Induction hob on two phase.

[Mike Johnson]

Hi all

I have an induction hob that is wired up on two phase's of a three phase supply (oven on the third phase) the requirement for an isolation switch is giving me a bit of a headache as I can't seem to find a three pole domestic switch, any ideas?

Mike

 

[malcolmsanford]

To be honest I doubt very much you will find a "domestic" 3 phase switch that will give you the power rating you need.

How big is this beast for "domestic" use ? You could get a normal single pole switch and isolate through a contactor.

 

[Engineer54]

Is this a domestic 3 phase Kitchen installation, or a small commercial kitchen that's been wired based on a Domestic installation??

 

[Deleted member 26818]

Can you not use a fan isolator?

 

[Spudnik]

Why a 3ph isolator at all?

Surely the diversity will bring it down to near 40A?

(And yes i am guessing BIG time on the rating )

 

[Mike Johnson]

It is a domestic kitchen in a French house which has a three phase supply, the beast in question is 8500 W, under French regulations the appliance must be able to be readily switched off, either from a wall switch or by being unplugged, so I am really looking for a solution that looks neat and unobtrusive.

Mike

 

[Andyfm]

Rotary Isolator tucked out of the way somewhere?

 

[Guest123]

A wylex 921 is probably the most unobtrusive TP&N isolator.

http://www.google.co.uk/search?q=wy...=709&bav=on.2,or.r_gc.r_pw.r_cp.,cf.osb&cad=b

 

[Mike Johnson]

Can't be tucked away, regulations say it must be readily available.

Lenny

Thanks for the link that looks like the best solution.

Mike

 

[Engineer54]

My Induction Hob, is roughly the same rating as yours, and mines been working fine on a 32A RCBO since i installed it...

If it's 2 phase and earth, (no neutral fo the hob) You can use a standard single or double box, DP cooker control switch!!!

What i'm saying is that you can use 2 of these standard single DP cooker switches in one of those boxes that allows 2X single face plates. So one switch can control the Hob, and the other the Oven. eg, two lines on one switch (hob) and line neutral on the other (oven)...

 

[Mike Johnson]

Two phase and earth, (No neutral for the hob)

How would that work on a Hob please explain I am keen to learn?

As I said on the original posts this is a two phase hob, the oven is on the other side of the room and requires its own isolator under the French Regulations, each phase is 20amp and the hob requires the two supplies to stop the main trip going out whith all four rings in operation, I am trying to ballance the load with the oven on the third phase.

Lenny has given me the best solution above.

Mike

 

[malcolmsanford]

Because phases are 3 separate wave forms.

If we took 3 generators and positioned them equidistantly 120 degree apart around a rotating magnet we would generate 3 completely separate ac waveform each with a phase displacement of 120 degrees of each other.

You therefore have a potential difference similar to the LINE-NEUTRAL of a single phase supply between the 2 phases. Here in the UK we have a 400/230 supply, often in continental Europe you will have 380/220 and in the US 208/127

So a lot of the American 208-230v volt Equipment will be of 2 phases.

 

[Mike Johnson]

Thanks for the reply.

I understand how an electric brushless motor works on the 120deg principle, but I don't see how an electrical element can work using two phase's of a three phase supply, (180 degs to each other) is there some tutorial I can go to that will explain it to me?

Mike

 

[Engineer54]

Two phase and earth, (No neutral for the hob)

How would that work on a Hob please explain I am keen to learn?

As I said on the original posts this is a two phase hob, the oven is on the other side of the room and requires its own isolator under the French Regulations, each phase is 20amp and the hob requires the two supplies to stop the main trip going out whith all four rings in operation, I am trying to ballance the load with the oven on the third phase.

Lenny has given me the best solution above.

Mike

You can use as i already stated a normal Double Pole (DP) cooker switch that will fit a standard size flush back box or a standard white surface box for each, Hob and the Oven. It's not practical, or maybe not to French code to have a single isolator/switch controlling two cooking appliances that are distant from each other...

Try as you will, you won't ''balance'' the loads between a hob and and oven. What is the protective device in the CU/DB for this 3 phase supply?? Is it from one 3 or 4 pole breaker or 3 single pole breakers?? Are all the conductors in a single sheathed cable, or are they in singles in conduit??

 

[Mike Johnson]

I am not trying to isolate both from one isolator, I have two isolators, one each for the hob and oven, I want to isolate the two phase hob from one switch, the three phase's are controlled from the fuse box from a three combined 20amp (20amp/phase) cartridge breaker the wires are single sheathed in a conduit that runs to a three phase socket near the hob, I have plugged into this with the correct three phase plug and run this to an isolation switch on on to a cable outlet, thence onto the hob in heat proof 6mm cable, my problem prior to Lenny pointing it out was that I did not know there was a three pole switch available.

Now I just have to find a three pole cable outlet and 6mm four core cable.

Mike

 

[Engineer54]

I am not trying to isolate both from one isolator, I have two isolators, one each for the hob and oven, I want to isolate the two phase hob from one switch, the three phase's are controlled from the fuse box from a three combined 20amp (20amp/phase) cartridge breaker the wires are single sheathed in a conduit that runs to a three phase socket near the hob, I have plugged into this with the correct three phase plug and run this to an isolation switch on on to a cable outlet, thence onto the hob in heat proof 6mm cable, my problem prior to Lenny pointing it out was that I did not know there was a three pole switch available.

Now I just have to find a three pole cable outlet and 6mm four core cable.

Mike

Ah, cartridge fuses, not exactly the best arrangement when protecting multi phase circuits....

So what your saying is, you have an isolation switch already for the oven, your just referring to the hob's means of isolation. So yes, a 3 pole switch would work, but then so would a DP switch, by making safe the unused phase (even removing fuse at th DB) and switching just the 2 phases at the DP switch. A DP switch is going to look far less industrial than a triple pole switch in the kitchen. Then you would only need a 2 pole socket outlet and 3 core cable. Do the French use a specific outlet and plug top for 2 phase +E ?? You may find that they do! It'll have to be a big-un to connect 6mm 3 core cable in the plug tops ....But it's your choice!! I really think it might be a good idea to have a talk with the local electrician!!

Personally, i would seriously think about getting your local electrician to upgrade your DB to a MCB distribution board too. At least then, if fault on one phase of a multi phase breaker appears the whole breaker trips not just one of the breakers, which is very bad news for any multi phase motors you may have.

 

[Mike Johnson]

Please read my post carfully there is not an unused phase, yes the French use a specific outlet and plug for a three phase kitchen connection and yes it is big and I know that they do, a DP switch would not work as it will not isolate the neutral, the main board is already an MCB.

Thank you for your contribution I now have enough information to be able to change my hob connection to a switched 3P isolator.

Mike

 

[Engineer54]

Am i loosing the plot here or what??

You say you have a 2 phase+E hob fed from a 3 phase + N/E (5 conductors) socket outlet. So why on gods earth are you switching the neutral when it's not required?? Oh, and a 3 pole switch will also not switch the neutral either, you need a 4 pole switch to do that!!!! So, what's the other phase and the neutral at this socket outlet going to be doing then??

In my world, when someone states ''Fuse Board'' and ''Cartridge'' that would imply cartridge HRC fuse carriers. If you have MCBs, RCD'S etc then it's a Distribution Board, or Consumer Unit, ...Not a Fuse board!

I'm pretty sure you don't really know what your doing to be honest, your playing around with 3 phase stuff that you don't understand. So i'll tell you again, for your own sake and your families sake, ...get your local French electrician in to do this work for you!!!

 

[Mike Johnson]

I am switching the N because its required under the French Regulations.

Two phase and neutral to the hob switched for isolation, three poles switch will work, only three leads, E passes straight through.

Other phase and neutral connected to oven through a seperate isolator.

Sorry for the incorrect teminoligy I will throw myself on my sword the next time I get it out to clean it.

Mike

 

[Engineer54]

You really do need to make your mind up about this hob, You have clearly stated this hob to be 2 phase + E, now your saying it's 2 phase + N + E???

You have told us you have 2 supplies one for the hob and one for the oven, Now your talking about both being supplied from this single point 3 phase socket outlet????

Yes your terminology, will get you into a lot of trouble, especially when you don't really know what the hell your doing playing around with 3 phase stuff in a kitchen...