I know of three visible defects in this picture. One is obvious; two are less obvious but more important.
I’ll give you one of the less obvious ones because I didn’t intend to include it in the photo and not all of the info is readily visible: Notice that there are both Square D and Cutler Hammer breakers in this Square D panel (the CH breakers don’t fit properly).
That leaves the obvious and not so obvious defects involving the center breaker. Everything you need to see to identify the issue is readily visible in the photo.
I’m posting this for discussion as it is a problem that I see on occasion (usually when I’m doing an IR inspection of a panel), but almost never hear discussed and it does present a potential fire hazard.
What is the issue and why is it a problem? Experts may wish to wait a bit before dropping the answer.
Ok experts stay out. I want to figure this one out. From what I remember…they need to be linked because if the breaker trips there is a possibility that power can still be going to the defective appliance.
In TX, it generally doesn’t matter what the code was at the time of of the build. We’re required to write up 1920s Knob and Tube systems for not having Arc Fault Interrupts - believe it or not! If you leave that tidbit out of your report TREC has a penalty matrix with your name on it.
The common tie is required because the common neutral can become energized. I think the safety issue is when working on the panel. Since there are two ungrounded conductors, power can still be going to the circuit the technician turned off. Am I even close?
This issue is with the tandem breaker. The tandem breaker is a single pole device, both breakers are being supplied from the same 120V feeder. The shared neutral (grounded conductor) is carrying the combined load of both circuits, which in a worst case scenario can place over 30A load on a 14AWG conductor and it has no overcurrent protection.
When the circuits are supplied by a two pole breaker, the shared neutral only carries the difference in the load between them (can’t exceed the capacity of the breaker)
Example: red conductor has 10A load and black conductor has 12A load. If supplied by a single pole device the shared neutral will have a 22A load (easy to pick up on IR). If supplied by a two pole device the shared neutral will only be carrying a 2A load.
Watch for MWBCs connected to single pole tandem breakers.