I’m setting up my new GF and have no option but to use an extension cord. I know the manual says to directly plug it in to an outlet but there is no outlet available in the only space I have near a window. I have read other posts and see that a 12 gauge ext cord was suggested. Since I am new and not familiar with electrical issues, I just want to see if other people are using extension cords or if my house will catch on fire if I use one 
While you should definitely get Support to weigh in officially, I believe the focus on plugging directly into an outlet has more to do with not wanting to introduce a surge protector / UPS which could actually interfere with or cause complications with the Glowforge’s built in surge protector.
I would look for an appliance grade extension cord, OR look for a longer power cable that is of a high grade, since the power cable itself is an industry standard connection.
Just my 2 cents (and free advice is worth exactly what you paid for it).
Best of luck - you will certainly enjoy your Forge!
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I believe the primary issue you would need to be concerned about is voltage drop. And this will quickly get into #beyond-the-manual territory, since the official recommendation is straight into an outlet.
How far of an electrical cord run are you looking at?
Instead of running an extension cord, you could just buy a longer power cord.
Check out these. Looks like it comes in 6’, 10’, 15’, 25’, and 50’.
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I have been running an extension cord since day 1 (over a year). No issues. I use a very heavy duty extension cord that is about 10 feet long. Your mileage may vary.
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Many appliances (eg: portable AC units) say not to use an extension cord because most people have dinky little lamp-grade extension cords that would pose a significant fire risk. So the appliance manuals say never to use an extension cord, when you just need to get a sufficiently heavy-duty cord. Welding rigs can run on suitably heavy cords (10 gauge), and they can pull humongous loads.
Personally, I’d get a 12 or 14 gauge cord, because then I could also use it for a portable AC unit if I ever wanted to. 25ft 14 gauge cord can handle something like (back of envelope here, don’t quote me) 1800+ watts, 15 amps at 125V. In fact, I might just go buy one just in case now that you’ve reminded me.
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I’ve been running mine off a 25ft extension cord since way back in the PRU days - so 3+ years. No issues.
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Thank you all - That makes me feel better!
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In thinking about extension cord vs wall plug my first thought is what sort of wiring the wall plug has? Most newer houses are built to a code that had a minimum value. But not everyone has such a house. You could plug a 10 ga extension into a plug that has a long run of 14 or even 16 ga wire to it and it would not be the extension that was the problem.
I needed a 220 plug for welder or dryer and so ran a cable of 4 - 10 ga wires encased in a very thick rubber sheath about 30 feet from the house box to where it was needed with much of it under the house but on the ground.
When I sold the house they made me unhook it to pass inspection on a house that would be torn down.
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I have put in two “welder” plugs. first time, it was at peak copper pricing. that was a painful purchase about 300 bucks for the wire.
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I was living a few blocks from Skycraft and (gosh how much I miss them) and so was able to get huge cable for the price of a much smaller extension cord or similar at Home Depot .
oh man that would have been sweet!
I got the shortest I could find, which was 9 ft/14 gauge.
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14 ga is the problem that is pretty thin stuff
Not for short runs. 14ga wire can handle 20A but is down-rated as a conservative safety measure. Under 50 feet, a 14ga extension cord will be adequate for 15A. I’d bet the package rated the cord for 15A. 
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The Glowforge isn’t pulling too much. A little over 6 amps at peak (rated). And at 9 ft, you aren’t getting much voltage drop at all (resistance). I’d feel ok with a 14 AWG cord on that set up. I would use just the power cord and the extension cord though - no power strips with other stuff plugged in.
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Also, be sure to get a red one. It’s known to add 5hp… 
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Yes, I just have the GF > ext cord > wall. Thanks for assuring me
As you said, the manual directs plugging your Glowforge directly into the wall. I’m going to move this to the Beyond the Manual section of the forum so that the discussion can continue there.
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