Range cooker wiring

Sam Russell

I have a Britannia range cooker that has peculiar wiring (well, according to me).

The cooker has two electric ovens and gas hob. Now the two ovens are wired independently of each other, with the larger one has a clock for timing and auto control of the oven. It is controlled be a thermostat and a multi-function switch which controls which element or fan is powered. The neutral for all functions is fed back through a sole contact.

What I find strange is that the multi-function switch not only switches the live, but also the neutral. Now I cannot see why the neutral would be switched internal to the unit, but maybe there is a reason. The cooker is fed from a double pole isolation cooker feed as per normal for Ireland.

Now this is an Italian manufactured cooker, so is this an Italian requirement, or is it normal in Irish electric ovens?

Any ideas?

coylemj

Switching the live and the neutral is a 'belt and braces' approach, it might be because the Italian manufacturer is assuming a worst case scenario where (1) there is no external double-pole isolation switch and (2) the live and neutral supplies are wired the wrong way round.

2011

This is done for safety reasons. Complete isolation of all phases and neutral is always the most safe solution. Remember in certain circumstances the neutral can be live with respect to earth. This means that touching it can give you a shock. The manufacturer has no way of knowing what type of external isolation switch (if any) will be installed, particularly in Italy (the Wild West of electrical installations). For this reason they have quite sensibility opted for the safest option. This also means that in the event of reverse polarity complete isolation is achieved.

Andrea B.

Futher, switching both together, when under load, spreads the arching over 2 contacts, so allowing contacts to be made less complex.

Sam Russell

Andrea B. wrote: »

Further, switching both together, when under load, spreads the arching over 2 contacts, so allowing contacts to be made less complex.

The neutral switch is one contact taking up to 16 amps while the live goes through several contacts, the maximum is less than 10 amps. I suspect that the switch is only a 10 amp design.

The only non-resistive load is the oven fan, so not a lot of spark. Also, it is a very primitive switch so I doubt that simultaneous switching would be achieved.

Maybe, the Italians do not expect everything to be earthed correctly.

Andrea B.

Sam Russell wrote: »

The neutral switch is one contact taking up to 16 amps while the live goes through several contacts, the maximum is less than 10 amps. I suspect that the switch is only a 10 amp design.

The only non-resistive load is the oven fan, so not a lot of spark. Also, it is a very primitive switch so I doubt that simultaneous switching would be achieved.



Maybe, the Italians do not expect everything to be earthed correctly.

Is it possible that there is an export conformity for 2phase which i believes is sometimes used in US?

Sam Russell

Andrea B. wrote: »

Is it possible that there is an export conformity for 2phase which i believes is sometimes used in US?

Actually, that is a possibility as 220 V is through a centre tap earth in some US wiring. However, this is a Britannia which is manufactured by iLive in Italy and it looks like a very old design as far as electrics is concerned.

I would imagine it is a UK specific model (it says so on the plate) so I think US regulations would be a red herring.

2011

Sam Russell wrote: »

Maybe, the Italians do not expect everything to be earthed correctly.

In general they don’t believe in earthing.

Bruthal

Andrea B. wrote: »

Futher, switching both together, when under load, spreads the arching over 2 contacts, so allowing contacts to be made less complex.

That`s an interesting one which i thought about in passing a few times. I suspect it would be more like that if the 2 contacts are in parallel though, rather than series.

One in phase and neutral are both carrying the full load as they are in series.

But you would think there would be some sort of sharing, unless one contact always extinguishes before the other.

2011

Bruthal wrote: »

But you would think there would be some sort of sharing, unless one contact always extinguishes before the other.

You also get “switch bounce” too. I was shown footage of this by Phoenix Contact thy was filmed with a high speed camera and played back in slow motion. Fascinating to see.

Bruthal

2011 wrote: »

You also get “switch bounce” too. I was shown footage of this by Phoenix Contact thy was filmed with a high speed camera and played back in slow motion. Fascinating to see.

Yes sometimes program for this in micro controller projects as momentary switch or pushbutton bounce on a project can cause on-off or off-on cycle with an intended single button press.

2011

Bruthal wrote: »

Yes sometimes program for this in micro controller projects as momentary switch or pushbutton bounce on a project can cause on-off or off-on cycle with an intended single button press.

Yes, even basic PLCs have a scan cycle that is quick enough to read the bounce as multiple on/off cycles.

Sam Russell

2011 wrote: »

Yes, even basic PLCs have a scan cycle that is quick enough to read the bounce as multiple on/off cycles.

This range cooker electrics would not be a mystery to an electrician from the 1950s. I do not think PLCs were even thought of let alone invented when the wiring was designed. It has a 9 position switch with cams deciding which of the twelve contacts to make or break. Unfortunately, all return currents flow from the positive contacts goes through one neutral contact, which to me looks like an overloaded contact, hence the problem.

2011

Sam Russell wrote: »

I do not think PLCs were even thought of let alone invented when the wiring was designed.

Nobody is suggesting that range cookers have PLCs. You need to read all of the posts in the thread to understand the context. My post was in response to Bruthal's post in which he mentioned micro controllers. We went off on a tangent

Sam Russell

2011 wrote: »

Nobody is suggesting that range cookers have PLCs. You need to read all of the posts in the thread to understand the context. My post was in response to Bruthal's post in which he mentioned micro controllers. We went off on a tangent

I fully understand all of the posts, but the original question remains unanswered.

Rephrasing my original question:

'Is it normal practice in electric cookers made for the Irish market to switch the neutral as well as the live?'

The reason for asking is that in my cooker the neutral passes through a single contact while the live passes through four contacts. As a consequence, the neutral contact is likely to be overloaded. I do not buy the safety argument because a single failure of this (overloaded) contact renders every part of the wiring to be at live voltage.

I think it is bad practice, but is it a requirement under Irish regulations to switch both live and neutral inside the cooker?

2011

Sam Russell wrote: »

'Is it normal practice in electric cookers made for the Irish market to switch the neutral as well as the live?

It would be normal (or certainly not unusual) for a cooker made for the EU market to switch the neutral. I don’t think any cooker is made specifically for the Irish market.

The reason for asking is that in my cooker the neutral passes through a single contact while the live passes through four contacts. As a consequence, the neutral contact is likely to be overloaded. I do not buy the safety argument because a single failure of this (overloaded) contact renders every part of the wiring to be at live voltage.

How do you know that the neutral contact would be overloaded? To know this you would have to know what it is rated for and what the maximum design current could be. Perhaps the contact is rated for 40A and the maximum possible current that could flow though it is 20A.

As this cooker is manufactured in the EU it will have to be CE certified. During this process the safe operation of the cooker would have to have been assessed.

I think it is bad practice, but is it a requirement under Irish regulations to switch both live and neutral inside the cooker?

You think what is bad practice? Switching the neutral or not switching it?

There is no such requirement as far as I am aware. In ireland we would be bound by EU Directives for appliance not Irish regulations.