Monday, March 07, 2005

The Polyphaser PLDO

The Polyphaser PLDO-120US15A Inline Impulse Suppressor is designed to protect equipment power circuits from large voltage surges. I am using it in my ham station in connection with a "single point ground" system to protect against lightning surges. The Polyphaser catalog does not give design details, but I wanted to know just how my equipment is going to be protected. Here is what I've found to date. (Click for more detail on photo.)


PLDO-120US15A Photo


The unit is solidly built. I traced the schematic: (Click for more detail.)


PLDO-120US15A Schematic


Most of the protection comes from MOV devices that begin to fire above 130 V. The inductors, by rough estimate, are about 1.2 ┬ÁH. That converts to 15 ohms of series reactance at 1 MHz. If the second stage MOVs are in conduction, the inductor should provide a significant voltage drop. The series resonance of the two inductors and the capacitor is at about 400 kHz.
I am puzzling over the handling of the system grounds. The AC ground connection naturally goes to the PLDO case, which will bolt onto my local ground plane - where all the surge arresting gear is to be mounted. The AC ground is carried back about 30 feet to the AC service entrance. From that point to a solid earth connection (water pipe entrance) is another 40 feet or so. [I believe this is according to code. The situation is complicated by the location of the house on granite ledge, which rules out a driven ground rod.]
These ground paths go through the crawl space under much of the house. The ham shack antenna feed entrance and ground plane are on an exterior wall, with a possible earth ground only a few feet away. On the one hand, we shouldn't have the radio ground system with a separate ground from the AC, but on the other hand, that AC system "ground" is rather inductive and lengthy compared to a direct ground near the radio room.

1 comment:

Anonymous said...

There is nothing to be puzzled about, if you want effective earth grounding you need to locate the shunt-type protection device in the vicinity of a suitable low impedance earth ground strap+spike at the edge of the foundation.

In other words the site and location of the power coupling may need to be moved, these are simple physics requirements and the device cannot move your gear for you so it does what it can.