Several 4-conductor cables are installed in a ladder cable tray without a cover and without exceeding the cable tray fill limit. Each 4-conductor cable comprises four 1/0 AWG THHN copper conductors, each of which is considered current-carrying. What is the allowable ampacity of each 1/0 AWG THHN copper conductor?

The allowable ampacity is 136 amperes

Explanation:According to the National Electrical Code the ampacity for insulated conductors of type 1/0 AWG THHN is 170 amperes(from tables) for cables no exceeding 3

But we are presented with 4 cables in a tray,

Going by the National Electrical Code where conductors exceeds 3, the allowable ampacity shall be reduced to 80% the of the ampacity gotten from table.

Hence the allowable ampacity for 4 copper cables of type 1/0 AWG THHN is (80/100) *170=136 Amperes

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