Immersion fuse or MCB?

[UNG]

I did say it could be any other appliance.

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

 

[Steve-S]

#1 refers to a 3kw immersion heater.

Later clarified. But this digression does not answer the prime points

 

[Steve-S]

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 see nothing circular. Link the link below:

Immersion fuse or MCB? | Page 2 | on ElectriciansForums

Find Immersion fuse or MCB? Advice and Help. How-to Immersion fuse or MCB? in the UK Electrical Forum advice boards on ElectriciansForums.net Est.2006 | Free Electrical Advice Forum. Immersion fuse or MCB? on ElectriciansForums.net Electrical Advice Forum.

www.electriciansforums.net

 

[westward10]

Later clarified. But this digression does not answer the prime points

I answered your prime points from #1.

 

[Steve-S]

I answered your prime points from #1.

The points are in the link below. If you cannot offer a solution then fine.

Immersion fuse or MCB? | Page 2 | on ElectriciansForums

Find Immersion fuse or MCB? Advice and Help. How-to Immersion fuse or MCB? in the UK Electrical Forum advice boards on ElectriciansForums.net Est.2006 | Free Electrical Advice Forum. Immersion fuse or MCB? on ElectriciansForums.net Electrical Advice Forum.

www.electriciansforums.net

 

[westward10]

The points are in the link below. If you cannot offer a solution then fine.

Immersion fuse or MCB? | Page 2 | on ElectriciansForums

Find Immersion fuse or MCB? Advice and Help. How-to Immersion fuse or MCB? in the UK Electrical Forum advice boards on ElectriciansForums.net Est.2006 | Free Electrical Advice Forum. Immersion fuse or MCB? on ElectriciansForums.net Electrical Advice Forum.

www.electriciansforums.net

Yes that refers to an immersion heater.

 

[Steve-S]

Best you you say "I do not know", or not get involved.
I am waiting for some responses.

 

[mainline]

All within regs to have an immersion of a 13A fuse. Millions are.

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.

 

[westward10]

Best you you say "I do not know", or not get involved.
I am waiting for some responses.

I have responded your posts refer to an immersion heater.

 

[Steve-S]

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.

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.

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.

 

[mainline]

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.

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.

 

[Steve-S]

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.

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.

 

[davesparks]

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.

The current carrying capacities in the regs book do not represent the point at which a cable suddenly goes from working safely to being 'fried' as you put it.

The current carrying capacities in the regs book have already taken in to account the behaviour of fuses and MCBs and allowed for this.

As long as you follow the cable size calculation process in the regs correctly the resultant cable size will be suitable.

 

[davesparks]

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.

Unless it's is buried in a lot of insulation in a very high ambient temperature a 13A fuse will protect a 2.5mm cable perfectly well.

And MCBs are not superior when compared to fuses, they are just more convenient for resetting.

 

[Steve-S]

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.