Mains voltage

[SUNRAY]

That would make sense, but Harry seems to be talking about oil, not air - and, of course, none of this has anything to do with my original comment about hollow transmission cables

Kind Regards, John

Someone mention hollow transmission cable?

A bit of aerial cable:

 

[JohnW2]

Someone mention hollow transmission cable?

Yep, that was me - in relation to large/long-distance cables, I though as a means of addressing 'skin effect' in such situations, even at 50/60 Hz.

A bit of aerial cable:

That coax is obviously intended for use at might higher frequencies than 50/60Hz, so skin effect is far more of a consideration.

As far as I am aware, there is no 'performance benefit' to be had by having hollow conductors. However, the higher the frequency gets, the more it becomes the case that the inner parts of the conductor are contributing little to the performance - so, for a given external diameter (or the same CSA) one gets much the same performance by making it hollow, but with it being cheaper, lighter and using less copper.

Kind Regards, John

 

[bernardgreen]

Skin effect at Ultra High Frequency

The underside of copper track on common fibre glass PCB substrate has a rippled surface due to the un-even surface of the substrate. The top of the copper sheet is by comparison flat.

UHF signals travelling along a PCB track take longer to travel along the rippled under side of the track than the same signal travelling along the top side of the track.

A UHF receiver designed to use glass flat PCB substrate was very sensitive and prototypes in the laboratory exceeded expectations.

Production items did not perform as well, some items had sensitivity about half that of the prototypes. Investigation discovered the production manager had not used glass flat substrate but instead had specified PCB material using bonded fibre. His reason was the problems of soldering on glass flat substrates. Poor soldering technique means the copper detaches from the substrate and thus yields were low.

 

[reds42]

Given unexpectedly clement weather today, I've attempted to get a better photo, in case you want to play with it.

I'm going to agree that it looks like X1.3 the diameter of a M20 bolt on the outgoing cables to houses making that a 35mm2 cable. The incoming cable to the post definitely looks much larger, and I still think in all likelyhood that is 95mm2, which to my mind would make sense given its feeding multiple houses.

 

[JohnW2]

I'm going to agree that it looks like X1.3 the diameter of a M20 bolt on the outgoing cables to houses making that a 35mm2 cable.

That's certainly still my best bet.

The incoming cable to the post definitely looks much larger, and I still think in all likelihood that is 95mm2, which to my mind would make sense given its feeding multiple houses.

Maybe. However, per the comments I made when I posted the new photo, you seem to have measured the larger cable in it's initial bit, where (understandably) it appears not to be 'tightly twisted', hence with an apparently larger size. Would your conclusions/speculations change if you considered the bit of the 'large cable' at the extreme right of the photo?

Of course, all of what we have both done is crucially reliant on the bolt being M20. Given the information you've found, that seems pretty likely but I have to say that, accepting that it is next-to-impossible to judge, by simply eyeballing it from the ground I would have guessed that it was less than M20 (which is a pretty large bolt, larger than most I normally deal with 'in my hands').

Unfortunately, there don't seem to be any other things up there to give a 'dimension reference'. The pole is slightly tapered, so the bottom measurement is no use. Is there any hope of finding sny information on the likley dimensions of any ofthe bits of metalwork up there?

Kind Regards, John

 

[bernardgreen]

Take some simple steps ( a ladder ) to get a definite answer with a micrometer

 

[reds42]

Maybe. However, per the comments I made when I posted the new photo, you seem to have measured the larger cable in it's initial bit, where (understandably) it appears not to be 'tightly twisted', hence with an apparently larger size. Would your conclusions/speculations change if you considered the bit of the 'large cable' at the extreme right of the photo?

I thought the extreme right was quite possibly in some state of twist that may not of given the view across the cable at its fattest dimension - hard to establish without more of the cable in shot. Also given that cable is moving backwards away from the post perspective could throw out the accuracy of the comparison with the bolt - it may appear narrower than it is further as you move away from the post. I thought by the time the cable got to the point I measured it would minimise perspective distortion and would likely be in its fully bundled form, although I appreciate the end towards the bracket is clearly splayed out a bit.

But yeah, as per Bernards suggestion a micrometer would certainly provide the definitive answer!

 

[JohnW2]

Take some simple steps ( a ladder ) to get a definite answer with a micrometer

That, of course, is what would ultimately be needed. However, quite apart from 'other' considerations (not the least of which being that I would have to 'trespass', a well as 'safety' ones), even getting a ladder up there would be far from easy, since there's a spider's web of telephone cables a few feet below the power ones!

Kind Regards, John

 

[JohnW2]

I thought the extreme right was quite possibly in some state of twist that may not of given the view across the cable at its fattest dimension - hard to establish without more of the cable in shot. Also given that cable is moving backwards away from the post perspective could throw out the accuracy of the comparison with the bolt - it may appear narrower than it is further as you move away from the post. I thought by the time the cable got to the point I measured it would minimise perspective distortion and would likely be in its fully bundled form, although I appreciate the end towards the bracket is clearly splayed out a bit.

Yes, you may well be right. I could try to get a photo of the cable more remote from the pole, but then it would not include the bolt - so, Bernard's suggestion apart, I don't know what more/else I could do.

Kind Regards, John