How to Wire a Flygt ENM 10 Level Switch

The Flygt ENM 10 is the simplest component in a pumping station and it still gets wired wrong. Three conductors come out of the cable; you use two and insulate the third, and which two depends on what the switch is doing. Get it backwards and the pump starts when the well is empty. This article sets out the colour code, the two connection cases, alarm wiring, the voltage rule, what changes in an Ex installation, and the faults we see that look like wiring errors but are something else.

Everything below follows Xylem's current Installation, Operation and Maintenance Manual for the ENM 10, document 899751_16.0. Where we add field practice, we say so.

What you are connecting

Inside the sealed body is a single microswitch with a changeover contact, operated by the tilt of the body. The cable carries three conductors:

Conductor	Colour	Role
1	Grey	Common — connected in every configuration
2	Black	Used when the switch must act on a rising level
3	Brown	Used when the switch must act on a falling level

The grey conductor is always in circuit. The choice is between black and brown, and the one not used must be insulated — properly, with a heat-shrink or an insulated crimp, not taped and tucked.

Emptying a sump or filling a tank

This is the decision that matters. A switch controlling a drainage pump must start the pump when the level rises; a switch controlling a filling pump must start it when the level falls. Same component, opposite conductors:

Conductor	To empty a sump	To fill a tank
1 — grey	Connect	Connect
2 — black	Connect	Insulate
3 — brown	Insulate	Connect

Almost every Flygt wastewater installation is the first case. If you are replacing a switch in a wet well and find brown connected, somebody before you either wired it for a tank or made the mistake this article exists to prevent. Check before copying.

Start and stop with two switches

A single ENM 10 cannot run a pump on its own, because the level at which it tips and the level at which it falls back are a few centimetres apart — the pump would cycle constantly. The manual requires two switches as a minimum: one clamped at the start level, one at the stop level, with a third added wherever an alarm is needed. The same part serves every position; nothing distinguishes a start switch from a stop switch except where it hangs and how the panel uses it.

In the control circuit, the upper switch closes on a rising level and energises the pump contactor through a relay that holds itself in; the lower switch, which closed earlier as the level passed it, opens again when the level falls below it and drops the circuit out. The pump therefore runs from the moment the upper switch tips until the moment the lower switch hangs vertical again. The distance between the two clamping points is your operating band — wider means fewer starts per hour, narrower means tighter level control.

In a two-pump station the usual arrangement is four switches: a common stop, a start for each pump at staggered heights, and a high-level alarm above them all. Staggering the two starts is what gives you duty/standby and prevents both pumps from starting into the same inflow.

Alarm wiring

An alarm switch follows the same logic as a pump switch, and the same table:

Conductor	High-level alarm	Low-level alarm
1 — grey	Connect	Connect
2 — black	Connect	Insulate
3 — brown	Insulate	Connect

The high-level alarm is the one that earns its keep. It is the only thing that tells anyone the start switch has failed before the well overflows. Hang it above the highest start level with enough margin that normal surges do not trip it, and wire it to something that is actually monitored.

Low-current circuits and PLC inputs

There is one case where the standard switch is the wrong part even though it works on the day. A PLC digital input or a modern building-management card draws a few milliamps. That is dry-circuit switching, and a standard contact can develop a surface film over months that such a small current cannot break through. The symptom is an intermittent fault that appears long after commissioning. For those circuits Xylem lists a gold-contact version of the ENM 10, rated 1 mA at 5 V DC, under separate part numbers. If you are switching a relay or a contactor coil, you do not need it.

Ex installations

In a classified zone the rules change in three ways. First, the switch itself must be the black Ex version, not the blue standard one — the conductive casing is what prevents static build-up. Second, the circuit must be intrinsically safe, which means the Flygt Ex safety barrier, part number 84 01 07, installed outside the hazardous area; the Ex approval of the switch alone does not make the circuit safe. Third, the Ex switch is limited to 20 m immersion depth regardless of cable length. The barrier has an LED that changes state when the switch toggles — the manual's own commissioning check is to watch it do so.

Do not mix a standard switch into an Ex circuit “just for the alarm”. Every switch in the hazardous area is Ex, or none of the approval holds.

Faults that look like wiring errors and are not

Field practice, not the manual. Most call-outs for “the float switch is wired wrong” turn out to be one of these:

Symptom	Likely cause	Check
Pump never starts	Start switch wired for a tank (1 + 3), or cannot tip because it is tangled with another cable or snagged on the guide rail	Continuity across 1 and 2 with the body tipped by hand; look at the cables
Pump never stops	Stop switch held tipped by the pump discharge or a bracket; or a contact welded after switching a load above its rating	Lift the switch; continuity with the body vertical
Pump short-cycles	Start and stop clamped too close together; or a non-return valve passing and refilling the well from the main	Measure the operating band; watch the level after a stop
Works for months, then intermittent	Standard contact on a low-current input (see above); or a joint in the cable inside the well	Replace with the gold-contact version; never joint a cable in a wet well
Alarm never trips, or is always on	2 and 3 swapped	Compare against the table above
Switch slow or sticks near horizontal	Fat and grease on the body	Clean the plastic surface — the manual lists this as routine maintenance

Mounting mistakes that cause electrical symptoms

The manual is short and specific on mounting: the cables must not be tangled during installation, and each switch's cable must hang freely from the others. The ENM 10 hangs immersed from a fixed clamping point rather than floating on the surface precisely so that several of them can share a well without fouling. Use the dedicated cable holder, part number 83 46 02, at the clamping point; it is where cables otherwise wear through. Order the cable long enough to reach the terminal box in one run — a junction inside the well is both a future fault and the end of the IP 68 rating. Standard cable lengths are 6, 13, 20, 30 and 50 m, each under its own part number.

When to replace rather than diagnose

The ENM 10 is hermetically encapsulated and cannot be opened or repaired. If the cable, the protective sleeve or the casing shows damage, the manual's instruction is to replace the switch. Because the units in a well are the same age and have seen the same duty, most maintenance schedules replace them as a set rather than one at a time; replacing one and leaving three equally old ones in place usually means another visit within the year. A set of switches is the cheapest line on any pumping-station spares list, and the one whose failure costs the most — see our note on what a pump failure actually costs.

Frequently asked questions