‘PICAS’ stands for Paper Insulated Corrugated Aluminium Sheath cable. These 11kV cables feature a corrugated aluminium sheath, to improve flexibility, the corrugation valleys are filled with bitumen to prevent moisture penetrating along the underside of the outer red PVC sheath, which is added for corrosion protection.

Removing the outer PVC sheath and Bitumen from PICAS Cable

Firstly, the red oversheath should be heated gently with a soft-flame gas torch. Care should be taken to avoid overheating the PVC as this will produce toxic fumes and may even burn.

Once the sheath is warm, but not too hot to touch, it can be cut using a flat bladed cable knife. Start with a circumferential cut then make a lengthwise cut along the cable with the knife to avoid piercing the aluminium. Now you can remove the outer sheath.

With the PVC sheath removed, the bitumen compound can now be cleaned from the cable. Starting from the open end, using solvent wipes and heat from a gas torch, the compound should be thoroughly cleaned from the surface of the aluminium. Care should be taken as to not overheat the cable, doing so could lead to early joint or termination failure.

Removing the Aluminium Sheath From PICAS Cable

Always wear protective gloves when removing the aluminium sheath, the metal can be sharp.

Using a Chinagraph pencil, mark the aluminium sheath at the removal point as indicated on the relevant jointing instruction. If the mark falls between one of the valleys, move the mark to the next crest towards the cut end of the cable.

The aluminium sheath of the PICAS 11kV cable can be removed with a sheath removal tool, which resembles a pipe cutter but has a special twin cutting wheel at one end of the jaw and two positioning rollers at the other end. Always inspect your cable jointing and sheath removal tools as a cutting wheel in bad condition will have to be replaced prior to use to avoid unnecessary damage to the cable.

Apply the tool to the cable with the cutting wheel spanning a corrugation crest. Tighten the tool until the cutter just indents the crest, and then rotate to cut the metal. Gently increasing the cutting pressure by closing the screw control.

The aluminium should be removed in sections, no longer than 250mm each.

With the cores exposed, the cable is now ready for use with the required MV joint or termination.

For more information on cable stripping procedures and tools, please contact us. Learn more about our offer of power cable lugs.

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The transient nature of lightning with its associated fast rise times and large magnitude currents mean that special consideration needs to be given to earthing, for lightning protection to be effective.

Many factors such as soil resistivity variations, installation accessibility, layout and existing physical features are all site specific and tend to affect decisions on grounding methods employed. The primary aim of a direct strike earthing system is to:

– Efficiently dissipate lightning surge energy into the ground
– Help ensure safety of equipment and personnel

Effective Earthing and Lightning Protection Systems

A good earthing systems will feature the following 7 characteristics:

1. Good electrical conductivity
2. Conductors capable of withstanding high fault currents
3. Long life – at least 40 years
4. Low ground resistance and impedance

​The basic philosophy of any grounding installation should be an attempt to maximise the surface area of electrodes of conductors with the surrounding soil. Not only does this help to lower the earth resistance of the grounding system, but it also greatly improves the impedance of the grounding system under lightning surge conditions.

5. Equipotential bonding

Equipotential bonding helps ensure that hazardous potential differences do not occur between different incoming conductors such as metallic water services, power systems, telecommunication systems and the local ground, and also minuses step and touch potentials.

6. Good corrosion resistance

The ground electrode system should be corrosion resistant, and compatible with other conductors that are buried and bonded to the ground system. Copper is by far the most common material used for grounding conductors. In general, some form of maintenance or inspection procedure should be adopted to ensure the long-term effectiveness of a grounding system.

7. Electrically and mechanically robust and reliable

Mechanical coupling can be used to join ground conductors, but suffers from corrosion effects when dissimilar metals are involved. As well as mechanical strength, CADWELD connections provide excellent low impedance, long life electrical connections with excellent corrosion resistance. More information on the benefits of exothermically bonded connections can be found here.

A Typical Earthing System

For more information on our range of lightning protection products, visit the earthing section of our website.

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UL is the abbreviation for the Underwriters Laboratories, this is an independent organisation in the United States to control and certificate product safety. UL provide safety related certification, validation, inspection and testing services to a range of clients including manufacturers, retailers, policy makers and regulators.

Contained within their extensive list of testing and product standards, the UL also specified the flammability test for UL94 for plastic materials. UL94 is a material burning test done on a defined specimen of raw material of the product in question. It does not, however, carry out a flame test on the final product.

UL94 differs between a horizontal burning test UL94 HB and a vertical burning test UL94 V.

For the vertical test UL94 V, there are three flame ratings defined: UL94 V0, UL94 V1 and UL94 V2.

UL94 HB – Horizontal Burning Test

	Test Criteria:	Burning rate of specimen in mm/min.
	Classification:	According to HB

UL94 V – Vertical Burning Test

	Test Criteria:	Afterflame time of specimen. Drip of flaming particles.
	Classification:	According to V0, V1 or V2

In all these burning tests, an open flame is applied for a specified time to the specimen. As the burning behaviour also depends on the thickness of the material, it is important to classify the material not only according to HB, V0, V1 or V2 but also to mention the thickness of the specimen.

The following table is a summary of test procedures and requirements of the above four UL94 classifications:

Looking at the vertical test (V0, V1, and V2) results, it is evident from the above table that a material that complies with the UL94 V0 rating is considerably more flame resistant than products meeting the UL94 V2. When tested, materials that meet V2 ignited the cotton cloth via flaming particles or drops, meaning the product may not be suitable for areas where there is flameable material near by.

It is important to be aware that just because a material is UL94 tested and compliant, there can be a considerable difference in fire performance and safety between two materials, especially between UL94 V2 and UL94 V0.

ETS Cable Components current stock a range of UL94 rated electrical products, including:

– Single Bolt Nylon Cable Cleats – Including LUL approved version
– Two Bolt Nylon Cable Cleats – Including LUL approved version
– Red HV Cable Cleats
– Flexicon Trackside and Rail Vehicle Interior Flexible Conduit
– 3M Scotch 77 Tape
– Powersafe Connectors

For more information on our range of UL94 rated products, please contact our Sales Team.

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Exothermically welded connections and mechanical connections are very similar in their applications, yet their performance can differ greatly.

As UK distributors of nVent ERICO Cadweld welding systems, we explore the benefits of a exothermic bonded connection over mechanical connectors.

The CADWELD Weld

– Will carry more current than the conductor.
– Will not deteriorate with age.
– Is a molecular bond that eliminates any risk of loosening or corrosion.
– Will resist repeated faulty currents.
– Can be quality controlled simply by visual inspection.

Reliability

As the molecular bond eliminates the concept of surface contact, an electrolyte cannot penetrate between the conductors and cause oxidation and deterioration in the course of time.

Corrosive Environments

This reliability is of particular interest for humid or chemical environments or for bonds directly buried in the ground.

Ability To Withstand High Current

The melting temperature of CADWELD filler material is higher than the melting temperature of copper (1082^oC). For this reason, in the event of abnormal heating due to a high fault current, the conductor is destroyed before the connection.

Conductivity

The CADWELD connections form a solid bond around the conductors assuring continuity. The cross sectional area of the weld has greater current carrying capacity than the conductors.

Performance

Standard CADWELD welds have a cross section greater than that of the conductors to be joined, which compensates for the difference in resistivity between the conductor and the welding material. Consequently, under fault conditions, the weld will always remain cooler than the conductor.

If special applications do not allow for the required increase in cross section to be employed, the use of the formula:

Which will make it possible to define precisely the resistance of the CADWELD weld.

Comparison between CADWELD bonded connections and mechanical connections

CADWELD Weld	Mechanical Crimped Connection
	Actual Contact Surface
The CADWELD bonded connection provides permanent conductivity over the whole of the section due to a molecular bonding between the metal surfaces.	The mechanical connection presents a significant difference between the apparent contact surface and the actual surface.

Exothermic Welding Video Playlist

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