Använd 80% -regeln för kontinuerliga belastningar (eftersom brytaren kommer, även om du inte gör det)
Medan 210.22 tycks indikera att du har hela 30A tillgängliga för dig:
210.22 Permissible Loads, Individual Branch Circuits. An individual branch circuit shall be permitted to supply any load for which it is rated, but in no case shall the load exceed the branch-circuit ampere rating.
Du måste tänka på att brytaren kan ha andra idéer, som anges i 210.20 (A):
(A) Continuous and Noncontinuous Loads. Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load.
Exception: Where the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent device shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.
Skälet till varför trädgårdsskyddsbrytare till UL 489 (och deras motsvarigheter i säkringsmark) kommer till slut att resa (eller blåsa) om du kör 100% av deras nominella ström genom dem i timmar i slutet. Medan det finns en sådan sak som en 100% -belastad brytare, återfinns de bara i industriellt arbete.
Vidare behöver grenkretsledningarna 80% avspänning för kontinuerliga belastningar, enligt 210.19 (A) (1):
(1) General. Branch-circuit conductors shall have an ampacity not less than the maximum load to be served. Conductors shall be sized to carry not less than the larger of 210.19(A)(1)(a) or (b).
(a) Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the minimum branch-circuit conductor size shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.
(b) The minimum branch-circuit conductor size shall have an allowable ampacity not less than the maximum load to be served after the application of any adjustment or correction factors.
Exception: If the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the branch-circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.
Så, du är begränsad till 5760W för en all-time-tid (eller åtminstone längre än några timmar i taget). Icke-kontinuerliga belastningar (säg en stor brunnpumpmotor) kan dock dra hela 7200W från kretsen, eftersom belastningens driftscykel ger tillräckligt med tid för att svalna mellan körningar.