I am part of a hobby project where we have a pair of fat, insulated #4 AWG stranded copper wires carrying +5V and ground. I want to tap into these wires every few inches to draw power off it (max draw of around 4A per tap), for a total of 24 tap pairs.

close up showing #4 AWG wire compared to finger tip

The 'best' idea I've had so far is sketchy: Drive some steel metal screws in through the insulation and into the center of the wire strands. Solder the connecting wires off of the heads of those screws, and eventually cover the heads in electrical tape or similar (to prevent people accidentally shorting across two posts).

Pan Head phililps metal screw

How much electrical loss would you expect from this connection? I'd prefer it if these were copper screws instead of steel, but the local hardware store does not have those. Is the resistance of steel negligible given the short travel distance?

Do you have a better suggestion for tapping into this wire? The best 'correct' solution I've found for an insulation-piercing tap that will handle #4 AWG appears to cost $15 for each tap. Since I need 48 taps, this path would be prohibitively expensive.

  • \$\begingroup\$ lookup busbars, vtewarehouse.com/downloads/catalog/VTE-18-Busbar-High.pdf \$\endgroup\$ – sstobbe May 22 '17 at 15:55
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    \$\begingroup\$ I'm inclined to ask why you're using high-current low-voltage power as opposed to local regulation. In any case, I'd strongly recommend using proper insulation-piercing taps if you need high current. I wouldn't trust the connection made by a screw into a wire. Can you switch the wire out for a busbar maybe? \$\endgroup\$ – Hearth May 22 '17 at 15:56
  • \$\begingroup\$ @Felthry I appreciate the busbar suggestion, but the taps have to be distributed at specific points along a 9+ foot long curved path. \$\endgroup\$ – Phrogz May 22 '17 at 16:00
  • \$\begingroup\$ Soldering to steel screws is going to be tricky. \$\endgroup\$ – Jack B May 22 '17 at 16:00
  • \$\begingroup\$ Busbars can be bent or made curved, and you can drill+tap into them at any point \$\endgroup\$ – pericynthion May 22 '17 at 16:01

That's a problem I have faced too and I solder taps and coat with polyurethane sealant (hardware store tube) for outdoor 10W LEDs along fence.

I have used 3mm bolt/nuts and crimp lugs for <5mohm on interior chassis instead of a paint masked welded grounded lugs with star washers which got UL approval.

IDC connectors are hard to find and not reliable outdoors.

Zinc plated steel and copper straps will get galvanic corrosion eventually unless air tight seal (polyurethane). What about brass screws?

I use to test with 10A load and measure voltage drop to measure initial resistance of contact.

Corrosion is inevitable and depends on climate.

i think self tapping screws with self-tapping washer? (or piece of 1/8th FR4 with a hole to act as a compression nut, then grind off tip and air tight seal.

Automotive uses water tight connectors for headlamps etc. which are good for servicing loads.

Let me know what you end up with.. I use AWG16 solid round copper, but your cable is better but braid will stretch and screw pressure will relax braid and force air in, which is why I suggested compression nut to self tapping screw. Robertson style. with crimp or solder lug of suitable shortest length,screw. unless you have a better way less labour intensive.


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