Is this a NO-NO? - 13a socket on 40a RCBO cooker circuit?

[Stevethetiler]

Guys.

Could do with someone confirming the above for me. I had a new CU put in just over 12mths ago and the firm that did it also did some work in the kitchen for us. (sockets etc.)

Now, its only just come to light that they "may" have done a boob and I just want someone to quote me with some regs or something that state that what they have done is not permissable. (it may be permissable, I just want the avenue of recourse and would be handy to know before I shoot my mouth off LOL)

Basically, I have a Crabtree CU (all RCBO's) and the cooker circuit is a radial protected by a 40a/30ma RCBO.

It is run in 6mm t&e from the CU to the 45a DP cooker isolator switch and from there, it currently goes to an unswitched socket in a cupboard next to my oven/hob. (all 6mm)

My 2.8kw electric oven and gas hob are plugged into the socket via 13a and 3a plugs respectively.

Now - it recently dawned on me after another thread I posted //www.diynot.com/forums/viewtopic.php?t=267476 and some of the replies I got stated that it was a no-no to have a 13a socket run off a 40a circuit.

Basically, what I am trying to do is establish wether the installers put the wrong size RCBO in and wether or not I have any come-back on them for doing so. To get it changed is gonna set me back around £80.00 so I would prefer not to have to spend it if I dont have to.

Any advice greatfully recieved and if anyone can quote me regs to backup what I "think" is a no-no, that would be great.

TIA
Steve.

 

[flameport]

Nothing wrong with a socket outlet on a 40A circuit.

 

[electronicsuk]

The debate is with regard to whether or not an accessory such as a socket to BS1363 should be protected by anything larger than a 32A OCPD. In your case there is no cause for concern, as the maximum load that can be pulled through the socket is limited by the fuses in the plugtop. Furthermore, as you're only feeding the one single or double socket outlet, you aren't asking the terminals at the rear to carry any current to additional outlets elsewhere, so they'll never have more than 2*13A passing through them.

If it worries you, just fit a 32A RCBO instead, and keep the larger cable in place should you need it in the future for a larger oven.

To be honest, it sounds as if you've been left with a pretty good installation. Not many sparks would fit a consumer unit fully loaded with RCBOs and run in a future-proof cooker circuit.

 

[Stevethetiler]

The debate is with regard to whether or not an accessory such as a socket to BS1363 should be protected by anything larger than a 32A OCPD. In your case there is no cause for concern, as the maximum load that can be pulled through the socket is limited by the fuses in the plugtop. Furthermore, as you're only feeding the one single or double socket outlet, you aren't asking the terminals at the rear to carry any current to additional outlets elsewhere, so they'll never have more than 2*13A passing through them.

If it worries you, just fit a 32A RCBO instead, and keep the larger cable in place should you need it in the future for a larger oven.

To be honest, it sounds as if you've been left with a pretty good installation. Not many sparks would fit a consumer unit fully loaded with RCBOs and run in a future-proof cooker circuit.

Well, I kinda insisted that the cooker circuit was future-proofed. I did alot of the work myself in terms of chasing the walls, dropping the cables, fitting the gang boxes and sockets....I even wired them all up prior to connection at the CU.

The electricians were very good in supervising my work stage by stage so , hats off to them for that in every respect as it saved me alot of money.

It was only through advice/posts on my linked thread above, I thought that maybe it shouldnt have had a 40a RCBO on it and should have been less.

As it happens, Im having to ammend the wiring to allow for a new oven to be hardwired. The RCBO will get changed down to a 20a as that was what was recommened on the other thread.

Just one thing crossed my mind, say I have (and this is NEVER gonna happen but you dont know about the next property owners) two appliances rated at 13a plugged into that socket (maybe a vacuum and a kettle for example).......also, got the 15a oven and 3a gas hob too....

Would this be considered as dangerous if a 20a RCBO is replacing the 40a one.....

I have been told/advised that it needs to be changed due to the new oven being hardwired (3.6kw) whilst the gas hob remains plugged into that socket on its 3a plug.

EDIT: Considering my new setup will utilise the same circuitry on 6mm cable...the plug is staying in place to provide ignition to my gas hob but the cable between the socket and 45a DP switch is going to be "cut" and a Click Dual Cooker Connection plate is to be fitted.

One load side of this will carry on supplying the socket on 6mm, the other load point will be used to hardwire the new 3.6kw oven into.

Is there an issue regarding keeping the RCBO at 40a - I just wanna make doubly sure it definetly needs to be changed down to 20a (or whatever size RCBO would be recommended)

TIA

 

[electronicsuk]

Just one thing crossed my mind, say I have (and this is NEVER gonna happen but you dont know about the next property owners) two appliances rated at 13a plugged into that socket (maybe a vacuum and a kettle for example).......also, got the 15a oven and 3a gas hob too....

Would this be considered as dangerous if a 20a RCBO is replacing the 40a one.....

I have been told/advised that it needs to be changed due to the new oven being hardwired (3.6kw) whilst the gas hob remains plugged into that socket on its 3a plug.

I don't think I've read the original thread, so perhaps this is why I'm confused. I got the impression at the start of this thread that you have a 45A DP switch feeding a 2-gang unswitched socket outlet. In that case, how could you ever have a vacuum cleaner and kettle plugged in at the same time as the oven and gas hob ignition?

In any case, it wouldn't be inherently dangerous to load the circuit beyond 20A, but it would be a design flaw to install a circuit that's so easy to overload.

 

[Stevethetiler]

Just one thing crossed my mind, say I have (and this is NEVER gonna happen but you dont know about the next property owners) two appliances rated at 13a plugged into that socket (maybe a vacuum and a kettle for example).......also, got the 15a oven and 3a gas hob too....

Would this be considered as dangerous if a 20a RCBO is replacing the 40a one.....

I have been told/advised that it needs to be changed due to the new oven being hardwired (3.6kw) whilst the gas hob remains plugged into that socket on its 3a plug.

I don't think I've read the original thread, so perhaps this is why I'm confused. I got the impression at the start of this thread that you have a 45A DP switch feeding a 2-gang unswitched socket outlet. In that case, how could you ever have a vacuum cleaner and kettle plugged in at the same time as the oven and gas hob ignition?

In any case, it wouldn't be inherently dangerous to load the circuit beyond 20A, but it would be a design flaw to install a circuit that's so easy to overload.

Sorry for the confusion. Thats how its set up at the moment. If you read my last post, it explains the new proposed setup (caused by a replacement oven that needs hardwiring - couldnt change what they were gonna give me)

I guess, with the new setup, the unswitched double will only have my gas hob plugged into it and the 3.6kw oven hardwired on what has been suggested, a 20a RCBO.

I just thought that (and im probably overthinking things) if , for whatever reason, both of the sockets on the unswitched double were in use with x2 13a appliances AND the oven was on full throttle, wether or not it would be dangerous.

Just trying to cover every base.

 

[electronicsuk]

Change the unswitched double socket to a fused connection unit feeding the hob ignition, problem solved.

 

[Stevethetiler]

Change the unswitched double socket to a fused connection unit feeding the hob ignition, problem solved.

So if I do that, do I need to change the 40a RCBO down to a lower one? - considering the new 3.6kw oven is going to be hardwired and run off the same radial....is that too large a breaker?

Im just concerned as have been given various advices about the size of the RCBO. I want it to be SAFE.

If I can do what you suggest - swap the socket for a FCU fused at 3a, hardwire my 3.6kw oven all off the same radial thats on a 40a 30ma RCBO, that would save me £80.00!

Obvioulsy if it needs to be lower because of the oven, then I have to stump up!

 

[EFLImpudence]

Remember, as always, the CPD ( RCBO in your case ) is there to protect the cable - not what you put on the end of it.

 

[Stevethetiler]

Remember, as always, the CPD ( RCBO in your case ) is there to protect the cable - not what you put on the end of it.

Haha - funny, I was just expalinging that to the missus that its a common misconception that the fuse in the CU or plug protects the appliance/s but INDEED it protects the cable from meltdown.

Considering my cooker radial is 6mm all the way, if I do the following, can I avoid changing the 40a RCBO?

1. Change the unswitched double for a fused connection plate (fused at 3a for the gas hob)

2. Run the 3.6kw electric oven off the same circuit.

As stated, the wiring FROM the 45a DP cooker isolator is in 6mm. This load cable will then go to a "Click 45a dual cooker connection plate" wired into that plate as the "supply"

The two load connectors on the cooker connection plate will then be connecred as follows:

load 1: 6mm to a fused connection plate located in the cupboard adjacent to the left of the oven. Gas hob wired into that plate at 3a.

load 2: 3.6kw oven hardwired via manufacturers supplied oven flex.

Assuming that is ok, is there a need to change/downgrade the RCBO from 40a? - and if so, should it be 20a or 32a?

TIA of a response.

 

[EFLImpudence]

As already said the RCBO is protecting the cables so...

if you connect the supplied flex to the Cooker Connection Unit you will have to change the RCBO to whatever the Manufacturer's Instructions state (probably 16A).
If you could connect 6mm² cable to the oven you would not have to change the RCBO. Changing the RCBO is probably the easier though. PLUS...

Whatever you do you will also need a Fused Connection Unit (with a 3A or 5A fuse - according to MI) connected to the CCU for the gas igniter.

Is your present socket in the cupboard surface mounted or flush? Either way you can get 'dual' boxes to which you can attach both the CCU and FCU. They are slightly wider than the present 'double' box.

 

[Stevethetiler]

As already said the RCBO is protecting the cables so...

if you connect the supplied flex to the Cooker Connection Unit you will have to change the RCBO to whatever the Manufacturer's Instructions state (probably 16A).
If you could connect 6mm² cable to the oven you would not have to change the RCBO. Changing the RCBO is probably the easier though. PLUS...

Whatever you do you will also need a Fused Connection Unit (with a 3A or 5A fuse - according to MI) connected to the CCU for the gas igniter.

Is your present socket in the cupboard surface mounted or flush? Either way you can get 'dual' boxes to which you can attach both the CCU and FCU. They are slightly wider than the present 'double' box.

new cooker install

• Stevethetiler
• 18 Mar 2011
• 1

Using a Click PRW217 Dual cooker connection plate 45a

Click PRW217

• Stevethetiler
• 18 Mar 2011
• 1

two load outlets to the left, supply to the right. the load outlet wired in is currently to a...

Best way to describe this!

I have ammended the radial today. As you can see from the pic, I have installed a dual cooker connection plate. The right side cable is the supply from the load side of the 45a Cooker control switch. (located at worktop level to the right of my hob)

The left side of the cooker connection plate is wired into one of the loads of the click PWR217. It then goes directly up behind the cupboard next to the oven housing on the left to a unsiwtched double which is surface mounted on the side of the carcass. You can just make out at the top left of the pic, the black flex from the gas hob going through the carcass and immediately on the other side is the double unswitched socket. It currently has a 3a plug on the other end!

This is where my old oven and hob were plugged in.

Obviously, the socket is still in situ, but can easily be changed to a FCU fused at 3a for the gas hob.

The other load on the left of the dual cooker plate pictured (currently empty) is for the new 3.6kw electric oven. This will be wired in by Hotpoint ( i imagine they will do the least work possible so would use the flex)....alternatively, I could wire it in myself using 6mm as suggested if it avoids having to change the RCBO from 40a down to whatever.

 

[ajrobb]

Interesting point about the load on the socket terminals. So it sounds like it would not be acceptable to put a 13 A socket in the middle of a 40 A circuit, but terminating an unfused spur the socket doesn't carry more than its own load.

There might be the possibility of a short between live and neutral pins in a 13 A plug, for example. Or someone using a safety cover to open the shutters... I don't know if a 32 A CB would offer better protection against such abuse.

 

[flameport]

if you connect the supplied flex to the Cooker Connection Unit you will have to change the RCBO to whatever the Manufacturer's Instructions state (probably 16A).

Not necessarily.

Overload protection is not required for the oven cable, as there is no way it could be overloaded (the oven is a fixed load).
Therefore the RCBO only needs to provide fault current protection, and the minimum required size of the conductors in the cable is probably very small (under 1mm), unless the PSCC at the oven position is abnormally high (it won't be), or the RCBO has a very high energy let-through (also unlikely).

This can be confirmed by reference to the manufacturer specifications for the RCBO and calculation of the expected PSCC at the oven location.

While there is that regulation about complying with manufacturer instructions, in the instance of ovens designed for use elsewhere in Europe, the manufacturers instructions are quite frankly a load of trash, and are just describing the expected oven circuit found in most EU countries.

 

[EFLImpudence]

Fair enough - but I would be uncomfortable having maybe a 1.5mm² flex only 'protected' by a 40A CPD.