Wiring oven and hob - pics & questions

Bruthal

M cebee wrote: »

what's all that nonsense about the 6sq earth and people getting electrocuted

If its not a 6sq earth, your going to be fried by your own cooker:pac:

Bruthal

robbie7730 wrote: »

If its not a 6sq earth, your going to be fried by your own cooker:pac:

Im thinking you thought i was serious here M cebee:D

M cebee

afaik cookers on 30ma rcd is not unusual in uk

don't think there's much trouble

Bruthal

evosteo wrote: »

The earth is to provide protection for the cable and device and to some extent you as well. If an earth fault occurs (live connects to the earth) then the current will flow from the live wire through the earth and back to the source and this should be an easier return path than from the live wire, through you, your shoes, the concrete you stand on, the ground, and then back to the source. So the earth wire should provide an easier return path. The earth should be connected to any metal parts where you are likely to touch them.

Well the earth wire is to keep the cooker, and any earthed equipment or appliances at equal potential to each other, and ideally at the same potential as the ground and neutral, which is achieved by being a very low impedence path, and this also ensures fast operation of protective devices. It really only has a solid connection to ground and neutral when the installation is neutralised, as a single earth rod in a TT setup is not a great connection to earth, which is why these would have a slight time delay RCD covering everything.

If there was no earth wire to the cooker, and a live to cooker frame fault occured, no fault current would flow, or very little. If you then touch it, a very small current will flow, but nothing that can operate any size MCB. And depending on your connection to earth, a shock may be received, although a shock may not be received at all if the live frame of the cooker is the only thing your in contact with while standing on dry floor with shoes/runners on.

So the earth wire is like a monitoring setup as well, showing if any faults occur, as well as keeping the cooker frame at ground potential.

If an isolated system was used from the ESB transformers, then no shocks would be recieved, except when one conductor ends up connected to earth through a fault, and then other conductors would now have potential to earth, but would not be known about, creating potential hazards.

And the earthed faulted conductor could well be a phase, in which case the other phases would have 400v potential to earth. So earthing the neutral gives a reference point as well as a fault monitoring setup. By earthing the neutral, i mean earthing the star point at the transformer and at multiple points all along the neutral conductors from the star point, which is a seperate item to neutralising a house installation.

knighted_1

[QUOTE=robbie7730;73063985

If there was no earth wire to the cooker, and a live to cooker frame fault occured, no fault current would flow, or very little. If you then touch it, a very small current will flow, but nothing that can operate any size MCB. And depending on your connection to earth, a shock may be received, although a shock may not be received at all if the live frame of the cooker is the only thing your in contact with while standing on dry floor with shoes/runners .[/QUOTE]

what would happen if you touched the oven while standing barefoot on a tiled floor ?

Bruthal

knighted_1 wrote: »

what would happen if you touched the oven while standing barefoot on a tiled floor ?

You will feel it if the oven frame was live, but it probably wont give a severe shock if the floor is completely dry. Not that i would recommend trying it.

The dangerous shocks are one hand on a live connection or item, and the other on an earthed metal object. Thats where the current operated RCD comes into its rightful place as one of the best electrical safety inventions in my opinion.

knighted_1

robbie7730 wrote: »

You will feel it if the oven frame was live, but it probably wont give a severe shock if the floor is completely dry. Not that i would recommend trying it.

The dangerous shocks are one hand on a live connection or item, and the other on an earthed metal object. Thats where the current operated RCD comes into its rightful place as one of the best electrical safety inventions in my opinion.

but there's no rcd protection on an oven - on most cookers now it's the neutrals that are switched to operate controls on oven so each element has a live just sitting there - if earth cable is broken assume no earth -if I touch that live while I am earthed to the floor i am going to get the full bang and no rcd will go off as there is none on the circuit -

interesting discussion to see each persons view on it

Bruthal

knighted_1 wrote: »

but there's no rcd protection on an oven - on most cookers now it's the neutrals that are switched to operate controls on oven so each element has a live just sitting there - if earth cable is broken assume no earth -if I touch that live while I am earthed to the floor i am going to get the full bang and no rcd will go off as there is none on the circuit -

interesting discussion to see each persons view on it

I know there is no RCD in this situation of course. I remember when showers had no RCD, which is unthinkable now.

RCDs possibly will be on cookers in time. At present they are required on portable appliances where they are seen as likely to be more at risk of having plug leads or the appliances themselves damaged from being moved around, plugged in and out, compared to a fixed appliance hard wired in. Or on water based appliances such as immersions, pumps, showers. Also on lights outside the house that are not fitted to the actual house.

Good earth connections are important on all items anyway.

M cebee

knighted_1 wrote: »

but there's no rcd protection on an oven - on most cookers now it's the neutrals that are switched to operate controls on oven so each element has a live just sitting there - if earth cable is broken assume no earth -if I touch that live while I am earthed to the floor i am going to get the full bang and no rcd will go off as there is none on the circuit -

interesting discussion to see each persons view on it

you can rcd the circuit and it will disconnect the circuit in the event of direct contact or exposed metalwork with no cpc

but it's not that big of a deal really


if the exposed metal is earthed and disconnection times are met there's no real hazard without rcd

Bruthal

M cebee wrote: »

you can rcd the circuit and it will disconnect the circuit in the event of direct contact or exposed metalwork with no cpc

It will if you contact the live exposed frame of the cooker for example. But a decent shock will be felt in order to trip the RCD, it wont trip by a person just touching the exposed live metal if they are just touching it and only in contact with the dry floor in shoes. But it would certainly prevent electrocution alright.

if the exposed metal is earthed and disconnection times are met there's no real hazard without rcd

True, once someone doesnt come along and do a DIY connection and not earth properly.

micks_address

Hi guys sorry to dig up an old thread. We have a gas hob that is being disconnected by plumber tomorrow to be replaced by an electric induction hob. Our oven is the other side of the kitchen but the cooker switche is to the right of where the hob will be fitted and the cooker wire runs from the switch to the electric oven. I'm not doing this myself getting a neighbour who is an electrician to look at it but will he just be able to put in a junction type box on the existing cable to the oven and hook the induction hob in to that?
Cheers
Mick

tomdempsey200

micks_address wrote: »

Hi guys sorry to dig up an old thread. We have a gas hob that is being disconnected by plumber tomorrow to be replaced by an electric induction hob. Our oven is the other side of the kitchen but the cooker switche is to the right of where the hob will be fitted and the cooker wire runs from the switch to the electric oven. I'm not doing this myself getting a neighbour who is an electrician to look at it but will he just be able to put in a junction type box on the existing cable to the oven and hook the induction hob in to that?
Cheers
Mick

your electrician will need to check the 'total connected load' to see if it's suitable for connection to the 6sq


i think you can apply diversity here?

diversity is the first 10amp + 30% percent of the remainder

in the back of the rules they also give a figure of 10kw cooking load for connection to a 6sq

tomdempsey200

the switch is supposed to be 2m max from either appliance btw