Sump Pump and Battery Backup Installation
Purpose
A backup sump pump is bought for one night: the storm that takes the power out while the water table is up. It gets tested on a dry afternoon with the house energized, which tests almost nothing. Three things decide whether it works on that night, and all three are set at install: the backup float sitting above the primary float, each pump having its own check valve, and a battery whose state was measured rather than assumed. This procedure proves the system under the condition it was sold for, with AC pulled.
Scope
Covers installation or replacement of a residential and light commercial groundwater sump pump in an open or vented pit, with or without a battery backup, from the pit to the first joint outside the building.
Does not cover the discharge line past the rim joist, its pitch or its freeze protection, which the sump discharge routing SOP owns. Does not cover a sealed sewage basin or ejector, which carries a hydrogen sulfide and confined space profile addressed by the sewage ejector replacement SOP. Does not cover whether a sump is the right remedy for a wet basement, or the routine annual visit.
Roles and responsibilities
| Role | What they own | The handoff |
|---|---|---|
| Dispatcher | Whether the basement is wet now, and whether the house has flooded on an outage before | Puts the flood history on the ticket; a house that flooded during an outage is a backup sale, one that has not is a conversation |
| Technician | Measured inflow, electrical isolation, both float levels, the AC-pulled proof, the battery reading | Returns inflow in gpm, both cut-in levels, battery resting voltage as found and the timed backup run; an install without those is not signed off |
| Lead or owner | Electrical scope where a circuit is missing or shared, and any pit replacement | Owns the call to bring an electrician in, since a shared circuit is the most common reason a backup dies with the primary |
Procedure
Measure the pit and the water actually entering it before sizing anything. Record inside diameter and depth in inches, then with the pump unplugged time the level rise and convert it to gallons per minute. Acceptance: diameter and depth in inches, plus an inflow rate in gpm over a timed interval, or "no measurable rise in 15 minutes" written down. Wrong looks like sizing off the horsepower of whatever was in there. Stop rule: an inflow the intended pump cannot clear at the actual head is a plan question for the lead. Hazard: an open pit at floor level is a step-in hazard and a drowning hazard for a small child, so it stays covered or guarded any minute you are not standing over it, and never overnight.
Open the circuit, prove it dead, and record what that receptacle is. Identify the breaker, open it, and verify absence of voltage at the receptacle with a tester proved on a known live source immediately before and after. Acceptance: under 1 volt at the receptacle on an instrument proved live on a known source before and after, since induced voltage on a de-energized conductor routinely reads a fraction of a volt, plus circuit number, dedicated or not, GFCI or not. Wrong looks like unplugging the pump and calling that isolation while your hands go into standing water beside a live receptacle. Stop rule: a circuit you cannot positively identify stops the install until the lead brings an electrician. Hazard: electrical utilization work, which 29 CFR 1910.147 excludes at (a)(1)(ii)(C), so the practice is 29 CFR 1910.333(b)(2) by a qualified person under 1910.332, live-dead-live per NFPA 70E-2021, 120.5, and 29 CFR 1926.417 in construction. Whether that receptacle must be GFCI protected is set by NEC Article 210.8(A) in the edition your jurisdiction has adopted, and that scope has widened across recent cycles, so pull the adopted edition.
Set the pump on a solid base and set float travel to the pit, not to the box. Seat it on a brick or the manufacturer's stand so the intake clears the silt layer, then set the tether so cut-out leaves the volute submerged per the manufacturer and cut-in sits below the lowest inlet invert. Acceptance: cut-in and cut-out measured from the pit floor in inches, float swinging clear of wall and pipe through its whole travel. Wrong looks like a tether short enough to stop and restart every 30 to 90 seconds under steady inflow, which burns the motor out inside a year. Stop rule: a float that fouls anything anywhere in its travel gets moved now. Hazard: your arm is in the pit, so the circuit stays open per step 2 and nothing goes near the intake while the pump can start.
Build the discharge so each pump has its own check valve and a union you can service. Run full-size pipe off the outlet with no bushing down, a true union check mounted vertically 12 to 18 inches above the pump outlet with the body arrow up, and the relief hole the manufacturer specifies drilled between outlet and check. Acceptance: check height in inches, orientation confirmed against the arrow, pipe size matching the outlet, one check per pump, both discharges joined at a wye downstream of both checks. Wrong looks like one shared check with the backup teed in below it, which lets each pump push its column back through the idle pump. Stop rule: a relief hole drilled above the check drains the standing column back into the pit and is re-drilled, not left. Hazard: primer and solvent cement release vapor that is an inhalation exposure in a closed basement, so work to the product SDS with the space ventilated and containers capped between joints, and any respirator only under a written program per 29 CFR 1910.134.
Set the backup float above the primary float and prove the gap. Mount the backup per its instructions and set its cut-in above the primary's by the offset the manufacturer states. Acceptance: both cut-in levels in inches from the pit floor with the difference stated, and a rising-level test showing the primary starts first. Wrong looks like floats set level or the backup set lower, so the backup shares every ordinary storm and the battery is flat by the night it is needed. Stop rule: a pit too shallow to give both floats their travel is a pit replacement, not a shortened tether. Hazard: hands in the pit again with the circuit still open, and a backup pump is not dead because AC is off, so its battery stays disconnected until step 6.
Install battery and charger to the stated chemistry and torque, and record resting voltage. Confirm the charger lists the chemistry you are fitting, set it, land terminals to the stated torque with the negative last, and write the install date on the case. Acceptance: chemistry match confirmed against the charger label, resting voltage recorded before connection, terminals at the stated torque, charger reaching float inside its stated window. Wrong looks like a battery of a chemistry the charger does not list, which either undercharges permanently or gasses. Stop rule: a battery that will not reach float in that window is not signed off as a backup. Hazard: a lead acid battery vents hydrogen while charging, so it goes in the ventilated location the manufacturer specifies and never a sealed box, and a wrench bridged across the terminals vaporizes metal and sprays it, so rings come off, the wrench is insulated, and eye protection is on.
Restore power and prove both pumps and the alarm by pulling AC, not by lifting a float. With the lid on or the pit guarded, close the breaker, fill the pit and watch the primary start, stop and evacuate; then pull AC at the plug, fill again to prove the backup starts on battery, and trip the alarm float. Acceptance: primary starting and stopping at the step 3 levels, level staying within about half an inch of the shutoff level for 60 seconds after the pump stops, backup starting on battery inside its stated delay with a timed run, alarm sounding at its float. Wrong looks like a hand-lifted float, which proves the switch and nothing about the pump, check valve or battery. Stop rule: a rebound over half an inch is drain-back and goes back to step 4 before anything else is tested; a backup that will not start on battery is not handed over. Hazard: this step puts energy and water back with people in the room, so no hand is in the pit when the breaker closes, the lid or guard goes on first, and the outside termination is checked from beside it, not in front of it.
Seal, label, and hand over what the alarm actually means. Fit the lid and gasket where the pit sits in habitable space, label the breaker and receptacle, and show the customer the alarm test and the battery replacement interval. Acceptance: lid seated with fasteners in, breaker labeled, customer able to repeat back what to do when the alarm sounds. Wrong looks like a customer who believes the alarm means the system is working. Stop rule: nobody home to be shown means it goes in writing on the invoice with a follow-up call logged. Hazard: none physical here, it is done beside a closed pit; what hurts lands months later on a homeowner who silences an alarm telling them the primary has already quit.
The record this produces
Ten fields filed against the property rather than the invoice: pit diameter and depth; measured inflow in gpm with its interval; circuit number, dedicated or not, GFCI or not; primary cut-in and cut-out in inches from the pit floor; backup cut-in and the offset; check valve height and count; battery chemistry, resting voltage as found, install date; the timed backup run on battery; post-shutoff rebound in inches; alarm test result.
The office reads the battery date to schedule replacement instead of waiting for a customer to notice. The next tech reads measured inflow against this one, because a pit whose inflow has doubled in three years is a foundation drainage finding, not a pump finding. The lead reads the rebound figure: a system that passed at half an inch and now rebounds two has a check valve at the end of its life.
One worked pass, including a failure
Two story house, unfinished basement, existing pit, pump quit during a storm and left water about an inch across the slab.
Step 1: the pit measures 18 inches inside diameter, 24 deep. With the old pump unplugged the level rises 4 inches in 10 minutes. Area is about 254 square inches, times 4 inches is 1,018 cubic inches, and at 231 cubic inches per gallon that is 4.4 gallons in 10 minutes, so 0.44 gpm. Step 2: the receptacle reads 0.2 V on a tester checked live before and after, dedicated but not GFCI protected, so the adopted NEC edition is checked and the answer goes on the ticket. Steps 3 to 6 run clean: primary cut-in 11 inches and cut-out 5 from the pit floor, backup cut-in 14 for a 3 inch offset, separate true union checks 14 inches above each outlet joined at a wye above both, battery resting inside the manufacturer's full range and the charger at float in its stated window.
Step 7 fails. The primary starts and stops at the set levels, but after shutoff the level rebounds 2 inches in under a minute against an acceptance of half an inch. Two inches here is 254 square inches times 2, or 509 cubic inches, which is 2.2 gallons; against the 0.44 gpm from step 1 that is five minutes of this pit's own inflow arriving in one, so the pump restarts on its own discharge. Stop rule taken, back to step 4: the relief hole had been drilled an inch above the check rather than below it, draining the standing column into the pit. Hole plugged, a new one drilled below the check, step 7 re-run.
Second pass: rebound holds under half an inch, AC pulled, the backup starts inside its stated delay and runs 41 seconds to clear the pit, alarm sounds at its float. Step 8 closes with the lid gasketed, breaker labeled, and the customer repeating back that the alarm means the primary has already stopped.
References
- 29 CFR 1910.333(b)(2) for electrical safe work practices, with the 1910.147(a)(1)(ii)(C) carve-out routing electrical utilization work there, 29 CFR 1926.417 as the construction counterpart, and NFPA 70E-2021, 120.5 for live-dead-live in step 2.
- NEC Article 210.8(A) for GFCI protection of basement receptacles, in the edition your jurisdiction has adopted.
- Pump, check valve, battery and charger manufacturer literature: relief hole size and location, float offset, terminal torque, charger chemistry settings, battery replacement interval.
- 29 CFR 1910.134 for the written respiratory protection program any respirator use in step 4 depends on.
- See related: the Plumbing sump discharge routing and freeze protection SOP, the sump pump annual service SOP, and the sump check valve selection reference.