Beatrice Lang
Green slime, also known as green goo or cable cancer, is a common problem in homes with electrical installations dating back to the 1960s and 1970s. The phenomenon is characterised by the appearance of a sticky green substance leaking out of PVC-insulated wiring at switches, electrical plugs, hot points, and light fittings. The slime is caused by a reaction between the copper conductor and the plasticiser used in PVC cables, which can be accelerated by heat in the wiring and high temperatures caused by overloading or loose connections. While the green slime does not pose a significant health hazard, it can cause severe skin reactions and eye irritation. The problem will likely reoccur even after cleaning and replacement of the accessory, eventually requiring a rewire.
| Characteristics | Values |
|---|---|
| Common Name | Green Goo, Cable Cancer, Cable Greening, Green Slime |
| Cause | Reaction between the copper conductor and the plasticiser used in PVC cables |
| Accelerants | Heat in the wiring, high temperatures caused by overloading or loose connections, moisture |
| Colour | Blue-green |
| Consistency | Sticky |
| Health Hazards | No significant health hazard, but may cause skin irritation and severe eye irritation |
| Cleaning | Surfaces may be cleaned with a rag soaked in a petroleum- or alcohol-based solvent such as methylated spirits |
| Prevention | Change switch plates to ones that don't react with PVC |
| Rewiring | Recommended in most cases, to be done by a certified professional |
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What You'll Learn
The reaction between copper conductors and plasticisers in PVC cables
The green slime that appears on electrical plugs is a phenomenon predominantly associated with older PVC-insulated cables. It is caused by the plasticizer, a substance compounded with PVC during the manufacturing of electrical cables, slowly decomposing and reacting with the copper conductor. This reaction produces a sticky, insoluble substance that is green in colour. While this substance poses no significant health hazards, it can cause minor skin irritation for sensitive skin.
The plasticizer migration rate is influenced by the temperature of the cable, with higher temperatures causing the plasticizer to decompose faster. This can be due to overloading or loose connections, which generate heat through arcing between the conductors. As a result, the insulation becomes brittle and cracks, allowing the plasticizer to migrate out.
The degradation of the plasticizer can be accelerated by high temperatures. In one study, PVC-P insulation with an internal metal conductor was oven-aged at 110 and 120 °C to simulate 30 years of service life at 25 ± 3 °C. The activation energy of the plasticizer migration rate was found to be equal to the enthalpy of evaporation of DEHP, a common plasticizer used in PVC insulation.
While newer or better-quality cables contain antioxidants to prevent the accelerated decomposition of plasticizers when heated, even these cables can eventually succumb to the green slime issue. It is recommended that any affected areas be rewired by a certified professional to mitigate the risk of electrical fires. Simply wiping away the green slime will not solve the underlying problem.
To summarise, the reaction between copper conductors and plasticizers in PVC cables can lead to the formation of green slime due to the decomposition of plasticizers and their reaction with copper. This issue is more common in older cables and can be accelerated by high temperatures. While newer cables are better protected, they are not immune to the problem, and any occurrence should be addressed by a qualified electrician.
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The presence of moisture
Moisture can enter the electrical system through various pathways, such as leaks, drafts, or high humidity levels. When moisture comes into contact with the copper conductors in the wiring, it triggers a series of chemical reactions. Firstly, the moisture causes the copper to oxidize, forming copper oxide, which has a distinctive green colour. This oxidation process is accelerated by the presence of heat, as the warm environment increases the rate of the reaction.
Additionally, the moisture can attract and bind with other substances within the electrical system, forming corrosive compounds. For example, in older PVC-insulated cables, moisture can interact with the plasticiser, a chemical compound added to improve the flexibility and insulation properties of the cables. Over time, the plasticiser can break down, releasing hydrochloric acid, which then attacks the copper conductors. This reaction forms copper chloride, also known as verdigris, which has a blue-green colour. The presence of moisture further corrodes the copper, exacerbating the problem.
The combination of oxidation and corrosion processes contributes to the formation of the green slime observed on electrical plugs. The slime is not only unsightly but also poses potential safety hazards. It can become conductive under certain conditions, creating low-resistance paths and increasing the risk of short circuits. Therefore, addressing moisture issues is crucial in preventing and mitigating the formation of green slime. This can be achieved through leak repair, improving ventilation, or using dehumidifiers to reduce humidity levels.
It is important to note that the presence of green slime indicates a more profound issue with the electrical system. While cleaning the slime may provide a temporary solution, it is recommended to consult a certified electrician to inspect and address the underlying cause to prevent future occurrences and ensure the safety of the electrical installation.
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High temperatures caused by overloading or loose connections
The green slime that appears on electrical plugs is predominantly associated with older PVC-insulated cables operating in warm or hot environments. This phenomenon is due to the decomposition of the plasticiser, which breaks down over time, releasing hydrochloric acid from the PVC insulation. The acid reacts with the copper conductor to form copper chloride, which has a blue-green colour. This process can be accelerated by high temperatures caused by overloading or loose connections.
Loose connections can cause high amperages, leading to discolouration and potentially dangerous electrical issues. Overloading occurs when too many devices are plugged into a circuit, causing it to exceed its maximum current capacity. This can lead to increased temperatures, accelerating the decomposition of the plasticiser and the formation of green slime.
In addition to high temperatures, the presence of moisture can also contribute to the formation of green slime. Moisture can track into the back of outlets through wires, attracting further corrosion and reacting with the plasticiser. This results in the formation of conductive paths, increasing the risk of short circuits.
To address these issues, it is important to ensure that connections are tight and secure, reducing the risk of high amperages and overheating. Circuit breakers should be turned off before inspecting and tightening connections to ensure safety. Additionally, addressing any sources of moisture can help prevent corrosion and the attraction of copper chloride, mitigating the formation of green slime.
While newer or better-quality cables contain antioxidants to prevent decomposition when heated, even these cables can eventually break down and succumb to the green slime issue. Therefore, regular inspections and maintenance by certified professionals are crucial to identify and address any potential problems before they become safety hazards.
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The use of lower-quality PVC cables
The green slime phenomenon is predominantly associated with lower-quality, older PVC cables. This issue is more common in cables that are over 25 years old and operating in a warm or hot environment. The phenomenon is less likely to occur in cables manufactured after the 1970s.
PVC cable insulation consists of PVC and a plasticiser. The PVC alone is a hard and inflexible material, commonly used for conduit, pipes, window frames, and similar building applications. The addition of a plasticiser transforms the PVC into a flexible material suitable for cable insulation.
Over time, the plasticiser in lower-quality PVC cables starts to decompose and react with the copper in the cables, producing a green colour. This process is accelerated by high temperatures caused by overloading or loose connections. As a result, a sticky green slime leaks out of the cable insulation. This slime is a nuisance due to its sticky and insoluble nature, and it can cause cosmetic damage to sockets, switches, and walls. While it poses no significant health hazard, it can cause minor skin irritation and stain fabrics and other materials.
To address the issue of green slime, it is recommended to replace the affected cables. While the slime can be cleaned away with petroleum or alcohol-based solvents, this only postpones the inevitable, as the insulation will eventually become brittle and crack. Rewiring the entire property may be necessary in some cases.
It is important to note that even higher-quality cables with antioxidants can still be affected by the green slime issue over time. However, antioxidants help prevent the accelerated decomposition of plasticisers when heated.
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The PVC reacting with the plastic the switch unit or plug socket is made of
The green slime that can appear on electrical plugs and in wall sockets is caused by a phenomenon known as plasticiser migration. Plasticisers are compounded together with PVC to produce the soft, extrudable materials required for electrical cable manufacture. Over time, the plasticiser in the PVC insulation slowly decomposes, reacting with the copper in the wiring to produce a green slime that can leak out of cable insulation. This process is accelerated by high temperatures caused by overloading or loose connections. While this green slime is not highly toxic, it is irritating to the skin and eyes and can be difficult to wash off the skin.
The phenomenon is predominantly associated with older PVC-insulated cables (over 25 years) operating in warm or hot environments. It is more common in cheaper or older PVC cable grades but can still occur in newer cables. In the long term, the migration of the plasticiser out of the cable insulation will cause the insulation to become brittle and crack. This can lead to a complete breakdown of the wiring and the need for a full replacement.
While the green slime itself does not pose a significant health hazard, it is a sign of degrading electrical insulation. As such, it is important to address the issue and not simply wipe away the slime. The affected area may need to be rewired by a certified professional. In some cases, it may be necessary to put aside money for a complete house rewire, especially if the wiring is very old.
To prevent the green slime from occurring in the first place, it is recommended to use newer or better-quality cables that contain an antioxidant. This prevents the plasticiser's decomposition rate from accelerating when heated, providing better protection against the formation of the slime. However, even the best cables can still eventually succumb to the phenomenon given enough time.
If you discover green slime on your electrical plugs or in your wall sockets, it is important to contact a qualified electrician for advice and potential rewiring services. Do not attempt to remove any fittings from walls or ceilings, as this could require immediate rewiring. While it may not be necessary to rewire the entire house, it is a good idea to start preparing for that possibility financially.
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Frequently asked questions
Green slime, also known as green goo or cable cancer, is a sticky green substance that can appear on electrical sockets or switches. It is caused by a chemical reaction between the copper conductor and the plasticiser used in PVC cables.
The plasticiser in PVC cables breaks down over time, releasing hydrochloric acid from the PVC insulation. This acid attacks the copper conductor, forming copper chloride (blue-green verdigris). The verdigris attracts moisture, which corrodes the copper and reacts with the plasticiser to form the green slime.
The green slime can be cleaned with a rag soaked in a petroleum- or alcohol-based solvent such as methylated spirits. However, this only addresses the surface-level issue. To fix the problem, it is recommended to contact a certified electrician to inspect the wiring and determine if rewiring is necessary.
