Napit Codebreakers #13

Napit Codebreakers #13

Need help with cracking those EICR codes?

The technical team at NAPIT, with the help of the 18th Edition Codebreakers publication, answer your latest coding queries.

ASH ALLUM: This picture is of some type of junction to extend the kitchen ring. What is going on here?

From looking at the photo, and the sizes of conductors, I’m assuming there is a ring final circuit and a lighting circuit/two-way/switch drop being extended. It’s a fundamental requirement of BS 7671 that an installation can withstand mechanical damage (given its environment), and that joints and terminations are made in an adequate enclosure. There is also a possibility that some of these types of connectors will leave access to live parts.

In this scenario, the connectors are not rated for mechanical damage and the conductors are not supported against strain. There is a possibility that this kind of poor installation method could cause arcing at the joints in the conductors. When a sheathed cable of any type is stripped back, the exposed single insulation must be protected against mechanical damage; this can only be achieved by taking it into a suitably rated enclosure.

Even though this appears to be a roof space, cable containment is still important and the cables, in this case, could benefit from some support or containment, to ensure conductors are not able to flex. These cables have solid conductors and excessive flexing can lead to cracks in the conductors, which can cause arcs.

CM ELECTRICAL SERVICES: We spotted this during a recent inspection – red sleeving over the earth, then the earth was put in the live thermal, the neutral put in the earth and the live was put in the neutral. It’s obviously been like this for years, and the customer says it’s always worked fine!

This has the potential for serious injury. If a Class I item of equipment with earthed exposed conductive parts were to be used here, the casing or exposed conductive parts could very well be at live potential, which could mean that anyone in contact with it and the general mass of earth could receive a shock, proportional to the potential difference between the exposed conductive part and the general mass of earth.

It’s very unlikely there is an RCD supplying the circuit, as a correctly operating one would have identified the supply current leaving the RCD being different to the returning current, as the return in this instance is the cpc.

Without RCD protection, the circuit will most likely always appear to be normal, as the cpc and neutral in a TN-C-S (PME) earthing system, are connected in the service head, and at the star point of the generator/transformer for a TN-S or TT installation. It wouldn’t become apparent there was an issue until the correct polarity checks were carried out.

There will also be current-carrying capacity issues with the cpc, now being used to carry neutral current, as it is not sized for this, and has a potential for overload/overheating This is a simple enough fix, but the potential for danger, from what is likely a DIY install, is very high.

I would be concerned with the rest of the installation, especially if there are signs of alterations, additions and DIY work. The use of red sleeving, which is obviously from an off-cut of cable and not really sleeving as we would normally use, is also a flag that this is very likely a DIY install from before 2005, given the cable colours.

G GIBBON: If you need to run a live and neutral feed out, along with a switch line, and you’ve only got T&E cable to hand, an ingenious way is to forget about the earth and use it as a neutral instead. Don’t forget to rip some lengths of black insulation off some cable and slide it on for good measure. Unbelievable!

Granted, the use of the cpc as a switch live or any other live conductor is extremely dangerous. What we also have to look at here are the exposed live parts, due to the heavily damaged junction box, strain on terminations and inadequate joints.

It is a fundamental requirement that a cpc is carried to every point and accessory in an installation, in accordance with Reg 411.3.1.1. By using the cpc as a live conductor, there is no protection for the circuit, which may become modified elsewhere, if it is not known the cpc is now a live conductor. This has the potential to cause serious injury and is not acceptable for any reason.

The cpc in a T&E cable is not sleeved with basic insulation, because in normal scenarios it is not designed to carry load current, only fault current for a short duration. When using the T&E cpc as a live conductor, which will now carry normal design current, the fundamental requirement of BS 7671 to provide basic protection has been removed.

The damage to the junction box is extensive and has left access to live parts, with strain on conductors which could lead to an even more dangerous situation. In a loft, or other areas accessible by ordinary persons, this damage could quite easily have a fatal outcome.

WILLIAM MARTIN CULLETON: I found this while fault-finding on a kitchen lighting circuit. Who put that joist in the way? They’re lucky not to have also drilled through the ring main!

This is exactly the reason you should mark out where recessed lights and equipment are going to be located, and then check that there are no obstacles. If there are, re-measure and remark.

Before BS 7671 is looked at, I have to mention that Building Regulations will have also been breached here, and this should be noted on the EICR as an observation only. Not only has structural integrity been diminished, but the threat from thermal effects, directly applied to the combustible joist is now very high.

If we look at BS 7671, any wiring system must be designed and installed to take account of its environment. Destroying a support joist and putting a recessed light against it in this way infringes BS 7671. It is very likely that the heat generated by the recessed light in this scenario will not be dissipated as required by its design, which is also something we need to take account of.

As a general rule, unless the manufacturer states a minimum distance from a joist, Regulation 422.3.1 should be adhered to. This is not always possible, especially for recessed lights, so that is why manufacturers’ distances should be used. As a general rule these will be between 50-100mm from a joist but, as stated, manufacturers’ instructions should be used in each case.

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