What Is Green Goo in a Consumer Unit?

If an electrician has ever opened your fuseboard and mentioned green goo, or you have spotted a green, sticky substance around your electrical connections, you are looking at copper corrosion. It is technically called verdigris — a chemical reaction that happens when copper wiring is exposed to moisture over time.

Green goo forms on the copper connections inside your consumer unit, usually around the terminals where cables are secured. It starts as a thin green film but can build up into a thick, paste-like deposit that coats the connections and surrounding components.

This is not something to ignore. Green goo is a sign that moisture has been getting into your consumer unit, and it can cause serious electrical problems if left untreated. We see this regularly during EICR inspections across Rotherham and South Yorkshire, particularly in older properties and homes with boards mounted on external walls.

Why Does Green Goo Form?

The root cause is always moisture. Copper is a reactive metal, and when it comes into contact with water — even small amounts of condensation — it oxidises and produces copper carbonate, which is the green substance you can see.

The most common reasons we find green goo in consumer units in Rotherham and South Yorkshire include:

Consumer unit on an external wall. If your fuseboard is mounted on a wall that faces outside, temperature differences between indoors and outdoors can cause condensation to form inside the enclosure. This is the most common cause we see.

Poor sealing around cable entries. If the knockouts on your consumer unit were not properly sealed when cables were run in, moisture from the surrounding wall or loft space can get in.

Leaks from above. A slow roof leak, leaking pipe, or condensation running down from a cold loft can drip onto or near the consumer unit over months or years.

Damp in the property. Homes with rising damp, penetrating damp, or poor ventilation can have high enough humidity levels that condensation forms inside the board.

Age of the installation. Older consumer units — particularly the rewireable fuse boards still found in many properties across Rotherham, Maltby, Wickersley and surrounding areas — are more vulnerable because their enclosures are less well sealed than modern units.

Why Is Green Goo Dangerous?

Green goo is not just a cosmetic issue. It creates real electrical safety risks:

Increased resistance at connections. The corrosion builds up on the contact surfaces between the cable and the terminal. This increases electrical resistance, which means the connection generates more heat when current flows through it. Over time, this can cause the terminal to overheat and potentially start a fire.

Loose connections. As the copper corrodes, the cable can lose proper contact with the terminal. A loose connection arcs and sparks — both fire hazards. We often find burnt or discoloured terminals alongside green goo during inspections.

RCD and MCB failure. If corrosion reaches the internal mechanisms of your RCDs or MCBs, they may not trip when they need to. This means the safety devices designed to protect you from electric shock or fire may not work.

Degraded cable insulation. In severe cases, the moisture that caused the green goo also attacks the PVC insulation on your cables, making it brittle and prone to cracking. This exposes live conductors and creates a shock risk.

Failed EICR. Any consumer unit with significant green goo will fail an Electrical Installation Condition Report. This is classified as a C2 observation (potentially dangerous) or even a C1 (danger present) depending on severity.

What Do We Do About It?

When we find green goo during an EICR or routine inspection, the recommended course of action depends on how severe the corrosion is.

Mild corrosion (thin green film on a few connections). If the board is otherwise in good condition and the connections are tight, we can clean the affected terminals, re-terminate the cables, and seal the cable entries to prevent further moisture ingress. We will also investigate and address the source of the moisture.

Moderate to severe corrosion (thick deposits, multiple affected circuits, signs of overheating). In most cases, the right answer is a consumer unit replacement. A modern metal consumer unit with proper IP ratings and sealed cable entries will solve the problem at its root. We fit consumer units that comply with the latest BS 7671 wiring regulations, with RCBO protection on every circuit.

We carry out fuseboard replacements across Rotherham, Sheffield, Barnsley, Doncaster and the whole of South Yorkshire. The work typically takes four to six hours and includes full testing and certification.

How to Prevent Green Goo

Prevention is straightforward once you know the cause:

Address damp issues. If your property has damp problems, getting them resolved will protect your electrics as well as the rest of your home.

Seal cable entries. All unused knockouts and cable entries on your consumer unit should be properly sealed with grommets or blanking plates.

Ventilation. Ensure the area around your consumer unit has adequate ventilation to prevent condensation buildup.

Regular inspections. An EICR every five years for homeowners and on change of tenancy for landlords will catch green goo before it becomes dangerous.

Upgrade old boards. If you still have a rewireable fuseboard or an old plastic consumer unit, upgrading to a modern metal-clad unit with proper sealing is the single best thing you can do.

Frequently Asked Questions

Is green goo an emergency?

It is not usually an immediate emergency, but it should not be left. If you can see signs of overheating — burnt plastic, discolouration, a burning smell — turn off the main switch and call an electrician straight away. Otherwise, book an inspection as soon as you can.

Will my EICR fail because of green goo?

Almost certainly, yes. Green goo indicates moisture ingress and corroded connections, both of which are coded as C2 (potentially dangerous) or worse on an EICR report.

Can I clean the green goo myself?

No. Never open your consumer unit or touch any electrical connections yourself. This is work that must be carried out by a qualified, registered electrician. There are live parts inside a consumer unit that can kill.

Book a Free Inspection

If you have spotted green goo in your fuseboard, or you are due an EICR, get in touch. Mat will inspect your consumer unit, explain exactly what is going on, and give you clear options with no pressure.

WhatsApp Mat About Green Goo

Or call 07817 171954 — we cover Rotherham, Sheffield, Barnsley, Doncaster and all of South Yorkshire.