[TowerTalk] Lightning Protection for Orion Rotor

[Jim Thomson]

Date: Sat, 24 Dec 2016 20:17:43 -0800
From: Grant Saviers <grants2 at pacbell.net>
To: john at kk9a.com, towertalk at contesting.com
Subject: Re: [TowerTalk] Lightning Protection for Orion Rotor

MOVs provide overvoltage protection but have a downside as they degrade 
with every snubbing shunt and eventually fail.  On an AC power strip, a 
failed to short MOV burned up a nearby ham's shack here when the plastic 
power strip case ignited.     If on antenna control lines, sufficient 
degradation can be experienced over time to prevent normal operation.  
As one antenna manufacturer discovered before they switched to TVS  
diodes.  Of course any transient suppression device can be vaporized 
with sufficient power surges, but some pretty hefty capacities are 
available.
http://www.littelfuse.com/products/tvs-diodes.aspx

Grant KZ1W

## Which is why a lot of MOVS  come with an internal fuse built into them.  These
types have 3 x leads. The 3rd lead is slightly offset  from the mid point between the
2 x main leads. Done that way so the MOV can not be inserted into the PC board backwards. 

##  Fuse is in one leg of the standard MOV.. but internal to the MOV.  They tap the output junction of
the fuse.. then  wire to the 3rd lead.  There is 120 vac on that 3rd lead...which activates the red led
on the better quality power bars.   IF the MOV eventually shorts out,  from one too many hits, the
internal fuse will open off...and with no 120 vac on output of the fuse, the led will also go out. 
That tells the end user, he no longer has any protection available. 

##  Movs are great, but they should be fused.   The fusing can be done external..done all the time. 
You see this done on the main 200A panel in homes.  We used the 208 3 phase version at the telco
I worked for, with 3 x huge hockey puck sized MOVS,  one per phase, and each with its own fuse.
Output of fuse was wired over to both a Neon... now a led used these days.... and also the 120 vac
coil of a 4PDT mech relay.   If a mov shorts out, neon  or led also goes dark..and the  normally operated relay
drops out, due to no more coil voltage.   With relay dropped out,  contacts close, and that puts a ground to the
alarm gathering  point.    Then the alarm can be seen at a remote alarm monitoring center. 

##  of course, when the commercial AC power goes off  for any reason, like a fallen tree etc,  ALL the neons
-leds will go out... and all 3 x relays  will drop out.... bringing in the same alarm....... failed lightning protection.
No big deal since the incoming power to main panel  is also alarmed, so it too will go into alarm. 

##  Plenty of house fires  started by  shorted... UN fused  MOVS in everything from power bars to you name it. 
Sad really.  You install a device thinking it  will protect the delicate equipment, but after successive hits, it eventually
shorts out, creates a ton of heat, fire starts, meanwhile the 15A  breaker in the panel  never tripped. 

##  any of these devices will work, but use the correct sized..and type of fuse for them. 

Jim   VE7RF