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I have a Generac 22kw home standby generator. I bought it with the intention of installing it in the near future, so it is currently sitting in my garage. I decided to open it up and see a few things, and one thing that stood out was the incoming wire size from the generator to the 100 amp breaker. It's 8 AWG and the output is black/red 3 AWG. Can someone explain this to me?Generator breaker

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    I am not an electrical technician, but based on common sense, I think it guards against drawing power more/faster than the capability of supply/generation.
    – r13
    Commented Jun 6, 2021 at 18:16

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Sure, manufacturer have different rules on the gauge of the wires in equipment, there are tables in the code book that give tables for wire sizes within the machine panels and the ampacity when the wire exits the piece of equipment these values do not have the safety factors like the building code requires because inside the equipment panels higher ampacities are not as dangerous as running inside a wall that is flammable and may be insulated.

You can see similar size differences in the tiny wire that may feed your 200 or 300 amp panels look at the connection at the house the feeder wire from the utility is tiny going up to the pole same thing.

So equipment manufactures and utility providers are governed my different rules than perimeter wiring is. The difference it it’s smaller because it is evaluated differently than house wiring.

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They're under totally different codes.

  • Pole lines up to your weatherhead comply with NESC.
  • All installed wiring in your house complies with NEC.
  • Appliances and equipment comply with the UL "White Book", a whole family of UL standards for various products.

UL = Underwriter's Laboratories. Laboratory = testing lab. Underwriter = insurance company. UL was formed by your fire insurer, you can see the self-interest there - make you use safer stuff, pay fewer claims.


Wiring inside the generator must comply with the UL White Book, and is fairly lax because wires are very short and well-protected.

Your wiring from generator to house must comply with NEC. That is the strictest of the many standards since wires must be able to cool inside walls packed with insulation.


100A = If terminations at both ends are rated for aluminum (very likely), #1 aluminum. Or, #3 copper. NEC 310.15(B)(16).

You cannot use #4Cu or #2Al for 100A. (only 85A and 90A respectively). Some people think those wires can do 100A, but they're reading the wrong table. 310.16 and 60-75 degree column are correct. See your panel labeling for why you can't use the 90 degree column.

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Guys URD is Made For Higher Heat Temps giving it the feature to run 100amps no problem.

The wire type plays a large role when sizing wire This comes from the manufacturer of the USE-2 URD & So Forth

2-2-2-4 Quadruplex Aluminum URD Cable Specifications*: Phase Conductor-Size: 2 AWG Conductor Strand: 7 Neutral Conductor-Size: 4 AWG Conductor Strand: 7 Insulation Thickness: 0.060 inches Outside Diameter: .938 inches Allowable Ampacity-Direct Burial: 153 Amps Allowable Ampacity-In Duct: 115 Amps Weight: 0.367 lbs per ft

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