Belowground sewage ejector systems4/11/2024 ![]() ![]() Selection of the backup-battery chemistry and construction-such as the newer sealed Absorbent Glass Mat (“AGM”), gel-cell, and Lithium-Ion (“Li-ion”) technologies-are beyond the scope of this article, with each offering tradeoffs of cost, ease-of-maintenance, discharge characteristics, and longevity. Optionally, the backup pump may also be a battery-operated DC or AC/DC pump powered, for example, by a 12-volt wet-cell battery (marine battery) and trickle charger (Figure 3). For best reliability-and to avoid tripping the subpanel circuit breaker when both pumps are active-the backup pump should also connect to a dedicated GFCI-protected branch circuit (typically 120 VAC, 15 A or 20 A). In the event of a primary-pump mechanical or electrical failure, Figure 2 illustrates a recommended back-up pump to prevent the basin from overflowing into the basement or crawlspace. Proper hysteresis allows sufficient time to empty the effluent basin without short-cycling the sump pump. Hysteresis is the difference between the initial switch-on wastewater level and the subsequent switch-off level-similar in principle to an HVAC thermostat regulating temperature when cycling a furnace every 10 to 20 minutes. The former switches only the hot conductor, whereas the later switches both the hot and neutral conductors to the pump-providing an extra measure of protection.ĭischarge Hysteresis and Recommended Backup Pump Depending on the pump model, the float switch may be single-pole or double-pole. When sewage or other wastewater fills an empty sump tank, after a few minutes a level-sensing float-switch activates the pump, which remains active until the fluid level discharges below a preset threshold. Sewage-ejector and dewatering sump pumps are common in basements and below-grade drainage basins (Figure 1). The full case study, measurement methodology, and results follow below. If left unresolved, abnormal leakage current presented a serious safety hazard that could result in electrical shock or electrocution. ![]() As the sewage pump worked reliably for years without tripping the original GFCI-and recognizing that replacing the GFCI did not remedy the new tripping problem-BUILDERA measured suspected leakage current to determine whether a possible pump electrical short was the GFCI-tripping root cause. Upon replacing the GFCI with a new one, the power-tripping problem persisted. After 10 years of reliable operation, a California homeowner experienced nuisance (ghost) tripping of a basement Ground-Fault Circuit-Interrupter (“GFCI”) whenever activating the sewage pump. ![]()
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