By Dink Stockert, WA5LNL1

This AC Over-Voltage Protector [OVP] is designed to protect your repeater from spikes and over-voltage [lightning] coming in from your AC utilities. The OVP is good for 15 to 20 amps at 120 VAC. The OVP box is equivalent to a PolyPhaser power line protector  [pldo-120us20a: about $350].

Construction inside a metal box is best. A #6 solid copper wire should attach to the box to earth ground to make it work! The OVP is made to hang on the wall, then feed your repeater cabinet. Use a copper (Cu) lug, remove the paint under the lug and apply a layer of Noalox anti-oxidant joint compound under the lug. Please see the photos for construction details.

Inside your repeater cabinet you should have another power strip (maybe an Iso-bar) with OVP. Always have more than one protector in series. All wiring should be done with #12 copper. The AC cord should be a minimum # 12 gauge. The main coils are wired on 1/2"dia. PVC pipe x 8 1/4" long with 2" screws to hold off the coil forms. Wind 59 turns of #12 Cu and leave extra wire at each end for hookup. Use the 130vac 23mm size MOVS.  Mount (2) MOVS* per leg [H to N, N to G, H to G] and (3) MOVS on the output of the EMI filter.

The EMI filter needs to have a [bare]  #12 cu. wire soldered from its metallic case to ground. Fusing at 15A would be better than 20A if you do not need the extra power. Making coils [5 to 7 turns, 1/4" diameter] with left over wire between hookups never hurts. Lightning gets dizzy in the coils and quits!

 Total costs =$52.50  +\ - your junk box parts

 *MOVS wear out with time and even faster with only minor spikes. So if you are using an OVP that is 5 years old and not blown up; change the MOVS.

Transzorbs do not wear out and clamp voltages accurately with no over shoot.

If youve got the bucks, you can substitute a General Semiconductors Transzorb [#587b151, 15A, which will blow a 15A fuse (and not blow up)




  1. 1    Pull-Box, 10"x10"x4", Hubbell SC101004,  [Lowe's]

  2. 1   2-socket, surface-mount steel electrical box   [Lowe's]

  3. 1   Steel outlet cover  [Lowe's]

  4. 1   Dual 20A AC outlet, gray color – commercial grade  [Lowe's]

  5. 1   AC cord +plug #12 gauge (Buy an extension cord and cut the outlet off).

  6. 1   15A/20A ceramic 3AG fuse + fuse holder [Hosfelt, 31-774, 342014A]

  7. 1   EMI filter, 20A     [Hosfelt 927-188]

  8. 2   Capacitor, .01uF @ 1.6Kv [Digikey 495-1372-ND]

  9. 1   17 in.  PVC, 1/2"  [Lowe's]

10. 2   Ground lugs for #6Cu.   [Lowe's]

11. 1   AC wire clamp  [Lowe's]

12. 1 1/2" steel nipple and 2 nuts to secure outlet box     [Lowe's]

13. 1   Yellow wire nut   [Lowe's]

14.  4   RF Chokes, ~ 0.12 mH; 7 turns  #12 insulated solid copper house wire, wound on ¼ drill. (L1, L5 black wire, L2, L6 white wire)

14.  2   RF Chokes: ~ 10.24 mH2; 59 turns #12 insulated solid copper house wire, wound on 13/16 o.d. white PVC. (L3 back wire, L4 white wire). 22 feet of wire required for each coil.

15. 22 ft. white #12 Cu solid wire [Lowe's]

16.  9   MOVS :130vac/150vac, quarter size,23mm [Hosfelt V150LA20B]

17.  Optional General Semiconductor Industries Transzorb # 587b151 (15A), or 587b201(20A)  [Arrow]


Figure 1. An AC Overvoltage Protector



Hosfelt; Electronics, Inc.

Arrow Electronics, Inc.

Digikey, Inc.              




1 Consultant, Intertie, Inc.


2         Inductance values nominal, calculated as air core inductor, using formula, page 6.22, ARRL Handbook 2001. American Radio Relay League, Newington, CT  06111. Permeability of PVC pipe was not considered.

Copyright November 10, 2004, Intertie, Incorporated. All rights reserved

Revised: 02/12/10 by KC5PIY, Webmaster.
Copyright 2003 by Intertie, Inc. All Rights Reserved
No use of these symbols or phrases is allowed without the express written permission of Intertie, Inc.