There are numerous types of corrosion, but the ones that are discussed here are the ones that are most likely to be encountered with underground power cable facilities. In this initial explanation, lead will be used as the referenced metal. Copper neutral wire corrosion is not discussed here. Stray DC currents come from sources such as welding operations , flows between two other structures, and -in the days gone by - street railway systems. Anodic corrosion is due to the transfer of direct current from the corroding facility to the surrounding medium, usually earth.
This report, which is part 1 of a series, provides current ratings for metric sizes of paper-insulated, lead-sheathed cables to BS A further part covers plastic-insulated cables. Ratings are given for cables installed direct in the ground, in underground ducts and in air. Flat TPS is more common than circular, and is used for fixed wiring of domestic and industrial lighting, power outlets, appliances, and HVAC units.
Circular TPS is common in industrial and commercial installations but generally not in domestic installations. Flat " twin and earth " conductor TPS cable for single-phase plus earth. Flat " three and earth " conductor TPS cable for three-phase plus earth.
Green and yellow sleeving is sold separately, to be applied at the ends. The cross section on the main conductor s is given first, and then the cross-section of the CPC.
a. nonmetallic-sheathed cable. Type NM and NMC cables are found in NEC article NEC Article The different sizes of wire and cable. The larger the number, . In some case, fixture wires may be used as a substitute for branch circuit conductors? True or False? Electric cable with a lead outer sheath would be very old indeed. Over the years the insulation around the inner cores would have deteriorated and any installation still using this type of cable should be considered unsafe and isolated immediately as a failure of the inner insulation could cause the outer lead coating to become live. Jan 15, Lead sheathed cables may be found in some installations dating from before about These have rubber insulated, tinned copper conductors and an outer sheath of lead. For reasons of protection against indirect contact (electric shock) it is essential that the lead sheath of every such cable is, and will remain, properly earthed.
In older properties pre cable with imperial sizes are found, sometimes without CPC. Also available in smaller conductor sizes are versions containing three current-carrying conductors and a circuit protective earth conductor.
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These configurations are commonly used for applications such as switched light circuits, battery-backed emergency lighting which requires a switched and unswitched supply, extractor fans with a run-on timer which require a switched and unswitched supply, mains-powered interlinked smoke alarms, and central heating thermostats.
In the Republic of Ireland the situation is different from that in the UK.
Variant Today lead sheathed cables may be found in some installations dating from the
Prior to IS I. However, fromthe option for the uninsulated and reduced CPC has been removed from the standard ISand as such is no longer permitted in new Southern Irish installations.
From Wikipedia, the free encyclopedia. Type of electrical cable for building wiring.
The examples and perspective in this article may not represent a worldwide view of the subject. You may improve this articlediscuss the issue on the talk pageor create a new articleas appropriate.
Cables may be messenger-supported either by spirally wrapping a steel band around the cables and the messenger or by pulling the cable through rings suspended from the messenger. Distance Self-supporting cable is suitable for only relatively short distances, with spans in the range of feet. The introduction of these types of cables goes back to the 's, making some of the first cables produced over 70 years old. head and tail pressure differences can drain oil from the top of a cable while the lead at the bottom of the cable may swell due to the increased pressures. removal of old cables and installation of new cables. The Ettco wire shown above was found in a home, contributed by fatgirlnmotion.com reader Aaron, worrying if Ettco wire contained insulation, notes that. Label on the wire reads ETTCO WIRE & CABLE - V. It is 14 AWG. Aaron's Ettco wire looks like a paint-coated asphalt-impregnated-fabric sheathed electrical wire widely used from about
April Learn how and when to remove this template message. Examples include variations in the concentration of the electrolyte through which the cable passes, variations in the impurities of the metal, or a wide range of grain sizes in the backfill. These concentration cells corrode the metal in areas of low ion concentration.
Lead sheathed cables may be found in some installations dating from
Differential aeration is a specific form of local cell corrosion where one area of the metal has a reduced oxygen supply as compared with nearby sections that are exposed to normal quantities of oxygen.
The low oxygen area is anodic to the higher oxygen area and an electron flow occurs through the covered oxygen starved material to the exposed area normal oxygen level.
Differential aeration corrosion is common for underground cables, but the rate of corrosion is generally rather slow. Examples of situations that can cause this form of corrosion include a section of bare sheath or neutral wires that are laying in a wet or muddy duct or where there are low points in the duct run that can hold water for some distance.
PVC insulated and sheathed cables in a domestic installation - some possible problems? By: Leon Markwell. The thousands of kilometres of PVC insulated and sheathed cables in current use are not without installation and operational problems and this article looks at some that are found in domestic installations. Dec 28, Two other sources, both from the cable manufacturing industry, suggested the reason for CII to seek a ban on lead-sheathed cables could be "an effort of some . Sustained Current Ratings for Paper-Insulated Lead-Sheathed Cables to BS Part 1 (ac 50 Hz and dc).This report provides current ratings for metric sizes of paper-insulated, lead-sheathed cables to BS A further part covers plastic-insulated cables. Ratings are given for cables installed direct in the ground, in underground ducts and in air.
A cable that is installed in a duct and then the cable goes into a direct buried portion is another good example of a possible differential aeration corrosion condition. There are numerous other forms of corrosion that are possible, but the most probable causes have been presented.
An example of another form of corrosion is microbiological action of anaerobic bacteria which can exist in oxygen-fiee environments with pH values between 5. The life cycle of anaerobic bacteria depends on the reduction of sulfate materials rather than on the consumption of free oxygen.
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Corrosion resulting fiom anaerobic bacteria produces sulfides of calcium or hydrogen and may be accompanied by a strong odor of hydrogen sulfide and a build-up of a black slime. Good post! Power cables are the most important in electric fields. I am much impressed by your blog.
Thanks for such a useful information. Consideration for corrosion should be taken further than just power cables, their cleats and support structures also need to be protected against corrosion.
Choosing the correct materials and finishes is key to minimising its effects.
Search for:. Premium Membership. More Information. The point of entry of the stray current usually does not result in lead corrosion, but the point of exit is frequently a corrosion site.