’’ position.

Line and load markings on a circuit breaker are intended to limit connections
thereto as marked.
 
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kwired

Electron manager
Location
NE Nebraska
Good day!

what will happen if a load is connected to the line side (and vice versa )of a circuit breaker that is not listed as interchangeable? We have this recent proj. in where the contractor did this kind of connection and cause a wire burn-out. they are claiming that the CB is interchangeable. CB is square-d easy pact 100A.

thanks in advance
AAEB
Conductor burn out would have happened either way. Probably an improperly torqued connection, or defect within breaker. Current entering one side must leave the other.

If it has electronic features - that could require supply to be at one end vs the other but it would be marked line/load if that is the case.
 

AAEB

Member
Location
Southeast Asia
Conductor burn out would have happened either way. Probably an improperly torqued connection, or defect within breaker. Current entering one side must leave the other.

If it has electronic features - that could require supply to be at one end vs the other but it would be marked line/load if that is the case.
thanks sir, but why does the CB doesn't react on the burn out? we'd checked the (red) trip button and it works pretty well, does it means that there is a defect within the CB?
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Poor connections often result in "burnout" while limiting the current to less than the trip point of the OCPD.
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
Retired Electrical Engineer - Power Systems
meaning to say that position of the CB has nothing to do with the burn out?
Correct.
Line and load have nothing to do with your 'burn out'.

The line and load issue has to do with energized and de-energized parts when the cover of the breaker is opened and its internal parts are exposed.

As others have pointed out, 'burn out' is associated with poor terminations.
 

kbsparky

Senior Member
Location
Delmarva, USA
A GFCI type breaker can not be back-fed, just to make it clear here.

The Square D type breakers mentioned in this thread have a small red "trip" button on them, which is not the same thing as a GFCI test switch. It is a mechanical trip button, which does not need power to operate.

Many such breakers can be reverse-fed to accommodate bottom feed applications, keeping the handle orientation upright.
 
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kwired

Electron manager
Location
NE Nebraska
thanks sir, but why does the CB doesn't react on the burn out? we'd checked the (red) trip button and it works pretty well, does it means that there is a defect within the CB?
when you have a loose connector that heats up you do not have a short circuit or ground fault, and you do not have an overload. The breaker is not going to trip because there is no overcurrent condition. If the loose connection is on a breaker lug and it gets hot enough to migrate enough heat to the thermal overload mechanism of the breaker it may trip, but almost every time I've seen this it doesn't trip breaker. Heat just does not get to the right spot, and breaker was not designed to protect from this problem, in fact breakers are designed to depend on the attached conductor to act as a heat sink and take some heat away from breaker.
 

AAEB

Member
Location
Southeast Asia
when you have a loose connector that heats up you do not have a short circuit or ground fault, and you do not have an overload. The breaker is not going to trip because there is no overcurrent condition. If the loose connection is on a breaker lug and it gets hot enough to migrate enough heat to the thermal overload mechanism of the breaker it may trip, but almost every time I've seen this it doesn't trip breaker. Heat just does not get to the right spot, and breaker was not designed to protect from this problem, in fact breakers are designed to depend on the attached conductor to act as a heat sink and take some heat away from breaker.
As far as I know, thermal overload mechanism is located near the load side of the CB (in a normal position), if the overheating (due to loose connection) occurs on the load side, the heat will immediately reach the TOM and will cause a trip. Since the local contractor here connects the loads on the line side of the CB, it takes time before the TOM senses the overheating, and that's why the burnout occurs.

Am I correct?
 

iwire

Moderator
Staff member
Location
Massachusetts
As far as I know, thermal overload mechanism is located near the load side of the CB (in a normal position), if the overheating (due to loose connection) occurs on the load side, the heat will immediately reach the TOM and will cause a trip. Since the local contractor here connects the loads on the line side of the CB, it takes time before the TOM senses the overheating, and that's why the burnout occurs.

Am I correct?
No, that is not true.

Current is the same throughout the conductor in the breaker, the amount of heating will be the same when used in either direction.

Again, all molded case circuit breakers are suitable for use in either direction unless factory marked with line and load.
 

mivey

Senior Member
the amount of heating will be the same when used in either direction.
I do not agree. With a loose connection on one side of the breaker the heating will not be the same all the way through the breaker. Look at some past IR scans you might have of a loose connection at a breaker and you can see a temperature differential across the breaker.

As far as where the temperature sensor is inside the breaker, I have no idea.
 

iwire

Moderator
Staff member
Location
Massachusetts
I do not agree. With a loose connection on one side of the breaker the heating will not be the same all the way through the breaker.
I agree with that, but in the case of a loose connection the problem is with the loose connection not the direction the breaker is being used.

My comment was regarding normal conditions. Under normal circumstances the heating in the breaker will be the same in either direction.
 

mivey

Senior Member
My comment was regarding normal conditions. Under normal circumstances the heating in the breaker will be the same in either direction.
I concur and see no way the reverse breaker would cause a wire "burn-out" as the OP supposed.
 
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