Here's a perspective from a guy in the trenches. The original IntelliFlo came out several years ago. This was the 4 speed version. Suppliers knew there was a better one in the pipeline and really did not push the 4 speed as they called it "not the real one". Once the real one (VS3050, 3.2 whatever you choose to call it) came out in our area, it went into a one year pilot program in 2007 with the cooperation of Southern California Edison. Technicians were trained and held accountable for their work and watched very closely on the quality of the installations. This was done by a 3rd party in partnership with Pentair. Installations had to be perfect in terms of efficiency as we were paid a $250.00 rebate for installing and you did not get it until the job passed the inspection. These jobs were being subsidized and owners had a great chance to get in cheaply. Throughout 2007, the sell on the product was 100% on the installer. We had to sell it and gradually, news media picked up on it late in 2007 and the word was out that there was a better option. The program shut down at the end of 2007 as planned and I assume they are in evaluation mode as the paperwork states. Evaluation includes design modifications of impeller based on findings from the authorized installer network and it is geared to getting this product to the masses much cheaper. This is pretty much how every new product comes to market and is well documented through SCE. Now 2/3 of the way into 2008, the product has full name recognition although function may not be understood. I can only mention the name and just about everyone has heard it. Verified savings records sell the product. Those records are from those who have put one in and told a friend. Those who do not have one are pre-sold by the time I find them and I just need to make the final impression. I do far less work to sell the pump now but as with any industry, sales are slow due to the economy. A smart installer packages the pump with other products to make the sale ans the bottom line is the pump is doing excellent and I have never had to go out and uninstall a motor or drive on any job I have ever done. And, the fact still remains that is you put a watt meter on a standard pool motor at full speed, it will always draw more than an IntelliFlo at the same rpm. You cannot argue that fact no matter how much the word is out there that these pumps are somehow inefficient at high speeds. This myth is perpetuated by those who have never touched the pump.

Thanks for the excellent responses. Currently I can answer these questions. 1) Initially the service entrance voltage was 140 - 141V. Way too high. A transformer supplying power to our unit was changed and readings are now correct. Oddly, at 141V the tripping was just as frequent. I would have thought higher voltage would have lowered the Amps drawn, and there would have been less frequent tripping. Can this high voltage (for a couple of months during construction) have caused the breakers to become prone to tripping? Voltage is now correct at both ends of the run. No run is longer than 75 feet or so from the main panel. 2) I kept the nature of the equipment back as it might cloud the issue a bit. Yes there is an inrush as this is studio flash equipment. That being said, there is no problem using this gear anywhere else in the city (I have been). Even the 15A on the stove is fine, but even a 30A SqD trips repeatedly. The units plug in with standard 16GA cords. I have changed the cords to 15' 14GA heavy-duty high-visibility (orange and black) cords mostly for visibility. The equipment repair technician says a transformer charges capacitors and only basic switches and so-on are between the line-in and the transformer. No capacitors directly connected to the line-in. There is a 'slow' setting (or gentle) on the unit for situations where the units must work on non-dedicated circuits that already have significant loads on them. This 'slow' setting trips as often as the normal setting. Again, they work everywhere else (on normal setting), even the stove outlet. 3) Counterfeit: I compared a breaker to the photos in the article. #C is not identical. Most of my tab is exposed, not 1/2 as pictured otherwise they match. 4) Multi-wire branch: I think so, 1 Neutral for 2 circuits. A single unit can trip a breaker or several units at the same time can trip 1 or more breakers in no particular pattern. My previous set-up was 12GA 3-wire BX cables with 2-20A sharing 1 neutral with no issues. 5) The breakers are QO type HACR 20A. 6) An ammeter was put on the units. There is a very brief peak over 20A. It measures between 28 to just over 30A. There was some talk about this brief peak measurement being unreliable for an exact figure. A cheaper meter read anywhere from 20A-38A. A better quality Fluke was typically under 25A. The 30A SqD trips with the same frequency as 20A so simply swapping to 30A (even in the short term) isn't an option. Thanks for your knowledgeable responses and effort to help with this. Tom

Thanks for the reply, Brickeyee, and I'm sorry I couldn't get back to this sooner. I've read a bit about the problems with harmonics that seem to happen mostly in commercial settings where a bunch of computers or fluorescent lighting is wired on MWBCs on three-phase Wye systems, and the arguments for so-called super-neutrals. But what I suppose I'm not getting in the context of the OP's scenario is the effect on the neutral when the currents are 180 degrees apart. I would have thought that the neutral would still present a decent enough in-phase 0V reference to the computer's power supply when it's fed by an opposite-pole leg. But if it's inductance that really tends to confound things, that's beginning to make sense to me. terribletom - Just trying to understand the angle you are coming from. Is your argument that the neutrals are going to be connected in the panel anyway? Thanks for asking, billl. Well, no, I wasn't theorizing to that extent. I was merely seeking to isolate the problem beyond mere voltage drop (which can, of course, be "felt" by independent ccts from the same panel--more so if it's a small panel and the two hots come from the same pole). It's specifically the current-carrying characteristics of a shared neutral on a MWBC that I was interested in. So I thought that by distinguishing between circuit types, I'd get a more targeted answer. Let's say this is more about learning than arguing, eh?

DavidR, Phases are nothing more than comparing multiple electrical waves with respect to time. So assuming two waves, if they both peak at the same time, they're said to be "in" phase, or 0 degrees "out of phase". When the power company creates power, they do exactly what you suggest, and put the windings 120 degrees apart, and deliver 3 phases of power. That's why if you look at overhead transmission lines, they're always in groups of three. However, that's not the only way to create a phase difference. As Brickeyee pointed out, single phase motors use capacitors to start (and sometimes run) the motors. What they're doing with the capacitors is creating a second phase. Residential US power comes from a single phase which is delivered to the house via a center-tap transformer. By definition, the two hot legs are 180 degrees out of phase with each other. By convention, though, we don't call this 2-phase, because at one time, power was delivered as 90-degree out of phase, and was called 2-phase. (I'm not sure if this still exists anywhere). One thing that you might find interesting is that the fans on many computers and audio equipment are 3-phase to both prolong their lives, and to make them quieter. All it takes is a little bit of electronics to transform single phase into multiphase power.