I'm still looking at wires for my Prusa i3, to go between the power supply and RAMPS 1.4, and the power supply and the MK2a Heatbed.

I also recently found a 400 ft. Wire Storehouse that I bought from Harbor Freight which has wire sizes in it from AWG 10 through AWG 22 (and additionally speaker wire, Zip Cord and Bell).

I also bought some reading material, I picked up Wiring Simplified 44th edition, and in it on page 28, Table 4-1, there is a table with information about the Ampacity of copper wires including their maximum temp (C), and maximum carrying current (Amps) based on their insulation types.

Unfortunately, the 400 ft. Wire Storehouse does not provide any information in regards to the insulation type or quality and this makes it difficult for one to choose the correct wire based on the specification in the table.

Given that the thing only cost $30 for 400 Ft. of wire, it would lead me to believe that the cheapest grade of insulation was used; as I understand it, the TW type wire.

I also read a forum somewhere in which people were complaining about the cheapness of the wire in this kit, stating that one ought to wear gloves when working with it as there is probably lead in the insulation as well as the wire.

The largest copper wire I have found in the table that I have (AWG 10) says that it is rated at 30 AMP regardless of which type of insulation it has, should I be using the speakerwire instead? That isn't listed in the table. Also it should be noted that though the ratings for the Ampacity are 30 AMPs, the max temperatures are different; with the TW being at 60 C.

As far as I can tell if I use the AWG 10 (TW?) to connect everything it won't matter, but I just thought I'd check here to be sure first since my power supply is rated at 30 AMPs and that's probably the same as the wire....

  • $\begingroup$ If nobody knows how to answer this, can it please be moved to the electrical engineering stackexchange; I'll probably be laughed off the face of the earth there, but at least I'll have an answer. $\endgroup$
    – leeand00
    Commented Apr 13, 2016 at 17:38
  • $\begingroup$ There's a warning on the side of the 400 ft. Wire Storehouse that reads "Risk of electric shock! Do not use on wiring that carries more than 300 volts" that doesn't really narrow things down much about which of the wires it's talking about, but at least that means the 12 Volts from the power supply will be okay. $\endgroup$
    – leeand00
    Commented Apr 13, 2016 at 21:44
  • 1
    $\begingroup$ Those few abbreviations you have there are not even nearly all of them. This here is a nearly complete list: multicable.com/Content/Wire_Abbreviations_and_Descriptions.asp And the rule is: No label or specification: Assume the worst. For all possible properties. Heat resistance, insulation quality, amperacity, etc. Which in the case of Amperacity means: Take the worst value you do have a specification for and multiply it by 0.8. Or the worst resistance per meter and multiply by 1.2 - I may edit this into an answer at some point. Don't hold your breath though $\endgroup$
    – Asmyldof
    Commented Apr 14, 2016 at 11:30
  • $\begingroup$ Is the worst TW? Or something else? $\endgroup$
    – leeand00
    Commented Apr 14, 2016 at 17:31
  • $\begingroup$ This appears relevant: diy.stackexchange.com/questions/51966/… $\endgroup$
    – leeand00
    Commented Apr 19, 2016 at 19:09

2 Answers 2


THHN wire is thermoplastic high heat-resistant nylon coated wire.
THWN is thermoplastic heat- and moisture-resistant nylon coated wire.

"T" stands for thermoplastic insulation covering the wire itself.
"H" stands for a heat resistance of the insulation max 167°F.
"HH" stands for a heat resistance, but increased max 194°F.
"W" is for moisture resistant.
"N" is for a nylon coating make the insulation oil and gas resistant.

In my opinion the Wire Storehouse is good for simple stuff, but I would not use it for something I consider important. It's quality is poor on the insulation rating and the number of strands is low. Higher strands number allows for more flexible wire.

If you get high end audiophile type speaker wire it could be considered as you can find high strand number with good quality insulation properties in heavier gauges.

Or your local auto parts store will carry 8 and 6 gauge wire with better insulation properties.

  • $\begingroup$ Old AC adapters are a convenient supply of unusually fine stranded wire, and will usually have the wire info printed on it: gauge, volts, amps, max temperature. $\endgroup$ Commented Jun 17, 2022 at 21:42

No "mystery meat" wire in AC electrical

That kit is random Chinese "no-name" hookup wire and cannot be used for AC power. It's fine for low voltage hobbyist tinkering, which is what it's sold for. If it was better than that, they'd say.

But who knows? Maybe the boat didn't arrive and they needed some 12 AWG to finish some kits, so they ran to the electrical supply and bought bona-fide Southwire THHN. If so, the wire would be labeled "UL Listed" and "THHN/THWN-2". Then you can use it for AC power.

Without "UL Listed" or "UR Recognized" or other mark from a credible NRTL, any other labeling is lies. CE is not an NRTL.

Proper THHN/THWN-2 is available locally, dirt cheap.

Competent hardware stores and lumberyards will cheerfully sell it by the foot. So like 6 feet for a dollar-ish.

(However they are often not located in strip malls, so some may need to rethink their shopping mindset if they want value).

Any good tinkerer/hacker ought to know the location of every good family-owned hardware store, real lumberyard, and electrical supply houses, bonus points for HVAC supply.

TW, THW and THWN-2 are NOT "good, better, best".

More like the Ford Edsel, Thunderbird and Escape: "obsolete, obsolete, and currently sold product".

Why not keep making TW, THW and THWN? No money savings there. It would cost more to keep 4 separate production lines than to just make everything dual-rated THHN/THWN-2. So that's what they do.

it would lead me to believe that the cheapest grade of insulation was used; as I understand it, the TW type wire.

No, wiring doesn't work that way. You can't even assume it's a "T" family - there are also XHHW and RHH/RHW and the "S" family cordage, just in NEC Chapter 3 wiring methods. And many other families not approved for AC power.

Unfortunately, the 400 ft. Wire Storehouse does not provide any information in regards to the insulation type or quality and this makes it difficult for one to choose the correct wire based on the specification in the table.

Doesn't matter what the ad copy says, it matters what the markings on the wire say. Wire that is unmarked is literally nothing.

Wire manufacturers know this. Chinese wire manufacturers don't care. But that Harbor Freight pack never claimed to be anything else, did it?

  • $\begingroup$ All I had to do was read the first bolded headline (didn't even see the rest of the answer) and I knew this was a Harper answer! You have a distinctive writing style. (Distinctive as in good, clear, simple, somewhat sarcastic. ;) $\endgroup$
    – FreeMan
    Commented Jun 22, 2022 at 16:28

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