Technical Guidence

  • Recommended Cable -
    Drum Handiling Practices
  • Recommended Cable Storage Practices
  • Pre-Installation Instruction
  • Cable Installation Guide
  • Cable Installation Feed-In- Setup
  • DC "Hi-Pot" Testing Guidelines
  • Properties of Fire Performance in Cable

RECOMMENDED CABLE HANDLING PRACTICES
Cable Drum should never be shipped flat side down. Cable Drums that arrives in this manner should either be rejected or may be accepted after thorough inspection.

Evidence of damage during shipment may be ascertained by inspecting the Cable's protective covering, if damage is found, the same should be immediately reported to the Transporter.

Cable Drums should never be dropped from the delivering vehicle to the ground. It should be ensured that the unloading equipment do not come in contact with the Cable surface or the protective wrap, if provided with e protective wrap.

If unloading of Drum is accomplished by Crane, then it should be ensured that either a cradle supporting the Drum flanges or a shaft through the bore hole is used. If Fork-lift is used it should be ensured that forks must lift the Drum at 90 to the flanges and the forks must be long enough to make complete lifting contact with both flanges. It must be ensured that under no circumstances should the forks come in contact with the cable surface or the protective wraps.

In the event of an inclined ramp is used for unloading, it should be ensured that the ramp is wide enough to accommodate both the flanges completely. The stopping of the drum at the bottom shall be done by using the drum flanges and not the surface of the cable.

HOW TO HANDLE CABLE

RECOMMENDED CABLE STORAGE PRACTICES

Storage & Storage Maintenance
Finished cable have no established shelf-life. Oxidation and discoloring can be caused to the conductor if exposed to moisture and atmospheric conditions. Uncovered / unsheltered cable will degrade due to exposure to direct sunlight and/or the elements. This can be avoided by protecting the cables ensuring no degradation of insulation.

In general, cables meant for indoor application should be stored indoor. However, cable suitable for outdoor application may be store d outside but proper care should be taken that the cables are provided with end seals to prevent ingress of moisture / water into the cable.

Cable should be stored in a sheltered area and should be covered with Masonite or Dark film wrap to block sun rays. Cables with sub-zero temperature marking may be stored in low ambient temperature area. However, Cables without sub-zero marking should never be stored in low temperature area.

Cable drums should never be stacked or stored on their sides and must remain in upright position. Cable drums should be stored with protective covering or lagging in place. If a length of the cable is cut from the drum, the cable end should be immediately sealed to prevent ingress of moisture. If a part length is returned to storage, the drum's protective covering should be restored.

Drums should be stored on a flat, hard surface so that flanges do not sink into the earth. The weight of the reel and cable must be carried by the flanges at all times. Wooden drums should be stored off the ground to prevent rotating.

Cable reels and lagging must not be stored for an extended time period in direct contact with water or dampness. Timbers or metal supports must be placed under the drum flanges to provide elevated storage of the drums away from direct contact with water or damp soil.

Cable reels and lagging must not be stored for an extended time period in direct contact with water or dampness. Timbers or metal supports must be placed under the drum flanges to provide elevated storage of the drums away from direct contact with water or damp soil.

Drums should be stored away from the construction equipments where falling or flying objects may cause damage to the cable. Cable should be stored in areas where chemical or petroleum will not be spilled or sprayed on the cable.

Cable should be stored in an area away from open fires of high heat zone.

In the event drums are relocated, they should be handled as suggested in the "Recommended Drum handling practices" section and inspection made on each drum during relocation.

If the cables are stored in a secure area and are not subjected to the adverse effects of weather, an annual inspection would be sufficient. Where the drums are exposed to weather, a bimonthly inspection should be carried out to observe any sign of deterioration.

If the drums are exposed in a non-secure area inspection at frequent intervals may be required depending upon the circumstances.

Records of delivery date, manufacturer, installation date, any extenuating circumstances, along-with all test reports should be kept on file.

Recommended Minimum Permissible Bending Radius

While installing the cables, the following minimum bending radius should be observed so that the Cable, particularly insulation is not damaged. Wherever possible larger bending radius should be maintained.

Rated Valtage (KV) PVC & XLPE Cables
Single Core Multicore
Upto 1.1 Kv 15D 12D
Above 1.1 to 11 Kv 15D 15D
22 Kv & 33 KV 20D 20D
Where D is the Outer Diameter of cable

PRE-INSTALLATION INSTRUCTIONS

Overview

To ensure reliability and safety during cable installation the following points may be checked prior to installation :

  • The selected cable is appropriate for the desired application.
  • No damage has occurred on the cable in transit or storage.
  • Review all applicable codes and practices to verify that the selected cable is suitable for the application.
  • Any existing cable damage is promptly identified precaution may be taken to ensure that no further damage occurs. This can be ensured by proper cable inspection, handling and storage.

Cable Inspection

  • Inspect every cable reel for damage before accepting the shipment. Extra caution may be taken if,
  • A Drum is lying flat on its side.
  • Several drums are stacked together.
  • Other freight items are stacked on the Drum.
  • Nails have been driven into the drum flanges to secure shipping blocks.
  • Drum flange is damaged.
  • Cable covering is removed stained or damaged a drum has been dropped (likely chance of hidden damage).

Cable Handling

All nails and staples should be removed from the drum flanges before moving a drum. Avoid all objects that could crush, gouge or impact the cable while moving. Cable should never be used as a means to move a drum.

Recommended bending radii should be observed while unreeling, use swivels to prevent twistling and overruns.

INSTALLATION

Overview

Generally cables are subjected to more mechanical stress during installation than they ever experience in actual operation. Handling and pulling the cable as per manufacturers recommendations is of prime importance. The following are the 5 prime considerations in cable installation :

  • Ambient Temperature
  • Equipment
  • Conduit fill
  • Mechanical fit in raceway
  • Physical limitations

Installation Temperature

Low temperatures are causes for concern while installing cable in low ambient temperature area. Cable installation should be avoided when the ambient temperature is less than the cold bend temperature rating of the cable plus 15 centigrade. Minimum installation temperature may not be marked for cables meant for normal temperature region.

Prior to performing a low temperature (less than 10F) cable installation, cable should be stored for a minimum of 24 hours at a Temperature of 55F or higher. Cable should be pulled more slowly and trained in place the same day it is removed from storage. Avoid impact, drop, kink, or bend cable sharply in low temperatures. It should also be ensured that ambient temperature should be less than the maximum temperature limit of the cable.

Equipment

Proper usage of appropriate equipments are crucial for a successful cable installation. The details of equipments needed for most installations are as below :

  • 0-1/5/10 kip Dynamometer
  • Basket grip pullers
  • Cable cutter
  • Cable pulling lubricant Cable tray bend sheaves
  • Cable tray rollers
  • Capstan type puller
  • Diameter tape
  • Drum arbor
  • Drum brakes
  • Drum jacks
  • Duct cleaning mandrels
  • Duct testing mandrels
  • Electric safety blankets and clamps
  • Extension cords and GFCI protection
  • Fishtape or string blower / vacuum flood lamp
  • Gang rollers, with minimum 4 ft effective radius
  • Gloves
  • Guide-in flexible tubing (elephant trunks)
  • Hand winches (come-a-long)
  • Hipot tester
  • Lint-free rags
  • Make-up air blowers and hose
  • Manhole cover hooks
  • Manhole edge sheaves
  • Measuring tapes
  • Personal Safety clothings
  • Plywood sheets
  • Portable Electric Generator
  • Pre-lubing devices
  • Pulling ropes
  • Pump, diaphragm
  • Radios or Telephones
  • Several wire rope slings of various lengths
  • Shackles / Clevis
  • Short ropes for temperature tie-offs
  • Silicone caulking (to seal cable ends)
  • Swivels
  • Warning flags, signs

CABLE INSTALLATION FEED-IN SETUP

The following diagrams illustrate various cable feed-in setups

DC HIGH POTENTIAL (HI-POT) TEST OF CABLE (APPLICABLE FOR 3.3 KV AND ABOVE)

Overview

  • This procedure is intended to provide general guidelines for high potential DC testing of power cables.
  • All tests made after cable installation and during the guarantee period shall be made in accordance with applicable specifications.
  • All safety precautions must be observed during testing at high voltage.
  • Read and follow the operator's manual for the particular test set being used.

Test Equipment

DC test equipment is available in wide range of voltage grades. Accessories like barriers, rubber gloves, non-conducting rubber hats must be used for safety point of view. An appropriate safety officer may be consulted.

Test Procedure

As guided in IS 1255. The details are as below :

The following must be ensured before performing any DC high potential test :

  • All equipments must be disconnected from the cable system i.e. Transformers, Circuit Breakers, motors etc. This will cause damage to such equipments and will prevent test interruptions due to flashovers and/or trip-outs resulting from excessive leakage current.
  • Maintain adequate clearance (approx. 75 cm) between the circuit test ends and any grounded objects and to the other equipments not under test.
  • All circuit conductors not under test should be grounded with cable shields including nearby equipment.
  • Termination kit manufacturers should be consulted for maximum test voltage recommendations with time limits. Follow IS:1255 guidelines.
  • The DC test voltage may be applied either continuously or in predeterminded steps to the maximum value as per applicable specification.

Continuous method

Test voltage is to be applied at an approx. increment rate of 1 Kv per sec or 75% of the rated current output of the equipment, whichever is less. Some equipment may take longer time to reach the maximum test voltage because of the amount of charging current.

Step method

Test voltage is to be applied slowly in 5 to 7 increments of equal value to the maximum specified limit. Sufficient time-gap is to be maintained at each step to allow the leakage current to stabilize.

Hi-pot testing procedure

Unless circuits of high capacitance are involved, this requires only few seconds. Record leakage current at each step.

Test voltage at the prescribed value and stipulated time as per specification needs to be applied. The following times are normally considered sufficient. At the end of the test period, set the voltage control to zero, allow the residual voltage on the circuit to decay, then ground the conductor just tested.

Caution

It should be appreciated that DC charges on cables can build up to potentially dangerous levels if grounds are removed too quickly. Maintain solid grounds after the test on the cable for at least 4 times the duration of the test. On longer cable lengths it may be necessary to increase the grounding time.

Acceptance testing

After installation and before the cable is placed in regular service, the specified test voltage shall be applied for 5 minutes

Proof testing

At any time during the guarantee, the cable circuit may be removed from service and tested at a reduced voltage (1.5 times the rated voltage) for 5 minutes. Record the leakage current at one minute intervals for the duration of the test time involved

Testing problems

Extra leakage current

  • Failure to guard against corona
  • Failure to clean insulation surface
  • Failure to keep cable ends dry
  • Failure to provide adequate clearance to ground
  • Improper shield termination

Erratic readings

  • Fluctuating voltage to test set
  • Improper test leads

Environmental influences

High relative humidity Dampness, dew, fog Wind, snow Results vs. cable life

To date there is no established evidences for correlating DC test results and cable life expectenancy.

Note :

Frequent high voltage tests on cable installation should be avoided. This test is to be done only when absolutely necessary.

Acceptance Test

This test is performed to detect any defects in cable insulation and termination arising out of poor workmanship or mechanical damage. DC testing is not expected to reveal deterioration due to aging in service. This proof test confirms the integrity of the insulation and accessories before the cable is put into service. Testing recommendations during installation at the DC test voltage specified in the Table below, applied for 5 minutes before commissioning.

Maintenance test after installation :

After the cable is completely installed and placed in service, a DC proof test may be done any time within the first five years at a voltage 1.5 times the rated voltage applied for 5 minutes. After this period DC testing is not recommended. Test voltage here should be determined depending upon the condition of cable joints, terminations etc. or if repaired in some place, test voltage will not be lest than the rated voltage.

Rated Voltage (Uo/U) KV Test Voltage KV
1.9/3.3 5
3.3/3.3 9
3.8/6.6 10.5
6.6/6.6 18
6.35/11 18
11/11 30
12.7/22 37.5
19/33 60

Note :

DC test voltage are applied to find out gross problems such as improperly installed accessories or mechanical damage. This is not expected to reveal any deterioration due to aeging in service. There are some evidence that DC testing of aged cross-linked polyethylene cable can lead to early cable failures.

PROPERTIES OF FIRE PERFORMANCE IN CABLES



DETAILS OF FIRE TEST

In order to determine the behavior of cables in case of fire, a group of standards has been developed in order to establish conditions of fire and to measure the behavior of the cable in such situation, but it should be taken into account that those tests are used to assess the behavior of the cables under established, reproducible conditions and that they are not necessarily those of the actual installation. The current IEC regulation considers the following cases :

Flame retardant (Standard IEC 60332-1)

A flame in contact with the sheath of the cable for an established period of time should not lead to propagation. This prevents the cable from being the origin of a fire caused by a minor incident or an external source of heat coming in contact with the cable.

Flame spread (Standard IEC 60332-3-22)

A fire unrelated to the cable can affect a cable tray (worst case if it is in a vertical position allowing air circulation creating the socalled chimney effect). If the decomposition temperature of the organic materials is reached, an exothermic combustion (with the contribution of energy) of the cables takes place with the consequent propagation of the fire. The insulation and sheath compounds can be formulated to make this exothermic reaction limited (by the addition of inhibitors). To simulated this situation, the test consists of the application of a high energy gas burner to a bunch of cables arranged to reproduce a vertical cable tray with forced air. Under those conditions, the fire provoked in the cables should extinguish within a time established in the standard. Based on the amount of combustible material per meter for bunch exposed to the fire action, the IEC standard defines different

Zero halogen and low smoke cable

If the cables are immersed in a situation of fire and depending on the constituent materials, they can release gases which are toxic for the health of people or corrosive affecting the correct operation and preservation of the electronic and computer components in the vicinity. They can also release smoke which, due to its opacity, makes it difficult to see the escape routes from the spaces affected.

To minimize those effects, Laser Cable has developed the low smoke zero halagen series which minimizes harmful halogenated emissions (IEC 60754-1 and 60754-2) and reduces substantially the opaque smoke emissions in accordance with IEC 61034-1&2.

Fire-resistant (Standard IEC 60331)

For circuit integrity and all those systems which need to maintain service under fire conditions, there is the IEC 60331 standard where the fire conditions to which the cables are tested is defined, and which have to continue in service even if the fire has destroyed the organic parts of same.,br>
In the standard, the cable is exposed to a ribbon gas burner for a maximum time of 180 minutes or higher as specified in standard and at a minimum temperature of 750C or higher as specified in standard, while being subjected every 5 minutes to shocks simulating debris fallout. We produce better fire-resistant cables to withstand higher temperatures than standard, giving an extra margin of safety in this field. During the test and at the end of it the cable has to maintain circuit integrity although all of its organic parts have disappeared.