Repeated MCB Tripping and a Tingle from the Shaper Body

Why it trips

• Shaper full-load current: 2200 W / (230 V x 0.8 power factor) is about 12 A. A 6 A MCB is half the right size.
• Motor starting current is roughly 5 to 7 times full load, so 60 to 84 A for a fraction of a second. A 6 A type B MCB trips magnetically at 3 to 5 times rated - 18 to 30 A. The inrush crosses that instantly, so it trips on every start.
• The 1.5 mm2 copper run carries roughly 11 to 13 A in conduit - below the motor's own running current. The cable is undersized as well as the MCB.

Why 32 A is dangerous, not clever

• A 32 A MCB will not protect 1.5 mm2 cable. The cable's safe current is about 11 to 13 A; the MCB would allow more than twice that to flow without tripping, so the cable overheats behind the plaster or in the conduit and becomes the fuse. That is a fire risk hidden inside the building.
• It also does nothing for the shock hazard, which is the more serious complaint.

Correct sizing

• 2.5 mm2 copper minimum (4 mm2 if the run is long), on a dedicated 16 A type C MCB, or better a motor starter with a thermal overload set to the motor's rated current. Voltage drop check: 22 m of 2.5 mm2 at 12 A gives roughly 3 V running - acceptable; on 1.5 mm2 the drop at start would be around 30 V, enough to make lights flicker and starting sluggish.

Why the tingle is a different problem

The tingle is leakage current reaching the metal body, not an overload. An MCB responds to current above its rating; a 30 to 100 mA leakage will never trip it, but it is more than enough to stop a heart. What is needed is a 30 mA RCCB on the circuit or the whole board, plus a real earth path so the fault current has somewhere to go.

Priority logic: shock first, then protection, then the tripping nuisance. A person being tingled today may be electrocuted tomorrow; a tripping MCB only wastes time.

Step 1 - Make safe

• Isolate and lock off the workshop board; tag it.
• Remove the neutral-earth link in the socket immediately and destroy it. That link puts the metal body at neutral potential, which is why the tingle appears when a heavy load like the geyser shifts the neutral.
• Disconnect the earth clamp from the water pipe. A GI pipe is not an earth electrode - it is a path to other fittings and to anyone touching a tap.

Step 2 - Establish a real earth

• Run a continuous 2.5 mm2 earth conductor from each socket and the shaper back to the DB earth bar; no looping socket to socket, no pipe clamps.
• Rehabilitate the earth pit: clean it out, refill with alternate layers of charcoal and salt, water it, and fit an inspection chamber.
• 12 ohm at the pit is too high for a dependable fault path. Aim for a few ohms; a reading above about 8 ohm should be treated as non-compliant and re-done with a longer or additional electrode. Record the reading.

Step 3 - Fix the circuit

• Replace the 1.5 mm2 run with 2.5 mm2, fit a 16 A type C MCB, and provide motor overload protection.
• Tighten the loose neutral link and check every terminal.

Step 4 - Add the protective device

• Fit a 30 mA RCCB at the board, and test it with the test button plus a trip-time test.

Step 5 - Verify

• Earth continuity, insulation resistance, polarity at every socket, and RCCB operation before re-energising.

Reason for this order: earthing and bonding errors kill; sizing errors burn; tripping only annoys. Doing the MCB first, as proposed, would have left the lethal defect in place.

Instruments and records

1. Earth tester (three-pole or clamp type): earth pit resistance, before and after rehabilitation. Refuse to energise if it stays high - a reading like 12 ohm means a fault will not clear fast enough to protect anyone.
2. Insulation resistance tester (500 V): between conductors and earth, and between conductors, for the whole installation and for the shaper circuit separately. A healthy reading is of the order of 1 Mohm or more; a low reading means damaged cable or moisture, and must be found and fixed, not energised past.
3. Continuity tester: end-to-end resistance of each protective conductor from socket to earth bar, including the shaper. A reading of a fraction of an ohm to about 1 ohm is acceptable on these runs; open circuit or several ohms means a joint is bad.
4. Socket tester plus a visual polarity check at all 14 sockets: live, neutral and earth in the right terminals, and no neutral-earth link anywhere.
5. RCCB trip test: the test button, plus a trip-time test at rated residual current (should operate within about 300 ms) and at five times that current (within about 40 ms).
6. Load test of the shaper: start it three times with the RCCB and new MCB in place; check the voltage dip and that nothing trips.

Refuse to energise if

• earth resistance is still above the acceptable band, or any socket's earth reads open;
• insulation resistance is low or varies when the cable is flexed;
• the neutral-earth link has not been removed and verified;
• the RCCB fails to trip, or has been bypassed;
• the 1.5 mm2 cable is still in service with a larger MCB.

Write all readings in a test certificate with instrument serial numbers and date, and have the electrician and the school's in-charge sign it. A verbal 'it is working now' is not a commissioning record; the next person to touch that board needs the numbers.