I have to run cords so i can have my rigs on different breakers for now(adding 3 20 amp outlets in my basement soon) I then of course have the cord plugged into a quality surge protector.
Could these cords be causing my inability to get 4 5970's running even though I'm using the same exact hardware and software as others who have pulled it off?
They are just regular extension cords, 25 feet, 50 and 100 feet long for three rigs.
Even having fair bit of voltage sag from undersized extension cords should not result in instability of the system. Inside the power supply, all incoming power gets rectified to DC before being stepped down to the voltages the computer needs. These days power supplies also have power factor correction and sport universal input usually from 90-250vac or thereabouts. If your extension cords are dropping even 10-20 volts from 120v mains there is still plenty of room for the power supply to operate normally. If you have a low quality power supply or one that is being tested near its limits (which it probably will be running four 5970s) then it may be an issue.
On the other hand, if you're dropping 10 volts on a 120V circuit, you're pissing away 8% of your power consumed. You're basically paying to heat the air around the cord and effectively increasing your electricity costs by 9% (as measured at the computer). That would also mean you're drawing about 19 A and that cord should be feeling pretty toasty.
Get a volt meter and measure as close as possible to the computer (a Kill-a-watt meter will do). If you're measuring anything below 115V (~10A draw over 100ft on 14 gauge copper will do this), I'd consider using a shorter or lower gauge (thicker) cord.
And if you do manage to get a 20 volt drop on a 100 ft 14 gauge cord, you're drawing about 39 amps and can soon expect a fire. :-)
My advice is to run as short of circuit as possible, including the house wiring. If you're going to be drawing serious power 24/7 it certainly make sense to wire some plugs right off the breaker box or run 12 or 10 gauge (for 20A circuits).
If the circuit is 100 ft long and 14 gauge, and you're running 15 A off the end, you're losing about 8% of your power. If power is 10¢/kWh, that's costing you about 19.2¢/day, or $70/year.
Switch to 12 gauge, lose 5%, and spend $44/year in heating the air.
Switch to 50ft and 14 gauge, lose 4%, and spend $35/year.
Switch to 50ft and 12 gauge, lose 2.5% and spend $22/year.
And as a worse case, running 100ft cord + 50ft house wiring at 15A, you're wasting about $102 in electricity per year.
Play with the numbers.
TLDR: Wire some plugs off your circuit panel and save a ton of money.
