[TowerTalk] Rotator Cable Protection

[Lux, Jim]

On 10/18/21 6:05 PM, Michael Tope wrote:
> Hi John,
>
> Yes, I understand about the lack of shields on most rotator cables. 
> That is in part what prompted my question. It seems like the rotator 
> cable is "the elephant in the room" when it comes to grounding and 
> bonding. When you consider the cost of a rotator, especially some of 
> the larger ones designed to turn large HF arrays, it seems like it 
> would be something important to address.
>
> By the way, what has your experience been with the reliability of 
> having MOVs up on your tower(s)? I am asking in part because I am 
> helping with an installation that sits on a high ridge where the 
> rotator is controlled via 1700ft of heavy duty control cable (multiple 
> 12 AWG conductors), which in this particular case, happens to be 
> shielded. I am trying to decide whether bonding the shield at the base 
> of the tower and up at the rotator will be sufficient, or whether 
> adding some transient protection at the rotator and/or the tower base 
> is warranted. Climbing the tower is a PITA, so I don't want to include 
> transient suppressors that need frequent replacement (facility rules 
> require that we hire a professional tower climber to service anything 
> on the tower that can't be reached from the ground).

Exactly - say you put your transient suppressors in a box at the base of 
the tower.

BTW a good reason to not use MOVs, since they "wear out".


the motor is probably good for several kV overvoltage - even if you 
punch a hole in the insulation from a transient, if it's running at 
normal voltages, it doesn't cause a problem.  I had a problem with some 
5 and 10HP motors run off electronic variable speed drives. There's an 
issue with these drives (of some vintages, 20+ years ago) where there 
can be transients. That punches through the insulation - the motor runs 
fine, but it trips the ground fault protection.



>
> 73, Mike W4EF.............
>
> What has your experience been with MOV reliability?
>
> On 10/15/2021 8:05 AM, john at kk9a.com wrote:
>> Rotator cables typically have no shield to bond to the tower. I use MOVs
>> near all of my rotators to protect the motors and potentiometers.
>>
>> John KK9A
>>
>>
>> Michael Tope W4EF wrote:
>>
>> Jim, et al:
>>
>> What about control cables coming down the tower? I just skimmed through
>> the first edition of Ward's grounding book. It recommends bonding the
>> coax shields to the tower, but doesn't say anything about control
>> cables. Typically there is a least one rotator control cable in the mix
>> and oftentimes additional control cables for array switches and multiple
>> Tic ring rotators on larger more sophisticated installations. That seems
>> like an inconsistency, no?
>>
>> 73, Mike W4EF...........
>>
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