I have 4 stud M8 (5/16”) Bus bars which connects 4/0 and 3/0 copper lugs from the LiFePo4 batteries (2.5 kWh) and Inverters 2.6 kW split phase off-grid).

I wanted to know what can I use to clean the contact area with properly. Is 99% isopropyl alcohol sufficient?

Also, what should be the torque spec for the 4/0 and 3/0 lugs using an M8 nut?


  • That info comes with the bus bar / box etc
    – Solar Mike
    Nov 12, 2023 at 8:57
  • Unfortunately, it didn't.
    – Rick
    Nov 12, 2023 at 9:00
  • 1
    Should definitely be on the mfgr's web site, if not printed on the devices.
    – FreeMan
    Nov 12, 2023 at 12:28
  • This is imported Chinese junk -- the manufacturer does not have a website or apparently even a name, and you can find the same item listed under multiple bogus seller names in different places. I would be somewhat wary of using it, although really how do you screw up a bus bar. One of the listings describes it as nickel plated brass; I wouldn't trust that too much. Nov 12, 2023 at 21:08
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    @GlennWillen Based on the picture I'd worry most about flatness and smoothness. If it's not flat and smooth, contact surface may be reduced.
    – vidarlo
    Nov 13, 2023 at 0:44

1 Answer 1


For copper, cleaning is not that crucial. Alcohol is just fine, as it removes fat. So is any other solvent that removes fat. In general I've never cleaned mating surfaces unless there's visible dirt.

For torque, either look up the specific lugs you have - or go with a generic value. For generic value, I'd simply go with European DIN standard, as I'm located in Europe, and it has values for M8. Copper on copper is not as critical as aluminium.

  • The lugs appear to be copper but the bar is definitely not. One listing claims it's nickel plated brass, which is plausible but I wouldn't trust it to be accurate. Nov 12, 2023 at 21:09
  • Should not be important. The torques in the DIN standard doesn't reference mating material, only lug material - which is copper.
    – vidarlo
    Nov 13, 2023 at 0:43
  • Would you recommend I use a 20mm stainless steel flat washer on top of the lug, the split washer, and then the nut? What about using an anti oxidant like noalox?
    – Rick
    Nov 13, 2023 at 15:42
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    The PDF I linked to shows how the relevant DIN standard suggests it should be laid up, with spring washers. As the lug is unplated copper, a layer of terminal grease could be applied to stop oxygen attacking the Cu surface.
    – vidarlo
    Nov 14, 2023 at 16:05
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    "Oil" or "grease" might make more sense than "fat" here. In common English fat has no relation to electrical components.
    – isherwood
    Dec 12, 2023 at 16:21

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