Common vs. Independent Trip

[JDBrown]

The other day I came across a circuit breaker feeding a residential dryer that was marked "Independent Trip." I know that when I specify 2 pole breakers for 240V appliances, I always ask for common trip, but this is an existing installation. I'm trying to figure out if this is something I should recommend they replace, or if it's no big deal. With it being a dryer, I don't think there's a problem, because all the dryers I've ever seen have a 120V motor anyway (so no need to worry about "single-phasing" the motor). IIRC, the heating elements are also 120V -- the only reason the dryer needs 240V is to allow for more heating elements. But I'm not 100% certain that this is true of ALL electric dryers in the US.

By my reckoning, if only one pole of that breaker trips, you might lose any combination of: electronic controls, motor, and/or half of your heaters. I think this could cause a fire hazard if one of the heaters stays on but the drum and vent fan/blower are not spinning. On the other hand, it would probably take a pretty special set of circumstances to make that happen, and for all I know dryers might be required to shut down if they lose one phase anyway.

I have four questions that have come out of all this:

1. Is there a Code violation here?
2. Is this installation unsafe?
3. Are there any other issues with the existing installation that I might have missed?
4. Would you recommend replacing the breaker with a common trip type?

 

[don_resqcapt19]

Fuses are permitted to supply that load, and they are not "common trip".

 

[templdl]

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I have four questions that have come out of all this:

1. Is there a Code violation here?
2. Is this installation unsafe?
3. Are there any other issues with the existing installation that I might have missed?
4. Would you recommend replacing the breaker with a common trip type?

I don't have my code book handy but I would judge it as a code violation.
The installation may be unsafe depending upon what may have caused a trip.
I can't think of any other issues.
Yes, I would recommend that the breaker be changed.
The breaker you have described would be used on home run circuits where 2 individual 120v crkts are being feed using a common neutral. Should one ckt trip the other remains closed.
By using a 2p breaker with individual trips one ckt may trip without opening the Should either circuit need servicing the handle tie operates both poles together which assures that bother circuits are de-energized when maintenance is performed.
Please realize that should you have a 240v element should only 1p trip the 2nd pole that remains closed can back feed the other 120v circuit that has been deenergized.

 

[don_resqcapt19]

240.15(B) would require a common trip breaker for that application, but like I said, fuses are permitted to be used for that type of load and they are not "common trip". The use of a common trip device does make it safer, but the risk is not so high that the code has prohibited the use of fuses.

 

[qcroanoke]

The other day I came across a circuit breaker feeding a residential dryer that was marked "Independent Trip."

[/LIST]

I don't think I have ever seen a 2 pole breaker marked "Independent Trip"
And I have been around a few years.

 

[JDBrown]

I don't think I have ever seen a 2 pole breaker marked "Independent Trip"
And I have been around a few years.

The breaker is actually marked "Non Common Trip" -- that's what I get for doing these things from memory, I guess. It's one of these:

I wouldn't really call it a 2-pole breaker, though. I'd call it (2) 20 amp 1-pole breakers, and (2) 30 amp 1-pole breakers with a handle tie

Thank you for all the replies and information. I think I'm going to recommend replacement with a common trip unit for the dryer, but not necessarily as something urgent. More along the lines of, "I know you're planning to have some electrical work done in the next few months; you should have the Electrician replace that breaker while he's at it."

 

[curt swartz]

I have never run across a standard residential 120/240 volt clothes dryer with 120 volt heating elements. They have always been 240 volts. The only 120 volt loads are the motor, controls and lights.

 

[JDBrown]

I have never run across a standard residential 120/240 volt clothes dryer with 120 volt heating elements. They have always been 240 volts. The only 120 volt loads are the motor, controls and lights.

Thanks for the reply, Curt. I had an internship in college helping design and test dryer controls, but I didn't get to do much outside the control panel. I must have been remembering wrong about the heating elements. Thanks for the clarification.

 

[Little Bill]

The breaker is actually marked "Non Common Trip" -- that's what I get for doing these things from memory, I guess. It's one of these:
View attachment 8950
I wouldn't really call it a 2-pole breaker, though. I'd call it (2) 20 amp 1-pole breakers, and (2) 30 amp 1-pole breakers with a handle tie

Thank you for all the replies and information. I think I'm going to recommend replacement with a common trip unit for the dryer, but not necessarily as something urgent. More along the lines of, "I know you're planning to have some electrical work done in the next few months; you should have the Electrician replace that breaker while he's at it."

There is nothing wrong with using that breaker. It is a "quad" (that's what I call it anyway) and is commonly used in mobile home panels.

The 2 poles in the middle are for 240V loads and it is a common trip. The two outside breakers/poles are each 120V and are not common trip as they are two separate breakers.

Most of the ones I see are C/H and have a metal retainer around the 2-pole center breaker so that you don't turn it off by mistake when turning one or both of the outer breakers.

Edit: If you look at the diagram on the breaker, it shows the two inner poles tied together and the two outer poles are separate from each other. "not common trip" just means that every breaker won't trip due to only one having a reason to trip, or that you can use each independently with the two in the center being one.

 

[GoldDigger]

Edit: If you look at the diagram on the breaker, it shows the two inner poles tied together and the two outer poles are separate from each other. "not common trip" just means that every breaker won't trip due to only one having a reason to trip, or that you can use each independently with the two in the center being one.

Even the spec sheet for that breaker family is somewhat confusing.
But the bottom line is that this applies:

All circuit breakers shall be oper-
ated by a toggle-type handle and
multipole circuit breakers shall
have an internal common trip
mechanism. The circuit breakers
shall incorporate trip mechanisms
that are mechanically trip-free from
the handle. The handle position
shall provide visual trip indication

The handle tied center part of the quad in the picture is one multipole breaker with an internal common trip which is independent of each of the two outer handles, which are single pole breakers.
As mentioned, that family also contains models in which the outer two handles are also tied together and also constitute one multipole breaker with internal common trip, but independent of the other multipole breaker in the same assembly.

 

[Little Bill]

The handle tied center part of the quad in the picture is one multipole breaker with an internal common trip which is independent of each of the two outer handles, which are single pole breakers.

Now where have I heard that before?:roll::dunce:

The 2 poles in the middle are for 240V loads and it is a common trip. The two outside breakers/poles are each 120V and are not common trip as they are two separate breakers

.

 

[JDBrown]

The handle tied center part of the quad in the picture is one multipole breaker with an internal common trip which is independent of each of the two outer handles, which are single pole breakers.
As mentioned, that family also contains models in which the outer two handles are also tied together and also constitute one multipole breaker with internal common trip, but independent of the other multipole breaker in the same assembly.

If this is the case, then why are there separate BQ (Independent Trip) and BQC (Common Trip) series breakers? For example, here are links to catalog pages for the Independent Trip and Common Trip breakers:
http://www.cesco.com/resources/786676/378610-AttachmentURL.pdf
http://www.cesco.com/resources/786676/394869-AttachmentURL.pdf

As you can see from the linked pages, models #BQ2302120 and #BQC2302120 both exist. BQ2302120 is a quad breaker with (1) 2-pole 30 amp breaker and (2) 1-pole 20 amp breakers, and is "Independent Trip" or "Non Common Trip". BQC2302120 is also a quad breaker with (1) 2-pole 30 amp breaker and (2) 1-pole 20 amp breakers, but is "Common Trip". Based on this, I would have to say that Common vs. Independent Trip has nothing to do with the two outer breakers, since in both the Common Trip and Independent Trip cases they are separate single-pole breakers.

The only explanation that makes sense to me is that "Independent Trip" or "Non Common Trip" means the 30 amp 2-pole breaker is effectively (2) 30 amp 1-pole breakers with a handle tie, while "Common Trip" means the 30 amp 2-pole breaker is truly a 2-pole breaker that will open both poles regardless of which pole had the overload. This is still consistent with the portion of the spec sheet quoted by GoldDigger, which says, "... multipole circuit breakers shall have an internal common trip mechanism." Since it's really (2) 1-pole breakers with a handle tie, it's not technically a multipole circuit breaker. That's the only way I can think of that they would be able to label it "Non Common Trip".

Of course, just because it makes sense to me doesn't mean that's the way it really works. Can anybody verify or disprove my speculations?

 

[GoldDigger]

Of course, just because it makes sense to me doesn't mean that's the way it really works. Can anybody verify or disprove my speculations?

Looking at the spec for the BQC series, I am convinced by your argument that the BQ has a 240A pole pair, which does not constitute a single breaker. It would be suitable for MWBC as well as perhaps for an upstream protection for a circuit that contained some pure 240 volt loads with a two-pole common trip OCPD at each such load.
The fact that the two center poles were listed on the BQ sheet in a single column just indicated that they had to have the same value, not that they constituted one breaker.
And in the BQC, you can get the outer poles as either individual breakers or as a handle-tied pair. And that outer pair is also common trip.

Confusing, but you reasoned it out AFAICS.