[TowerTalk] Rotator Cable Protection

[Michael Tope]

At a minimum, I'll try to bond the shield at the top of the tower and at 
the base. I am going to put some terminal blocks in the big metal 
cabinet at the base of the tower, so it will be easy to easily splice in 
whatever protection is deemed prudent. If I could climb the tower 
anytime I wanted, I would consider putting some protection right at the 
rotator, but given the circumstances, I may elect to keep that end as 
simple as possible and hope for the best.

73, Mike W4EF...............


On 10/18/2021 8:07 PM, Lux, Jim wrote:
> 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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