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[Jonathan Johnson]

Hypothetical situation: I have to run power 300 feet using extension cords. I will be drawing 10A at 120V. I have two 100 foot extension cords of 12 AWG and one 100 foot extension cord of 10 AWG available. Does it matter which order the cords are connected in order to reduce voltage drop?

(I'd like to see a mathematical proof, but my math skills aren't strong enough where I'd trust my work.)

EDIT: I apologize for the brusqueness of this post in its earlier form.

[Stephen Swaffer]

For purpose of voltage drop, the extension cord are essentially resistors (albeit very low value resistors.)  Let the voltage drop from the first extension cord=E1, the second E2 and the third E3.

Then total voltage drop =E1+E2+E3.

The commutative property of addition tells us that the order doesn't matter-ie:

E1+E2+E3=E2+E1+E3=E3+E1+E2=E3+E2+E1

(Dad was a math teacher

[Steve M Smith]

Does it matter which order the cords are connected in order to reduce voltage drop?

No.  It's just resistances in series so they add up.

1 + 3 + 4 = 8 just as well as 3 + 4 + 1 = 8


Steve.

[Jonathan Johnson]

No.  It's just resistances in series so they add up.

1 + 3 + 4 = 8 just as well as 3 + 4 + 1 = 8


Steve.

That's pretty much what I figured. As I see it, the voltage drop on a particular cord could be expressed as a percentage which is constant regardless of voltage. And just like stacking coupons at the grocery store checkout, it doesn't matter what order the discounts are taken.

I asked the question because I've heard a lot of conventional wisdom (meaning: they probably don't understand the math) that suggests you should have the heaviest cord closest to the power source.

[Stephen Swaffer]

Obviously, if there are any multitaps involved, then the heaviest cord nearest the source makes sense as it would have the heaviest load-which affects voltage drop-which is probably the more common scenario.

[Mike Sokol]

No.  It's just resistances in series so they add up.

1 + 3 + 4 = 8 just as well as 3 + 4 + 1 = 8

Yup correct.... but this goes against "consumer logic" where the heaviest extension cord should go first. And of course, the current flow is exactly the same in all those wires in series as well. However, the skinny cords make the best fuses (this is a joke  ) since they have the most voltage drop per foot, and thus the most wattage loss which turns into heat.

[Lyle Williams]

Down here from a regulatory/safety point of view, the issue isn't voltage drop but fault current.  The resistance of a fault loop needs to allow a current 7.5 times the breaker value to flow (sufficient current for a near instant breaker trip.)

String enough thin extension cords together and you reach a point where the breaker trip is slow.  Add even more and you could theoretically reach a point where the breaker simply won't trip.

[Steve M Smith]

but this goes against "consumer logic" where the heaviest extension cord should go first.....However, the skinny cords make the best fuses (this is a joke  )

Well, if you're going to use one as a fuse (even jokingly) the thin one should go first... unless the neutral 'fuse' blows!!


Steve.

[Jonathan Johnson]

Here's an easy-to-use voltage drop calculator (note that it uses "one-way" distance, not round-trip):

http://www.calculator.net/voltage-drop-calculator.html

[Bill McIntosh]

Is there a difference based on the number of extension cords used?  (Assumption:  all the plugs and jacks are kept in good condition.)

I have some 40 foot and a 100 foot 12 gauge cords.  Would I see any reduced voltage inherently if I used 2 50 foot instead of a single 100 foot?

Most of our gigs I have the mains and sub within 20 feet of an outlet, so cutting the 40s down into 20s would be more convenient and make a cleaner stage.

[ProSoundWeb Community]