- Joined
- 11 Jan 2004
- Messages
- 43,322
- Reaction score
- 2,758
- Country
Just following your leadwinston1 said:
I thought your philosophy applied to all instructions?
MCB size for reference method? & Mini Kitchen Consumer Unit
- Thread starter Boolean
- Start date
OK - put knowing if the instructions are wrong to one side for a minute.
How do they know if the instructions are right?
Does anybody know what Winston is saying?
I can't see his words of wisdom any more
I can't see his words of wisdom any more
You have contradicted yourself. If your first priority is safety then you must have the installation periodically inspected and tested as REQUIRED by the IET Wiring Regulations.
Sorry for the absence folks, hard drive crash doom has led to a week of internet detox!
I take your point on board Risteard and the inspection is something I will eventually pay to have done, but in my mind at least, it is a thing to avoid problems at a future sale of the house(hopefully I'm never moving again) rather than for safety. I trust the council of those on these forums (e.g flameport, the Johns et al) more than I would a local trade professionals who's advice seems to be more about making their life easier and more profitable with scant regard to safety.
I've seen registered gas engineers doing landlords certificates who don't even own a manometer! I've seen gas leaks left on the meter caused by the distributor. On the electrics side I've seen registered electricians leave terminals not done up that burnt out the isolator and consumer unit! I've seen registered electricians do building regulations installation testing on a 18 way CU in less than 8 minutes!
The failure of the various competency schemes to provide assurance to the consumer is a national scandal, I haven't heard anyone say a good word!
Hopefully by the time I have some spare cash I will have found a local sparky that I trust for the inspection, but I'm hoping that I'm doing enough due diligence now to offset the risk of something being wrong. Most of my friends have bought houses without giving it a second thought. I've tried to explain the inadequacy of one of friend's earthing arrangements but they are not interested as they need the cash to spend on decorating! It would keep me awake at night as I'm not the kind of person who likes to be ignorant of these things. Granted a couple of hundred hours of reading can never provide the experience or knowledge of the professionals on these forums but I'm doing what I can.
I'm extremely grateful to those who give their time on these forums to share their knowledge and experience. I do the same myself, gratis, in certain areas of my life where I am more than competent, I'm sure we are all glad that society is not dead(yet!)!
Out of interest I had a look at the other 10mm circuit and oven installation instructions. Surprise surprise, the only guidance of fuse size was for a "suitably rated fuse or circuit breaker". It did specify at least 6mm T&E cable, no mention of flex form the outlet, luckily it is connected to the cooker wall plate with fairly new looking H07 flex.
One other concern is that the oven circuit has a 50A mcb, but the cooker isolator will likely only be 45A. Maybe this is also too high for the fixing method(in oval conduit in plaster, above ceiling below upstairs floorboards)? Is either of these discrepancies likely to be a problem at a future inspection? e.g. over rated fuse for the accessories\fixing method?
One other concern is that the oven circuit has a 50A mcb, but the cooker isolator will likely only be 45A. Maybe this is also too high for the fixing method(in oval conduit in plaster, above ceiling below upstairs floorboards)? Is either of these discrepancies likely to be a problem at a future inspection? e.g. over rated fuse for the accessories\fixing method?
It could be a 50A switch.
No, it's fine. The oven will never draw 45A
Just installed by someone who likes wasting copper and doesn't understand.
Any domestic cooking appliance will be happy on a 32A MCB with 4mm² cable installed to method C (6mm² in conduit).
Another thing I noticed is that the 10mm cable goes through the backbox(45mm, looks like plenty of space in there) of one the ring main sockets.
It has its insulation on and must have been done as space is tight to run the cables down, but is this normal practice? e.g. 2 cables from different circuits in one back box? I'm guessing not as the 2 way light switching on the stairs does this also, but perhaps the oven circuit is a special case?
It has its insulation on and must have been done as space is tight to run the cables down, but is this normal practice? e.g. 2 cables from different circuits in one back box? I'm guessing not as the 2 way light switching on the stairs does this also, but perhaps the oven circuit is a special case?
I just checked, it is a 45A MK socket and isolator
isn't the fuse also there to protect the cable and accessories against short circuit?
Would it be coded on an inspection?
They may have done this in the belief that the socket creates a 'safe zone' for the oven cable.
This is not strictly true but as it passes through the back box, it is difficult to argue against.
It shouldn't be (but who knows with the level of 'inspectors' nowadays?).
The fuse IS there to protect the circuit but the oven cannot overload it (draw more than it's rated load) so overload protection could be omitted by the regulations as long as fault protection is satisfactory - which, with 10mm² it will be, assuming it is not miles long.
Yes, there is already a
I've been reading dozens of horror stories of vendors held over a barrel with electrical inspection failures for work that doesn't need actually need doing, but the electrician knows that the vendor will pay for the work to prevent the hold up of the sale.
I'm not planning on ever moving again, but if we had to(you never know, family sickness or job or something) I don't want to end up in that boat, it has cost people £1000s.
I've been reading dozens of horror stories of vendors held over a barrel with electrical inspection failures for work that doesn't need actually need doing, but the electrician knows that the vendor will pay for the work to prevent the hold up of the sale.
I'm not planning on ever moving again, but if we had to(you never know, family sickness or job or something) I don't want to end up in that boat, it has cost people £1000s.
Last edited:
What about a phase to neutral mechanical fault? is that just presumed to be unlikely?
Is the fault protection related to the infamous adiabatic equation? I was trying to punch the numbers on that one to check the mini kitchen consumer unit fault tolerance.
(12m 10mmT&E on 40A mcb 80A 30ms RCCB supplying 2 x 4 meters of 2.5mm T&E each on 20A mcbs and a 32A mcb on 10mm for the hob outlet)
It seems with modern fuses(type B) you would be hard pushed to fail on that score with the 4mm cpc in 10mm T&E?
That's a short circuit - so, comes under fault current as opposed to overload.
Not really, that determines whether the CPC can handle the prospective earth fault current until disconnection by the MCB.
The prospective fault current, greater of short circuit and line to earth fault, is determined by the Line to Neutral Loop Impedance and the (Line to) Earth Fault Loop Impedance respectively.
You need the Loop measurements.
I can work it out (approximately) if you want.
You would.
Or you can work it out.
Assume external circuit impedance (Ze) is 0.2Ω.
10 mm² conductor has a resistance of 1.83mΩ per metre.
Other sizes are relative so can be worked out - e.g. 2.5mm² is 4 times as much.
Add the Ze to all conductor resistances involved in the circuit (L&N or L&E) and divide the voltage, 230, by the ohms (not mΩ).
This will give you the PSC current or PEF current.
Assume external circuit impedance (Ze) is 0.2Ω.
10 mm² conductor has a resistance of 1.83mΩ per metre.
Other sizes are relative so can be worked out - e.g. 2.5mm² is 4 times as much.
Add the Ze to all conductor resistances involved in the circuit (L&N or L&E) and divide the voltage, 230, by the ohms (not mΩ).
This will give you the PSC current or PEF current.