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| Junctioning 32A cooker circuit with a 13A spur. |
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| mikeselectricstuff:
--- Quote from: themadhippy 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. --- End quote --- so a lump of 1mm protected by a 32A mcb is fine? --- End quote --- 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. |
| themadhippy:
--- Quote ---1mm would not be OK, as a 13A fuse would not provide adequate protection for the cable --- End quote --- 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 --- End quote --- |
| SteveyG:
--- Quote from: themadhippy 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. --- End quote --- so a lump of 1mm protected by a 32A mcb is fine? --- End quote --- 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. |
| paulca:
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. |
| paulca:
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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