7 min read
The three cable types most often confused on site are NYY, NYA and NYAF. All three have copper conductors and PVC insulation; the letters in the name describe the material and the construction. Knowing the difference matters not only for ordering correctly but for the cable working reliably for years where it is installed.
What do the letters mean?
- N — standards-compliant cable
- Y — PVC insulation (a second Y means a PVC outer sheath)
- A — solid (rigid) conductor
- F — stranded, flexible conductor
| Type | Conductor | Outer sheath | Typical use |
|---|---|---|---|
| NYA | Solid, rigid | None (single insulation) | Fixed installation in conduit or trunking |
| NYAF | Stranded, flexible | None (single insulation) | In-panel wiring, moving connections |
| NYY | Solid or stranded | Yes (PVC sheath) | Underground, outdoors, main feeders |
Where NYA is right and where it is wrong
Because NYA is solid, it is the cheapest option per cross-section and gives a wide contact face when clamped into a terminal. In return it does not tolerate bending: run a cable to a panel door in NYA and, after a few hundred open-close cycles, the conductor fatigues and breaks. The fault is insidious — the cable looks intact from outside and the break is inside the insulation.
Why NYAF is the standard inside panels
Being stranded, NYAF bends to a much smaller radius at the same cross-section. Inside a panel, every run from the trunking to a device turns at least once through 90 degrees, and in dense panels that count reaches dozens. NYAF takes those bends without fatiguing the conductor. A ferrule is essential at the terminal: without it the strands spread, only a few end up under the screw, and heating starts at that point.
What sets NYY apart: the outer sheath
In NYY each core has its own insulation, and a common PVC sheath is drawn over them. That sheath is a second barrier against mechanical impact, moisture and UV. Every run going underground, onto a cable tray, outdoors or into a building entrance should be NYY. Underground it also gets a sand bed, brick protection and warning tape; however good the cable, it is defenceless against an excavator bucket.
Three common mistakes
- Running NYA underground: with no sheath the insulation takes on water quickly and RCDs start tripping.
- Using NYA to a panel door: within months the conductor fatigues and breaks, and the fault appears intermittent.
- Connecting NYAF without a ferrule: strands spread, contact resistance rises and the terminal overheats.
Sizing is a separate question
Even with the right cable type, the wrong cross-section gives the same outcome. Sizing follows whichever of three criteria is most demanding: current-carrying capacity, voltage drop and short-circuit withstand. On long runs the decider is usually voltage drop rather than current.
Working with Seval Kablo and Erse Kablo, we ship standard sizes from stock and project quantities by the drum. Send your single-line diagram or take-off list and we will check type and sizing with you.
Frequently asked questions
Is it a problem to use NYA instead of NYAF?
In fixed installations that are pulled once and never move again, there is no problem. But do not use NYA inside panels, especially on runs to the door or to any moving part; a solid conductor fatigues and breaks under repeated bending, and because the fault looks intermittent it takes hours to find.
Can NYY be used inside a building too?
Yes, and it is common on main feeders. The outer sheath gives extra protection. Its only drawback is being thicker and more expensive at the same cross-section, which is why it is usually not chosen for short internal runs.
When is halogen-free (HFFR) cable required?
In buildings where evacuation is difficult and occupancy is high: hospitals, schools, shopping centres, hotels, metro stations and enclosed car parks. Standard PVC cable produces dense smoke and corrosive gas in a fire; halogen-free cable reduces that substantially. Where the specification calls for it there is no equivalent — it must be followed exactly.
Is going up a cable size always the safe choice?
For heating and voltage drop, yes — but there are two limits. First, terminal and device capacity: if the cross-section exceeds what the device accepts, the connection cannot be made. Second, conduit and trunking fill: as size grows, fewer cables fit in the same route and they heat one another. Oversizing also raises cost directly.