securing breakers on bus


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Old 05-30-15, 04:37 AM
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securing breakers on bus

How can I tell if the breakers are securely attached to the bus bar of my square d panel?

Is pushing on the face of each one (with the cover on) to assure there is no movement in and out a sufficient test? Kind of like making sure they are snapped totally inward.

I noticed there is a little up and down movement/wiggle to the ones on the top of each row.... does that seem normal?
 
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Old 05-30-15, 04:52 AM
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Yes, the slight wiggle is normal.

When the breaker fully snap onto the bus you will not be able to push any farther.
 
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Old 05-30-15, 05:07 AM
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so its not a matter of force but rather whether it just snaps in or not.

Do they get loose cause heat? Or is it kind of like if its not snapped in sufficiently the circuit wouldn't work?

And do they push in as I suggest? From pushing on the center of the face of them? Do the snap in on the right side (center of bus) or (left side outside of bus)
 
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Old 05-30-15, 05:49 AM
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Most circuit breakers used in residential panels simply push onto the straight bus tab, often called a stab. The circuit breaker itself has a u-shaped clip inside that fits over the stab. This u-shaped clip is made of a spring metal with high electrical conductivity and sometimes will also have an external spring as well. It should take a fair amount of pressure to push the CB "home" on the stab.

The end of the circuit breaker away from the bus will have some method of securing it to the panel. Most common is a specially formed part of the plastic body that hooks onto the steel of the panel and allows to the CB to "swing" towards the bus stab. Square D type QO panels are bit different by having a second spring clip on the outboard end of the CB body that snaps over a rounded part of the panel.

Since the metallic parts of the CB are somewhat loosely fitted in the plastic body it is normal for the plastic body to move slightly even when the circuit breaker is properly installed. However, a loose clip on the bus stab WILL overheat under certain conditions and this overheating can destroy the spring tension of the bus clip as well as damage the bus stab itself.
 
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Old 05-30-15, 07:07 AM
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great explanation!

So would pushing on them with a finger as I describe, to check they don't push in farther, serve as a good indication that they are fully inserted (as pc stated).

I don't want to be pushing on them and one pops off!

I have a HOM panel, do you think that added spring you mention on QO is on the HOM as well?
 
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Old 05-30-15, 07:27 AM
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Run your finger down the face of the breakers. Are they all the same level ? If one wasn't snapped in it would be sticking out a considerable amount from the others.

The Homeline breakers and the QO breakers have completely different buss bar attaching methods. The H breaker use an additional spring and the QO does not.

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Last edited by PJmax; 05-30-15 at 08:04 AM. Reason: added pic
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Old 05-30-15, 07:49 AM
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The Square D HOMELINE (HOM) panels use the generic mounting method I described where the CB body is molded to fit onto a hook (for lack of a better term) on the panel and then pushed down onto the bus stab. Many manufacturers use the exact same method and that makes the various manufacturer's CB mechanically interchangeable among the several manufacturers. Note well that I stated mechanically interchangeable, they are NOT electrically changeable unless they have been tested and "Listed" for use in panels other than the same manufacturer.

To install these circuit breakers you first hold them at about a 45[SUP]o[/SUP] angle and hook the outer edge on the panel steel and then lever them down onto the stab until it won't go any more. Use firm, but not excessive pressure to make sure it is properly seated. Do not force it, if you have to use excessive force then something is wrong, usually using the wrong circuit breaker.
 
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Old 05-30-15, 08:22 AM
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excellent replies again.

Last question... if there was burning or over heating on a bus bar from a loose breaker.... do you guys remove the breaker and put it in another slot? Or is the stab safe to use with a new breaker?
 
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Old 05-30-15, 08:29 AM
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If the stab on the bus is damaged it should not be used. The poor connection could cause excess heat and/or a fire.
 
 

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