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My new whole-house surge protector comes pre-wired with four 12 gauge stranded wires 36 inches long.

Should the wire ends be tinned before installing to terminal bars and breakers?

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4 Answers 4

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Wires should NOT be tinned before connecting to breakers and neutral/ground bars. Tinning actually can mean a few different things - preparation for soldering, applying some sort of coating prior to making a permanent connection, etc. But normally you don't do anything to stuff that goes inside a breaker panel unless specifically authorized by the manufacturer. If it isn't in the instructions, don't do it.

One thing that is often done is to apply anti-oxidant paste - e.g., Noalox - when installing aluminum wires. As far as I can tell, surge protectors normally come with copper wires. Just torque to spec and you should be fine.

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I assume this unit is UL listed. Given that, the correct thing to do is follow the manufacturer instructions as written. Don't add steps. The instructions provide you with the installation method that was used for the safety testing and certification. If you add steps you're second-guessing the engineers who came up with the product and the engineers who tested it.

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No. I'm sure the instructions don't suggest that, and you need to follow the instructions, as written by the manufacturer, submitted to UL or ETL or some other NRTL, and approved.

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Wire ends that are to be installed in any kind of crimp or pressure terminal should never be tinned with solder. One reason is that solder will flow over time. This will cause the pressure on the connection to decrease, its resistance increases slightly, its self-heating due to the current flowing through increases, the solder becomes more soft and more able to flow.. the connection has an increased probability of eventually failing in a catastrophic way.

It can be appropriate to solder a wire to a terminal after proper crimping. Of course that's not applicable here because you're connecting to a screw terminal, not a crimp terminal.

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  • Would you add crimped ferrules to the stranded wire if you had the correct items to hand? Nov 17, 2023 at 16:55
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    @AndrewMorton I suppose it's possible that a person could have need of attaching stranded wire to a terminal only suitable for solid wire, or fine-stranded wire to a terminal that accepts only solid or coarse-stranded wire. It seems like a crimped ferrule would be a reasonable solution. I don't think I've ever encountered that situation though.
    – Greg Hill
    Nov 17, 2023 at 17:04
  • Great explanation. Thank you!
    – Scottie H
    Nov 17, 2023 at 18:14
  • @GregHill yeah, unfortunately, ferrules don't change anything under the UL rules (i.e. you'd need specific approvals to land ferruled wires on pressure connectors). Stranded pin connectors are what you're supposed to use, but are only available in larger sizes. Nov 18, 2023 at 2:53
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    Devices may allow for ferrules. The first two generations of Tesla wall connectors called out ferrules as allowed in the manual. You can't just add them willy-nilly though.
    – KMJ
    Nov 18, 2023 at 6:02

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