Capacitor Discharge Time and Bleed Resistor (NEC 460.6)

NEC 460.6 requires the residual voltage to fall to 50 V within 1 minute at or below 600 V (5 minutes above 600 V). V(t) = V0 e^(-t/RC), so R_max = t_limit / (C ln(V0/50)) and the continuous burn is V0^2/R. A 100 uF, 600 V cap needs a 241 kohm-or-smaller resistor, dissipating 1.49 W -- a permanently connected 220 kohm 2 W resistor does it. A 1 uF, 4160 V surge cap gets the 5-minute allowance, so 67.9 Mohm at 0.26 W suffices. The discharge means must be permanent or automatic on loss of line -- a manually switched bleed does not comply. A design aid; the equipment listing governs.

V(t) = V0 e^(-t/RC); t_discharge = R C ln(V0/V_safe); R_max = t_limit / (C ln(V0/V_safe)); P_continuous = V0^2/R.

The capacitor stored-energy discharge requirement of NEC 2023 460.6 -- residual voltage to 50 V within 1 minute at or below 600 V, 5 minutes above 600 V, by a permanent or automatic discharge means -- by name. A computational aid; the AHJ-adopted NEC edition and the equipment listing govern.

NEC is free to read at nfpa.org/freeaccess. The RC-discharge relation is first-principles; the 460.6 time limits and the permanent/automatic-connection requirement are in the published code.

Estimate. AHJ and licensed electrician govern. Verify against the NEC edition adopted in your jurisdiction.

Field names used by the API: capacitance_uf, initial_voltage, safe_voltage, r_max_ohm, p_continuous_w, limit_s

• Time limit residual to 50 V within 1 minute at or below 600 V, 5 minutes above 600 VNEC 460.6(A)
• Connection the discharge means must be permanently connected or connect automatically on loss of line; a manually switched bleed does not complyNEC 460.6(B)
• Continuous power the resistor dissipates V0^2/R while the bank is energized; rate it with marginfirst-principles