Once again, the right tool for the job

I witnessed an interesting debate this week within a small group of Franklin Electric’s Field Service Engineers. The topic was enclosure knockouts. Franklin Electric now offers some VFD accessories (reactors/filters) that are available in NEMA 4 enclosures that have no knockouts. That is, the conduit holes must be made by the installing contractor. Of course, a special hole saw or scoring tool is required to do this.

On one side of the table, the position was that the vast majority of water systems contractors don’t have these tools, and therefore we are not giving the customer what he wants. It’s up to us, the manufacturer, to supply enclosure knockouts across all water systems products.

CaptureHowever, on the other side of the table, a couple of others took the position that these products are going into higher end, sophisticated installations. As a result, many of these enclosures will be installed by the electrical contractor and this is their preferred method. They make conduit holes in enclosures as standard procedure and always have the tool kit to do it. This way, they can always cut only the exact hole sizes they need for the cable and Romex seals. And it leads to a better-sealed NEMA 4 installation since you don’t have to worry about water entry via the unused knockouts. Their position was that if a contractor is installing these enclosures, they simply need to invest in the right tool to do the job.

I was seeing both sides of the issue until I posed the question of, “So, how much is the tool and how long does it take?” The answer came back as, “Oh, probably less than $50 for a single and maybe $300 for an entire kit of several sizes; in terms of the actual process, just a few minutes”.  For me at least, that settled it, although it probably didn’t settle it with the entire group. Once again, as a professional contractor, you need to have the right tools to do the job. It’s especially true if that tool is a minimal investment that can lead to a higher quality installation.

Geothermal and current loops… it all comes around

These days, quite a few of you are installing closed loop geothermal systems. These systems use long loops of flexible pipe installed underground or underwater to heat or cool a building or residence. Of course, a pump keeps the fluid moving around the loop.

Now jump to variable speed, constant pressure water systems. If you are involved with these systems, especially larger ones, you’ve probably seen or heard the term “4 to 20 milliamp pressure transducer” or “4 to 20 milliamp current loop”. These are loops as well, but loops of electrical current instead of water. And once again, it’s terminology that gets thrown out there without much explanation. So, let’s explain.

Many variable frequency drives (VFDs), especially larger units such as Franklin Electric’s HPX, utilize these 4-20 milliamp loops in conjunction with a pressure transducer. “Transducer” is just a general term for a device that converts a mechanical measurement into an electrical signal. In our case, that parameter is going to be pressure, And, keep in mind that you’ll hear the terms transducer and sensor used interchangeably in our industry.

A small power supply in the drive sends out a low DC voltage to the transducer. In the case of the HPX, its 24 volts DC. These are the “4-20 mA” terminals on the HPX. In our geothermal system, this would be the pump. Two wires connect the power supply to the transducer. This makes “the loop” or the flexible pipe. The transducer then limits the amount of current passing through it based on the amount of water pressure it is experiencing. For example, the 4-20 mA transducer used with the HPX will allow 4 milliamps to flow if the pressure is 0 psi. The upper limit of pressure can be programmed into the HPX, and at this pressure, say 80 psi, the pressure transducer will allow 20 milliamps to flow. Hence the name 4 to 20 milliamp current loop. The VFD controller then knows exactly how much pressure is out there by the amount of current “in the loop”. Continue reading