I did you say the mcb trips I presume through a fault and it can be turned back on by the user even if the fault is still there resulting in a flash, bang from the mcb.Read what I wrote again. It was clear.
Discuss Immersion fuse or MCB? in the UK Electrical Forum area at ElectriciansForums.net
I did you say the mcb trips I presume through a fault and it can be turned back on by the user even if the fault is still there resulting in a flash, bang from the mcb.Read what I wrote again. It was clear.
Very clear what I am on about which no one has grasped after all these posts.I did you say the mcb trips I presume through a fault and it can be turned back on by the user even if the fault is still there resulting in a flash, bang from the mcb.
I did say it could be any other appliance.An immersion heater is a fixed resistive load and is not likely to overload and any fault whether this be between conductors or to earth will result in a high current fault which will be cleared by the protective device.
I think you have been here before trolling with your ridiculous scenarios and circular arguments which resulted in members getting bansI did say it could be any other appliance.
Later clarified. But this digression does not answer the prime points#1 refers to a 3kw immersion heater.
I see nothing circular. Link the link below:I think you have been here before trolling with your ridiculous scenarios and circular arguments which resulted in members getting bans
Therefore this will be my only response on the subject while adding you to the 101 list
I answered your prime points from #1.Later clarified. But this digression does not answer the prime points
The points are in the link below. If you cannot offer a solution then fine.I answered your prime points from #1.
Yes that refers to an immersion heater.The points are in the link below. If you cannot offer a solution then fine.
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No decent electrician these days would install a 13 amp fcu on a 3kw immersion.All within regs to have an immersion of a 13A fuse. Millions are.
I have responded your posts refer to an immersion heater.Best you you say "I do not know", or not get involved.
I am waiting for some responses.
A 20A switch and 16A breaker in the CU on a 2.5mm cable is not fine on a dedicated circuit as it still could cook a 2.5mm cable rated at 19A. 13A would be safer as it can pass current constantly over 13A meaning less risk of cooking a 2.5mm cable. But the regs say a 13A appliance can be on an FCU and off a ring. All legal. Many are off final rings and on FCUs.No decent electrician these days would install a 13 amp fcu on a 3kw immersion.
I would replace with 20 amp switch and 16amp mcb/rcbo.
An appliance would have a plug and fused accordingly so would be downstream fused.A 20A switch and 16A breaker in the CU on a 2.5mm cable is fine on a dedicated circuit. But the regs say a 13A appliance can be on an FCU and off a ring. All legal. Many are off final rings and on FCUs.
The point of this thread is how to stop a cable cooking, while the installation is still within regs, without ripping a house apart. A simple, quick, and cheap solution. One which combined the advantages of an MCB and fuse.
The fixed hard wired appliance may be any other rather than an immersion. Drop the immersion as it confuses many here. A fuse can constantly pass more than 13A over the rating of a derrated 2.5mm cable, which can be 19A - cooking time.An appliance would have a plug and fused accordingly so would be downstream fused.
A 3kw immersion heater isn’t going to “cook” the cable as you put it as already said it’s a resistive load and a short would trip the 32 amp rings ocpd even without the downstream fuse.
BS 1362 specifies the fusing current as 1.9 times the rated current. If the current exceeds the fusing current, the fuse must blow within 30 minutes. So a 13A fuse must blow within 30 minutes when carrying a current that exceeds 24.7A. 24.7A can fry a cable, especially when it is derrated say in an insulated wall.
MCBs are better, but a 13A fuse is a one-shot. MCBs are better for protection but can be switched back on again by the user as they are not one-shot.
A 2.5mm cable can be fried using a 13A fuse. Least is around 19A when in insulation. MCBs are superior of course.
The key to the thread is one-shot.
Very clear what I am on about which no one has grasped after all these posts.
1. A fuse has the advantage of being one-shot. A disadvantage is that under regs a cable can still fry using a fuse. A 13A fuse can run to near 25A until blowing, so it can draw a constant say 24.5A. A 2.5mm cable can be rated to 19A, which means it may fry. A 1.5mm cable serving say an immersion on a dedicated radial is rated 14A to 19.5A. And all within regs
View attachment 117604
A 16A MCB will draw over 20A for 2.75 hours cooking a 2.5mm cable rated at 19A. So best have a 13A MCB for a 13A appliance giving better protection of the cable on a one appliance dedicated circuit.
If a cable is constantly warm the insulation will deteriorate far quicker than always staying cool.Could you define exactly what you mean by 'cooking a cable' in this? If you mean it will get warm then yes it will, but if you mean it will be damaged in some way then no it won't.
If after using the ratings and calculations in the regs a 2.5mm is rated at 19A then this will be absolutely fine protected by that 16A MCB for the time it takes it to operate at 20A.
The current ratings in the regs do not represent the point at which a cable suddenly goes from working normally to being damaged.
Enticing? Enticing answers. I asked two questions, with no one really fully addressing them. Lots of peripheral stuff, interesting though it is. One unanswered is that I assume there an MCB that is not instantly re-settable by the user.This reminds me of the threads John-SJW used to create. Where he just kept enticing people to reply to them even though he was just spouting the same (and often wrong) stuff the whole time.
I think it must class as entertainment?
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