FAQ - High voltage wire and cable

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Richard Hull
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FAQ - High voltage wire and cable

Post by Richard Hull » Thu Feb 06, 2014 4:11 pm

Old televison anode wire is often rated up to 30kv with 20kv being the norm and is still somewhat commonly available from electronic jobbers. It can also be snagged from old color televisions, but rarely is over 12-18" long when clipped off its flyback and anode cup. Other selections of HV wire are also available from electronic suppliers. Demo fusors would utilize this sort of wire.

Once you hit 30 kv, used in real fusors, common industry standard HV wire becomes a specialty item. Silicone "noodle" wire, (super flexible), to 80kv is found but extremely expensive and un-shielded. The preference and "good practice" cabling above 60kv is always shielded and always rare and always very, very expensive. Industry standard connectors for voltages at this level are exceedingly expensive. A cable of 12 feet in length with proper NEMA rated plugs for 80kv would easily cost $600.00.

Proper HV rated shielded cables above 40kv are usually very heavy and very stiff due to a hard Polyehtylene core insulation.

I have used hamfests and other surplus sources for years to obtain HV wire up to 125kv rating for just a buck or so per foot. Yes, you have to luck onto the purchase.....Yes, you have to know what you are looking at to see and recognize it. The moment you want to single source the stuff and demand specifics from a dealer you are looking at big dollars per running foot in the most ruggedized forms and large minimum orders when you only need a few feet.

RG-8 is a common RF cable commonly pressed into use as HV cable for DC, but it is struggling against high tension break down at 40kv....You could push it, I suppose.

Here is what Spellman has to say about RG-8U RF cable use or mis-use in their AN-07 tech blurb.........

....."RG8-U has long been used as a high voltage output cable in the high voltage industry. There is a variation of RG8-U that utilizes a solid polyethylene core. Specifications for this cable do not specify actual "high voltage" ratings, since this cable was not designed and fabricated with high voltage usage in mind. So the reality is, there are no high voltage ratings for RG8-U. Over the years others in the HV industry have used this cable at 20kV, 30kV and even higher voltages. Spellman does use RG8-U cable, but limits it usage to applications where the maximum voltage that will be applied to the cable is 8kV or less.".....

You should not push this cable to extreme limits in fusor use. You need good cable rated for your voltage used. I would rate the fairly inexpensive RG-8U found at hamfests as fine for demo fusor use up to 20kv max.

As an engineer I approached Dielectric Sciences in a phone call this morning and asked for pricing on their 100kv rated, # 2121 cable and was surprised at the relatively low price per foot of $7.00!.... SNAG!!!.... If you are not ready to buy 50 feet as a very minimum basic order, please don't call us again! So... $350.00 plus shipping and you have your cable. Certainly, more than you need. This is not being nasty, It is an industry norm and serves to keep out the Tiny Tim players.

Get out and go to hamfests and surplus stores. E-bay even has the stuff on occasion.

Last year, I saw a 20 foot length of the nastiest cable I have ever seen laying on the ground at a hamfest. The key was it was a filthy gray color with oil and dirt caked all over it and was one inch in diamter. I picked up one end and saw a filthy white silcone interior with about an 18 gauge central, stranded conductor core and a braided shield in a doubled outer layer. I knew immediately what it was. I asked, " how much for the dirty cable"? The guy noted there was a lot of copper in it. I told him that I doubted if there was much more than two pounds in it. He called out $10.00 and I handed it over. I got very dirty just carrying the big heavy cable back to my car. Fortunately, I had a roll of paper towels in the trunk. Thirty or forty paper towels later the wire was mostly grime free and just barely clean enough to put in my trunk. Once home, another 30 minutes or so with bathroom tub and tile spray cleaner and some WD-40 revealed the cable was a beautiful battleship gray with markings reading 100kv - X-ray cable on its jacket. While few people on the earth's surface can use or even need this cable, I got it for about 1/50th its new cost. It is coiled up in my lab awaiting fusor V construction with my 85 kv supply.

Don't bypass filth, oil and nastiness..... Search... Investigate... Be able to "see at sight" and you will save, big time.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: High voltage wire and cable

Post by John Futter » Thu Feb 06, 2014 5:52 pm

Richard
Well done. Glassman use RG8 type cable to 70kV. We use it at work to 80kV BUT!!
We use RG213 which is a tight spec version of RG8, most of this spec tightening is due to much more care in keeping the inner perfectly concentric with the shield hence the RG213 spec gives 50 ohm +-2 ohms.
The maker of the cable also matters and we use the Swiss Huber Suhner RG213 it has lower leakage than the cheaper cables typically found hobby and ham outlets

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Re: High voltage wire and cable

Post by Richard Hull » Thu Feb 06, 2014 10:19 pm

I am positive I used RG-213 on a large Tesla coil primary. Is this cable double shielded silver plated stuff? That was the primary coil stuff I used prior to making Nemsis. (shorted the shield to the inner conductor.) I bought a 100 foot roll of the stuff at a hamfest back in the early 90's for a few bucks. I know it is normally wicked expensive.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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