Author Topic: Junctioning 32A cooker circuit with a 13A spur.  (Read 10994 times)

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Offline PlainName

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #25 on: February 11, 2022, 11:11:06 am »
Quote
A standard UK ring circuit (It is a weird UK thing for the non UK crowd) is typically fed by a 32A breaker, and nobody worries about a 2.5mm spur to a single socket.

Perhaps because it's a ring circuit, not a single-ended job.
 

Online paulcaTopic starter

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #26 on: February 11, 2022, 05:49:06 pm »
Also, why not reduce the MCB feeding the 6mm cable to 16 A anyway? You may find the manufacturer's instructions (which you're supposed to "take account of") require that anyway, and that is a cheap and straightforward job.

That's a good point.  With most UK appliances they come with a fuse in the "plug".  The oven is a hardwire, it says it has a 16A 'fuse' requirement NOT a 16A circuit requirement.  In Europe they apparently have a 16A 3 pin connector on a single 16A circuit... so ovens are often rated to 16A, not 13A like UK plug-in ovens.  The short of it is... it expects to be on a 16A fused spur in Europe.  So ... it probably doesn't have an internal fuse... and yes, should be fused at 16A at the consumer unit.  I have a spare in there, need to check it's rating, I could get lucky, but Screwfix sell them pretty cheap.

*Why flex here though? A bit of 1.5 or 2.5 mm2 T&E to a FCU would seem more conventional. If you do use flex you should really use ferrules.
**FCU = fused connection unit. It's a thing we have in the UK that takes the same type of fuses as the plugs but is for permanently installed things.
*** These ignition things take a couple of milliamps.

* I figured it was easier to work with and would allow me to leave the socket floating on the floor of the cavity rather than trying to fix it up anywhere.
** FCU.  Never heard of.  Adds a new dimension.
*** Yea.  The irony is I could probably run an ignitor circuit of a 18650 lion for months.  Only the circuitry is obviously going to use the mains voltage.

EDIT:  FCU:  Is that just the fused spur panels with the switch they use for dishwashers/washingmachines?  Ohh.... penny drop!  Of course.  They normally end up as a floating socket extension under the kick boards for easy use.  The fuse in the spur panel is to fuse that bit of cable, even through the dishwasher/et.al. has it's own fuse (UK plugs).
« Last Edit: February 11, 2022, 05:56:45 pm by paulca »
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Online paulcaTopic starter

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #27 on: February 15, 2022, 05:30:31 pm »
All done.  Both cookers working. 

6mm feed -> 60A junction 6mm + 2.5mm out.  2.5 goes to a single plug socket, 6mm goes to the new oven.

All I have as open items is to drop the 32A to a 16A MCB T3.
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Offline SteveyG

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #28 on: February 16, 2022, 12:12:53 am »
Also, why not reduce the MCB feeding the 6mm cable to 16 A anyway? You may find the manufacturer's instructions (which you're supposed to "take account of") require that anyway, and that is a cheap and straightforward job.

That's a good point.  With most UK appliances they come with a fuse in the "plug".  The oven is a hardwire, it says it has a 16A 'fuse' requirement NOT a 16A circuit requirement.  In Europe they apparently have a 16A 3 pin connector on a single 16A circuit... so ovens are often rated to 16A, not 13A like UK plug-in ovens.  The short of it is... it expects to be on a 16A fused spur in Europe.  So ... it probably doesn't have an internal fuse... and yes, should be fused at 16A at the consumer unit.  I have a spare in there, need to check it's rating, I could get lucky, but Screwfix sell them pretty cheap.

*Why flex here though? A bit of 1.5 or 2.5 mm2 T&E to a FCU would seem more conventional. If you do use flex you should really use ferrules.
**FCU = fused connection unit. It's a thing we have in the UK that takes the same type of fuses as the plugs but is for permanently installed things.
*** These ignition things take a couple of milliamps.

* I figured it was easier to work with and would allow me to leave the socket floating on the floor of the cavity rather than trying to fix it up anywhere.
** FCU.  Never heard of.  Adds a new dimension.
*** Yea.  The irony is I could probably run an ignitor circuit of a 18650 lion for months.  Only the circuitry is obviously going to use the mains voltage.

EDIT:  FCU:  Is that just the fused spur panels with the switch they use for dishwashers/washingmachines?  Ohh.... penny drop!  Of course.  They normally end up as a floating socket extension under the kick boards for easy use.  The fuse in the spur panel is to fuse that bit of cable, even through the dishwasher/et.al. has it's own fuse (UK plugs).

Most electric ovens and hobs these days tend to be designed for Europe. The nature of a heating cycle of an oven and hob mean it's unlikely to be a problem, but you can run into issues with the 13A plug getting pretty warm on appliances rated over 2 kW used for long periods, particularly in a poor quality socket.

It would have been acceptable to connect the oven and hob directly to the cooker supply with no additional fusing down, the oven itself is unable to create an overload situation (it's a fixed load), so provided the cable is adequately rated for the 3+ kW, nothing else is required. Of course you must do your tests to confirm the PFCC at the appliance is high enough to meet disconnection times.

There's no need to change the MCB.
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Offline themadhippy

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #29 on: February 16, 2022, 12:34:48 am »
Quote
so provided the cable is adequately rated for the 3+ kW, nothing else is required. Of course you must do your tests to confirm the PFCC at the appliance is high enough to meet disconnection times.

There's no need to change the MCB.

so a lump of 1mm protected by a 32A mcb is fine?
 

Offline mikeselectricstuff

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #30 on: February 16, 2022, 10:08:08 am »
Quote
so provided the cable is adequately rated for the 3+ kW, nothing else is required. Of course you must do your tests to confirm the PFCC at the appliance is high enough to meet disconnection times.

There's no need to change the MCB.

so a lump of 1mm protected by a 32A mcb is fine?
No.

There is no need to change the MCB, as the 2.5mm cable goes to a 13A socket, so the cable is protected by the fuse in the plug. As mentioned before, it is often permissable to protect the cable at the far end.
1mm would not be OK, as a 13A fuse would not provide adequate protection for the cable.

 
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Offline themadhippy

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #31 on: February 16, 2022, 11:51:30 am »

Quote
1mm would not be OK, as a 13A fuse would not provide adequate protection for the cable

1mm T+E is  rated for 16a clipped direct,  so more than capable of dealing with 3kw  and the only time a fuse is mentioned is that it aint needed

Quote
It would have been acceptable to connect the oven and hob directly to the cooker supply with no additional fusing down, the oven itself is unable to create an overload situation (it's a fixed load), so provided the cable is adequately rated for the 3+ kW, nothing else is require
 

Offline SteveyG

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #32 on: February 16, 2022, 05:14:30 pm »
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so provided the cable is adequately rated for the 3+ kW, nothing else is required. Of course you must do your tests to confirm the PFCC at the appliance is high enough to meet disconnection times.

There's no need to change the MCB.

so a lump of 1mm protected by a 32A mcb is fine?

If it meets the requirements of 433.3 in the regs, generally that there is sufficient protection or it is unlikely that the cable is to be mechanically damaged and that the appliance on the load side of the cable results in the conductors being unlikely to be subject to overload. The conductors must meet 434 for fault currents and disconnection times.

Consider a typical busbar chamber, that may be protected by only 400A fuses. The conductors attached to these will not all be 240mm². It's quite normal to tap off these in 2.5mm for things like fire alarms, local lighting where the above regulations are adhered to.
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Online paulcaTopic starter

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #33 on: February 17, 2022, 09:27:02 am »
In Europe the cooker point is most likely a single 2.5mm 16 Amp spur circuit.  Possibly with a larger circuit for the hob additionally.  It could be a 30A circuit that is split into 2x16A circuits locally to the device, but... 16A isn't enough to run a 6kW hob.

In the UK we typically have 30A cooker circuits, traditionally for a single floor standing, all in one cooker.  In modern times and in modern kitchen designs and.. falling price (and quality) of 'white goods' people are installing "built in" ovens and separate hobs.  This is presenting interesting challenges for people with refitted kitchens without direct access to the cooker feed which is buried in a concrete wall in a bit of PVC tubing (if you are lucky).

The main thing at play here however is that in the UK EVERY SINGLE plug in device has a fuse in it's plug.  So we 'know' that a plug socket on the end of a 2.5 spur can only carry 13 Amps.

Now... I could sell the house to a moron who buys a cheap Chinese double or triple adapter, with no fuse, and tries to run a kettle, a toaster and a tumble drier off that socket.  But, you can't always account for idiots and poor quality consumer side add-ons.  If you MUST buy a double or triple adapter, often found in appliance dense areas in kitchens to keep in frequently used devices plugged in, you get a 13Amp fused one.  These have been standard for decades because it was a common fire hazard in 1970s 1980s kitchen which only had 1 or 2 sockets.  Usually 1 on the 30A cooker control plate and one on the 30A mains ring.  So to run a kettle, an iron and a electric fan heater, they just stacked double adapters in the one socket and it would happily supply 2 or 3 13A devices... but of course that leads to heat, that and the double adapters generally were unstable with heavy flexes tending to pull them apart, so... incompletely high resistance contacts in the adapter stack led to huge heat and eventually arc'ing, sparks and or fire.  They even had TV adverts warning people of the dangers of adapter stacking.
« Last Edit: February 17, 2022, 09:28:58 am by paulca »
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Online paulcaTopic starter

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #34 on: February 17, 2022, 09:39:11 am »
Oh, a note on the installation, which was done by Curry's.  £44.

To be honest I was not expecting as much as I got.  The first thing the installer said was, "Oh, you can't have 2.5mm for your hob.  You need way more than....  oh, that's a gas hob.  Okay, fine, sorry."

He then test fitted the oven, which cleared the hob gas pipe by literally mm's.  Then he inspected the consumer unit to verify it was a single circuit with appropriate MCB.  Then tested the circuit with a fluke mains tested thing.  Not a full test, just a single end test which said, "GOOD".

I will pull the oven and reinspect the wiring in a few weeks and maybe fire and IR camera at the junction box while running the oven.  Just to check there are no relaxing connections.  The junction boxes and NOT maintenance free, but it is easily accessible.
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Online paulcaTopic starter

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #35 on: February 17, 2022, 10:08:24 am »
As a complete aside, not electrical related at all, but quite frankly the most scary part of this whole cooker swap over.....

The original plumber who installed the hob, didn't test it, wasn't "Gas SAFE" certified and just an "odd jobs" man who does a bit of plumbing. 

IT LEAKED!  FOR A WEEK!  Half a bottle of gas gone down into the under floor cavity of the house.... while I slept, while I played with my daughter.  There are SOME benefits to still having the underfloor breather vents for the (now removed) coal fire.  Even though they cause annoying drafts in winter.

I occasionally smelt gas, particularly when pulling the old oven out to inspect the wiring I had to do, but figured it was just because I'd used it recently and any "spilt" gas while lighting it, would collect in there.

I became more suspicious when, as a random impulse put my nose on the floor of the kitchen first thing in the morning when the cooker had been out of use for 12 hours.  I caught a few whiffs of propane, decided to turn the bottle off and wait 15 minutes and check with my nose again.  No gas smell!!!

So I pulled the oven out, turned the gas bottle on again and sprayed the gas pipe with kitchen cleaner spray.  It immediately fizzed and bubbled angrily.  I turned it back off.  I "weighed" the bottle in my hands and swung it around, it has got liquid propane in there still, but maybe only half a bottle.

Called another plumber out.  He asked why I don't get the previous guy out to fix his work.  I replied, "with a gas leak, you only get one strike.  I don't want him to fix it."

Looking at the joint, I seen unburnt flux, not just uncleaned flux, but unburnt flux and you could feel with your finger nail part of the joiner collar was not flowed with solder at all.  Additionally there was a drop of oil dripping off the pipe (before I had used the spray).  I figure this was machine oil impurity in the gas from the compressor that had been collecting over half a bottle of leaking through a tiny hole.

I did for about 5 seconds consider fixing it myself.  However, I knew none of my irons stood a chance against a cooper pipe and I doubt the heat gun on max would be capable either, besides, I only have leaded solder.    Anyway, the slap around the back of the head came internally rather rapidly with "IT IS GAS, NO!  GET PROFESSIONAL!".  Wiring, fine, careful, paranoid, planned, thought out and implemented cleanly and tested.  Fine.  Gas, no.  Just no.
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Online paulcaTopic starter

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #36 on: February 17, 2022, 10:12:12 am »
The chance of the house going "BOOOM!" was relatively remote.  What was NOT remote however would have been any spark in that oven cavity under the hob.  I had left everything disconnected and I am thankful for that now.  If I had wired the old oven back up, powered it and the relay clicked and arced while the hob was filling the oven with gas...  the leak had enough flow to become a right flame thrower, spreading through the undercounter cupboards trying to find ways up and out.
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Offline SteveyG

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #37 on: February 24, 2022, 03:45:16 pm »
In Europe the cooker point is most likely a single 2.5mm 16 Amp spur circuit.  Possibly with a larger circuit for the hob additionally.  It could be a 30A circuit that is split into 2x16A circuits locally to the device, but... 16A isn't enough to run a 6kW hob.

Technically, a 16A supply is fine for a cooking appliance up to 6.5 kW. Bear in mind Table 6.2 in the regs that allow for diversity to be applied to certain types of load ;)
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Offline Lectro

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Re: Junctioning 32A cooker circuit with a 13A spur.
« Reply #38 on: June 07, 2022, 02:57:59 pm »
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Second problem is I would need to cut the single tall vertical box out and replace it with a double box,
or use a contactum X1457


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