Copper power supply cables KH05VV-U (NYM-J)

NYM-J (KH05VV-U) – white copper installation cables with solid conductors for lighting, socket and three-phase circuits inside buildings. 2–5 cores, 1.5–10 mm², 300/500 V, sold by the metre. Below the products: matrix, cross-section and length selection, NYM vs CYKY comparison.

Selection by situation 3×1.5 for lighting 3×2.5 for sockets 5×2.5 three-phase CYKY-L outdoors and underground NHXMH-J halogen-free

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Copper installation cable · for indoor wiring

NYM-J (KH05VV-U) cables | 2–5 cores | 1.5–10 mm² | selection guide

White copper cable for fixed electrical installation inside buildings – lighting, socket, three-phase and sub-board circuits. Below: the range matrix, cross-section selection by current and length, and an NYM vs CYKY comparison.

sizes in range

2–5

cores: L, N, PE, L1–L3

1.5–10 mm²

copper conductor size

300/500 V

rated voltage

Asking: Kibirkštis – a young electrician who isn't afraid to ask. Answering: Fazė – an experienced engineer.

Key point:
NYM-J is the standard cable for indoor wiring: in walls, under plaster, in conduits and trunking. The conductors are solid (class 1), so the cable holds its shape and connects reliably to terminals. Outdoors and underground, choose CYKY-L. The right cable depends on the number of cores (single- or three-phase), the cross-section (load and installation method) and the length (voltage drop).

Quick selection by situation

Situation	Typical choice	View
Lighting circuit, 230 V	3×1.5 mm² (L, N, PE)	3×1.5
Socket circuit, 230 V	3×2.5 mm²	3×2.5
Water heater or other higher-power single-phase circuit	3×4 or 3×6 mm² – by power and length	3×4 · 3×6
Three-phase motor, pump, compressor (no N)	4×1.5 / 4×2.5 / 4×4 mm²	4×1.5 · 4×2.5 · 4×4
Three-phase cooker, 16 A three-phase socket	5×2.5 mm²	5×2.5
Workshop or garage three-phase circuit	5×4 / 5×6 mm² – larger size for longer runs	5×4 · 5×6
Flat or house sub-board supply, three-phase	5×10 mm² – per incoming protection and design	5×10
Control or signalling circuit without PE	2×1.5 mm²	2×1.5

⚠ Check: the table shows the most common cases. The final cross-section depends on load current, installation method and circuit length – see the tables below.

Full range in one matrix

Click a size to open the product page. All sizes are sold by the metre.

Cores \ mm²	1.5	2.5	4	6	10	Purpose
2 cores	2×1.5	2×2.5	2×4	–	–	No PE – special circuits only
3 cores	3×1.5	3×2.5	3×4	3×6	–	230 V: L, N, PE
4 cores	4×1.5	4×2.5	4×4	4×6	4×10	400 V without N: L1, L2, L3, PE
5 cores	5×1.5	5×2.5	5×4	5×6	5×10	400 V: L1, L2, L3, N, PE

Green cell – in our range. Need another size or a project quantity? Write to us – we will send a quotation.

How many cores: 2, 3, 4 or 5?

3 cores – single-phase 230 V
Phase L, neutral N and protective PE. Standard for lighting, sockets and single-phase appliances.

5 cores – three-phase 400 V
L1, L2, L3, N and PE. Suits both three-phase and mixed loads.

4 cores – three-phase without N
L1, L2, L3 and PE. Only for three-phase motors that need no neutral.

2 cores – no PE
L and N only. Not for sockets or class I appliances – special or control circuits only.

KibirkštisI'll also want to power a single-phase appliance from a three-phase circuit. Will 4 cores do?

FazėNo. A single-phase load needs a neutral, so take 5-core NYM-J. 4 cores – only for a purely three-phase motor.

Cross-section by load current and power

Indicative continuous current rating I_z for copper PVC-insulated cable to IEC 60364-5-52, at +30 °C ambient and a single circuit. B2 – cable in conduit on a wall, C – cable clipped directly to a wall or ceiling.

mm²	B2, 230 V (2 loaded cores)	B2, 400 V (3 loaded cores)	C, 230 V	C, 400 V	Typical breaker*	Power 230 V**	Power 400 V**
1.5	16.5 A	15 A	19.5 A	17.5 A	10 A	2.3 kW	6.9 kW
2.5	23 A	20 A	27 A	24 A	16 A	3.7 kW	11.1 kW
4	30 A	27 A	36 A	32 A	20 A–25 A	4.6–5.8 kW	13.9–17.3 kW
6	38 A	34 A	46 A	41 A	32 A	7.4 kW	22.2 kW
10	52 A	46 A	63 A	57 A	40 A	9.2 kW	27.7 kW

⚠ Important: * the breaker is chosen by the rule I_B ≤ I_n ≤ I_z. Grouped cables, cables in thermal insulation or at higher temperatures have a lower rating. The table does not replace an electrical design.
** Power allowed by the typical breaker at cos φ = 1: single-phase P = 230 V × I, three-phase P = √3 × 400 V × I. For motors cos φ is usually 0.8–0.9.

Length and voltage drop

Indicative maximum circuit length for a voltage drop of up to 3 %, with a load equal to the typical breaker current (copper, +70 °C, cos φ ≈ 1).

mm²	Load	230 V single-phase – up to	400 V three-phase – up to
1.5	10 A	≈ 25 m	≈ 45 m
2.5	16 A	≈ 25 m	≈ 50 m
4	20 A	≈ 30 m	≈ 60 m
6	32 A	≈ 30 m	≈ 60 m
10	40 A	≈ 40 m	≈ 75 m

Example: socket circuit 3×2.5 mm², 30 m, 16 A → ΔU ≈ 2 × 30 × 16 × 0.0225 / 2.5 ≈ 8.6 V (≈ 3.8 %) – more than 3 %. With 3×4 mm² – ≈ 5.4 V (≈ 2.3 %).
Single-phase ΔU = 2·L·I·ρ / S, three-phase ΔU = √3·L·I·ρ / S; ρ ≈ 0.0225 Ω·mm²/m.

NYM-J or another cable?

Cable	When to choose	Limitation
NYM-J / KH05VV-U (this category)	Indoor wiring in residential, office and commercial premises	Not for direct burial or unprotected outdoor use
CYKY-L	Outdoors, underground with protection, plant rooms	Black, stiffer, harder to install under plaster
NHXMH-J	Public buildings and escape routes where halogen-free cables are required	More expensive than PVC cables
H07V-K	Flexible single-core wires for panel building and conduits	No common sheath – only in conduit or a panel

Construction and general data

Product type	Copper installation cable NYM-J (AB Lietkabelis designation KH05VV-U)
Conductors	Solid (class 1) annealed copper
Insulation and sheath	PVC core insulation, white PVC sheath
Core colours	Green-yellow – PE, blue – N, brown / black / grey – phases
Rated voltage	300/500 V
Conductor temperature	Up to +70 °C continuous, up to +160 °C during a short circuit
Temperature	In service −30…+70 °C, installation not below −5 °C
Bending radius	At least 5 × cable diameter
Installation	In walls, under plaster, in conduits, trunking, surface-mounted indoors
Sales unit	By the metre

⚠ What to check before buying

KibirkštisBefore buying, I always check these points – it saves both money and a second trip to site.

System: 230 V single-phase → 3 cores; 400 V three-phase → 5 cores (4 – only without neutral).
Load: appliance power (kW) and load current (A), allowing for future expansion.
Length: the whole route from the board to the load plus a margin for connection.
Location: indoors – NYM-J; outdoors or underground – CYKY-L.
Protection: the circuit breaker and RCD must match the cable cross-section.
Project requirements: public buildings may require halogen-free cables.

Most common mistakes and their cost

✗ Mistake	Consequence
NYM-J buried in the ground or left outdoors	The PVC sheath ages and cracks, moisture gets into the cable
1.5 mm² cable on a 16 A breaker for sockets	The cable overheats – fire risk
Length ignored – 2.5 mm² for a 50 m run	High voltage drop, motors struggle to start
4-core cable for a three-phase circuit with single-phase loads	No neutral – a new cable has to be laid
Installed in the cold, below −5 °C	Insulation and sheath crack

Diagram: socket-outlet circuit – wrong and correct

Diagram. Socket-outlet circuit with NYM-J. Three things must match in a socket circuit: the cable cross-section must suit the circuit breaker, the protective conductor PE must run all the way to the outlet, and the circuit needs additional protection by a 30 mA RCD. Left – how it is often done, right – how it should be. The numbers in the diagram match the explanations below it.

KibirkštisI ran 1.5 mm² to the sockets – there are only a few of them. Will it do with a 16 A breaker?

FazėNo. The number of sockets does not matter – a 16 A breaker is too large for a 1.5 mm² cable, especially in a wall or in thermal insulation. For sockets use NYM-J 3×2.5 mm², a 16 A breaker and a 30 mA RCD, and always connect PE to the outlet.

Socket-outlet circuit with NYM-J – diagram: wrong and correct | elsprendimai.eu

☝ Click the diagram to open the enlarged version.

⚠ This diagram is for guidance only and may contain inaccuracies. Before connecting, check against the manufacturer's instructions and the device markings.
The qualified electrician carrying out the installation is responsible for it. UAB „Elektrotechnikos sprendimai“ accepts no liability for connections or possible errors.

Why – explanation by the numbers in the diagram

1Cable and circuit breaker

✗ 1.5 mm² + 16 A → ✓ 2.5 mm² + 16 A (lighting: 1.5 mm² + 10 A)

Why: The breaker protects the cable, not the appliance, so I_B ≤ I_n ≤ I_z and I₂ ≤ 1.45 × I_z must apply (IEC 60364-4-43). Under sustained overload a 16 A breaker is only guaranteed to trip at ~23 A (1.45 × 16 A). A 1.5 mm² NYM-J in a wall with thermal insulation has a current rating of 14.5 A, and 1.45 × 14.5 ≈ 21 A – the cable can run overloaded for a long time without the breaker tripping. In the same installation 2.5 mm² is rated 19.5 A (1.45 × 19.5 ≈ 28 A), so a 16 A breaker protects it. The number of outlets does not matter – what matters is how much current the connected appliances can draw at the same time.

2Protective conductor PE

✗ 2-core cable, no PE at the outlet → ✓ 3-core NYM-J, PE from the PE bar to the outlet contact

Why: The outlet earth contact connects the metal housing of the appliance to PE. Without PE, an insulation fault puts the housing at 230 V, yet the breaker does not trip – the fault current has nowhere to flow until a person touches the housing. With PE connected, the fault current flows through the protective conductor and the breaker or RCD disconnects the circuit quickly. That is why outlets need 3-core NYM-J only; 2-core NYM is only for circuits that need no PE.

3Additional protection: 30 mA RCD

✗ breaker only → ✓ 30 mA RCD (or RCBO); L and N pass through it, PE does not

Why: An RCD compares the current flowing in the L and N conductors. If part of the current leaks to earth – through damaged insulation or through a person – and the difference reaches 30 mA, the RCD disconnects the circuit within a few tens of milliseconds. A circuit breaker cannot detect such a small leakage current, as it only responds to overload and short circuit. That is why socket-outlet circuits up to 32 A require a 30 mA RCD as additional protection (HD 60364-4-41). PE is not routed through the RCD – otherwise the RCD would not see the leakage.

⚡ Safe installation – advice from Fazė

FazėA good cable won't help if it's installed in a hurry. These points protect against faults and electric shock.

Before work, isolate the supply, secure it against switching on and verify that no voltage is present.
Run cables in walls vertically and horizontally, not diagonally – so they aren't drilled later.
Do not bend tighter than the bending radius allows and do not damage the sheath when pulling through conduits.
Measuring insulation resistance before energising a new circuit is recommended.
Electrical installation work must be carried out by a qualified electrician.

FAQ

Asking: Kibirkštis, answering: Fazė.

KibirkštisWhat is the difference between NYM-J and KH05VV-U?

FazėIt is the same cable type: NYM-J is the widely used designation, KH05VV-U is the AB Lietkabelis product designation. The letter J means there is a green-yellow PE core.

KibirkštisCan NYM-J be laid outdoors or underground?

FazėNo. NYM-J is for indoor use. Outdoors and underground choose CYKY-L, and underground use mechanical protection and a warning tape.

KibirkštisWhich cable do I need for sockets?

FazėUsually 3×2.5 mm² with a 16 A breaker; for a long run – 3×4 mm².

KibirkštisWhy is a 2-core cable not suitable for sockets?

FazėIt has no protective PE conductor, so a metal appliance housing remains unearthed.

KibirkštisDo you sell by the metre?

FazėYes, all sizes are sold by the metre; for project quantities we prepare a quotation.