Angle Grinder Keeps Tripping the RCD? Here's What to Check

Every time you start your angle grinder, the RCD trips. Or it works for a bit then cuts out. This is frustrating but it's also a safety issue - the RCD is telling you something's wrong. Here's how to figure out what.

What the RCD Is Actually Detecting

An RCD (Residual Current Device) trips when it detects current leaking to earth - meaning electricity is going somewhere it shouldn't. This could be:

• Inside the grinder itself
• In the cable
• At the plug
• Or the RCD itself might be faulty

Check the Cable First

The cable is the most common culprit, especially on angle grinders which get dragged around sites and run over by everything.

Look for:

• Cuts or damage to the outer sheath
• Kinks where it's been crushed
• Damage near the plug or where it enters the tool
• Any exposed inner wires

If you find damage, don't tape it up and carry on. Replace the cable properly or replace the tool. Dodgy cables kill people.

The Brush Situation

If your grinder has brushed motor (most corded grinders do), worn brushes can cause arcing that trips RCDs. Signs of brush problems:

• Sparking visible through the vents
• Burning smell
• Tool running rough or losing power

Brushes are wear items and need replacing periodically. On most grinders, they're accessible through screw caps on the body. Fit new brushes - they're cheap and often fix the problem.

Dust and Debris Inside

Angle grinders suck in dust constantly. That metal and masonry dust is conductive. Build up enough inside and you get current leakage between components.

Blow out the grinder with compressed air (wear eye protection). Pay attention to the area around the motor and switches. A thorough clean sometimes solves RCD tripping.

The Switch

Grinder switches take a hammering - constant on/off, dust getting in, vibration loosening connections. A damaged switch can cause intermittent earth faults.

If the grinder trips only when you press the switch, or trips intermittently during use, the switch might be the issue. Switch replacement is possible but fiddly.

Moisture Inside

If the grinder's been left in a damp environment or used in wet conditions, moisture can cause earth leakage. Let it dry out thoroughly somewhere warm and try again.

If it's been properly soaked, internal corrosion might mean it's beyond saving.

Test It Elsewhere

Before blaming the tool, try it on a different RCD. RCDs themselves can become oversensitive or faulty. If it works fine elsewhere, the RCD might be the problem.

Also check what else is on the same circuit. Some RCDs are sensitive to the combined load of multiple tools. Try running the grinder on its own circuit.

Extension Lead Issues

Are you running through an extension lead? Check that too:

• Is the lead damaged?
• Is it uncoiled? (coiled leads overheat and can cause problems)
• Is it rated for the grinder's current draw?

A dodgy extension lead can cause RCD trips that seem to come from the tool.

When It's Not Fixable

If you've checked everything and the grinder still trips:

• It might have internal insulation breakdown
• The motor windings might be damaged
• The internal wiring might be compromised

At this point, unless it's an expensive tool worth professional repair, replacement makes more sense. Cordless grinders from DeWalt and Makita avoid the whole mains cable issue entirely and are now powerful enough for most grinding work.

Important: Don't Bypass the RCD

It might be tempting to plug into a non-RCD socket to "solve" the problem. Don't. The RCD is protecting you from electrocution. If it's tripping, something is wrong and needs fixing, not ignoring.