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To allow compliance with the LUL fire regulation standards, all joints for use within Section 12 of the London Underground Network must comply with the LUL 1-085 standard.

To enable compliance for joints required in Section 12 areas, 3M developed a universal joint protection system to manage this. It is known as the Smoke, Toxicity, Fire and Fume joint sleeve or STFF for short.

Installation of the STFF sleeve

The sleeve is slipped onto one of the cables ready to be joined and parked back along the cable. The joint is made off in the normal way and the STFF sleeve is now slid over the joint and held in place by two stainless steel cable ties, one at each end.

LUL approved HellermannTyton MBT-type stainless steel cable ties should be used to secure the joint sleeve over the joint. A MK9-SST tensioning tool can also be used to achieve maximum tension on the ties.

There are a number of variants of the STFF shield, including a sleeve design for joints or with a closed end, suitable for cable abandonment applications. A retrofit wrap around version can also be supplied if the joint has already been installed.

Suitable LUL Section 12 and Hazardous Area applications

Designed for use with all single or multi core HV and LV cable joints as well as cable abandonment applications, the STFF joint sleeve is approved on the LUL register (Register Number 1106) for use with 3M Cold Shrink jointing systems.

The joint protection sleeve has applications for jointing on LUL projects as well as other hazardous and petrochemical applications, both on and off-shore.

The 3M joint sleeve can only be purchased with the appropriate joint and is not available as a separate item.

For more information on the 3M STFF sleeves applications, prices and availability, please contact our Sales Team.

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Bentonite and Marconite have certain similarities, they are both ground enhancement materials used to lower the resistance to earth. However, there are a number of differences between the products and the applications they should be used for.

Bentonite Moisture Retaining Clay

Bentonite is often used to reduce the resistance between the soil and earth-electrode (earth rod or earth mat) by retaining moisture. The naturally occurring Bentonite compound consists mostly of montmorillonite, the sodium based clay swells to many times its size when mixed with water.

Available in both powder and granular form, preference usually lies with granular form as it is often considered easier to handle and prepare.

Marconite Conductive Aggregate

Marconite is a synthetic material manufactured specifically for earthing purposes. Utilising specific raw materials and minerals, mixed in carefully controlled ratios. The Marconite compound then goes through a range of manufacturing processes and thermal treatments, designed to create a consistent, fit-for-purpose earthing compound.

The resulting precisely measured, granular mixture is virtually dust free and has exceptional electrical properties.

Bentonite vs Marconite

Resistivity

All earthing aggregates can be called conductive with a resistivity of 5 ohms metres or less. Bentonite has a typical resistivity level of around 3 ohms.m. Marconite with a resistance level of .001 ohm.m, has a far low resistance than its competitors, even when mixed with cement, the resulting resistance level is still only 0.19 ohms.m.

Chemical balance

As Bentonite is a naturally occurring material, there can be anything from 15-20% impurities which can be corrosive and will corrode any earth-electrode connections, resulting in earthing system failure, which can cause costly damage and lengthy repairs.

Marconite is a chemically inert compound and as such is non-corrosive to steel or copper, it does not attack cement structures and has a pH level within the neutral range. Allowing Marconite to be used with all conventional types of cement, as well as most proprietary resin-based cements, adhesives and gypsum plasters.

Versatility

One of Bentonite’s key features is also one of its weaknesses. The ability to absorb rain water once installed, helps increase the conductivity but also makes the material liable to drying out and therefore shrinking or even being washed away entirely. Therefore requiring maintenance every few years, such as adding additional water or salts to continue to achieve the desired earth values.

Suitable for most ground conditions, Marconite becomes a permanent solid structure, especially when mixed with concrete and is not prone to these problems.

High strength

Due to its clay-like nature, Bentonite has limited strength levels, this added to the materials expansion when mixed with water, makes it unsuitable to be included within building structures themselves. Whereas Marconite can achieve strengths higher than Grade 25 concrete and therefore is suitable to be used as part of the building structure.

Cost effectiveness 

When it comes to cost, there is a clear difference between Bentonite and Marconite. Being considerably cheaper, Bentonite offers an earthing solution for cost conscious buyers, although the cost of maintenance every few years should be considered, it can still work out as an effective solution.

Marconite on the other hand is a more expensive product, however once installed, the permanent earthing solution requires no ongoing maintenance so this should be factored in when considering the more costly material.

Ease of use

Both earthing compounds are simple to instal as a backfill for earth-electrodes. However as Marconite can be used to replace sand and aggregates within conventional concrete mixes, it should be carefully mixed in ratios of 3 parts Marconite and 1 part cement by weight, with the addition of 1 litre of water per 4kg total mix.

Due to the slightly more complicated nature of using Marconite within a permanent concrete structure, it is available in a premixed bag. The 25kg premix sack contains pre-measured and pre-mixed ratios of Marconite and Portland Cement powder, requiring only 5 litres of water. Reducing on-site confusion and ratio errors. However the hydroscopic Portland cement used within the premix means it must be used within 6 weeks of purchase.

Marconite and Bentonite each have their own advantages and disadvantages for different applications, with cost and longevity of installation often being the deciding choosing factors. For more information on which earthing compound is best for your needs, please contact our Sales Team for advice.

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The Centaur Cable Saddles are the only solution for cleating large diameter High Voltage power transmission cables, that has been put through, and passed, the most rigorous of short-circuit testing procedures. The cable saddles were designed by Ellis Patents to fill the gap in the market which presented serious safety risks.

The Centaur product range typically handles 275kV to 400kV cables, from 100mm up to 162mm outside diameter, and is generally installed within tunnels and affixed to supporting steel-work.

Why is a short-circuit tested High Voltage cable cleat so important?

At present, neither the British or European standards take into account cleats on cables of this size. As a result, those specifying for such projects are very much left in the hands of the manufacturer, who in most cases, simply provide warranties for their products. The risk lies in the fact that none of the limited number of products available have been short-circuit tested, meaning warranties are based purely on calculations and mechanical tests.

How the Centaur Cable Saddles are tested

Using cables manufactured by ABB in Sweden, the centaur cleats were tested to 162kA peak (63kA RMS) for one second, in both three-phase and phase-to-phase fault installations. A copy of the full test report from KEMA is available upon request.

The saddles have also been successfully tested for corrosion resistance having been subjected to an independent salt spray test, carried out in accordance with BS EN 9227:2006 corrosion tests in artificial atmospheres.

Centaur Saddle Design features

The product consists of an extruded and pressed aluminium saddle and hinged aluminium over-strap retention which incorporates a LSFZeroHalogen (LSZH) nylon liner to cushion and protect the cable in the event of a short-circuit. The saddles are available in lengths of either: 400mm, 600mm and 800mm to allow for different mounting centres. The product range can also be supplemented by intermediate short-circuit straps as well as a roller system for easy pulling of cables.

For more information on the Ellis Centaur saddle range, please contact our Sales Team.

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