Godown Wiring Diagram: Sequential Tunnel Lighting Explained

The godown (tunnel) wiring circuit is a teaching staple in Indian electrical engineering courses, and for good reason -- it demonstrates a clever use of 2-way switches that achieves something genuinely useful: walk into a long passage, the lamp behind you goes off and the lamp ahead comes on, all without touching a second switch. The circuit uses sequential SPDT (2-way) switching and is worth understanding both as a practical installation and as a clean example of switching logic.

What Is Godown Wiring?

"Godown" is the Indian English term for a warehouse or storage passage -- a long, narrow space where you need light where you are, not where you were. The circuit connects a series of lamps and 2-way switches so that:

• Entering through the first door turns on Lamp 1 (between Door 1 and Door 2) and turns off anything behind.
• Moving to the next door turns on Lamp 2 and turns off Lamp 1.
• Exiting through the last door turns off the final lamp.

This is also called tunnel wiring or sequential lamp wiring in some references.

Safety

Warning: Godown wiring is a mains voltage (230V AC, 50Hz -- standard in India) circuit. Turn off the main supply at the distribution board (DB) and verify with a phase tester (neon tester) at each switch point before any work. All switches, lamp holders, and cables must be rated for 230V AC. Use ISI-marked (Bureau of Indian Standards) materials throughout.

Components Required

For a godown circuit with N lamps:

• N lamps (bulbs/fittings -- typically 40W to 100W, or LED equivalents)
• N 2-way (SPDT) switches -- one per door/entry point
• Supply: Phase (L) and Neutral (N) from the DB
• Wire: 1.5mm² PVC-insulated single-core (for 5A loads) or 2.5mm² for heavier loads
• Conduit (concealed or surface-mounted): PVC conduit per IS 9537

How the Circuit Works

Each 2-way switch has three terminals:

• Common (C): The single terminal that connects to one throw or the other.
• L1: First position output.
• L2: Second position output.

The trick is in how the switches and lamps are chained. Here is the logic for a 3-lamp, 3-switch example:

Neutral runs as a continuous conductor through the circuit and connects to one terminal of each lamp.

Phase connects to the Common of Switch 1.

Switch 1 L1 connects to one terminal of Lamp 1. Switch 1 L2 connects to the Common of Switch 2.

Switch 2 L1 connects to one terminal of Lamp 2. Switch 2 L2 connects to the Common of Switch 3.

Switch 3 L1 connects to one terminal of Lamp 3. Switch 3 L2 is a dead end (or loops back in some variants -- see below).

The other terminal of each lamp connects to Neutral.

Step-by-Step Wiring

Step 1: Run Neutral

Run a continuous neutral conductor from the DB neutral bar to each lamp holder. This wire does not go through any switches.

Step 2: Wire the Phase Chain

1. Run Phase from the DB to the Common (C) terminal of Switch 1.
2. Connect L1 of Switch 1 to one terminal of Lamp 1.
3. Connect L2 of Switch 1 to the Common (C) of Switch 2.
4. Connect L1 of Switch 2 to one terminal of Lamp 2.
5. Connect L2 of Switch 2 to the Common (C) of Switch 3.
6. Continue the pattern for additional switches and lamps.
7. The last switch's L1 connects to the final lamp. L2 of the last switch either terminates (open) or can loop back, depending on the installation variant.

Step 3: Lamp Connections

Each lamp has two terminals:

• One terminal connected to the switched phase (from its switch's L1 output, as above).
• One terminal connected to the common neutral conductor.

Step 4: Earthing

All metal-bodied fittings and switch plates must be earthed (connected to the earth conductor from the DB). Use 1.5mm² green/yellow-sleeved wire for earth connections.

Switching Logic (Truth Table)

Here is how the 3-lamp circuit behaves at each switch position. Assume S1, S2, S3 with positions L1 and L2:

Phase travels through the switch chain until it hits an L1 position -- that lamp lights. Switches beyond that point are irrelevant (they are in the dead-end L2 branch or their L1 output has no phase reaching it).

Extending to More Lamps

Add one more 2-way switch and one more lamp for each additional zone. The pattern is:

• Previous switch L2 → next switch Common → next switch L1 → next lamp → Neutral.

There is no practical limit to the number of lamps, but voltage drop across long cable runs must be checked. For long passages, calculate cable size using:

Voltage drop (V) = (2 × length × current × resistance per metre) / 1000

Keep voltage drop below 3% of supply voltage (6.9V for 230V). Use 2.5mm² or 4mm² cable for runs over 20m.

Godown Wiring vs Staircase Wiring

These two circuits are often confused. They look similar -- both use 2-way switches -- but they work differently:

• Staircase wiring: Two 2-way switches control ONE lamp from two locations. Toggling either switch toggles the lamp.
• Godown wiring: Each switch selects which of several lamps receives phase. Only one lamp is on at a time.

The distinction is in the purpose: staircase wiring is for toggling a single load; godown wiring is for zone-selection across a series of loads.

Common Mistakes

• Connecting Neutral through a switch: Neutral must run directly to each lamp, never through a switch contact. Switching neutral is illegal under IS standards and dangerous.
• Using wrong switch type: Standard 1-way switches will not work. SPDT (2-way) switches are required -- verify the switch has three terminals before purchasing.
• Phase and neutral reversed at DB: In Indian wiring, Phase (L) is identified by the neon tester glowing. Always confirm phase identity before wiring the Common terminal.
• Missing earth: All metal parts of fittings must be earthed. An earthed fitting limits touch voltage to a safe level if insulation fails.

Wire Colour Reference

Indian installations follow one of two colour codes, and it matters which one your godown was wired to, since mixing them on the same job invites confusion:

Older buildings and older stock in a supplier's bin may still use the red/yellow/blue/black scheme, while new wiring should follow the harmonized colours. The earth colour used earlier in this guide (green/yellow) already matches the harmonized code. Note that the UK's BS 7671 uses the same harmonized colours -- brown line, blue neutral, green/yellow earth -- since both follow IEC 60446. Whichever code you use, do not mix the two schemes within one installation, and never rely on colour alone without also verifying with a tester.

Code, Permits, and Load Planning for Godowns

A single-room godown circuit like the one described above is often within the scope of routine domestic-style wiring, but a full warehouse installation usually is not. A few general principles apply:

• Commercial and industrial premises -- which most godowns are, even small ones -- typically require the work to be carried out or certified by a licensed electrical contractor, with a completion certificate filed as required by the state electrical inspectorate before the supply is energised.
• Load calculation matters more in a godown than in a single room: tally the connected load of every lighting zone, any power outlets, and any fixed machinery (conveyors, exhaust fans, cold storage units) before deciding how many circuits and how large a distribution board you need. Undersized calculations are the root cause of the nuisance tripping covered below.
• Separate the lighting circuits from power circuits, and split a long godown into more than one distribution sub-circuit rather than feeding the whole building's lights from a single MCB. This limits how much of the building goes dark if one circuit trips.
• Always confirm local requirements with your electrical inspector or licensed contractor before energising a new installation -- requirements vary by state.

Troubleshooting Common Godown Wiring Problems

Testing Before Energising

Before switching on a newly wired or repaired godown circuit:

1. Isolate the supply at the distribution board and lock it off if possible.
2. Set a multimeter to continuity/ohms and check each lamp-and-switch path individually -- you should read continuity only when the switch is in the position that should light that lamp.
3. Check insulation resistance between phase and earth, and between neutral and earth, using an insulation tester (megger) if available. Low readings indicate damaged insulation that must be found and fixed before energising.
4. Check earthing continuity: measure resistance between the earth terminal at the DB and the metal body of each lamp fitting and switch plate. It should read close to zero ohms.
5. Re-energise the circuit and confirm correct operation at each switch position with a neon tester or voltage tester, verifying that only the expected zone lamp lights at each position.

Create Your Own Godown Wiring Diagram

Godown circuits are easy to follow on paper but surprisingly tricky to hold in your head during installation. Map it out first with CircuitDiagramMaker:

• Place 2-way switch symbols and lamp symbols in sequence
• Draw the phase chain through each switch Common and L2 output
• Label each L1 branch going to its lamp
• Run the neutral bus as a separate parallel conductor to all lamps
• Verify the switching logic matches your expected zone behavior

Create your own godown wiring diagram -- free

Key Takeaways

• Godown (tunnel) wiring uses a chain of SPDT (2-way) switches to illuminate only the lamp in the currently occupied zone.
• Phase connects to the Common of the first switch; it chains through L2 of each switch to the Common of the next.
• L1 of each switch feeds one lamp; only the lamp whose switch is at L1 receives phase and lights up.
• Neutral runs directly to all lamps -- never through a switch.
• To add more zones, extend the chain: previous L2 → next Common → next L1 → next lamp → Neutral.
• Godown wiring differs from staircase wiring: godown selects one of several lamps; staircase toggles one lamp from two locations.
• Use ISI-marked 2-way switches, verify with a neon tester, and earth all metal fittings per IS standards.

Frequently asked questions

Can LED lamps be used in a godown wiring circuit?

Yes, LED lamps and fittings work fine in a godown wiring circuit -- the switching arrangement only controls the phase connection, not the type of load. LEDs draw far less current than incandescent bulbs, which also reduces voltage drop over long passages and lets you use a lighter cable, though switch and wiring ratings should still match the supply voltage.

Is godown wiring more energy efficient than ordinary switching?

Yes, that is the practical point of the design. Because only the lamp in the currently occupied zone is lit at any time, a godown circuit uses less energy than a passage wired with independent switches left on for the whole length, or with a single switch controlling every lamp together, which is common in long storage buildings.

Can godown or tunnel wiring be automated with motion sensors instead of manual switches?

It can be adapted this way, since the underlying logic -- light only the occupied zone -- is exactly what occupancy sensors are built for. In practice, the SPDT switch chain is replaced with sensor-controlled relays wired to follow the same zone logic, which adds cost and complexity compared with plain manual switches.

What size MCB should be used for a godown lighting circuit?

MCB rating depends on the total connected load, not the switching method. A single lighting circuit is commonly protected by a 6A or 10A MCB, sized from the total wattage of all lamps on that circuit divided by the supply voltage, with some headroom left for future additions. Always size the MCB to the wire's current-carrying capacity as well.

Can an existing passage wired with ordinary one-way switches be converted to godown wiring?

Yes, but it usually needs rewiring rather than just swapping switches, because standard one-way switches have two terminals while godown wiring needs SPDT (2-way) switches with three terminals wired in a chain. Existing cable runs can often be reused if the conductor count and size are adequate for the new arrangement.

Does godown wiring require a three-phase supply?

No, a single godown passage is normally wired on a single phase, since a lighting load is modest and one phase plus neutral is enough. In a large warehouse with several long passages, each passage may be fed from a different phase to balance the building's overall load, but the sequential switching logic within each passage stays single-phase.