Word to the wise: this one had aluminum lugs on it. That might not be the best of ideas. Eventually, they start to get, well, melty. This would be bad anywhere but it's worse when they're a fifth of a mile away. A fifth of a mile, straight up.
BUILDING A 1:1 BALUN
4 years ago
12 comments:
That sort of thing honks me off, big time: The device pictured needs to be RELIABLE, most of all. Saving a few pennies during its construction makes no sense at all. If you're building them by the millions (automobiles) you need to look at every penny, but this thing is built by the dozens and is only slightly less easy to service than the Space Station, so you shouldn't fool around with the design and construction. Looks like a furnace man built the box: they couldn't have used a Hoffman enclosure?
Definitely looks like something in need of a nema 4x enclosure.
The two heavy cables going out through separate openings on the right side of the box look like a potential violation of NEC 300.20(B), that wants all conductors of a single circuit to pass through the same opening to prevent inductive heating. The metal between the holes makes a transformer with a shorted turn. If it has to be done, cutting a slot between the holes or using a non-metallic panel eliminates the shorted turn. I can't tell if the slot is there or the side panel material, so it could be fine, but the color change in the panel between the two openings makes me think it might not be...
wv: yboomes called
Jim D., JayNola: It's a NEMA 4X box, after 35 years in the air.
Jim R: It presumably wasn't in 1980... Also, how do we weatherseal them and/or the slot, exactly?
Oh... NOT good!
Roberta: What is the output voltage? From the output leads, (I'd bet <120amps)... Input at 480V X 12A, so what, 48-60 volts?
Just wondering.
The slot only needs to be a hacksaw width - it may be sufficient to run a bead of caulk along the hacksaw slot. That doesn't eliminate the cable clamps or locknuts, each of which is also a shorted turn around the conductor, but the Code doesn't seem to address them - just the enclosure or raceway.
The best solution would be to run both of those conductors through a single hole. McMaster carries multi-cord cord grips that might fit the bill:
http://www.mcmaster.com/#55595K4
I'm not an electrician, but I've had occasion to look at a codebook from time to time.
Jim R., I very much appreciate the input, but these have worked okay since 1980 and most kinds of caulk have a limited life in the environment where they are installed. The original engineering was by RCA -- and the the last time someone tried to out-engineer 'em, we ended up with aluminum lugs. :)
B: 24 VAC at -- and I haven't had the guys put a meter on it -- some 260 A.
Hmmm.
Some telcos had a solution to weathersealing.
They literally put the object into an upside down kettle, with the openings cut into the lid, underneath.
Use gravity to keep the damned weather out.
I guessed wrong on the wire size then.
B
So is this the heater thing from the other day or some other part?
This is indeed that heater thing, or one of the three transformers that do the work. The antenna is made of very large stainless steel wire, in three sections with a quadruple helix over thirty feet tall in each one, and the transformers heat them up. It's just about exactly as crazy as it sounds.
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