CW1308 Internal Telephone Cable

Q: Can CW1308 be used for outdoor telephone installations?

No. Standard CW1308 is an internal BT-specification telephone cable with a PVC sheath that is not UV-stabilised or weather-resistant. For outdoor installations, specify CW1128 (polyethylene sheathed, jelly-filled for moisture resistance) or CW1308B (external-grade variant with UV-resistant sheath). Using internal CW1308 outdoors will result in premature sheath cracking from UV exposure and moisture ingress into the pairs. National Cables manufactures CW1308 internal telephone cable to BT specification — for external telecom cable requirements, please consult our technical team.

BT Specification CW1308 Twisted Pairs ISO 9001:2015 RoHS Compliant

Solid 0.5mm bare annealed copper pairs with precision twist lay and colour-coded PVC insulation — built for voice and low-speed signalling on PABX risers, hotel telephone drops, intercom runs, and institutional distribution. Manufactured to BT Specification CW1308 as a made-to-order project cable.

Conductor

Solid bare annealed copper — IEC 60228 Class 1

Pair Count

2–100 pairs (project-dependent)

Conductor Resistance

Max 97.8 Ω/km @ 20°C (0.5mm)

Insulation Resistance

Min 50 MΩ/km @ 20°C

Capacitance Unbalance

Max 500 pF/km

Working Voltage

80V · 0°C to +70°C

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Made-to-order specialist. CW1308 internal telephone cable is manufactured to project specification. Standard sheath colour is white PVC. LSZH (halogen-free) sheath variants and external-grade CW1308B configurations available on request for specific project environments.

Technical Specifications

CW1308 — Typical construction and electrical parameters

Indoor telephone distribution for PABX, administrative blocks, and voice backbones. Electrical parameters are per BT Specification CW1308. Factory test certificates issued per drum serial on request.

Standard configurations — BT Specification CW1308

Pair Count	Conductor	Sheath	Conductor R max (Ω/km)	Insulation R min (MΩ/km)	Cap. unbalance (pF/km)	Typical application
Standard Stock Range — 0.5mm Solid Bare Annealed Copper
2 Pair	0.5mm	PVC White	Max 97.8	Min 50	Max 500	Domestic extension, door entry
4 Pair	0.5mm	PVC White	Max 97.8	Min 50	Max 500	Hotel room drops, small office
6 Pair	0.5mm	PVC White	Max 97.8	Min 50	Max 500	PABX horizontal distribution
10 Pair	0.5mm	PVC White	Max 97.8	Min 50	Max 500	Floor riser, MDF sub-distribution
20 Pair	0.5mm	PVC White	Max 97.8	Min 50	Max 500	PABX backbone, institutional riser
Extended Range — Made to Order
25–100 Pair	0.5mm	PVC White	Max 97.8	Min 50	Max 500	Multi-pair backbone trunks; 50P+ includes optional 1.38mm earth
2–20 Pair	0.5mm	LSZH White	Max 97.8	Min 50	Max 500	Hospitals, public buildings, high-risk fire environments
All values per BT Specification CW1308. Conductor resistance max 97.8 Ω/km at 20°C for 0.5mm; mutual capacitance max 56 nF/km. Confirm specification on factory test certificate per drum serial number.

Electrical parameters — 0.5mm solid conductor reference

Parameter	Limit / value	Notes
Conductor material	Solid bare annealed copper — 0.5mm standard	IEC 60228 Class 1 (solid)
Conductor resistance @ 20°C	Max 97.8 Ω/km	Per BT Specification CW1308
Insulation resistance @ 20°C	Min 50 MΩ/km	Per BT Specification CW1308
Mutual capacitance	Max 56 nF/km	Colour-coded PVC insulation, twisted pair construction
Capacitance unbalance	Max 500 pF/km	Per BT Specification CW1308
Max current per conductor	0.25A	Voice and low-voltage signalling use only
Working voltage	80V	BT voice and signalling circuits — not mains wiring
Operating temperature	0°C to +70°C	Fixed indoor installation
Sheath colour	White PVC (standard) · LSZH white (variant)	Black available on some pair counts

Specification Guide

CW1308 variants — which to specify?

BT Specification CW1308 covers internal telephone cable. Three principal variants serve different installation environments — all use the same 0.5mm solid copper conductor and twisted-pair construction.

CW1308 — Standard PVC

White PVC sheath for dry indoor installation — conduit, surface trunking, and cable tray in PABX rooms, hotel floors, and administrative buildings. The default specification for Commonwealth-region institutional voice cabling.

Standard indoor · white PVC sheath

CW1308 LSZH

Low Smoke Zero Halogen sheath — same conductor and pair construction, halogen-free outer jacket. Specified for hospitals, airports, transit stations, and any occupied building where smoke toxicity is a life-safety concern. IEC 60332-1 flame tested.

High-risk occupancy · LSZH sheath · IEC 60332-1

CW1308B — External Grade

Black LSZH sheath with aluminium polyester foil and UV stabilisation — rated for outdoor and underground duct installation. Specify when CW1308 runs exit the building or traverse exposed external routes before entering the next structure.

Outdoor / duct · black LSZH · Al-foil moisture barrier

Cable Construction

Cable construction — four layers.

CW1308-style internal telephone cable uses a layered construction optimised for voice-frequency transmission and reliable seating in MDF/IDC hardware.

Solid Bare Annealed Copper Conductor

0.5mm solid bare annealed copper (IEC 60228 Class 1) — stable, precise diameter for voice-frequency transmission and reliable seating in MDF / IDC punch-down hardware.

Colour-Coded PVC Insulation — Pair Colours

PVC insulation colour-coded per BT pair colouring convention — limits mutual capacitance (max 56 nF/km) and crosstalk on long horizontal runs. BT colour code: Pair 1 — White/Blue; Pair 2 — White/Orange; Pair 3 — White/Green, and so on.

Pair Twisting

Conductors are twisted into pairs with a defined lay pitch to reduce crosstalk and pickup on multi-pair risers and backbones.

PVC Outer Sheath

Grey PVC outer sheath for indoor installation, suitable for conduit, trunking, and surface routing in equipment rooms, PABX cabinets, and hotel floor wiring.

Key Characteristics

Key characteristics for voice-frequency distribution.

Voice-Frequency Electricals

Twisted pairs and low mutual capacitance insulation help keep attenuation and crosstalk within typical CW1308 expectations on long indoor runs.

Capacitance & loop R targets

Solid 0.5mm Bare Annealed Copper

Solid bare annealed copper (IEC 60228 Class 1) gives a precise, stable conductor diameter for voice circuits and reliable punch-down at MDF blocks, Krone frames, and IDC distribution points.

IEC 60228 Class 1 — solid

CW1308 Procurement Baseline

Dimensional and electrical language aligned to the BT CW1308 reference used in many institutional and Commonwealth-region telephone distribution specs.

BT CW1308 (reference)

Multi-Pair Indoor Backbones

Suited to 5-, 10-, and 20-pair (and project-specific counts) for risers, horizontal distribution, and equipment-room harnessing.

Scalable pair count

Controlled Overall Diameter

Pair colour logic and insulation wall are chosen to keep overall diameter practical for trunking, cable tray, and riser shafts in dense telecom rooms.

See OD table above

Indoor PVC Build

Grey or ivory PVC outer sheath for dry indoor environments — conduit, surface trunking, and controlled voids in administrative and equipment spaces.

Dry indoor only

Applications

Applications.

Commercial

PABX Internal Wiring

Internal wiring within PABX equipment rooms, connecting line cards, extension ports, terminal blocks, and MDF frames.

Hospitality

Hotel Voice Distribution

Horizontal drops from floor distribution to guest-room outlets on low-pair-count CW1308-style runs.

Security

Voice Intercom & Door Phones

Low-voltage audio and signalling between entrance panels and handsets where a twisted-pair telephone-class cable is specified.

Government

Exchange & MDF Rooms

Internal distribution between MDF frames, line plant, and PABX / carrier equipment in dry telecom rooms.

Industrial

Control Room Signalling

Low-voltage signalling circuits within industrial control rooms, including annunciator wiring, status indicators, and field telephone system internal connections.

Healthcare

Nurse Call System Wiring

Point-to-point wiring within nurse call head-end equipment rooms, connecting controllers, annunciator panels, and corridor display units at 24–48V DC signalling.

Certifications & Compliance

Standards this product is manufactured to.

CW1308 internal telephone cable is manufactured to BT Specification CW1308 as a made-to-order project item. Manufacturing operations are certified to ISO 9001:2015.

BT Spec CW1308

British Telecom Specification — Primary Standard

The BT proprietary specification for internal multi-pair telephone cable. Governs conductor material, insulation colour-coding, pair construction, sheath, and electrical performance for PABX, intercom, and voice distribution in Commonwealth-region institutional projects.

Conductor resistance max 97.8 Ω/km @ 20°C (0.5mm)

Insulation resistance min 50 MΩ/km @ 20°C

Capacitance unbalance max 500 pF/km

Factory test certificate per drum serial

IEC 60228

Conductor Standard — Class 1 Solid Copper

CW1308 conductors are solid bare annealed copper meeting IEC 60228 Class 1 dimensional and resistance requirements. Class 1 (solid) conductors provide stable diameter for reliable punch-down and IDC termination in MDF frames and distribution blocks.

Solid bare annealed copper — Class 1

0.5mm standard; 0.4mm, 0.6mm, 0.9mm on order

Stable diameter for IDC / MDF hardware

ISO 9001:2015

Quality Management System

Manufacturing operations certified to ISO 9001:2015, ensuring documented process controls and consistent specification output across every production run. Test certificates issued per drum serial for institutional supply.

ISO 9001:2015 Certificate — available on request

Documented process controls

Lot-level test evidence

Material traceability

IEC 60332-1

Flame Retardancy — LSZH Variant

The LSZH sheath variant of CW1308 is tested to IEC 60332-1-2 (single vertical wire flame propagation). The halogen-free compound also reduces smoke density and eliminates acid gas emission — meeting the life-safety requirements for hospitals, airports, and high-occupancy public buildings.

IEC 60332-1-2 flame test (LSZH variant)

Low smoke, zero halogen sheath compound

Standard PVC variant: CPR Euroclass Eca

Frequently Asked Questions

CW1308 telecommunication cable — technical questions answered.

Common questions from telecom contractors, security installers, IT infrastructure teams, and building services engineers specifying BT CW1308 internal telephone cable.

Can CW1308 be used for outdoor telephone installations?

No. Standard CW1308 is an internal BT-specification telephone cable with a PVC sheath that is not UV-stabilised or weather-resistant. For outdoor installations, specify CW1128 (polyethylene sheathed, jelly-filled for moisture resistance) or CW1308B (external-grade variant with UV-resistant sheath).

Using internal CW1308 outdoors will result in premature sheath cracking from UV exposure and moisture ingress into the pairs. National Cables manufactures CW1308 internal telephone cable to BT specification — for external telecom cable requirements, please consult our technical team.

What is the standard conductor diameter for CW1308?

Standard CW1308 uses 0.5mm solid bare annealed copper conductors (IEC 60228 Class 1). Additional diameters — 0.4mm, 0.6mm, 0.9mm — are available for specific pair counts on order.

Pair counts range from 2 pairs to 100 pairs, with larger multi-pair configurations (50 pairs and above) including an optional separate 1.38mm plain copper earth core. Confirm exact pair count, sheath material (PVC or LSZH), and earth conductor requirement at order specification.

How are pairs identified in CW1308 cable?

CW1308 pairs follow the British Telecom colour code. Typical pair identification:

Pair 1 — White/Blue + Blue/White
Pair 2 — White/Orange + Orange/White
Pair 3 — White/Green + Green/White
Pair 4 — White/Brown + Brown/White
Pair 5 — White/Grey + Grey/White

Higher pair counts continue the sequence with additional base/tracer colour combinations per the BT standard. For exact colour coding on larger pair counts or specific project requirements, refer to the product datasheet.

Does this cable comply with British Telecom specifications?

Yes. Our CW1308 internal telephone cable is manufactured to British Telecom specification CW1308, covering conductor material (0.5mm solid bare annealed copper, IEC 60228 Class 1), pair construction, PVC insulation and sheathing, colour coding, and electrical performance.

The "CW1308" designation itself is BT's own document reference. Verify the CW1308 marking on the cable print legend and request the product datasheet for specific pair count and sheath variant (PVC or LSZH) confirmation.

Is CW1308 suitable for low-voltage alarm systems?

CW1308 can be used for low-voltage signal wiring in intruder alarm systems where a multi-pair solid-copper signal cable is acceptable, typically for internal alarm loops and door-entry systems.

However, for alarm systems that must comply with specific insurance, EN 50131, or fire-detection requirements (BS 5839, BS 4737 categorised cables), dedicated alarm or fire-resistant cable may be mandatory. Always confirm cable requirements with the alarm system manufacturer's installation guide and your insurance/regulatory authority before specification.

Technical Procurement

Request project pricing.

PABX fit-outs, hotel telephone projects, and government EPABX supply. Tell us your pair count, approximate quantities, and project timeline.

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Pair count & drum lengthsQuote 5-, 10-, or 20-pair (or other project counts), standard reel length, and sheath colour — we confirm availability and lead time against current production.

Factory test evidenceRequest loop resistance, capacitance, and withstand tests as required; certificates are issued per drum / lot for institutional supply.

PABX installer supplyDirect supply to system integrators and PABX installers working on hotel, hospital, and corporate projects across North India.