ITE bus stab amperage limit for tandem breakers

Question

We want to run some sub-panels off of our 100 amp, 12 space, ITE main panel. (According to another forum, Gould bought ITE in 1976, and Siemens bought Gould in 1983.)

Siemens I-T-E Load Center has the following prohibition regarding tandem breakers:

"SUM OF QT BREAKER RATING IS NOT TO EXCEED 110 AMPS PER BRANCH CIRCUIT BUS STAB."

(The quoted text is printed on the back of the panel - I copied the above from the same forum.)

Now, the above seems clear, but let me ask anyway: does that mean I can exceed that limit with non-tandem breakers? For instance, can I have a tandem breaker on the one side, say with 2 15-amp branch circuits on it, and a 100-amp, simple breaker on the other?

I have to say it strikes me an odd limitation - the main breaker should cut off power at 100 amps...

I apologize for the silly question, but I would rather not burn the house down (or worse, go for an extended period without power when the inspector disagrees with the setup).

Answer 1

If I am reading your question right, then the answer to your question is yes. The reason being is that there it is highly doubtful the two non tandem breakers will be carrying full and constant loads at the same time. Of course you have to use the non-tandem breakers properly and not be using a 240V load off of them just 2 - 120V loads. This is set up to prevent overheating and damage to the bus. I am sure the manufacturer has "crash tested" these scenarios and that's why they have a restriction.

Added for clarity see comment.

I always try and use the contributors vernacular rather than trade nomenclature since it tends to confuse people. So let scrap that and insert some definitions.

1. A panel is divided into pole spaces.
2. A full size breaker takes up one pole space and service a 120V circuit.
3. A two pole breaker takes up two spaces and if it serves a 240V circuit the poles are interlocked mechanically or internally.
4. A half size breaker serves either two single 120V circuits or one 240V circuit in a one pole space. This is sometimes referred to as a tandem or piggyback breaker. (see the confusion).

You ITE Panel states that you shall not connect two pole breakers opposing each other (one on the left side and one on the right) in the panel, if the overcurrent protection adds up to 110A.

So I believe you question is can I install one two pole breaker and two one pole breakers in opposition even if they add up to over 110A? And my answer is Yes because if for no other reason it doesn't say you can't. For further explanation I tried to explain that the reason was to prevent overheating and damage to the bus.

I also tried to explain that you can not use this as a go around to install two, two pole breaker beside each other and then just remove the mechanical tie and say "Hey its really just two single pole breakers". Which by the way violates other code rules.

I am not sure what you meant in your comment about drop. I can tell you I am not talking about voltage drop. I am talking about overloading which will burn up the breakers and bus in you panel, and I am pretty sure that is what ITE has in mind also.

Hopes this helps

Answer 2

retired master electrician's response is not answering the original posters question. EdBeal's answer is correct.

the stab is the tab that the breaker snaps onto, and the "normal size" breakers next to each other horizontally snap onto the same stab.

a tandem breaker fits in a normal size spot so it's on the same stab, but you have to add up the amperage.

picture is easier. In my poorly labeled panel below:

• the top stab has 70A on it ... well below the 110A max.
• the 4th stab down has 60A total. The tandem breaker on the left counts as 40.
• the 7th and 8th stab both have 110A each ... at the max

I want to replace the 30A dryer two-pole breaker with a 50/30 quad breaker to get a 50A 240V and a 30A 240V circuit in the same space ... but I can't because the lower-right subfeed #2 dual breaker is 50A. That would be 130A on each of the 9th and 10th stabs.

I can add a 50/30 quad breaker, but I need to rearrange the breakers to keep each stab at/below 110A.

as best as possible you want to balance the load ... make the amperage draw on the odd numbered stabs (bus bar 1) the same as the even numbered stabs (bus bar 2). i.e. if you have high power 120V devices like microwaves and refrigerators, put them on different stab sets so the current is flowing on different bus bars when they are turned on at the same time.