Howard.... thank you for your replies.
1) Based on a 240 volt source, 60 amp load and 250 foot run, you will need 2 AWG stranded copper or 1 AWG stranded aluminum. The 1 AWG stranded aluminum will be more cost effective. The voltage drop calculation results in less than the recommended 3% voltage drop by the National Electrical Code. Both VD's are under the 3% rule, therefore, either of these sizes will work OK for the 250 foot run.
2) If using 2 AWG copper, you will need a 10 AWG stranded copper conductor for the equipment ground. If using 1 AWG stranded aluminum, you will need 8 AWG stranded aluminum for the equipment ground.
3) All sub-panels require a 4 wire circuit, ie, 2 hots, 1 neutral and 1 equipment ground. Size the 2 hots and the 1 neutral accordingly based on whether using copper or aluminum conductors.
4) At the sub and the main electrical panel, you will need an equipment grounding bar. At the sub, the neutral wire must remain isolated or floating from the panel enclosure. You will also require a main breaker sub-panel with a 60 amp breaker for the disconnect. You will also require a minimum of (1) one 8 foot ground rod.
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