what size wire in paralell is equal to 300 mcm and is there a reference table somwhere?

See Table 8 in Chapter 9

Roger

looking at that table it looks like 3/0 or 2/0 but i'm not sure any suggestions.

What are you trying to do?
Don

2/0 won't make it but, I think Don's question needs to be answered, it may save you some grief.

Roger

With alternating current, magnetic fields build up inside the cable and skin resistance comes into play, so cable ampacity doesn't scale linearly with cross-section. In addition, cooling is related to the surface area of the cable, and larger cables have less surface area than two smaller ones to dissipate heat. Ergo, you can safely (and legally) carry more current through 2x 150MCM than through 1x 300MCM, and 2x 1/0 may be sufficient depending on what you intend.

If you're talking DC, reference Chapter 9, Table 8. If you're talking 60Hz AC, reference a combination of 310.60 with the derating rules of 310.1(B)(2)(a)... and the myraid of other codes that may apply.

Table 310.16 takes all of this into consideration. Assuming THWN insulated copper conductors, 300 kcmil has an ampacity of 285 amps, therefore 2 paralleled 1/0 AWG conductors in separate conduit or cable would have equivalent current carrying capacity. It is necessary to keep these paralleled conductors in separate conduit or cables because of the heat buildup when more than 3 current carrying conductors are installed in one conduit (300.15(B)(2)(a))