6

I need to replace an induction hob that has been broken with another of the same model (IKEA Matmässig, just for sake of completeness).

Original connection options

The original connection to the mains was made according to the highlighted scheme below, 400V 2L-1N, corresponding to the two-phase set-up that is very common in the Netherlands.

2 live 1 neutral wiring

The only difference is that the connection to the Neutral terminal uses both the blue and grey wires to the Perilex-type plug. On the plug itself, the grey wire corresponds to the L3 pin. However, the actual supply to the socket is two-phase, and the pole corresponding to L3 on the socket has 0 volts on it.

Original connection options

The new version of the hob is slightly different. The connection options include a 400V two-phase connection scheme, and an additional scheme for the NL. It seems to me that either of these would work fine.

My questions:

  • what's the actual difference between the first and third schemes shown below?
  • if the Perilex system has a pole that is sometimes live (three-phase) and sometimes neutral (two-phase) isn't that a potential for unfortunate misunderstandings?

IKEA Matmässig connection options

15
  • 1
    @JimStewart There's definitely no switch, but in the second diagram, you can see the shunts that need to be installed to bridge the two neutral terminals (for 2L 1N) or to bridge both live and neutral terminals (for 1L 1N). Jul 23 at 11:26
  • 1
    If you have 400 V service, you definitely DO NOT use the jumper across L1 and L2. This would be a direct short and trip the breaker. The designation L1 L2 means they are different phases and cannot be shorted. The jumper would go across the two neutral terminals because the two phases can share the same neutral Jul 23 at 15:56
  • 1
    Looks like in the Netherland each phase has its own neutral. Why, I don't know. Is there perhaps a practice in the Netherlands where you do not actually have two phase power, so you feed the two sides from two breakers on the same phase, each with its own neutral? You might get more mileage doing a search in Dutch on this topic rather than English.
    – jay613
    Jul 23 at 17:34
  • 2
    @jay613, there are indeed homes in the Netherlands that are supplied with only a single phase. Usually smaller, older homes where it was believed that all expected demand could be supplied by a single phase. Jul 23 at 17:46
  • 1
    So maybe the third diagram provides for the appliance to deliver its full power potential in such homes? But do older homes with one phase exist only in the Netherlands? I don't think so. I think they exist in many countries. So I wonder if there's something else about the Netherlands?
    – jay613
    Jul 23 at 17:55
6

The original connection to the mains was made according to the highlighted scheme below, 400V 2L-1N, corresponding to the two-phase set-up that is very common in the Netherlands.

Actually, the common 400V 2 phase setup in the Netherlands is 2L-2N with the second neutral on what you indicated as the L3 pin.

And it is not even a proper 2-phase, but rather 2 single-phase connections joined together.

what's the actual difference between the first and third schemes shown below?

The difference is that you have 2 neutral wires that may need to be balanced against the corresponding live wire in the amount of current they are carrying, versus a single neutral wire.

With the old hob (and the left wiring diagram on the new one), if your panel has two GFCI-type circuit breakers that are tied together to supply the hob, there is a chance that both breaker independently measure a dis-balance between the current supplied on the hot wire and the current returning on the neutral wire and conclude there is a ground fault, when in reality some current is supplied on the live wire of breaker 1 and returning on the neutral wire of breaker 2.

With the right wiring diagram of the new hob, the hob can ensure that current arriving on L1 is returned on N1 and correspondingly for L2/N2.

if the Perilex system has a pole that is sometimes live (three-phase) and sometimes neutral (two-phase) isn't that a potential for unfortunate misunderstandings?

This I cannot really answer, as I am not an electrician. But you should be able to tell at the panel if the Perilex socket is supplied with 2 or 3 phases. It is just not safe to blindly plug in a new appliance without checking if the supply to the socket matches the needs of the appliance.

6
  • Thanks Bart, this makes sense (except that apparently, these Perilex sockets can be wired up arbitrarily, so the live and its return are not easily associated with each other). Jul 23 at 19:00
  • Is this an apartment in a mult-unit bldg or is it a semi or fully detached house? Jul 23 at 19:04
  • 2
    It's quite uncommon to have two independently-working ground-fault breakers protecting a circuit like this. Most commonly you just have two ordinary circuit breakers, the levers joined together with a clip so they trip together, with shared ground fault protection further downstream. Swapping the two neutrals shouldn't have any effect in most situations. Jul 24 at 14:46
  • @Tom van Der Zanden, in the 240 V 2L 2N arrangement would the appliance have an automatic shut-off if one of the two circuits would not supply current? Jul 24 at 20:45
  • 1
    @JimStewart Usually the control electronics are powered off a single circuit. If that circuit fails, the entire hob won't work. If the other circuit fails, the control electronics might detect it and shut down. If not, it will typically result in two out of the four burners not working. These hobs are typically designed as two separate, identical modules (each powered off its own circuit) powering two burners each. Jul 24 at 20:56
5

Sure, lots of people think the same thing. "Neutral is just neutral, who cares? It's all the same back at the panel." But we're not back at the panel. We're here. So it matters.

It sounds like they used 4-core+ground cable to bring 2 hots (black brown) and 2 neutrals (blue gray) from the panel to here. A little odd, but OK.

if the Perilex system has a pole that is sometimes live (three-phase) and sometimes neutral (two-phase) isn't that a potential for unfortunate misunderstandings?

Yeah, you're darned right! I would expect at the least for the wires to be painted, taped or sleeved to indicate their functionality.

So... First thing you need to do is look in the consumer unit and make SURE that's really true, and that cable's gray terminates at the neutral bar. Because if it goes to a hot phase, this is going to get "explodey".

Anyway, if both blue and gray go to the neutral bar, then you can wire it up as in diagram 3.

what's the actual difference between the first and third schemes shown below?

The hob is wired so that the current on terminal 1 is returned on terminal 4*, and the current on terminal 2 is returned on terminal 5*.

Therefore each hot wire returns its current on a separate neutral.

That is very important if a house is wired single-phase with both hots at the same phase potential (0 volts between them). If both tried to return on the same 1 neutral wire, it would overload that neutral wire.

"But it wouldn't be 1 neutral wire, it would be 2 neutral wires paralleled!" Are you so sure? Who's to say one of those neutral wires hasn't broken or had a poor connection? What you want, if a neutral wire breaks, is for the hob to quit working so the human goes and fixes it. If one neutral wire fails silently, the other one overloads silently. That's why paralleling isn't allowed (without exotic protections such as fusing).

Obviously this doesn't matter if the 2 hots are on different phases. But this allows phases to be rearranged without worry.


* or these, reversed.

2
  • Harper, in these cables with two neutrals are the neutrals marked so they are distinguishable? Jul 24 at 20:54
  • 1
    @JimStewart The Netherlands is conduit-land, so there are typically no power cables in the walls (at least not in residential installations), everything is done with wires in (rigid or flexible) PVC conduit. Neutrals are required to be light blue (unless you're in a very old house, where neutrals used to be red and blue was one of the phases, don't ask).
    – TooTea
    Jul 25 at 19:15
4

The secrets of cooktops

Most cooktops sold in Europe support being fed using either a single phase or two phases. The way this works is that internally the cooktop is split into two halves, so that one "L" terminal feeds say the left two zones and the other "L" terminal supplies the right ones. This holds for both traditional and induction cooktops.

Such a cooktop can then be connected in two main ways:

  • Single phase, both "L"s jumpered together and connected to the line wire, all of that on a single-phase circuit. The two halves of the cooktop are thus wired in parallel. Given that circuits are pretty much always limited to 16 A, this limits the total power available. Old-school traditional cooktops would trip the breaker when you turn all the zones on to max power, modern induction cooktops can typically be programmed to limit the total power.
  • Two phases, each connected to one "L" terminal and supplying one half of the cooktop. This gives you nearly 7.4 kW total, which is pretty much enough for everyone.

Note that "400 V" in these installation manuals never refers to the actual voltage. I've never seen a cooktop that would be really connected in a delta-like fashion, using the 400 V phase to phase voltage. "400 V" is just a supposedly customer-friendly shorthand for "three-phase service".

Now for the Netherlands

Many people are stuck in flats with only single-phase service. As I mentioned above, in most of the EU it has the annoying consequence of limiting your cooktop to 3.7 kW total (unless you have a >16 A circuit, which is typically not allowed for circuits like this). A Dutch workaround for this is that you feed the cooktop with 2x16 A from a single phase. This is called a "kookgroep", implemented by means of two single-phase breakers with a handle tie.

Your cooktop then doesn't need to care whether you have a true three-phase service or not. (Remember that cooktops don't really run on 400 V, so they don't care the least whether both "L"s are fed by the same phase or not.)

The catch here is that neutrals don't have overcurrent protection. That's not a problem with a two-phase feed, because 16A L1-N plus 16A L2-N is equivalent to -16A L3-N on the neutral. But if both halves are fed by the same phase, the neutral would see twice the current and catch fire. You can't just parallel the wires by connecting them at the ends, because the load would never split evenly. But you can use a separate neutral wire for each half of the cooktop, which is what the last diagram shows.

Now a specialty of the Netherlands is that the maintenance shutoff for a circuit is also required to interrupt the neutral. The typical breaker is thus not just single-pole like everywhere else, but 1P+N (single-pole overcurrent protection plus shutoff for the neutral). This is why you must never mix the neutrals of multiple circuits. However, it also makes ground fault protection (ALS) trivial to add because you just swap the breaker, no need to do anything with the wiring.

The Perilex thing

The dark secret is that not all Perilexes are born the same. Receptacles for cooktops (fed by a "kookgroep") are wired with two phases, two neutrals. Never try to plug a three-phase electric motor into a cooktop receptacle, even though it looks the same as a Perilex you might have in your workshop.

4
  • In the US locations where there is 3-phase wye where the phase voltage is 120 V, the voltage between any two phases is 208 V (from 120 x 1.732) and many appliances are rated for both 208 V and 240 V. The output ratings of our stove are proportional to the square of the ratio of the two voltages (240/208)² = 1.33. The factor 1.732 = sqrt (3) Jul 28 at 22:01
  • 1
    @JimStewart Sure, I know very well what the relation between 400 and 230 V is. I guess your US stove just connects the main load between the two live legs, thus running it on 208 or 240 V, because that's the sensible thing to do in the US. I am however fairly sure that European stoves use only 230 V internally, not 400 V. In other words, everything inside the cooktop is connected between one of the phases and the neutral, there's nothing internally connected phase to phase (400 V).
    – TooTea
    Jul 29 at 21:09
  • 1
    @JimStewart Designing an induction cooktop to use 400 V internally wouldn't be too wise, because 1) it wouldn't work at all with single-phase feed and 2) all the power components (e.g. main primary caps) would have to be rated for >650 V (400 V nominal plus 10% tolerance, thus the peak voltage can be as high as 622 V, plus some safety headroom), making them really expensive. Using only 230 V internally also likely makes it possible to use the same components for both the US and Europe.
    – TooTea
    Jul 29 at 21:13
  • TooTea, you clearly have this correctly figured out from multiple angles. Aug 2 at 3:19
2

I was able to find some additional information, so I will add this here.

Most importantly, the arrangement I have, with two live and two neutral terminals in the socket, is not two-phase. The live terminals are on the same phase. It's just a way, used in the NL, to deliver more power to the appliance.

Although the socket and plug are Perilex units designed for three-phase power, this arrangement is a non-standard but very common use of it in the NL.

Each installation of this kind is a one-off - there is no standard for which pins are live and which are neutral. That means each appliance connected has to be wired up for that particular installation.

2
  • Amazing. Truly amazing. So does the installer determine which holes in the receptacle in the wall are hot and then wire the plug to fit that? Did you measure the voltage difference between the two hot slots in the wall receptacle and get zero volts even though each L is 230 V compared to neutral? Jul 29 at 3:12
  • Yes. And also, yes. Jul 29 at 11:44
0

If you have 400 V service, you definitely DO NOT use the jumper across L1 and L2. This would be a direct short and trip the breaker. The designation L1 L2 means they are different phases and cannot be shorted.

The jumper would go across the two neutral terminals because the two phases can share the same neutral.

EDIT

The "NL" on the far right diagram makes me wonder if that would apply to you. The "L" would seem to apply to a 1-phase arrangement with two separate hots in the same cable but on the same phase. In that case the two could not share a neutral because this would overload the neutral. If this is the situation, there would be zero voltage between the two hots (both labeled "L").

EDIT'

To answer this question I did do some scribbling and looking up stuff and here is where the amplitude factor comes from for the voltage difference between two sinusoidal phases of the same frequency and same amplitude, but different phase.

sqrt(2(1 - cos phi)), where phi is the relative phase angle.

This gives the correct results for phi = 0, phi = 120 deg, and phi = 180 deg, which are, respectively, 0, sqrt(3), and 2. So the 3 in the factor for 3-phase power is not derived from the sqrt of the number of phases.

This factor explains how 3-phase in Europe gives both 230 V and 400 V, and in North America gives both 120 V and 208 V, and how US split phase gives 120 V and 240 V.

EDIT''

Despite the '400 V' in the label, the hob is probably not using the 400 V available phase 1 to phase 2. It must be using 230 V phase to neutral from each phase. A single neutral is capable of carrying the sum of the currents from the two phases at 120 degrees relative phase angle.

3
  • 1
    NL in the diagram means it applies to the Netherlands. The NL commonly uses the Perilex sockets and plugs for domestic cooking appliances, in a two-phase configuration. Jul 23 at 17:08
  • The diagram labeled "NL" indicates a 1-phase arrangement. There are two hot conductors each on the same phase. Each hot conductor has an associated neutral and these must not be mixed or switched at the breakers. There are two breakers which should be inked by a mechanical tie, but can be eIectrically independent or perhaps can be common trip. Jul 28 at 22:42
  • 1
    You're correct, the two live connections are on the same phase. Jul 29 at 11:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.