Should all breakers be "bolt in" ?

[Pierre C Belarge]

When we do IR's we seldom see connections issues with QO's but see numerous bolt CB's and connections issues. Most issues are loose bus hardware and/or stripped hardware.

Adding to Brian's post, I was going to mention the installers skill level and care of installation has a lot to do with electrical connections/terminations.
The job application is another consideration.

The question the OP asked is general in nature, and can be answered differently by any poster.

One of the reason for the copious number of different circuit breakers is the multitude of different installation conditions.

 

[480sparky]

Simple: A cord plug gets inserted and removed multiple times, which helps to "wipe" the contact surfaces which can prevent oxidation build-up which could cause heating issues. A stab-on breaker typically stays in place all of its' life.

By the same token, a stab-on breaker won't eventually lose spring tension from multiple remove-insert cycles.

I could see an issue when a receptacle is used over and over and over, and the blades tend to get loose. But how often have you seen a receptacle that gets used once have an issue? Say, a direct-vent water heater, or garage door opener, or an In-Sink-Erator, or a sump pump. You plug them in once, and never touch the cords again for years.

 

[electricmanscott]

Do you think that all circuit breakers should be the bolt in type?

No I do not.

 

[hurk27]

The only stab ins I have had a problem with was where the buss was aluminum, or copper plated aluminum, large motor load or high ambient moisture, solid copper busses are much better, with stab ons. bolt ons are only as good as the installer, if they don't torque there not going to last, GE half space breakers are the worst, there is just not enough contact space for those little breakers, I have had whole panels of GE fail, and had to put full space ones in it, T&B was the worst for the ITE type breakers, probably why they dumped their line of service equipment.

but in the end, almost every failure can be attributed to improper installs, or the wrong equipment for the wrong environment or loads like big motors.

here's what I follow:

Damp locations or outdoors. Solid Copper buss.
heavy start up or inrush, Bolt on or SD QO
Dry All the above including aluminum with dielectric grease on the stabs but mainly use SD Homeline they even come with the grease on the stabs

 

[nakulak]

I just got through spending a bunch of time balancing some lighting loads, checking connections, and scratching some more hair follicles off my nogging over some nuisance tripping light displays. finally I got the bright idea to tighten up the panel (store remodel - re-used two of the old panels ). problem solved. (they were'nt loose, they just weren't tight) thing is - you never have to do that with stab ins (if they aren't tight I guess they just go in the trash ?)

 

[brian john]

I just got through spending a bunch of time balancing some lighting loads, checking connections, and scratching some more hair follicles off my nogging over some nuisance tripping light displays. finally I got the bright idea to tighten up the panel (store remodel - re-used two of the old panels ). problem solved. (they were'nt loose, they just weren't tight) thing is - you never have to do that with stab ins (if they aren't tight I guess they just go in the trash ?)

First and second steps in nuisance tripping

1. Measure load
2. FOP test all CBs line to load.

 

[iwire]

Do you think that all circuit breakers should be the bolt in type?

I sure would miss Square D 'I-Line', so no.

 

[weressl]

Do you think that all circuit breakers should be the bolt in type?

Several things to consider:

• NFPA 70E makes live removal, replacement far more infrequent actiuvity than before, the advantage of plug in was/is live replacement.
• Current dependent.
• Plug-in have inherently more potential to fail than the bolt on both in installation and operation.
• It is more costly to manufacture a stab-on connector than a bolt-on connector.

 

[mxslick]

Several things to consider:

• NFPA 70E makes live removal, replacement far more infrequent actiuvity than before, the advantage of plug in was/is live replacement.
• Current dependent.
• Plug-in have inherently more potential to fail than the bolt on both in installation and operation.
  [*]It is more costly to manufacture a stab-on connector than a bolt-on connector.

(Bold/underline added by me)

I can agree with that but for one thing: Why is a bolt-on breaker (Let's say single pole 20 amp SqD for example) more expensive than the stab-on type? :-?

 

[weressl]

(Bold/underline added by me)

I can agree with that but for one thing: Why is a bolt-on breaker (Let's say single pole 20 amp SqD for example) more expensive than the stab-on type? :-?

The bolt on is a simple buss extension with a hole or tapped hole.

The stab requires a folded construction with either self or external spring/ thermal expansion compensation mechanism. It's a mechanically more complex assembly than the above.

Having said that, the actual pricing depends on volume sales, so even if a bolted assembly is less constly to construct, the sales price of the stab-on can be lower if the market demand is significantly greater for it.

 

[MarkyMarkNC]

[*]Plug-in have inherently more potential to fail than the bolt on both in installation and operation.
[/LIST]

Some Square D engineers would disagree with you on this one. I was told one time that they experience a higher failure rate given the same conditions with the bolt-in breakers (QO vs QOB.)

I don't remember the exact wording so my paraphrasing may be off a bit here, but the way he explained it actually made sense. In a high temperature or fault condition, the clamps on the QO breaker will expand and actually flex and grip the bus bar tighter, whereas the flange on the bolt in breaker will flex away from the bus bar - increasing resistance, and stretching or deforming the bolt.

Everyone assumes the bolt-in breakers are better, because that is what is always specified by engineers on many jobs, but that may not empirically be the case.

 

[weressl]

Some Square D engineers would disagree with you on this one. I was told one time that they experience a higher failure rate given the same conditions with the bolt-in breakers (QO vs QOB.)

I don't remember the exact wording so my paraphrasing may be off a bit here, but the way he explained it actually made sense. In a high temperature or fault condition, the clamps on the QO breaker will expand and actually flex and grip the bus bar tighter, whereas the flange on the bolt in breaker will flex away from the bus bar - increasing resistance, and stretching or deforming the bolt.

Everyone assumes the bolt-in breakers are better, because that is what is always specified by engineers on many jobs, but that may not empirically be the case.

What Square D was admitting/justifying at that point that their bolt-on connectors were NOT designed for thermal compensation? None of the bus connections were - at one point - hence the emergence the little ingenious device called Bellville washer.

The main issue in both cases that there is some spring tension required for thermal compensation as the conductive elements heat up and cool down in response to varying current. The modulus of elasticity - the capacity to 'remember' its previous state - of the material is changed by thermal aging, eg. the number and magnitude of heat cycle causes the material to loose that capacity. As a general statement to commonly available materials, the high modulus and conductivity does not go hand-in-hand, so often the force loading spring material, be it a Bellville washer or the spring around the stab is not to take part in the conductive path.

The short of it that either of those connections can be designed to equal performance and Square D just had a bunch of bad apples out there. I maintain that a bolt/nut/Bellville is cheaper to construct than a spring loaded bus stab.

 

[hurk27]

What Square D was admitting/justifying at that point that their bolt-on connectors were NOT designed for thermal compensation? None of the bus connections were - at one point - hence the emergence the little ingenious device called Bellville washer.

The main issue in both cases that there is some spring tension required for thermal compensation as the conductive elements heat up and cool down in response to varying current. The modulus of elasticity - the capacity to 'remember' its previous state - of the material is changed by thermal aging, eg. the number and magnitude of heat cycle causes the material to loose that capacity. As a general statement to commonly available materials, the high modulus and conductivity does not go hand-in-hand, so often the force loading spring material, be it a Bellville washer or the spring around the stab is not to take part in the conductive path.

The short of it that either of those connections can be designed to equal performance and Square D just had a bunch of bad apples out there. I maintain that a bolt/nut/Bellville is cheaper to construct than a spring loaded bus stab.

This has bothered me over the years, as it seems that manufactures have gotten away from spring loaded type connections, even terminals marked AL/CU now have a set screw dead headed right into the aluminum conductor, with out the spring to maintain the torque the aluminum will cold flow out from under the set screw, this was always a bad way of making a connection before, what happened?

 

[jim dungar]

Actually some Square D "plug-on" connections are designed to grip the busbar tighter due the higher magnetic forces that occur during a fault. These same magnetic forces can blow apart some bolt-on connections. Remember a connection for a 20A 120V breaker may have/need different considerations than that of an 800A 600V device.

 

[stickboy1375]

One word - Pushmatic.

I love those! really, I do!