I am facing a problem with LSF sheaths of cables, particularly larger conductor size and armoured cables. In hot weather conditions, the LSF sheaths are developing longitudinal splits particularly during pulling of cables. Which LSF compound manufacturer and grade do you recommend to acheive the best mechanical properties of sheath? Will application of any tape over the armour help in reducing the splitting? If yes, which tape can be used to retain the LSF properties?

Regards,
Sanjay

Please note that:

LSF (Low Smoke and Fume) cable is a UK designation (Low smoke and fume) and is usually to Ministry of Defence Standard DEF61-12 Part 5 LSF.

The materials used are normally sheathing compounds over XLPE or LSF insulations and they have reduced smoke and corrosive gas emissions in a fire when compared with standard pvc insulations.

As we understand it, LSF cable (Low Smoke & Fume) can be manufactured from modified PVC giving off anything up to 18% HCl emissions.

Cables giving off below 0.5% of HCl are classed as Low Smoke Halogen Free (LSHF), Low Smoke Zero halogen (LSZH) and could also be defined as LSF cable.

Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

I agree. When I said LSF, I meant LSZH cables. I look forward to your recommendations on the best LSZH compound manufacturer & grade and on the application of tape over armour wires to reduce splitting of sheath in hot weather.

Regards,
Sanjay

Hello Sanjay,

Without giving away any company secrets, can you tell us what kind of jacketing material (Not the compound manufacturer and designation) you are using now? Likewise can you tell us something about the wire armour underneath the jacket? (Steel or aluminum, helically applied with no crossovers at all?) If there are crossovers, does the jacket splitting start there?

Is the jacket compound you are using now temperature rated for the thickness and pulling normal forces you are placing on it? What is the thickness that you are using?

Have you simulated the problem in the laboratory so you are confident that it is not your jacketing process?

Have you already discussed this with your jacketing compound manufacturer and, if so, what was their reply?

What prompted you to consider a cushion layer tape over the armour?

Kindest regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com

We are using EVA based highly filled jacketing compound from European manufacturer.
The armour is hellically applied steel wires, without any cross overs.
We are using thicknesses as per IEC/BS standards.
The temperature rating for thickness and pulling forces not available.

We are sure, the problem is not due to process. The jacketing material acheives all the LSZF properties but the mechanical & thermal properties are inferior to PVC. Mostly on bigger sized cables (4x150 and above), the splits develop if there are obstructions during pulling like bad roller or corner in the cable tray. This effect is more pronounced in hot weather. When a split occurs, it can sometimes extend upto even 3 - 4 meters. The jacketing compound supplier also confirms that the material is much weaker than PVC due to high filling but cannot offer alternative.

The idea of binder tape over armour was to limit the outward pressure of armour wires on the jacket, particularly at the cable bends.

I am really looking forward to your recommendation on alternative manufacturers of LSZF jacketing compounds.

Regards,
Sanjay

Hello Again Sanjay,

This is just a thought:

Quite often just the opposite of cushioning is necessary to prevent the jacket from splitting. If, for whatever the reason, the core is very soft and spongy, the jacket deformation under larger than normal radial forces can cause the jacket to split. The solution in this case is to add inert, multi-end stranded fillers such as fiberglass to the cable core so that the core becomes quite firm and round.

If indeed you wish to try other jacketing compounds, I suggest you discuss your present problems and requirements with with the following companies:

AlphaGary Corporation www.alphagary.com/sp.cfm?pageid=930 (They have a UK office)

AEI Compounds www.aeicompounds.com/ (UK)

Teknor Apex Company www.teknorapex.com/ (US)

Hopefully others will offer you some good advice as well so please return often to see if additional comments have been posted.

Kindest regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com