how many amps could i expect at the end of a 625ft. run with 4/0triplex.?

Question

it is a 3phase 240volt system
would settle for single phase to destination
i figured 3/0 wire 15ft up the pole the 4/0 triplex to destination. thought i'd atleast get 100 amp.
been told it could be done without stepping up then back down with transformer.

Answer 1

4/0 wire is listed as .049 Ohms/1000 feet with a maximum current capacity of about 300 Amps. But what you need to do is use the resistance to figure the allowable voltage drop. Usually 3% drop is a maximum. For example 100 Amps running through 1000 feet of this wire would drop 4.9 Volts which is only about 2% voltage drop. So your plan for 100 Amps sounds okay. To figure the voltage drop you need to use the length to and from the load so you would double your distance to 1250 ft.

Answer 2

Resistance of AWG 0000 (4/0) cable is 0.049 ohm/1000 ft.
Basic flexible cable is rated at 125 C per CSA and 150 C per UL.

The ampacity (current carrying capability) of a single strand is 357 A in free air (i.e. at least the outside diameter of the cable jacket between individual cables in a run).

For 3 phase (3 wires together, one cable per phase, bundled so they're touching):
Allowable cable ampacity has to be reduced due to the contact. CSA gives this derating factor as 70 percent.
(Ampacity) = (Amp/cable) * (number cables) * (derate)
= 357 * 3 * 0.70
= 750 A

Using a single cable:
No derating (no other cables to add additional heating).
(Ampacity) = (Amp/cable) * (number cables) * (derate)
= 357 * 1 * 1
= 357 A

Either case will carry 100 A quite comfortably.

Note that if using 90 C (thermal rating of cable), you'll have to multiply both of the above answers by another 0.80 to compensate for the lower allowable thermal margin.