Which cable for an induction hob?

Two things settle which cable to use for an induction hob: the connection diagram in the hob's manual, and a cross-section calculation made for the particular installation. The diagram states how many live and protective conductors the circuit is to have, while the cross-section follows from the power of the hob, the way the cable is laid, the ambient temperature and the length of the run from the distribution board. Permanent installations use rigid copper cables such as YDY and YDYp — but which version goes into the hob circuit is decided on site by the electrician.

Single-phase (230 V) or three-phase (400 V) connection?

The answer to which cable suits an induction hob begins before the cross-section — with establishing how the hob is supplied. That is decided by the diagram in the hob's manual and by whether one phase or three has been brought into the property. Induction hobs have a terminal block with links, and their arrangement differs between a 230 V and a 400 V supply — always according to the hob manufacturer's manual.

The method of connection translates directly into the cable. With a single-phase supply the entire power of the hob flows through one line conductor, so the current in the circuit is at its highest. With a three-phase connection the load is spread across three phases and the current in a single conductor is correspondingly lower.

The same model may therefore need a different cross-section depending on whether it runs on 230 V or 400 V. Many hobs allow both arrangements, but the permissible connection schemes are listed only in the appliance's manual, and it is that manual which determines what cable has to be bought.

What cross-section for a 7 kW induction hob?

The question of which cable suits a 7 kW hob has no single answer divorced from a particular installation. Several factors affect the choice of cross-section at once:

• the rated power of the hob and the method of connection — single-phase or three-phase;
• the way the cable is laid: concealed in conduit, surface-mounted, or in a layer of thermal insulation;
• the ambient temperature and the number of circuits laid alongside each other;
• the length of the run from the distribution board to the hob, and therefore the permissible voltage drop;
• the requirements of the hob manufacturer's manual and of the installation design.

With a single-phase supply the whole power of such a hob loads a single line conductor, so the result of the calculation comes out higher than when the same power is spread across three phases. What cross-section is needed is settled by a calculation made for the particular installation and compliant with the applicable installation standards — not by the power read off the rating plate, nor by a value carried over from another installation. In YDY and YDYp cables from three cores upwards the largest available conductor is 2.5 mm², so a higher calculated result falls outside that range.

With a three-phase connection the current is spread across three phases and the calculated result is correspondingly lower. If the calculation indicates 2.5 mm², the five-core version corresponding to it is YDY 5×2.5 450/750 V — whether that cross-section is right for a particular hob, run and method of installation is, however, settled by the electrician making the connection.

In detached houses it is especially easy to overlook the length of the run: a dozen or more metres from the distribution board to the kitchen is already a stretch over which the voltage drop has to be calculated, not estimated.

How many cores: a 3-, 4- or 5-core cable?

The number of cores follows from the connection diagram, not from what is convenient to install. The diagram in the hob's manual and the installation design state how many line conductors the circuit covers and whether a neutral and a protective conductor are needed in it. With a three-phase connection — that is, where a cable for a three-phase hob is required — the terminal diagram states this directly.

In the EŁKTRIM range rigid installation cables come in two-, three-, four- and five-core versions. The four-core variants are currently available in both collections, and the five-core only in the round YDY. Core identification complies with PN-HD 308 S2:2007, and each product page gives the colour scheme:

• 3 cores: blue, green-and-yellow, brown;
• 4 cores with a protective conductor: black, brown, green-and-yellow, grey;
• 4 cores without a protective conductor: black, blue, brown, grey;
• 5 cores: black, blue, brown, green-and-yellow, grey.

In this scheme the protective conductor is green-and-yellow and must not be used as a live conductor — neither as a line nor as a neutral. The four-core version exists in two arrangements, with and without a protective conductor, so the required arrangement is read from the hob diagram and from the installation design, and the number of cores is not reduced on one's own initiative.

From the distribution board to the hob: YDY or YDYp?

Both types are rigid installation cables with solid copper conductors, PVC insulation and sheath, sold in 100 m coils; the outer sheath is white or black, while the insulation of the individual conductors carries the colours listed above. The product pages state that they are intended for permanent installation, without additional mechanical protection, for surface-mounted and concealed installation in dry and damp environments, at an operating temperature from −30 °C to +70 °C.

What differs is the shape: YDY is round, YDYp flat. The flat shape can be more convenient when laying in chases and under a layer of plaster, while the round one is easier to pull into protective conduit — and only that variant is available in five-core versions. Which of them goes into the hob circuit follows from the installation design and from the way the run is routed.

The rated voltage given in the product name also matters. The designations 300/500 V and 450/750 V describe the cable itself — the strength of its insulation — and not the voltage present in the circuit; Polish domestic installations work at 230/400 V. Among YDYp cables the 300/500 V designation applies only to the two-core versions, while all YDY cables and the three- and four-core YDYp versions are rated 450/750 V.

Protection of the hob circuit

A hob is supplied by a separate circuit run from the distribution board, not from a general socket circuit. The overcurrent protective device is chosen together with the cable cross-section — so that it protects the cable at the expected load — while the scope of residual current protection follows from the installation design.

For that reason this guide gives no ready values of current or breaker ratings: they depend on the installation and are set on site by the electrician, after checking the manual of the hob or induction cooker. Work on an electrical installation should be carried out by a qualified electrician.

What to order for an induction hob

Once the connection diagram and the result of the calculations are known, what remains is the choice of type and number of cores. The five-core versions, used with a three-phase connection, are in the YDY cables collection, and the flat two-, three- and four-core versions for concealed installation are in the YDYp cables collection. All are sold in 100 m coils, and when ordering it is worth paying attention to the number of cores, the cross-section and the rated voltage given in the product name.

If the calculation indicates a cross-section larger than 2.5 mm² — as happens with a single-phase supply to a high-power hob or induction cooker — there is no suitable variant among YDY and YDYp cables from three cores upwards. It is then worth discussing the choice before ordering: questions about technical support and help with selection are taken through the contact form, and by telephone the support team answers on +48 669 055 666 (service in Polish, Mon–Fri 8:00–15:00).