My neighbor wants to operate a circular saw 100 feet from an outlet in his garage. He has a 50 foot 12 gauge cord and a 50 foot 14 gauge cord. He insists the 12 gauge cord should go first from the outlet. I said it didn't matter which cord went first in this case, and that it was the same amp/voltage wise at the saw.

 

You are correct.

 

You are correct. It does not matter. What matters is the gauge of the wire.

How much current does the saw take?
If it takes 5 to 8 A, then you need 12 AWG cable.
If it takes 8 to 12 A, you need 10 AWG cable.

 

My neighbor wants to operate a circular saw 100 feet from an outlet in his garage. He has a 50 foot 12 gauge cord and a 50 foot 14 gauge cord. He insists the 12 gauge cord should go first from the outlet. I said it didn't matter which cord went first in this case, and that it was the same amp/voltage wise at the saw.

Electrically, it doesn't matter. There are other considerations that might make one preferable to the other. If the saw will be moving around quite a bit, it might make it easier to have the lighter and/or more flexible cord be at the saw end. You might also consider the ground over which each cord will be lying and use the heavier and/or more resilient cord in the section that has the rougher terrain (rocks vs soil, for instance).

I'd recommend treating your combined cords as if it were a 100 ft 14 AWG cord. Most such cords are rated for up to 13 A, but I'd recommend not pushing that too hard. If practical, I like to not go above half the rated current.

 

If the saw has sufficient power at the end of two cables, then the cable gauges are ok.
If it doesn't, then he should try changing the 14G cable to 12G.

 

Motors are grumpy on long wires. They will start up slower. Probably have less power than normal. The saw will pull very little power with no load. The harder the work the more current. At startup the current is very high.
Start out a little carful. Don't let the saw stall out. Soon you will know how strong the motor is under this condition. You might check the connections if they are getting hot under load.

 

My neighbor wants to operate a circular saw 100 feet from an outlet in his garage.

We should be having this conversation with his neighbor.

 

An older portable circular saw, like my older portable electric drill motors, uses a brush type series connected universal motor. So the required supply current depends very much on the mechanical load on the motor.
I run my plug-in electric mower on two #16 wire extension cords, end to end. That totals about 120 feet. It does run slower than with a single 50 foot #12 cord, but so what??? The 50 foot cord is not nearly long enough.