Splicing high voltage wire.

Discussion in 'Amateur Radio Amplifiers' started by N4ZAW, Apr 20, 2021.

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  1. N4ZAW

    N4ZAW Subscriber QRZ Page

    I have my SB220 back on the bench, and just noticed the high voltage secondary wire of the plate transformer going to B+ read "RG58U" on the side of it!!! So naturally, I proceeded to rip it out of there, only to discover someone had spliced the original wire and used a length of outer jacket from a piece of RG58u to insulate a previous splice.. The splice was also heatshrink insulated underneath the rg58u jacket.
    The original (it looks like the old asbestos type) coming out of the transformer is about 2 inches too short.
    At least whoever did this was smart enough to sheath the two secondary wires with some 40KV PTFE "conduit" for the entire length run. I plan on reusing that nice sheath. Anyhow, while I wait for the replacement HV rated wire to be delivered, is it kosher to splice HV wire in the first place? And is there any special procedure for this?
  2. SM0AOM

    SM0AOM Ham Member QRZ Page

    Generally, splicing HV wire is OK as long as some basic precautions are observed.

    Usually, just one insulating layer is not sufficient so at least two high-grade insulation barriers
    of PTFE or similar grade should be used, one could be a PTFE sleeving over the splicing point covered by another piece of heat-shrink tubing.

    The use of the PVC outer covering from coaxial cable as HV insulation should be avoided.
    PVC, and especially the coloured variants, is not intended for HV use. The pigments may be somewhat conductive and cause local breakdown or arcing.

    For really high voltages, above 5-10 kV peak or so, sharp edges on solder joints may cause field concentrations and arcing. It is advisable to always aim for smooth joints and surfaces.

    KB0MNM, PY2RAF and N4ZAW like this.
  3. W3SLK

    W3SLK Ham Member QRZ Page

    I would see if you could find some good non-resistive HV automotive wire or wire used for ignition on a furnace or neon sign. I believe that is good to 20KV. Karl-Arne makes a good point. So long as a load remains on the line and the voltage doesn't exceed 5KV you should be able to use a 'good' splice, (I will leave that subject to interpretation!). I have plate transformers with 2500VAC on them running in proximity to ~1/4-3/8 of an inch without any issues
    N4ZAW likes this.
  4. NG1H

    NG1H XML Subscriber QRZ Page

    The HV wire used in amateur amps is relatively cheap. In the $10-20 range.
    KU3X likes this.
  5. N4ZAW

    N4ZAW Subscriber QRZ Page

    Yes, it's ordered and on the way.
    I appreciate all the input from everyone here, and will follow the good advice. I realize it's kind of a stupid question on it's face. After all, power providers splice HV distribution cables all the time. and this amplifier has had no obvious difficulty with it's existing makeshift splice. But I wasn't 100% sure, given this particular application.
  6. W9WQA

    W9WQA Ham Member QRZ Page

    if it cant touch anything you could let the bare splice just hang there. it aint going anywhere.
    keep the covers on so kids cant play there...

    waaayyy too much wooorryying goin on here...
  7. W1QJ

    W1QJ Ham Member QRZ Page

    The AC voltage is only about 1100vac so many types of wire will work and if the splice is covered with layers of heat shrink it could add up much higher than the 1100 volts.
    N4ZAW likes this.
  8. WA4SIX

    WA4SIX Ham Member QRZ Page

    Each layer of Home Depot heat shrink is rated to 600VDC. You can get higher rated if you go to Mouser or the like.

    N4ZAW likes this.
  9. WQ4G

    WQ4G Ham Member QRZ Page

    Pieces of HV wire can be found in the Anode Circuits of old Microwave Ovens. Sometimes old Microwaves can be had for a few dollars. Last one I bought to rob the wire from was $5.

    N4ZAW likes this.
  10. KU3X

    KU3X Ham Member QRZ Page

    Last edited: Apr 21, 2021

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