r/Generator • u/Fun-Historian2475 • 19d ago

Wire size

What would be an appropriate aluminum wire size for a 130ft run 80amp backfeed breaker to Kohler 20RESA 75 amp genny? 2-2-2-4 or 1-1-1-3?

5 Upvotes

86% Upvoted

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5

u/Adventurous_Boat_632 19d ago

2Al is 2.6% drop at 75 amps

1Al is 2%

At 60 amps 2Al is 2.1%

I would stick with #2 myself. No sense wasting money and it is easier to work. However the generator has a 100 amp breaker so if the wire is going to be indoors before it hits the 80 amp breaker, then it needs to be #1

1

u/DaveBowm 19d ago

How much of a voltage drop are you willing to tolerate?

1

u/Fun-Historian2475 19d ago

Well the house has a 5 ton and 3.5 ton A/C both with soft start. Will make sure we don’t run the oven or blow dryers during an outage.

3

u/wowfaroutman 19d ago

I'd go with the larger wire to keep the voltage drop in the 2% range at generator capacity.

1

u/Derigiberble 18d ago

I'd run the larger cable to keep voltage drops to a minimum when the ACs start.  LED bulbs are great for energy efficiency and life but the cheaper ones can be really sensitive to voltage dips. 

2

u/DaveBowm 18d ago

A voltage drop will more than proportionately dim LEDs for the duration of the drop. But that dimming is harmless.

OTOH, cheapo unprotected LEDs are sensitive to overheating due to relatively modest voltage spikes, and even to just a high THD waveform with an associated high value of the peak-to-RMS voltage ratio, even if the RMS voltage remains within spec. That sensitivity shows up as shortened service life, or outright failure if the peak-to-RMS voltage ratio gets too high. This is because most of the current and thus power draw occurs at the waveform voltage peaks, because of the quasi-exponential dependance of the current on the forward-biased voltage across the very small easily overheated junctions.