The British Approvals Service for Cables (BASEC) is a recognised sign of assurance of independent cable testing and approval. BASEC’s technical team answer hundreds of questions each month from electrical contractors from across the UK covering many different cable related issues. Here are BASEC’s ‘TOP 10’ technical questions in 2011:
1) I am installing some armoured cable and it is developing lumps. What is happening and can I stop it?
If armoured cable is harshly treated the armour wires can become displaced, twisted or stretched, leading to bulges in the sheath material. Cable are uniform and circular in cross section when manufactured, but mishandling can result in bulges and kinks which can cause difficulties in pulling into ducts, termination at glands, as well as being unsightly. Such problems can be caused by incorrect pulling from drums, the introduction of loops and kinks, pulling round too tight a bend, re-drumming too quickly, and other poor practices. If cable is delivered in this condition the supplier should be contacted and if necessary the cable replaced. If it begins to occur during installation, stop and check the pulling conditions, and refer to the supplier.
2) I am terminating cable and the lugs are still loose no matter how hard I crimp them. What should I do?
Firstly, check you have the correct size of lug for the cable’s nominal size. Never use a smaller sized lug just to get it to fit, or the lug could overheat at high current loads. Lugs are designed to take the same electrical current as the conductors they are terminating. Some cable manufacturers make cables with conductors more compacted than normal – this is permitted in the standards – and this sometimes results in additional play when terminating. The solution is to use the manufacturer’s recommended brand of lugs rather than generic products, so that they are correctly sized.
3) I have seen what looks like green gunk seeping out of some old twin and earth cables. What is it and what should I do?
Green gunge (also known as green goo) is sometimes seen exuding from the ends of older PVC insulated and sheathed cable. It is normally seen in cables made in the 1960s and 1970s, but not generally seen in modern PVC cables.
Its origin is the plasticiser used to provide flexibility in the PVC polymer compound. This is generally di-octyl phthalate, which over time or with excessive heat has reacted with the copper conductors to produce copper phthalate (hence the green colour) suspended in the liquid plasticiser. The material is a health concern, so should be handled with care – gloves should be used and waste disposed of properly.
Although there does not appear to be a problem with the electrical performance or safety of the cable itself, any exuded gunge should be removed as it can cause corrosion or affect the action of switches and terminations, potentially resulting in tracking / overheating. It can also cause cosmetic problems such as staining. The affected circuits should be rewired as soon as possible.
The original manufacturer of the cable should be contacted if there are any additional questions.
4. Is there a compatibility problem with cable sheath and insulation materials in contact with polystyrene?
When polymeric insulating materials are in contact with PVC sheath cables, plasticiser migration can take place and cause problems. This migration takes place as the plasticisers used in PVC show signs of solubility in polystyrene. This results in deterioration of the cable sheath and in turn this significantly affects the lifetime of the cable. Where there is direct contact between the two materials, the cable sheath becomes harder and more brittle.
This process can take a long time, and greatly depends on the amount of contact area between the cable and insulation materials however it can be rapid in environments where a lot of polymeric material is used such as temporary buildings.
It is recommended that a suitable conduit, such as leaving an air gap or using a polyethelene or polypropelene tape, between the cable and the insulation is used to ensure that there is no direct contact between the cable and the polystyrene.
5. Is YY cable suitable for use on fixed installations?
Yes, YY cable’s flexible layers make it attractive for linking fixed and mobile equipment – as well as projects involving light mechanical stress and fixed installations. It is found in use in transport infrastructure, building and construction and automation and process control industries as a signal and control cable for machine tools, in assembly lines and plant engineering. If it is to be used in installations subject to the IEE Wiring Regulations, an assessment of equivalent safety and performance should be undertaken and recorded. Care should be taken that any necessary mechanical protection is provided for the cable.
6. Is it acceptable to have welded joints in cable conductors, with heat shrink tubing over the welded joint?
BASEC does not permit approve d manufacturers to make welded joints in multi-strand conductors after insulation has been applied, because this makes the cable non-compliant to the relevant standard. Welding introduces stiffness in the conductor and attempts to insulate the conductor will not be as good as the correctly extruded insulation material. BASEC does permit the jointing of individual strands of copper wire or armour wire, because this is anticipated in the standards, and BASEC also will permit very small repairs on extruded materials. Contractors finding obvious joints in cores of cables, sometimes covered with heat shrink tubing, should seek assistance.
7. I’ve had cable in the past where it has been difficult to separate the sheathing from the insulation, what does this mean?
Cable needs to be strippable in order to install it successfully and safely. A dusting of chalk powder is applied to insulated cores before sheathing or other outer layers are added, but sometimes the amount of chalk is insufficient or a manufacturing fault results in no chalk being applied. A quick check with a fingernail before first fix installation can provide reassurance. If concerns are raised, then try to strip the cable using tools. If the sheathing or bedding does not come away cleanly from the insulation of the cores then contact the supplier and arrange to have the cable replaced.
8. What markings should I look for on cable, how can I be sure it’s compliant?
To help safeguard against the risk of installing cable which is substandard, contractors should ensure that the cable supplied by the distributor is the correctly specified cable and check the markings on insulation or the cable sheath - not just the packaging. BASEC has a simple guide to help contractors check their cable markings.
Look for:
Independent third party approval such as BASEC or HAR
Name of cable manufacturer - their identification stamp
Standard number the cable should be made to (BS)
Purchase records – keep them!
Environment – ensure the cable is compliant for its use
CE marking on packaging
Traceability information to track cable through supply chain
Make sure checks are made on delivery to ensure it complies before installation. If a company installs unsafe cable, not only do they risk costs that could put them out of business but they will have also contravened health and safety regulations.
9. What do I do if I think the cable I have purchased is faulty?
Any concerns about a cable must be referred to the immediate supplier in the first instance, which should be a wholesaler or cable distributor, asking for the problem to be investigated. This is best done before the cable is installed to avoid compounding the problem. If necessary the supplier will contact the cable manufacturer, who should be able to provide prompt technical assessment and assistance in resolving the concerns. If these cannot be resolved and the cable is marked with an approval mark such as BASEC, then BASEC may be able to assist.
10. I am often aware of problem cable alerts in the trade magazines and forums, however the problem is that they often come after it has been installed. If I this happens, what should I do?
Problems with a cable are usually limited to a particular type of cable, a particular size or core combination, and usually to a small number of batches, rather than to all cables from a particular manufacturer. The problem may also be variable, in that only certain lengths of cable are affected. Batch numbers may be found on the sheath marking or on the supply reels or drums, and if from affected batches the supplier (wholesaler or distributor) should be contacted in the first instance, and for advice on what to do next. Usually it is best not to start to replace cable unless the situation has been discussed with the supplier.
For more information about BASEC visit: www.basec.org.uk, email: technical@basec.org.uk, or contact BASEC directly on 01908 267300.
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