Tandem/piggyback QO breakers

[electricguy]

Last July I had a call to a rental ,property for tripping breakers. The property had an electrical service upgrade a few years ago.

The breakers in question were old style 15 amp tandem breakers with the push stabbed in connection for for the circuit.
there is a fridge on one breaker and a cloths washer, deep freeze and recently a portable 1500 W heater.
The buss has arc'd under the load. And now the breaker will not seat on the buss with a good electrical/mechanical connection. this is a 6 circuit panel with 4 tandems and 2 single pole breakers in it. so there is 10 loaded circuits now. I have suggested a sub panel with enough circuits to only install SP breakers.
I have tried to explain this via email to the customer but she wants further information.


this is what i put on the quote to her


SUBPANEL IS OVERLOAD WITH TOO MANY CIRCUITS FOR THE 6 /11
PANEL, THIS HAS CAUSED OVERHEATING OF A SECTION OF BUSS AND
NOW HAS DISTORTED THE ELECTRICAL BUSS IN PANEL.
It needs a bigger sized panel and the double breakers replaced with
single breakers. Please not this is not the panel we used to install note this isnt the panel we used to install
the washer and dryer circuits last summer.
Her reply is

Can you provide some more description for what exactly is being done? Did something break since your original analysis of the electrical a few months ago? How would this work prevent issues going forward?


Any ideas on how to word a response would be appreciated.

 

[Kdog76]

Sounds like you have a good handle on this already. I would point out that the panel is basically unusable because of the buss bar. (She may not know what that means, so keep it plain english: i.e., where the breaker snaps in to the panel is the part that is broken, preventing a breaker to properly fit in to the panel. or something to that effect).

Then give her a little info on how a loose breaker in that panel can cause arcing & sparking, overheating, and cause the problems you describe. Then sell her on your professional recommendation (i.e. swap out the panel OR if you trust that you can fit a two-pole breaker to feed a sub-panel in there)

It sounds like she trusts your judgement here, & just looking for clarification, so I'd give her just enough info to explain the problem, why it occured, what your fix is, and why your fix will prevent the problem from reoccuring. Should be no worries here. Good luck!

 

[ceb58]

As they say a picture is worth a thousand words. Take a shot of the bad buss to send her and explain that due to the arcing it is now not feasible to use this panel and it needs replacing.

 

[LarryFine]

Tell her: "The internal parts of the panel, which are hidden from view when the breakers are in place, has been permanently damaged by heat from overloading, because the panel is too small for the number of circuits and the amount of power being used.

"The damage occurs slowly over time in the beginning, but the buildup of heat speeds up the damage, which in turn causes more heat. The only possible outcomes are loss of power or even fire, and the only cure is replacement with proper, new equipment."


Hey, that sounds so good, I might have to use it myself sometime!

 

[zappy]

Just wondering...

Just wondering...

So it's a new panel with old style breakers in it? Or are you talking about a subpanel? Isn't the subpanel protected by a two pole breaker? So how could the bussbar get damaged from a overload, if a breaker is protecting it? It sounds like there was a arc from the breaker being loose on the bussbar.

 

[electricguy]

ES the buss is damaged from probally a combination of things remember this part of the stab is being using for some high draw loads it is doing the work of 2 breakers on the one stab.

 

[zappy]

ES the buss is damaged from probally a combination of things remember this part of the stab is being using for some high draw loads it is doing the work of 2 breakers on the one stab.

Never thought of that. That lil nub of metal on the buss can't handle it. Is that why using twin breakers is a bad idea?

 

[480sparky]

ES the buss is damaged from probally a combination of things remember this part of the stab is being using for some high draw loads it is doing the work of 2 breakers on the one stab.

So what's the difference between a 20a tandem and one leg of a 40a 2-pole breaker that can draw 40 amps?

 

[growler]

So what's the difference between a 20a tandem and one leg of a 40a 2-pole breaker that can draw 40 amps?

I don't think there is any difference. The question I would have about this installation is how many circuits is the panel rated for. With a QO type breaker the tandems will snap in anywhere so there may be a problem of overfill ( to many circuits). If it's rated for that many circuits then there shouldn't be a problem.

 

[480sparky]

I don't think there is any difference. The question I would have about this installation is how many circuits is the panel rated for. With a QO type breaker the tandems will snap in anywhere so there may be a problem of overfill ( to many circuits). If it's rated for that many circuits then there shouldn't be a problem.

Depends on which type of tandem you use.

 

[brian john]

I do not think the type of installation had ANYTHING to do with the failure, it is the bus stab (as I read the post) that has failed, this is a connection issue between the CB and the bus. Most likely the CB tension clamp was to loose and resulted in the arcing. This bus is rated for the installation described BASED ON WHAT WAS POSTED.

I would explain there is a connection deficiency due to a failure of one CB, the proper fix for this would be a new panel, in installing the new panel we recommend.

 

[growler]

Depends on which type of tandem you use.

Yes, I should have said there is a tandem that can be snapped in anywhere in a QO type panel.

I would still check the rating of the panel. They test those things to make sure they should work under a certain load. I trust the manufacturer to do the testing, all I do is the installing.

I like a larger panel with more room but that doesn't mean I don't think the smaller one's will work. If the manufacturer rates a panel for 12/20 amp cicuits then I expect that they have tried it out and have had no problems. They gave it a UL sticker at some time for some reason.

 

[satcom]

Never thought of that. That lil nub of metal on the buss can't handle it. Is that why using twin breakers is a bad idea?

There are some older panels that snap, crackel, and pop where twin breakers were used, most of the newer panels don't seem to have these problems.

 

[jim dungar]

Yes, I should have said there is a tandem that can be snapped in anywhere in a QO type panel.

While it is true that there are non-CTL QO breakers that can physically be located anywhere in the panel, it is a mis-application of the UL listing to do so. The non-CTL breakers are "intended" for installation in panels that were built prior to CTL being a requirement (i.e. built before the mid-60's), that is why they contain the phrase 'for replacement purposes only'.

Every QO panel has a wiring diagram that indicates if the panel is rated for tandem breakers and what locations they should occupy.

 

[macmikeman]

While it is true that there are non-CTL QO breakers that can physically be located anywhere in the panel, it is a mis-application of the UL listing to do so. The non-CTL breakers are "intended" for installation in panels that were built prior to CTL being a requirement (i.e. built before the mid-60's), that is why they contain the phrase 'for replacement purposes only'.

Every QO panel has a wiring diagram that indicates if the panel is rated for tandem breakers and what locations they should occupy.

Gosh Jim I sure would like to make a blow up label of this post and fasten it to the breaker rack at the big orange store. I have seen whole shelves stocked with boxes of non CTL twin breakers over there and not one disclaimer posted.....

 

[satcom]

While it is true that there are non-CTL QO breakers that can physically be located anywhere in the panel, it is a mis-application of the UL listing to do so. The non-CTL breakers are "intended" for installation in panels that were built prior to CTL being a requirement (i.e. built before the mid-60's), that is why they contain the phrase 'for replacement purposes only'.

Every QO panel has a wiring diagram that indicates if the panel is rated for tandem breakers and what locations they should occupy.

Excellant post!

 

[480sparky]

Gosh Jim I sure would like to make a blow up label of this post and fasten it to the breaker rack at the big orange store. I have seen whole shelves stocked with boxes of non CTL twin breakers over there and not one disclaimer posted.....

Big Orange has only one goal in mind: Sell product.

They could care less about safety.

 

[kwired]

Most 6 space QO have alum buss

Most 6 space QO have alum buss

Square D does have a copper buss for 6 and 8 circuit panels in their catalog, I have never seen one and am guessing not many are sold. these panels if have a weak connection from breaker to buss will deteriorate much faster than a copper buss will as you can probably imagine.

only QO breakers I have ever seen with stab in terminals were probably at least 30 years old. If one of these was installed in the new panel with aluminum buss it probably had a weak connection right away now it needs replaced.

 

[sameguy]

Who put in the new pan. with old brkrs.? Your fault? If not tell them that is why the buss is damaged, if the connection at the stab was tight with an old brkr. then the near over loading of two hr. could have dried out the grease and with no exercising of the brkr. it failed at the buss connection; due to the internal components had frozen from lack of grease. A new pan. and brkrs. are needed, who pays is an other story if you did the new pan./old brkrs.
Brkrs. will dry out over time with no exercising regardless and turn off and never turn on or wont turn off even when the handle is in the off position.

 

[One-eyed Jack]

Use Larry Fine's post. Is by far the best post on this subject. No amount of blame is going to cure the burnt buss. It must be replaced to restore the integrity of the distribution point.