I agree totally with Gary. Common grounding point is essential to avoid voltage differences between equipment during a strike. When you get a strike the grounding point will rise, so you want to make sure everything that is grounded goes up together. As the leading edges of the voltages strikes are very sharp, low inductance grounding is important, so a large size cable or strip, smooth curves from the expected strike source to ground point and definitely no loops in those equipment ground cables. Covering every possible strike source, so ground kits on the transmission lines, surge protectors on tower light wiring, a main surge arrestor located at the incoming AC breaker or if you have a generator set at the AC entry before the Transfer panel. All Telephone lines or external T1's or control lines should have suitable grounded surge protectors. Transtector has a great line of AC & Telephone, T1 protectors and they have just merged with Polyphasor. They even have a web page with items approved for Motorola R56 installations.
The coax Polyphasor are really there to stop a high voltage developing between the center and shield. Thats just a small part of the problem. You need ground kits along the transmission lines, one at the top, one in the middle and one just before it enters the building, AC protectors, and a well grounded tower. All that will connect to common point to a good buried external grounding system using Exothermic Cadwelded connections with hopefully a less than 4 ohms ground resistance. A now you are all set to take on those strikes :) Peter On Wed, Aug 18, 2010 at 8:39 PM, Gary Schafer <gascha...@comcast.net> wrote: > > > Here is a little primer on lightning: > > > > Having your antenna grounded does not drain off any charge that helps > prevent a strike. As a matter of fact grounding the antenna makes it > slightly more prone to a strike but not grounding it is much worse as you > have no control over what path the energy will take if not grounded. > > > > When a storm cloud moves over the area charge builds on objects on the > ground. The ground items, towers etc start to emit streamers. When a strike > is imminent step leaders come down from the charged cloud and move in > approximately 150 foot steps. Changing directions with each step. When a > step leader gets close enough to a streamer a connection is made. What > follows is a plasma trail which is a very low impedance path that the > lightning charge follows. > > > > Lightning can be thought of as a current source. In other words if there is > a 10 KA strike it is going to develop that much current into whatever it > strikes. If for example it hits your tower and the total impedance to ground > is quite low then the voltage developed across the tower will be relatively > low. But if the ground system is not a good one then the voltage will rise > higher. It will still develop the 10 KA current. > > > > Bonding all equipment to a common point is one of the first steps to take. > Just adding a polyphaser coax protector to the coax line will only equalize > the current between center conductor and shield. If power is not protected > and everything bonded together the coax protector will do little good. Even > without a coax protector, just bonding everything is a great first step. > > The whole idea is to keep everything at the same voltage level when a > strike occurs. > > > > 73 > > Gary K4FMX > > > ------------------------------ > > *From:* Repeater-Builder@yahoogroups.com [mailto: > repeater-buil...@yahoogroups.com] *On Behalf Of *Tony KT9AC > *Sent:* Wednesday, August 18, 2010 9:25 AM > > *To:* Repeater-Builder@yahoogroups.com > *Subject:* Re: [Repeater-Builder] Polyphaser Question > > > > > > Remember the objective is not to take the brunt of a lightning strike, but > to drain off any static that would attract that strike. Lightning is just a > spark looking to close the gap, and if your antenna is closer to DC ground, > it will find something closer to its potential (i.e. static charged) to hit. > > Any protection is better than nothing, and don't scrimp on buying the > cheapest used protector. Its your equipment your protecting and potentially > avoiding liability. I buy new Polyphasers for our site and sleep just fine. > > On 08/18/2010 08:56 AM, wd8chl wrote: > > > > On 8/17/2010 11:55 PM, Ray Brown wrote: > > What do you do when you want to install a small UHF linking repeater on > > a 4-story building that has no lightning protection on its' roof? (this > is to > > link an ambulance at a hospital to its' base repeater 40 miles away) > > > > From what I've heard, it may not be a good idea to hook it to the HVAC, > > either. > > > > (sigh) > > > > > > Ray, KB0STN > > No. I would find the nearest copper pipe from either the in-house water > system or the sprinkler system, and clamp to that (making sure you don't > crimp the pipe!!!) using #6 or maybe #8 wire if it's REALLY close (less > then 5') > Again, not as good as a dedicated system, but MUCH better then nothing. > > > >
