What is the difference between a "handle tie" and "common trip" in circuit breakers?

Question

This image shows a quad-breaker with handle ties.

^{Image borrowed from this DIY question}

One of the comments noted that despite the "handle ties", this is not a "common trip" breaker. I, in my ignorance, previously assumed that a trip on one of the tied breakers would have forced the tied mate to trip as well and that this would, therefore, also be a "common trip". It seems I was wrong.

What is the difference between a "handle tie" and a "common trip"? For bonus points, when should each be used?

As was pointed out in an answer on that original question, this quad-breaker is labeled

ALL POLES HAVE
NO COMMON TRIP

Does this mean that "common trip" is internal to the breaker and can only be identified by reading the labeling, while "handle tie" is the external plastic/metal piece that physically ties the handles together? If so, does that mean (theoretically) that one could have a common trip breaker without a handle tie?

Answer 1

It ain't about the handle-tie

Common trip does NOT work by one handle tripping, and that action dragging the other handle over via the handle-tie. That is not how that works.

That wouldn't work because the handles "trip free" - that is, if the breaker needs to trip and a padlock or naughty human is impeding the handle from moving, the breaker just trips anyway. So if the other half of the breaker impeded the handle from moving, the side that tripped would just trip anyway, and common trip would not occur.

This means you cannot 'bolt on' common trip by adding a handle-tie.

Common trip works by an internal mechanism within the breaker. Either the breaker has it, or does not. In the case of this Siemens breaker, it does not. Eaton also makes a line of non-common-trip quadplex breakers just like these, but they also make nearly identical breakers with common trip inner and outer. Other makers build them with inner common-trip and outer independent trip.

So from a common-trip perspective, a handle-tie is nothing but "trip theater".

The real purpose of a handle-tie, as manassehkatz discusses, is to assure common shutoff when the handle is used as an "off" switch. And provide a visual cue that the circuits are related.

Answer 2

Common trip means if one trips, so does the other.

Handle tie means if a person turns off one, they turn off the other.

Common trip effectively includes handle tie but handle tie doesn't guarantee common trip.

Common trip makes sure that if part of an appliance has trouble, the entire circuit is shut off.

Handle tie makes sure that related circuits, such as two halves of a multi wire branch circuit are turned off at the same time, to protect people working on one circuit from getting shocked by the other one.

The problem is not only "the trip of the top breaker could twist that long, thin looking handle leaving the bottom breaker live instead of forcing it to trip", but also because many breakers don't actually cause a big sudden external handle "flip". In fact, sometimes it isn't so obvious that a breaker has tripped because the handle has hardly moved at all! A true common trip is an internal mechanism, where the thermal or GFCI or AFCI trigger event causes both of the protected wires in the circuit to be disconnected at the same time.

Answer 3

A basic requirement for such breakers is that their tripping is independent of handle position. Ergo, you can completely immobilize the handle and it must never defeat proper operation, i.e. tripping. So common trip and a common handle are independent matters, and you can have common trip breakers without a common handle, as well as common handle breakers without common trip.

Common trip is handled outside of view, by mechanical interconnects going between the side panels of the breakers. Those are not visible when the multipole breaker is handled as a unit. But if you disassemble the breaker into individual poles (this is potentially destructive and voids warranty), you'd find little mechanical links that connects the trip mechanism across the breakers. So if one pole trips, it will set off other ones to trip.