3-pole MCBs are designed to protect three-phase machinery, distribution boards and plant equipment by disconnecting all live conductors together under a fault. They ensure balanced protection across phases, prevent voltage imbalance and keep three-phase loads running safely under BS 7671.
Quick Answer: A 3-pole MCB breaks all three live conductors simultaneously during overload or short-circuit events. They’re essential on three-phase motors, HVAC plant, industrial equipment, commercial distribution boards and any circuit where phase-linked disconnection is required for safety.
Browse the full range: 3-Pole MCBs
Jump to:
What a 3-Pole MCB Actually Does
A 3-pole MCB provides simultaneous disconnection of all three phase conductors (L1, L2, L3) under fault conditions. This keeps the load balanced and prevents dangerous single-phasing - a major risk on motors and industrial equipment.
They deliver:
- Overload protection (thermal trip)
- Short-circuit protection (magnetic trip)
- Phase-linked switching under faults
- Safe operation of motors and plant equipment
Without a 3-pole device, a fault on one phase could leave the others energised - causing equipment damage, overheating or dangerous torque imbalance.
Where 3-Pole MCBs Are Used
Any circuit carrying a three-phase load requires linked protection. These devices are standard across commercial, industrial and plant installations.
Use a 3-pole MCB for:
- Three-phase motors (pumps, compressors, conveyors)
- Industrial machinery and processing equipment
- Commercial HVAC plant and chiller units
- Three-phase distribution boards feeding sub-circuits
- Large extraction and ventilation fans
- Workshop machinery such as lathes and table saws
They are required whenever phase-linked disconnection is needed to keep loads balanced and prevent equipment damage.
Why Three-Phase Protection Must Be Linked
Three-phase loads rely on all phases remaining energised together. If one phase drops out unexpectedly, motors and machinery can stall, overheat or suffer mechanical stress.
A 3-pole MCB prevents:
- Single-phasing (the main cause of motor burn-out)
- Voltage imbalance
- Overheating of industrial loads
- Dangerous mechanical torque issues
This is why BS 7671 requires linked protection on three-phase circuits - and why 3-pole devices are standard in commercial and industrial settings.
Installer-Favourite 3-Pole MCBs
These units are commonly used on motors, HVAC plant, industrial machinery and commercial distribution boards.
Browse the full selection: 3-Pole MCBs
FAQs
Three-phase protection raises specific questions for installers, especially around single-phasing and machinery safety. These FAQs cover the essentials.
Do 3-pole MCBs isolate the neutral?
No - they disconnect all three live conductors. If neutral switching is required, use a 4-pole MCB.
Can you use three single-pole MCBs instead?
No. They won’t provide linked disconnection and can cause dangerous single-phasing.
Are 3-pole MCBs mandatory on motors?
Yes - motors require phase-linked protection to prevent burn-out or mechanical stress.
Do 3-pole MCBs work with RCDs and RCBOs?
Yes. They are typically used upstream, with RCDs/RCBOs providing earth leakage protection.
👉 Need phase-linked protection for motors or commercial plant? Shop all 3-Pole MCBs