[ARC5] Troubleshooting Tips from the Late Nick Broline, #3

[Christopher Bowne]

Thanks for all these tips!  I only recently became aware of the availability of “whole house” MOV protectors that can be installed across the incoming power line in one’s circuit breaker/distribution panel.  Super easy to install - 4 wires  - to neutral, ground, and to each hot side of the incoming 240 via a spare circuit breaker.  

We once had the pole pig across the street from the house take a lightning strike that caused a lot of damage to loads that were on service during the strike - blew
up light bulbs, a clock radio, and the refrigerator.  And blew out a hole around the ground rod at the service entrance about a foot in diameter. According to my wife (I was out of town on work travel at the time), the concussion of the thunderclap actually made window shades that were pulled down wind up all over the house, just like in a horror movie. Luckily, this happened in mid 80s, before we had any really expensive electronic stuff in the house and Diane had gone around and unplugged or turned off as many loads, including my ham gear,  as possible in advance of what sounded like was going to be a whopper of a storm when it came through.

If you buy one of the whole house protectors, make sure they have enough lead length on the attached connection wires. The GE one I bought had a only a very lqshort neutral pigtail that would have required making a spliced connection to add enough length to reach the neutral bus bar within the circuit breaker panel.  I ended up returning it and went with one made by Square D.

73 de Chris AJ1G
Stonington CT

Sent from my iPhone

> On Jul 10, 2023, at 22:22, David Stinson <arc5 at ix.netcom.com> wrote:
> 
> Choosing MOVs to protect your power supplies:
> 
> This is a long treatment of what you are asking for in your MOV selection.
> Depending on how your MOV manufacturer specifies the device, it may not be
> what you want.
> 
> Your 122V power system has a peak voltage of 1.4 x the rms value (122V)l, or
> 173V.  This peak voltage should be the voltage used in selecting the MOV.
> One with a lower rating would mean it would be attempting to conduct on the
> peak of every half cycle.
> 
> Looking at an offering from the Mouser catalog for the Bourns MOV products I
> see they have provided application assistance by specifying the RMS voltage
> design center, the DC hold-off voltage, then more data that gives us insight
> as to how they turn on, or start conducting, and how hefty it is.
> 
> Their line for part number
> MOV-20D201K is called a 130V rms MOV that can operate across a 170V dc
> source without drawing significant current.
> Continuing down the listing, they specify the voltage at which it will draw
> 1 ma: 185V min, 200V nominal, and 225V max. Now we can see these are not
> precision voltage devices, so we need to select one with some "elbow room"
> at the top voltage. They do no go to full conduction at the threshold
> voltage, either. They turn on gradually Increasing the voltage just causes
> them to draw incrementally larger currents, and the voltage across them also
> rises. Note that the lowest threshold voltage at 1 ma. is comfortably below
> your peak line voltage.
> 
> MOV's are not anything like back-to-back Zener diodes, which will have sharp
> knees at turn on. They would certainly try to clamp a transient at their
> rated voltage.....once......unless one uses very large honkin' diodes. For a
> transient like a lightning strike somewhere distant from the protected
> product they would clamp the transient once, then possibly be destroyed by
> the peak energy they are subjected to. Most likely they would short, and
> that would blow the fuse.
> 
> MOV's are designed to take such transient "on the chin" and continue
> protecting without destroying themselves.....but they are limited in the
> number of times they can do that, and that is normally not a problem. A good
> way to think of them is their ability to absorb a relatively large amount of
> energy instantaneously and will draw a very high peak current (6500 A in
> this part number) for a few microseconds in the process. This makes them a
> good and cheap circuit protector that knocks off the sharp edges of
> transient waveforms.
> 
> The product I used as an example is about 1" in diameter and is a fairly
> typical size. It looks like it would be a suitable selection for your needs.
> 73
> Nick Broline W5FUA
> 
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