Debating two-wire vs. three-wire motor designs.
In my last column, I made mention of the fact that, years ago, if you wanted to get a real argument started at a driller or pump installer meeting, all you had to do was say that an oil-filled motor was the design or vice versa – that a water-filled design was the best – and you had an instant argument.
Now, if you wanted to escalate the argument to the point where people really took offense, you could point out that either a two-wire motor or a three-wire motor was the best design. Now we are talking true two- and three-wire designs without the required ground wire of today (where we have, in effect, a three-wire and four-wire arrangement). In the past, some manufacturers sold pumps that strictly had three-wire motors, and other manufacturers made pumps that strictly had two-wire motors. Each of these designs had – and still has – advantages and disadvantages. For many years now, most manufacturers offer both types of motors, and I am talking of domestic and commercial pumps in sizes of 1⁄3 HP to 2 HP, which I mentioned last time. To correct myself, I don’t believe any manufacturer offers a two-wire motor larger than 11⁄2 HP, although I could be mistaken.
The two-wire design has – and always has had – the advantage of simpler installation. I have even seen two-wire installations that used a lamp cord for the power supply to the motor control, usually a pressure switch. Actually, if the cord has heavy-enough gauge wire in it, there really is nothing wrong with this type of installation, especially on a 115-volt hookup. With the two-wire design, all the installer had to do was get the power supply through the controller and on down to the motor, and the unit was ready to go. If the motor controller was in a not-very-nice location – like a damp well pit or well house or indeed outside – this type installation had some attractive features. If and when service was necessary, the two-wire design again was much simpler, and the motor either ran or did not, whereas three-wire designs, coming in the next paragraph, were and are more complicated to diagnose if trouble occurs.
The three-wire design, on the other hand, uses a control box, which contains, among other parts, a starting relay, a starting capacitor and perhaps a running capacitor. The advantage of this design is that the motor is going to have more starting torque than a two-wire has, but the control box needs to be mounted somewhere. If we are in that damp well pit mentioned above or outside, the control box location is going to be a big problem. Control boxes don’t like dampness – or rain and snow for that matter. Now I am talking here of single-phase motors. If we are using a three-phase motor, we absolutely have to have a starter, and we have got to figure out a good location for it, no matter what.
One advantage a three-wire design has is that, many times, service problems can be fixed by repairing the controls. A burned-out starting capacitor and/or a bad starting relay will cause the pump not to operate. As these components mostly are plug-in, a few minutes time and the motor is fixed, and customer is back in water. If the service man decides to test these components before replacement, this can complicate things a little bit, but testing to see what really is wrong is what the good service man is going to do pretty much every time.
Strangely, I once got into a discussion with a very, very well-qualified sales representative who had worked for two really good pump manufacturers. He maintained that one of the big advantages of a two-wire motor over a three-wire was that the former either ran or didn’t, and if it didn’t, up went the boom of the pump hoist and out came the pump, either to be replaced or at least get a new motor. He said that you could justify to the customer a fairly expensive repair bill where you had to use a pump hoist, boom truck or other lifting device; whereas if only a repair of the control box was needed, it could be done with a few parts, very few tools and either a small pickup, car or even a motor scooter for transportation to the job site, and many customers would complain about the cost of the repair – something he maintained they would not do if you had to replace the pump. I have repaired hundreds – if not thousands – of control boxes in my career, and I have never had a complaint that the service was too quick or too expensive.
One last factor entering this two-wire vs. three-wire debate is that you can replace a three-wire with a two-wire easily, but going the other way is going to be difficult and expensive as you did not have the right wiring. Nowadays, just about all manufacturers offer both two- and three-wire pumps, and we only have a few motor manufacturers supplying the whole industry, so the old discussions, arguments and even fights are null and void. My position, having sold both types, is that both two- and three-wire pumps produce water, and eventually will fail no matter who made it and how it is installed.
Shirley and I attended the 2011 Michigan Ground Water Association Convention this week, and I must say, I came away kind of depressed. Compared to a few years back, we had far fewer exhibitors than we used to, and if memory serves me, we once had 22 rigs on display – this year, we had one. I can’t say this is anybody’s fault, but it sure is tough to see a small convention when we once had a huge one. It was good to see old friends, but some of them were not present due to health concerns, and a few had passed away since our 2010 convention. It seems our entire industry is down. Is this the way it is in your state?
In my monthly weather report, I can say that our snow has all melted. We had some days in the 60s this week, but as I write this column, we are having a nasty, sleety rain with a brisk breeze that makes it feel extra cold, and some bad lightning. Welcome to spring in Michigan. Until next month, work hard and safe, and remember your loved ones.
“Let Me Tell Ya”: More about Submersible Pumps
May 1, 2011