Right,

We are changing the range cooker to:

a 6 gas ring hob which has a 13A cable and plug to power the gas
ignition system.

2 seperate gas single ovens/grills. (these are fully gas for the grill
and oven parts) These will be installed side by side under the 6 ring
gas hob mentioned above.

This means we can have two ovens, or two grills or one grill and one
oven at any one time for dinner parties.

Each one of these gas grill/ovens also has a mains lead with a 13A plug
on it to power the clocks and gas ignition system.

Above all this is the extractor fan, which again has a mains lead and
plug on it.

Now I have a 32A cooker circuit. This currently goes to a 45A DP cooker
switch.

Now my two questions a

1. Is it acceptable to run 6mm2 cable from this double pole switch to a
triple gang wall socket behind the cooker so that I can plug the gas hob
in and the two seperate grils/ovens into?

2. Is it acceptable to power the cooker hood from the cooker circuit
rather than from the kitchen ring fing circuit? Again this would be via
a 13A fused neon spur. My reasoning is that the cooker hood fan and
light only really gets used when cooking takes place......

On 21/04/14 10:52, Stephen wrote:
Right,

We are changing the range cooker to:

a 6 gas ring hob which has a 13A cable and plug to power the gas
ignition system.

2 seperate gas single ovens/grills. (these are fully gas for the grill
and oven parts) These will be installed side by side under the 6 ring
gas hob mentioned above.

This means we can have two ovens, or two grills or one grill and one
oven at any one time for dinner parties.

Each one of these gas grill/ovens also has a mains lead with a 13A plug
on it to power the clocks and gas ignition system.

Above all this is the extractor fan, which again has a mains lead and
plug on it.

Now I have a 32A cooker circuit. This currently goes to a 45A DP cooker
switch.

Now my two questions a

1. Is it acceptable to run 6mm2 cable from this double pole switch to a
triple gang wall socket behind the cooker so that I can plug the gas hob
in and the two seperate grils/ovens into?

2. Is it acceptable to power the cooker hood from the cooker circuit
rather than from the kitchen ring fing circuit? Again this would be via
a 13A fused neon spur. My reasoning is that the cooker hood fan and
light only really gets used when cooking takes place......


If it is a 32A MCB/30A fuse in the CU for this circuit, then yes - it's
a 32A radial which is "standard", albeit uncommon. You can hang as many
sockets off it as you like - only problem is the 6mm2 cable means you'll
only get one set of cables into a socket unless you split with a
junction box.


However your triple socket is unlikely to support a combined load of 32A
- more like a total of 20A if it's anything like most double sockets.
You'll need a deep backbox too for the cable as it's nearly as flexible
as rebar.

On 21/04/2014 11:00, Tim Watts wrote:
On 21/04/14 10:52, Stephen wrote:
Right,

We are changing the range cooker to:

a 6 gas ring hob which has a 13A cable and plug to power the gas
ignition system.

2 seperate gas single ovens/grills. (these are fully gas for the grill
and oven parts) These will be installed side by side under the 6 ring
gas hob mentioned above.

This means we can have two ovens, or two grills or one grill and one
oven at any one time for dinner parties.

Each one of these gas grill/ovens also has a mains lead with a 13A plug
on it to power the clocks and gas ignition system.

Above all this is the extractor fan, which again has a mains lead and
plug on it.

Now I have a 32A cooker circuit. This currently goes to a 45A DP cooker
switch.

Now my two questions a

1. Is it acceptable to run 6mm2 cable from this double pole switch to a
triple gang wall socket behind the cooker so that I can plug the gas hob
in and the two seperate grils/ovens into?

2. Is it acceptable to power the cooker hood from the cooker circuit
rather than from the kitchen ring fing circuit? Again this would be via
a 13A fused neon spur. My reasoning is that the cooker hood fan and
light only really gets used when cooking takes place......


If it is a 32A MCB/30A fuse in the CU for this circuit, then yes - it's
a 32A radial which is "standard", albeit uncommon. You can hang as many
sockets off it as you like - only problem is the 6mm2 cable means you'll
only get one set of cables into a socket unless you split with a
junction box.


However your triple socket is unlikely to support a combined load of 32A
- more like a total of 20A if it's anything like most double sockets.
You'll need a deep backbox too for the cable as it's nearly as flexible
as rebar.



OK, what about the following then:

run 6mm2 cable from cooker switch down to a junction box, fit two lots
of 6mm2 cable from this junction box to a double socket each. Then plug
the two gas ovens into one of the double sockets and then plug the hob
and extractor fan in the other double socket?

Regards

Stephen.

On 21/04/14 11:04, Stephen wrote:

OK, what about the following then:

run 6mm2 cable from cooker switch down to a junction box, fit two lots
of 6mm2 cable from this junction box to a double socket each. Then plug
the two gas ovens into one of the double sockets and then plug the hob
and extractor fan in the other double socket?

Regards

Stephen.

It is arguably possible to run 2.5mm to each socket (but only one socket
or double socket per cable) from the JB as the plugtop fuse protects the
preceding cable against overload. As no double socket is rated 20A
total, this is within limits for most installation methods of 2.5mm2.

I'm not sure if that's *totally* regs compliant, so I'll wait for one of
the resident experts to comment - however, it is in principle no worse
that any other spur done in 2.5mm2. In this case, it is merely a spur
off the end of a distribution circuit.

"Stephen" wrote in message
...
On 21/04/2014 11:00, Tim Watts wrote:
On 21/04/14 10:52, Stephen wrote:
Right,

We are changing the range cooker to:

a 6 gas ring hob which has a 13A cable and plug to power the gas
ignition system.

2 seperate gas single ovens/grills. (these are fully gas for the grill
and oven parts) These will be installed side by side under the 6 ring
gas hob mentioned above.

This means we can have two ovens, or two grills or one grill and one
oven at any one time for dinner parties.

Each one of these gas grill/ovens also has a mains lead with a 13A plug
on it to power the clocks and gas ignition system.

Above all this is the extractor fan, which again has a mains lead and
plug on it.

Now I have a 32A cooker circuit. This currently goes to a 45A DP cooker
switch.

Now my two questions a

1. Is it acceptable to run 6mm2 cable from this double pole switch to a
triple gang wall socket behind the cooker so that I can plug the gas hob
in and the two seperate grils/ovens into?

2. Is it acceptable to power the cooker hood from the cooker circuit
rather than from the kitchen ring fing circuit? Again this would be via
a 13A fused neon spur. My reasoning is that the cooker hood fan and
light only really gets used when cooking takes place......


If it is a 32A MCB/30A fuse in the CU for this circuit, then yes - it's
a 32A radial which is "standard", albeit uncommon. You can hang as many
sockets off it as you like - only problem is the 6mm2 cable means you'll
only get one set of cables into a socket unless you split with a
junction box.


However your triple socket is unlikely to support a combined load of 32A
- more like a total of 20A if it's anything like most double sockets.
You'll need a deep backbox too for the cable as it's nearly as flexible
as rebar.



OK, what about the following then:

run 6mm2 cable from cooker switch down to a junction box, fit two lots of
6mm2 cable from this junction box to a double socket each. Then plug the
two gas ovens into one of the double sockets and then plug the hob and
extractor fan in the other double socket?


What does the cooker switch feed ATM? Does it not feed a cooker outlet
plate?

--
Adam

The current draw of each of these units is going to be quite small if all that is being powered is the ignition, clocks, lights and indicators. The fact that they are supplied with 13A plugs means they can be plugged into any ring main socket and do not need a dedicated cooker circuit. If however, you do wish to have a single switch to to turn the lot off and you do not want someone in the future to mistakenly think it is a 45A cooker circuit use a 20A double pole switch on the ring main and spur off that.

Richard

On 21/04/2014 12:35, ARW wrote:
"Stephen" wrote in message
...
On 21/04/2014 11:00, Tim Watts wrote:
On 21/04/14 10:52, Stephen wrote:
Right,

We are changing the range cooker to:

a 6 gas ring hob which has a 13A cable and plug to power the gas
ignition system.

2 seperate gas single ovens/grills. (these are fully gas for the grill
and oven parts) These will be installed side by side under the 6 ring
gas hob mentioned above.

This means we can have two ovens, or two grills or one grill and one
oven at any one time for dinner parties.

Each one of these gas grill/ovens also has a mains lead with a 13A plug
on it to power the clocks and gas ignition system.

Above all this is the extractor fan, which again has a mains lead and
plug on it.

Now I have a 32A cooker circuit. This currently goes to a 45A DP cooker
switch.

Now my two questions a

1. Is it acceptable to run 6mm2 cable from this double pole switch to a
triple gang wall socket behind the cooker so that I can plug the gas
hob
in and the two seperate grils/ovens into?

2. Is it acceptable to power the cooker hood from the cooker circuit
rather than from the kitchen ring fing circuit? Again this would be via
a 13A fused neon spur. My reasoning is that the cooker hood fan and
light only really gets used when cooking takes place......


If it is a 32A MCB/30A fuse in the CU for this circuit, then yes - it's
a 32A radial which is "standard", albeit uncommon. You can hang as many
sockets off it as you like - only problem is the 6mm2 cable means you'll
only get one set of cables into a socket unless you split with a
junction box.


However your triple socket is unlikely to support a combined load of 32A
- more like a total of 20A if it's anything like most double sockets.
You'll need a deep backbox too for the cable as it's nearly as flexible
as rebar.



OK, what about the following then:

run 6mm2 cable from cooker switch down to a junction box, fit two lots
of 6mm2 cable from this junction box to a double socket each. Then
plug the two gas ovens into one of the double sockets and then plug
the hob and extractor fan in the other double socket?


What does the cooker switch feed ATM? Does it not feed a cooker outlet
plate?


it currently feeds a range cooker, we are essentially replacing a single
free standing range cooker with 3 seperate cookers comprising of a gas
hob and 2 off gas ovens & grills, along with the cooker hood.

On 21/04/2014 12:46, Tricky Dicky wrote:
The current draw of each of these units is going to be quite small if all that is being powered is the ignition, clocks, lights and indicators. The fact that they are supplied with 13A plugs means they can be plugged into any ring main socket and do not need a dedicated cooker circuit. If however, you do wish to have a single switch to to turn the lot off and you do not want someone in the future to mistakenly think it is a 45A cooker circuit use a 20A double pole switch on the ring main and spur off that.

Richard


I am trying to preserve integrity and/or diversity within the kitchen, I
already have 4 separate circuits going to the kitchen.


a ring main final circuit
ground floor lighting
smoke & CO detectors circuit
and of course the 6mm2 32A RCBO protected cooker circuit.

The reason why I want to put the two gas ovens/grills, hob and cooker
hood on to the 32A 6mm2 RCBO is for two reasons:

the first is we can still cook if the ring circuit pops in the kitchen,
and vice versa with a microwave & kettle if the cooker circuit pops.

The second is that it makes life easy if in the future we wish to rip
all the gas cookers out and go for an all electric cooker so hence I
wish to retain and use the cooker circuit.

I appreciate the current draw is very low on a gas cooker.

On 21/04/2014 12:35, ARW wrote:
"Stephen" wrote in message
...
On 21/04/2014 11:00, Tim Watts wrote:
On 21/04/14 10:52, Stephen wrote:
Right,

We are changing the range cooker to:

a 6 gas ring hob which has a 13A cable and plug to power the gas
ignition system.

2 seperate gas single ovens/grills. (these are fully gas for the grill
and oven parts) These will be installed side by side under the 6 ring
gas hob mentioned above.

This means we can have two ovens, or two grills or one grill and one
oven at any one time for dinner parties.

Each one of these gas grill/ovens also has a mains lead with a 13A plug
on it to power the clocks and gas ignition system.

Above all this is the extractor fan, which again has a mains lead and
plug on it.

Now I have a 32A cooker circuit. This currently goes to a 45A DP cooker
switch.

Now my two questions a

1. Is it acceptable to run 6mm2 cable from this double pole switch to a
triple gang wall socket behind the cooker so that I can plug the gas
hob
in and the two seperate grils/ovens into?

2. Is it acceptable to power the cooker hood from the cooker circuit
rather than from the kitchen ring fing circuit? Again this would be via
a 13A fused neon spur. My reasoning is that the cooker hood fan and
light only really gets used when cooking takes place......


If it is a 32A MCB/30A fuse in the CU for this circuit, then yes - it's
a 32A radial which is "standard", albeit uncommon. You can hang as many
sockets off it as you like - only problem is the 6mm2 cable means you'll
only get one set of cables into a socket unless you split with a
junction box.


However your triple socket is unlikely to support a combined load of 32A
- more like a total of 20A if it's anything like most double sockets.
You'll need a deep backbox too for the cable as it's nearly as flexible
as rebar.



OK, what about the following then:

run 6mm2 cable from cooker switch down to a junction box, fit two lots
of 6mm2 cable from this junction box to a double socket each. Then
plug the two gas ovens into one of the double sockets and then plug
the hob and extractor fan in the other double socket?


What does the cooker switch feed ATM? Does it not feed a cooker outlet
plate?



as its a free standing range, its simply a 6mm2 cable running from the
wall cooker switch to the actual cooker itself. There is no cooker
outlet plate to speak of.

On 21/04/2014 10:52, Stephen wrote:
Right,

We are changing the range cooker to:

a 6 gas ring hob which has a 13A cable and plug to power the gas
ignition system.

2 seperate gas single ovens/grills. (these are fully gas for the grill
and oven parts) These will be installed side by side under the 6 ring
gas hob mentioned above.

This means we can have two ovens, or two grills or one grill and one
oven at any one time for dinner parties.

Each one of these gas grill/ovens also has a mains lead with a 13A plug
on it to power the clocks and gas ignition system.

Above all this is the extractor fan, which again has a mains lead and
plug on it.

Now I have a 32A cooker circuit. This currently goes to a 45A DP cooker
switch.

Now my two questions a

1. Is it acceptable to run 6mm2 cable from this double pole switch to a
triple gang wall socket behind the cooker so that I can plug the gas hob
in and the two seperate grils/ovens into?

Yes, but probably excessive... A triple socket will include a 13A fuse,
so you could use 2.5mm^2 cable and know it will still be adequately
overload protected. The cable will have adequate fault current
protection provided by the 32A MCB at the origin of the circuit.

2. Is it acceptable to power the cooker hood from the cooker circuit
rather than from the kitchen ring fing circuit? Again this would be via
a 13A fused neon spur. My reasoning is that the cooker hood fan and
light only really gets used when cooking takes place......

Yup, that would be fine.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

You do not say wether your original electric range was connected directly to the 45A switch or through a cable outlet. If the latter simply wire in a 4-way fused extension into the outlet, considering the low current draw this will be more than adequate.

Richard

On 21/04/2014 15:14, Tricky Dicky wrote:
You do not say wether your original electric range was connected directly to the 45A switch or through a cable outlet. If the latter simply wire in a 4-way fused extension into the outlet, considering the low current draw this will be more than adequate.

Richard



Actually, I've had a brainwave..... given that I want to keep the
existing 6mm2 32A RCBO radial cooker circuit in case we ever go back to
a fully electric cooker...... and maintain diversity/integrity w.r.t. to
the other kitchen circuits... How does the following sound?

run 6mm2 T&E to double pole coker isolator switch above worktop.

run smoe more 6mm2 T&E from this switch to a cooker outlet thats mounted
somewhere below the worktop.

I then create a mini-ring cicuit using two double sockets and 2.5mm2
T&E. I then attach the two ends of the 2.5mm T&E into the cooker outlet
socket...

This would be like a 2.5mm2 ring circuit attached onto a 6mm2 32A radial
cicuit.

I could then plug the gas hob, the two gas grill/ovens and the cooker
extractor hood.......


So If I ever go back to a fully electric cooker, I just take off the
small mini ring main and attach the cooker to the cooker outlet plate.

This way, I am not in a situation where there is a risk of up to 32A of
current passing through a 2.5mm2 spur to a socket at any time.

On 21/04/2014 16:26, Stephen wrote:
On 21/04/2014 15:14, Tricky Dicky wrote:
You do not say wether your original electric range was connected
directly to the 45A switch or through a cable outlet. If the latter
simply wire in a 4-way fused extension into the outlet, considering
the low current draw this will be more than adequate.

Richard



Actually, I've had a brainwave..... given that I want to keep the
existing 6mm2 32A RCBO radial cooker circuit in case we ever go back to
a fully electric cooker...... and maintain diversity/integrity w.r.t. to
the other kitchen circuits... How does the following sound?

run 6mm2 T&E to double pole coker isolator switch above worktop.

run smoe more 6mm2 T&E from this switch to a cooker outlet thats mounted
somewhere below the worktop.

I then create a mini-ring cicuit using two double sockets and 2.5mm2
T&E. I then attach the two ends of the 2.5mm T&E into the cooker outlet
socket...

This would be like a 2.5mm2 ring circuit attached onto a 6mm2 32A radial
cicuit.

I could then plug the gas hob, the two gas grill/ovens and the cooker
extractor hood.......


So If I ever go back to a fully electric cooker, I just take off the
small mini ring main and attach the cooker to the cooker outlet plate.

This way, I am not in a situation where there is a risk of up to 32A of
current passing through a 2.5mm2 spur to a socket at any time.

Its not like you were in the first place given the number of sockets
(i.e. one double per spur) and even then only small loads on each socket.

For all practical purposes in this case it really makes no difference if
you make the final connection to the sockets by ring or a pair of spurs
- although the latter would make it a "standard" circuit - in that spurs
in 2.5mm^2 are allowed (although less common) from 4 or 6mm^2 32A radials.

Keeping the cooker isolator and the outlet is probably a good idea since
it allows you options and will save more work if going back to an
electric cooker etc.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

I think you are overthinking this, to draw 32A you would need to hook up appliances that would draw in excess of 7kW. Somehow I do not think what you have will come anywhere near that. A 4-way extension socket protected with a 13A fuse will allow almost 3kW. Look at the specification plates on the appliances add up the wattage and that will give you the total this circuit will draw.

Richard

On 21/04/2014 16:26, Stephen wrote:

Actually, I've had a brainwave..... given that I want to keep the
existing 6mm2 32A RCBO radial cooker circuit in case we ever go back to
a fully electric cooker...... and maintain diversity/integrity w.r.t. to
the other kitchen circuits... How does the following sound?

run 6mm2 T&E to double pole coker isolator switch above worktop.

run smoe more 6mm2 T&E from this switch to a cooker outlet thats mounted
somewhere below the worktop.

I then create a mini-ring cicuit using two double sockets and 2.5mm2
T&E. I then attach the two ends of the 2.5mm T&E into the cooker outlet
socket...

This would be like a 2.5mm2 ring circuit attached onto a 6mm2 32A radial
cicuit.

You're over-engineering this. Given that the circuit is protected by an
RCBO (presumably Type B) there'll be no problem at all in running short
radial spurs in 2.5 T&E.

Also I can't see any problem with your original triple-socket idea. The
loading for the clocks and ignition will be milliamps and, for the fan,
an amp or two at the most. If you use the MK 3-gang socket it comes
with a built-in 13 A fuse for overload protection if 'abused'. If
you're paranoid you could reduce this to 5 A (say) and also change the
RCBO in the CU to 16 A.

Alternatively you might want to consider whether a neater job could be
done by discarding the 13 A plugs and wiring all the appliances into
strategically placed fused connection units.

--
Andy

On 21/04/2014 17:25, Tricky Dicky wrote:
I think you are overthinking this, to draw 32A you would need to hook up appliances that would draw in excess of 7kW. Somehow I do not think what you have will come anywhere near that. A 4-way extension socket protected with a 13A fuse will allow almost 3kW. Look at the specification plates on the appliances add up the wattage and that will give you the total this circuit will draw.

Richard


it was more to do with ensuring its compliant to IEEE regs and also to
protect against a situation of a full on short on 2.5mm2 cable on a 32A
RCBO considering that 2.5mm2 cable is only rated up to 20A.

Hence my thought of creating a 2.5mm2 min ring main of 2 double sockets
on the end of the cooker outlet fed by 6mm2 cable wihin the cooker's
immediate vicinity to feed the two gas grill/ovens, the gas hob an dthe
cooker extractor hood

In article , Stephen
wrote:
On 21/04/2014 17:25, Tricky Dicky wrote:
I think you are overthinking this, to draw 32A you would need to hook
up appliances that would draw in excess of 7kW. Somehow I do not think
what you have will come anywhere near that. A 4-way extension socket
protected with a 13A fuse will allow almost 3kW. Look at the
specification plates on the appliances add up the wattage and that will
give you the total this circuit will draw.

Richard


it was more to do with ensuring its compliant to IEEE regs and also to
protect against a situation of a full on short on 2.5mm2 cable on a 32A
RCBO considering that 2.5mm2 cable is only rated up to 20A.

Hence my thought of creating a 2.5mm2 min ring main of 2 double sockets
on the end of the cooker outlet fed by 6mm2 cable wihin the cooker's
immediate vicinity to feed the two gas grill/ovens, the gas hob an dthe
cooker extractor hood

IEEE is an American body, over here was the IEE, now the IET.

The cable rating is concerned with heating - not short circuit current.

--
From KT24

Using a RISC OS computer running v5.18

Alternatively you might want to consider whether a neater job could be
done by discarding the 13 A plugs and wiring all the appliances into
strategically placed fused connection units.

I did wonder about this but my issue is lack of space for switchable
FCUs between worktop and wall cupboards

basically I have along the same wall:

along the bottom:

Door no 1 | 600mm highline cupboard | 600mm gas grill/oven no 1 | 600mm
gas grill/oven no 2 | 600mm highline cupboard | door no 2.

The gas hob is above the two grill/ovens inset into the worktop.

Along the top:

door no 1 | 600mm cupboard | 1200mm cooker hood & housing | 600mm
cupboard | door no 2.



I want the room light switch and a double socket on the left hand side
of the cooker, ( bear in mind the minimum separation distance of 300mm
too....)

and then a cooker isolator switch and a double socket on the other side
of the cooker area.

If I do FCU's for the hob, two grill/ovens and the extractor fan, I have
to find room for 4 seperate switchable FCUs with them all being a
miminum of 300mm away from the hob.

Hence my interest in having a single cooker switch feeding all four
while being compliant with regs....

On 22/04/2014 18:21, charles wrote:
In article , Stephen
wrote:
On 21/04/2014 17:25, Tricky Dicky wrote:
I think you are overthinking this, to draw 32A you would need to hook
up appliances that would draw in excess of 7kW. Somehow I do not think
what you have will come anywhere near that. A 4-way extension socket
protected with a 13A fuse will allow almost 3kW. Look at the
specification plates on the appliances add up the wattage and that will
give you the total this circuit will draw.

Richard


it was more to do with ensuring its compliant to IEEE regs and also to
protect against a situation of a full on short on 2.5mm2 cable on a 32A
RCBO considering that 2.5mm2 cable is only rated up to 20A.

Hence my thought of creating a 2.5mm2 min ring main of 2 double sockets
on the end of the cooker outlet fed by 6mm2 cable wihin the cooker's
immediate vicinity to feed the two gas grill/ovens, the gas hob an dthe
cooker extractor hood

IEEE is an American body, over here was the IEE, now the IET.

The cable rating is concerned with heating - not short circuit current.


Ok, OK, IET.... its hard keeping track of when things change like Corgi
to GaSafe! :-)

7th Ed wiring regs or whatever it is called now!.....

On 22/04/14 18:21, charles wrote:
In article , Stephen
wrote:
On 21/04/2014 17:25, Tricky Dicky wrote:
I think you are overthinking this, to draw 32A you would need to hook
up appliances that would draw in excess of 7kW. Somehow I do not think
what you have will come anywhere near that. A 4-way extension socket
protected with a 13A fuse will allow almost 3kW. Look at the
specification plates on the appliances add up the wattage and that will
give you the total this circuit will draw.

Richard


it was more to do with ensuring its compliant to IEEE regs and also to
protect against a situation of a full on short on 2.5mm2 cable on a 32A
RCBO considering that 2.5mm2 cable is only rated up to 20A.

Hence my thought of creating a 2.5mm2 min ring main of 2 double sockets
on the end of the cooker outlet fed by 6mm2 cable wihin the cooker's
immediate vicinity to feed the two gas grill/ovens, the gas hob an dthe
cooker extractor hood

IEEE is an American body, over here was the IEE, now the IET.

The cable rating is concerned with heating - not short circuit current.


It's also to do with ensuring the protective device operates quickly
enough (0.4s for most domestic circuits).

In article ,
Stephen wrote:
On 22/04/2014 18:21, charles wrote:
In article , Stephen
wrote:
On 21/04/2014 17:25, Tricky Dicky wrote:
I think you are overthinking this, to draw 32A you would need to hook
up appliances that would draw in excess of 7kW. Somehow I do not think
what you have will come anywhere near that. A 4-way extension socket
protected with a 13A fuse will allow almost 3kW. Look at the
specification plates on the appliances add up the wattage and that will
give you the total this circuit will draw.

Richard


it was more to do with ensuring its compliant to IEEE regs and also to
protect against a situation of a full on short on 2.5mm2 cable on a 32A
RCBO considering that 2.5mm2 cable is only rated up to 20A.

Hence my thought of creating a 2.5mm2 min ring main of 2 double sockets
on the end of the cooker outlet fed by 6mm2 cable wihin the cooker's
immediate vicinity to feed the two gas grill/ovens, the gas hob an dthe
cooker extractor hood

IEEE is an American body, over here was the IEE, now the IET.

The cable rating is concerned with heating - not short circuit current.


Ok, OK, IET.... its hard keeping track of when things change like Corgi
to GaSafe! :-)

7th Ed wiring regs or whatever it is called now!.....

the 7th Edition cam eout a bit before your time, I suspect. It was issued
in 1916 and replaced by the 8th in 1924. My first copy was the 13th. It's
now the 17th. Just say BS7671.

--
From KT24

Using a RISC OS computer running v5.18

If it's a short you are worried about then changing the RCBO is the answer or a smaller MCB if you do not want to go to the expense of fitting a RCBO.

Richard

On 22/04/2014 18:13, Stephen wrote:
On 21/04/2014 17:25, Tricky Dicky wrote:
I think you are overthinking this, to draw 32A you would need to hook
up appliances that would draw in excess of 7kW. Somehow I do not think
what you have will come anywhere near that. A 4-way extension socket
protected with a 13A fuse will allow almost 3kW. Look at the
specification plates on the appliances add up the wattage and that
will give you the total this circuit will draw.

Richard


it was more to do with ensuring its compliant to IEEE regs and also to
protect against a situation of a full on short on 2.5mm2 cable on a 32A
RCBO considering that 2.5mm2 cable is only rated up to 20A.

A "full on short" is what is known as a "fault current" or prospective
short circuit current. The nominal rating of the cable is pretty much
irrelevant since the current flow will be 100s if not 1000s of amps.

Hence what matters is can the cable survive long enough under adiabatic
heating conditions to allow the protective device to operate, without
melting, bursting into flames etc first. You also need to make the worst
case assumption that its going to start at its maximum nominal conductor
temperature of 70 deg C.

The way you would assess this if designing your own non standard circuit
would be using the adiabatic equation:

s = sqrt( I^2 x t ) / k

Where s = the cross section of the cable in mm, I the current, t the
time to clear the fault, and k a factor dependant on the makeup of the
cable - typically 115 for a PVC insulated cable.

So say you have a fault current of 400A, that will open your RCBO on the
magnetic response part of its trip. So allow a nominal 0.1 secs.

that means we get sqrt( 400^2 x 0.1 ) / 115 = 1.09mm

Which is smaller than any of the conductors in a 2.5mm T&E - hence it
will survive.

This is a different situation from protecting it from an overload. e.g.
drawing a sustained 40A from it.


(2.5mm^2 cable in its "clipped direct" or embedded in masonry
installation method is good for 27A BTW)

Hence my thought of creating a 2.5mm2 min ring main of 2 double sockets
on the end of the cooker outlet fed by 6mm2 cable wihin the cooker's
immediate vicinity to feed the two gas grill/ovens, the gas hob an dthe
cooker extractor hood

No need - the single cable is adequately fault protected - this is why
we allow spurs in 2.5mm2 cable from ring circuits and radials wired in
larger diameters.

--
Cheers,

John.

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On 22/04/2014 18:23, Stephen wrote:

Alternatively you might want to consider whether a neater job could be
done by discarding the 13 A plugs and wiring all the appliances into
strategically placed fused connection units.

I did wonder about this but my issue is lack of space for switchable
FCUs between worktop and wall cupboards

[... snip ...]

If I do FCU's for the hob, two grill/ovens and the extractor fan, I have
to find room for 4 seperate switchable FCUs with them all being a
miminum of 300mm away from the hob.

Hence my interest in having a single cooker switch feeding all four
while being compliant with regs....

Yes, if you retain the cooker control switch (CCS) as a master isolator
for the group there'd be no need for individual switching for the hob &
ovens. You could use three unswitched FCUs (with flex outlets) suitably
placed, out of sight. They would be need to be accessible for fuse
replacement, preferably without tooo much dismantling - but this is the
same issue as when using plug & socket connections. This does assume
that the CCS is not too far away, preferably no more than 2m from any of
the cooking appliances. Label the CCS to indicate its function, e.g.
"Hob & ovens (ign)"

The cooker hood/fan should, I suggest, have its own accessible switched
FCU (whether or not it's fed via the CCS). This should be wall mounted
at above worktop height, either in the 'run of sockets' or higher, near
the appliance. This is to provide a readily recognisable means of
'switching off for mechanical maintenance' as required by the regs. An
FCU feeding a separate flex outlet plate, linked via a run of 1.5 T&E
buried in the wall, might be appropriate here.

--
Andy

On 22/04/2014 22:42, Andy Wade wrote:
On 22/04/2014 18:23, Stephen wrote:

Alternatively you might want to consider whether a neater job could be
done by discarding the 13 A plugs and wiring all the appliances into
strategically placed fused connection units.

I did wonder about this but my issue is lack of space for switchable
FCUs between worktop and wall cupboards

[... snip ...]

If I do FCU's for the hob, two grill/ovens and the extractor fan, I have
to find room for 4 seperate switchable FCUs with them all being a
miminum of 300mm away from the hob.

Hence my interest in having a single cooker switch feeding all four
while being compliant with regs....

Yes, if you retain the cooker control switch (CCS) as a master isolator
for the group there'd be no need for individual switching for the hob &
ovens. You could use three unswitched FCUs (with flex outlets) suitably
placed, out of sight. They would be need to be accessible for fuse
replacement, preferably without tooo much dismantling - but this is the
same issue as when using plug & socket connections. This does assume
that the CCS is not too far away, preferably no more than 2m from any of
the cooking appliances. Label the CCS to indicate its function, e.g.
"Hob & ovens (ign)"

The cooker hood/fan should, I suggest, have its own accessible switched
FCU (whether or not it's fed via the CCS). This should be wall mounted
at above worktop height, either in the 'run of sockets' or higher, near
the appliance. This is to provide a readily recognisable means of
'switching off for mechanical maintenance' as required by the regs. An
FCU feeding a separate flex outlet plate, linked via a run of 1.5 T&E
buried in the wall, might be appropriate here.


Thank you for your valuable comment... So are you saying its NOT regs
compliant to use the CCS as a means of switching off the cooker hood for
the purposes of mechanical maintenance? I would have thought this would
be safer as this also ensures the cooker is off as well too....

The CCS will be in the run of sockets and would be in your words, "be
wall mounted at above worktop height, in the 'run of sockets'in order to
provide a readily recognisable means of 'switching off for mechanical
maintenance'"

I am happy to stick a label on the CCS to make it clear that its hob,
two grill/ovens and extractor fan if that makes any difference.

On 23/04/2014 06:40, Stephen wrote:
On 22/04/2014 22:42, Andy Wade wrote:
The cooker hood/fan should, I suggest, have its own accessible switched
FCU (whether or not it's fed via the CCS). [...].

Thank you for your valuable comment... So are you saying its NOT regs
compliant to use the CCS as a means of switching off the cooker hood for
the purposes of mechanical maintenance?

No, I'm not necessarily saying that. I'd accept it if the CCS was the
the only means of disconnection: you have provided means of isolation
and switching off, as required by regs 537.2 and 537.3. The
bloody-minded, though, might argue that the CCS is not continuously
under the control of the maintenance-person, citing reg. 537.3.1.2,
which requires suitable provision to ensure that the supply can't be
inadvertently restored during maintenance. (Someone, not realising that
the Hob & oven switch also controls the fan, might switch it back on, in
order to pre-heat an oven, say...)

My point really is that a additional control switch would remove any
doubt about such arguments, /and is just a much more conventional
arrangement/, making the labelling simpler and clearer. One switch for
the cooking appliances and one for the hood: simples.

--
Andy