Meter Tail Regulations
If you’re in the process of installing a new consumer unit or conducting electrical inspections, it’s crucial to have a solid understanding of the meter tail regulations in effect. As of the current year, which is 2024, these regulations fall under the guidelines set out in the 18th edition of the wiring regulations, often referred to as BS7671.
Although there isn’t a specific document titled “meter tail regulations,” various sections within BS7671 pertain to the installation of cables, including the essential meter tails. Let’s break down the key sections of BS7671 that apply to meter tails:
Now, since this guide primarily aims to assist you with 18th edition electrical inspections (EICRs), our focus will mainly revolve around what you should be looking for during such assessments. However, it’s also vital to understand the considerations for installing meter tails in a new electrical setup.
For a comprehensive grasp of meter tail regulations, it’s advisable to cross-reference this information with our “Consumer Unit Regulations Guide 2024,” as it includes specific sections that relate to meter tails. This additional resource can provide further insights into this critical aspect of electrical installations and inspections.
Requirement for adequate support for Meter Tails/Cables
This is something which is far and away the most common issue with meter tails. They are often hung from the meter over to the consumer unit (or even fuse board on older installations). This is often on the fashion of a large “lazy loop” as the thick cable does not bend too easily.
Adequate support for meter tails or cables is a fundamental requirement, and it’s worth noting that this is one of the most frequently encountered issues in the field of electrical installations. Meter tails are commonly observed to be hung in a rather haphazard manner, stretching from the meter to the consumer unit, or in older setups, the fuse board. This arrangement often takes the form of a large, somewhat sagging loop, resembling a “lazy loop.” The reason for this practice is the relative inflexibility of the thick cable, which doesn’t lend itself to easy bending.
To ensure the safe and effective functioning of the meter tails, it’s imperative to address this concern. Proper support and organization of these cables are vital not only for neatness but also to avoid potential hazards. Let’s explore some key considerations for addressing this issue:
- Secure Fixtures: Install appropriate fixtures or cable clips that provide sturdy support for the meter tails. These fixtures should be designed to handle the weight and rigidity of the cables.
- Avoid Lazy Loops: As mentioned, the “lazy loop” configuration should be avoided. Instead, aim for a more direct and structured path from the meter to the consumer unit. This minimizes the risk of accidental damage and tripping hazards.
- Maintain Clearance: Ensure that the meter tails are routed to maintain adequate clearance from any obstructions or other wiring. This helps prevent overheating and potential damage.
- Proper Bending Radius: While meter tails may be less flexible than other cables, they still have a minimum bending radius that should not be exceeded. Be aware of this specification when planning the cable’s path.
- Compliance with Regulations: Always follow the regulations and guidelines outlined in the 18th edition wiring regulations (BS7671) regarding the installation of meter tails. These regulations exist to ensure safety and efficiency in electrical systems.
In summary, addressing the issue of adequate support for meter tails is essential for maintaining a safe and organized electrical installation. By avoiding lazy loops, using secure fixtures, maintaining clearance, and adhering to regulations, you can enhance the reliability and safety of the meter tail arrangement.
I’ve personally encountered an instance that might leave you baffled – a tenant hanging an umbrella by the handle from the drooping meter tails! It’s a stark reminder of the casual approach that some people take towards electrical safety. Loose connections within main switches and electric meters are, without a doubt, a substantial source of fire risk. This underscores the critical importance of securing meter tails in a manner that places no undue strain on the terminations.
To achieve this, there are several methods to consider:
- Meter Tail Gland: A modern solution is to use a meter tail gland on the consumer unit. These are designed to provide a secure and strain-free connection for the meter tails, reducing the risk of loose terminations.
- Clips and Fixings: Alternatively, clips specifically designed for securing meter tails can be employed. In an 18th edition installation, it’s essential to use heat-resistant fixings for this purpose, ensuring they can withstand the demands of the electrical system.
When inspecting older installations, especially those where meter tails pass from an external cabinet through a wall cavity to the consumer unit, attention to detail is crucial. In most cases like this, the cable passing through the wall provides adequate support, assuming the length of the tails within the meter cabinet is not excessive.
However, a potential issue arises when the cable runs through thermal insulation, a situation frequently found in modern houses with cavity wall insulation. In such cases, a close inspection should be conducted (where feasible) to ensure there has been no thermal damage to the cable due to the installation method. Detecting and addressing such issues is vital for ensuring the safety and functionality of the electrical system.
So, the takeaway here is to always prioritize secure and strain-free connections for meter tails. Whether using modern meter tail glands, heat-resistant fixings, or diligent inspections, these efforts go a long way in mitigating fire risks and ensuring electrical safety.
Do Buried Meter Tails Need RCD protection?
It might sound peculiar, but indeed, meter tails buried in walls at a depth of less than 50mm from the surface require additional protection in the form of a 30mA RCD (Residual Current Device). This is a safety measure to prevent electrical hazards in such scenarios.
It’s essential to highlight that when cables are buried in walls containing metal parts, they must be RCD protected, regardless of the cable’s installation depth. This is a non-negotiable safety measure, as metal parts can conduct electricity and pose significant risks.
A common installation method for meter tails involves running them from an external meter cabinet through the wall cavity, and then into the consumer unit through the rear of the board. While this method may not align precisely with meter tail regulations specified in BS7671, it’s worth noting that this setup generally doesn’t present any apparent risks to the cable, especially when thermal insulation is accounted for (as mentioned in the previous section).
However, when it comes to cables buried less than 50mm beneath the wall surface, the situation changes. This is a scenario that’s not encountered very often, but there are specific cases where it arises. For instance, in older buildings converted into flats, where 16mm T&E cables are used as meter tails or submain cables. These cables may run throughout the building to supply individual flats.
In such cases, it’s challenging to trace the precise route of the cable through the building’s structure. Given the more significant nature of the submain cable, it’s advisable to seriously consider upgrading it. An ideal solution here is to use SWA (Steel Wire Armoured) cable, as it doesn’t require RCD protection in accordance with meter tail regulations.
Adding a 30mA RCD at the beginning of such a setup could lead to nuisance tripping issues and wouldn’t meet the requirement for the division of circuits to minimize inconvenience. Therefore, upgrading the cable to SWA provides a more effective and compliant solution.
Meter Tail Regulations – Identification Of Conductors
When delving into these regulations, it’s crucial to keep in mind the correct identification of conductors. This is vital for maintaining electrical safety and ensuring the system operates as intended.
On a single-phase supply, you’ll typically have two conductors: Live (L) and Neutral (N). However, when dealing with three-phase supplies, all three phases require distinct identification, along with the Neutral conductor. This differentiation is usually achieved through the colour of the conductor, a standard practice in electrical installations.
It’s worth noting that beyond the meter, there should be no unsheathed basic insulation. Exposed wires or cables pose a significant safety hazard, so this requirement is in place to mitigate risks.
In line with these considerations, some meter tails are now being manufactured with coloured sheathing. This design ensures that each conductor can be accurately identified, promoting safety and making it easier to work with the electrical system. When working with such meter tails, it’s essential to follow the manufacturer’s guidance and ensure that the colour coding is adhered to throughout the installation process. This helps maintain the integrity of the electrical system and minimizes the potential for errors during installation and maintenance.
The most common type of meter tails you’ll encounter is the plain grey sheathed variety. These cables, by their appearance, are indistinguishable from one another. However, it’s crucial to implement external identification measures to differentiate the conductors. This can be achieved in several ways:
- Lettering or Numbering: A simple and effective method is to label the conductors with letters or numbers. This external identification makes it easy to discern which conductor is which. For example, you might label them as L1, L2, L3 for the phases and N for Neutral.
- Colour Coding: While plain grey sheathed meter tails lack distinct colours, you can use color-coded tape or heat shrink sleeves to mark the conductors. This visual distinction simplifies identification and helps prevent errors.
- Conduit or Trunking: If the meter tails are enclosed within conduit or trunking, labelling or colour coding can be applied to the outside of these protective enclosures.
- Identification Sleeving: Using pre-printed identification sleeves is another effective method. These sleeves can be slipped over the cable ends, providing clear labels for each conductor.
- Terminal Blocks: For connections at the consumer unit or meter, you can use terminal blocks that come with clear labelling options. This ensures proper connection and identification of the conductors.
- Marking at Joints: When conducting splicing or connecting meter tails, clearly mark the conductors at these junction points to avoid any confusion.
External identification not only helps electricians during installation but also simplifies future maintenance and troubleshooting. It’s an essential practice for ensuring the accuracy, safety, and functionality of the electrical system, especially when dealing with meter tails that have plain grey sheathing.
Meter Tail Regulations for TT Installations
TT earthing arrangements have distinct requirements that go beyond those of Terra-Neutral (TN) systems. The primary difference lies in the need for additional safety measures due to the potential risks associated with TT systems.
In TN systems, the low loop impedance ensures that the main supply fuse or other main Overcurrent Protective Devices (OCPD) would disconnect if the meter tail were to accidentally contact the external enclosure of a metallic consumer unit or distribution board. This level of protection stems from the electrical characteristics of the TN system.
In the past, plastic (insulated) consumer units were exclusively used with TT earthing arrangements, as they mitigated the risk of live conductors coming into contact with the metallic enclosure. However, changes introduced in AMD3:2015 to the 17th edition of the wiring regulations mandated that all main switchgear in domestic properties must be of a non-combustible type, meaning metal enclosures.
The challenge with TT systems is that their loop impedance is generally much lower, which means they can’t be relied upon to disconnect the supply in the required time to prevent electrical hazards in the event of a live conductor coming loose and contacting the metal enclosure. As a result, specific regulations for meter tails in TT installations are more comprehensive compared to standard TN setups.
In TT installations, one critical requirement is ensuring the secure placement of the meter tails within the enclosure itself. This can be achieved through the use of a gland on the consumer unit body. Additionally, there are consumer units available with two hoop clamps positioned directly above the main switch. These clamps provide an added layer of protection to minimize the risk of accidental contact between the meter tails and the metal enclosure.
The goal of these regulations is to enhance safety in TT earthing arrangements and reduce the likelihood of electric shock or fire hazards associated with the use of metal consumer units in such systems.
Indeed, when installing a metal consumer unit in a TT earthing arrangement system, it’s imperative to make sure that the meter tails have their full ‘double insulation’ – more accurately, the outer sheathing of the cable – extended all the way to the entry point of the main switch. This meticulous practice is essential to minimize the risk of any potential contact between live conductors and the metallic enclosure when used within a TT system.
The ‘double insulation’ concept, where both the conductor insulation and an additional outer sheathing protect the cables, adds an extra layer of safety. It reduces the chances of inadvertent contact or short circuits within the enclosure, which could otherwise lead to electrical hazards, such as electric shock, fires, or damage to equipment.
By ensuring that the meter tails maintain their full ‘double insulation’ up to the entry point of the main switch in a metal consumer unit, you greatly enhance the overall safety of the TT earthing arrangement system. This practice aligns with the regulatory requirements for TT systems and is a crucial step in preventing potential electrical issues and associated risks.
Choosing The Correct Size Cable
Sizing meter tails for domestic and small-scale three-phase installations involves relatively straightforward requirements. It’s important to ensure that the cable size is appropriate for the specific application to maintain safety and efficiency:
- 16mm are fine for 60A, 63A & 80A main supply fuses (BS88/BS1361 Type2)
- 25mm are required for 100A main supply fuses
When inspecting electrical installations with 16mm meter tails, it’s essential to be aware of certain considerations regarding the supply fuse and the cable size. Here are some crucial points to keep in mind:
- BS1361 Type2 Supply Fuse Holders: Newer BS1361 Type2 supply fuse holders often have “100A” written on a label, indicating the maximum-sized fuse that can be fitted. However, it’s important to note that the heads may contain lower-rated supply fuses, such as 80A, particularly in newer homes. Therefore, the labelled maximum does not necessarily reflect the actual rating.
- Avoid Disturbing the Main Fuse: When conducting inspections on installations with 16mm meter tails, it’s generally best practice not to disturb the main fuse, whether it is sealed or not. Checking the rating of the main fuse can be challenging without the appropriate documentation.
- Check for Separate Stickers: In some cases, there might be a separate sticker that indicates the actual rating of the fuse fitted, rather than the maximum rating of the fuse carrier. If such a sticker is present, it can provide the needed information.
- Consult the Distribution Network Owner (DNO): If information on the main fuse rating is not readily available, you may need to reach out to the DNO for clarification. However, even they might not always have detailed information, especially for older installations.
- Consider Future-Proofing: In new domestic installations, it’s advisable to fit 25mm meter tails. This is a proactive approach that considers the increasing demand for electrical power, especially with the rise of Electric Vehicles (EVs) and modern technologies. Many DNOs now specify 25mm as the minimum cable size for new connections to accommodate these growing current demands.
Ultimately, ensuring that meter tails are appropriately sized and that the main fuse rating aligns with the installation’s needs is essential for electrical safety and efficiency. When in doubt, consulting with a qualified electrician or the DNO can help you make informed decisions about meter tail sizing and main fuse ratings.
Rules on Max Length Of Meter Tails
Regulations regarding the maximum length of meter tails can vary and are often specified by the Distribution Network Operators (DNOs) rather than following the standards outlined in BS7671. It’s essential to be aware of these DNO-specific requirements, as they may differ from one area to another. Here are some important points to consider:
- Maximum Length of Meter Tails: Many DNOs stipulate that the maximum allowable length of meter tails should not exceed 3 metres without implementing another method of fault protection between the main service head and the consumer unit or distribution board. This requirement is in place to ensure that electricians don’t rely solely on the main service fuse (usually a BS1361 type 2) for fault protection.
- Methods of Fault Protection: To comply with the DNO’s regulations, one common solution is to install a “switch fuse” between the meter and the consumer unit. This switch fuse includes its own built-in fuse that provides additional fault protection for the meter tails if they are longer than 3 metres.
- Upfront DP MCB: In some cases, an upfront Double-Pole Miniature Circuit Breaker (DP MCB), often with a rating of 63A or 80A, is installed to provide protection to the tails after the switch fuse. However, this approach can sometimes lack selectivity, as a fault downstream may result in the upfront MCB tripping.
- Application in Flats/Apartments: These arrangements are commonly seen in flats and apartments where the incoming supply and meter are located much farther than the 3-metre limit set by the DNO. In such scenarios, a room dedicated to switchgear and meters on the ground floor is often utilized. The meter tails enter a switch fuse in this room before running up the building to serve each individual property.
- Different Cable Types: The cable used between the switch fuse and the property’s consumer unit is often something other than traditional meter tails. Steel Wire Armoured (SWA) submains or split concentric cables are commonly employed in these cases.
- Contacting the DNO: If you are unsure about the specific regulations of your local DNO or need to ensure compliance, it’s recommended to contact them directly. They can provide you with the necessary information and guidance to ensure that you do not extend the meter tails beyond their maximum allowable length, which is typically around 3 metres.
Adhering to the DNO’s requirements for meter tail length is essential to maintain electrical safety and regulatory compliance, particularly in situations where the standard 3-metre limit cannot be met due to the layout and location of the meter and consumer units.
Summary Of Regulations 2024
For a quick summary of the most important meter tail regulations, here’s a concise list of the key points:
Adequate Support: Ensure that meter tails are adequately supported to prevent strain on the connections
Sizing Based on Current Rating:
- EICR: Use 16mm cable for up to 80A and 25mm cable for up to 100A.
- New Installations: Typically, DNOs may require 25mm cables to accommodate modern demands, especially for Electric Vehicles (EVs).
TT Installations: Meter tails must have continuous sheathing all the way to the main switch. Special consideration should be given to preventing strain on connections, often achieved using hoop-type cable grips above the main switch.
Protection for Cables Buried Close to Walls: If any cables are buried less than 50mm from a finished wall surface, they must be provided with 30mA RCD protection. Note that this protection may not meet selectivity requirements between protective devices when used up-front.
Proper Conductor Identification: Conductors must be correctly identified to avoid confusion regarding polarity.
Maximum Length per DNO Regulations: Distribution Network Operators (DNOs) often specify that the maximum length of meter tails cannot exceed 3 metres without some form of consumer fault protection in between.
These regulations cover the fundamentals of meter tails, ensuring safety and compliance with industry standards and DNO requirements.