Fused spurs

[Dambo]

I wonder if someone could clarify this for me. With regards a fused spur - Why does it need to be fused if the plug itself contains a 13A fuse?

 

[bulmer]

If something is wired from a fused spur, it won't have a plug.

For example, a combi boiler in a kitchen will have a fused spur near to it. The boiler is the wired into the fused spur.

 

[ianmacd]

you could hang 2000000000000000 sockets off a spur and they could all draw 13A without the fuses going and thats like 26000000000000000A so the wire will melt but at least the delorian will get its 1.21 gigawatts. If its a fused spur then the fuse int eh spur will go before the wire melts and you will never get back tot he future.

(numbers deliberately exaggerated)

Ian.

 

[bulmer]

Don't think the breaker would hold out for long though lol

 

[ianmacd]

I seem to have a real problem typing the today (well most days and most words actually).

 

[bulmer]

Looks like the '0' key must be sticking slightly

 

[m4tty]

The fuse in the fcu is there to protect the cable from fcu to socket and the appliance plugged in is protected by its own fuse hth

 

[Dambo]

you could hang 2000000000000000 sockets off a spur and they could all draw 13A without the fuses going and thats like 26000000000000000A so the wire will melt but at least the delorian will get its 1.21 gigawatts. If its a fused spur then the fuse int eh spur will go before the wire melts and you will never get back tot he future.(numbers deliberately exaggerated)

Ian.

Like the exaggeration!

If the spur wasn't fused though and loads of sockets were taken from the spur then surely the MCB would trip in the event of an overcurrent?

 

[ianmacd]

Like the exaggeration! If the spur wasn't fused though and loads of sockets were taken from the spur then surely the MCB would trip in the event of an overcurrent?

Possibly not before the cable had melted and set fire to the house. Most ring mains are protected at 32A and wired in 2.5mm that has a max rating of 27A (at best) so as you can see the cable is already over rated before the overcurrent device disconnects the supply.

Ian.

 

[Dambo]

Possibly not before the cable had melted and set fire to the house. Most ring mains are protected at 32A and wired in 2.5mm that has a max rating of 27A (at best) so as you can see the cable is already over rated before the overcurrent device disconnects the supply.Ian.

3 Questions Ian:

1) In a ring main, if one of the legs is broken, the other leg will then have to take the full load i.e. potentially 32A on a cable only capable of taking 27A. Isn't this dangerous?

2) Can spurs be taken off radial circuits? If so am I right in saying they wouldn't need to be fused as the cable rating would be higher that the MCB?

3) Am I right in saying the more the appliances on a circuit = the lower the overall resistance of the circuit = the higher the overall current?

 

[Andy™]

3 Questions Ian:1) In a ring main, if one of the legs is broken, the other leg will then have to take the full load i.e. potentially 32A on a cable only capable of taking 27A. Isn't this dangerous?

yes, its dangerous

2) Can spurs be taken off radial circuits? If so am I right in saying they wouldn't need to be fused as the cable rating would be higher that the MCB?

you can add another branch to a radial at any point. you can also take another branch from that branch at any point. providing all wiring is same CSA, and complies with max length. you can also use a 2.5 on a 4mm radial but only to feed one socket (same as a ring)

3) Am I right in saying the more the appliances on a circuit = the lower the overall resistance of the circuit = the higher the overall current?the more appliance switched on, the lower the resistance, and the more current that will flow

my red

 

[Lurch]

2) Can spurs be taken off radial circuits? If so am I right in saying they wouldn't need to be fused as the cable rating would be higher that the MCB?

It's not really a spur if it's on a radial. As long as the cable is correctly rated you can run cables to anywhere from anywhere on the circuit.

 

[Dambo]

Thanks Andy. Final questions about the above points:

For 1) Wouldn't it be safer to avoid using ring mains for this reason?

For 2) So the spurs could be non-fused as the MCB provides adequate overcurrent protection?

For 3) Does this apply to parallel circuits only?

 

[Andy™]

Thanks Andy. Final questions about the above points:For 1) Wouldn't it be safer to avoid using ring mains for this reason?yes. but as i said in another thread, a fault on L or N is noticed immediately, but a fault on the earth wont be. at least with a ring, you have 2 earth paths

For 2) So the spurs could be non-fused as the MCB provides adequate overcurrent protection?

all wiring is rated above what OPD is, so no problem with adding anything to anywhere

For 3) Does this apply to parallel circuits only?ohms law appliance to anything. the apliance has a resistance, so current will flow through circuit to that. current will also flow to the other appliances on the circuit

my red

 

[Nikos]

I wonder if someone could clarify this for me. With regards a fused spur - Why does it need to be fused if the plug itself contains a 13A fuse?

If the fused spur is used as a means of isolation supplying 1 x socket outlet wired in 2.5mm T+E for an appliance, as the socket outlet is not easily available or accessible for example, then a 20amp D.P. switch may be used as the means of isolation also, as the maximum current drawn at the socket outlet by the connected appliance will be limited by the fuse fitted in the plugtop.

 

[Dambo]

Does the more appliances on a circuit lead to reduced overall resistance irrespective of whether it is a parallel circuit or a series circuit?

 

[Lurch]

Not sure what you're asking exactly. In a standard electrical installation appliances will be in parallel. No series connections will be used.

So your question is, if I'm reading it right, null and void.

 

[Dambo]

Not sure what you're asking exactly. In a standard electrical installation appliances will be in parallel. No series connections will be used.So your question is, if I'm reading it right, null and void.

I know series connections aren't used but I was just curious to know the answer.

 

[Lurch]

Well if we're on to parallel\series then we're on to resistors in general, and more resistors in series = more resistance and more resistors in parallel = less resistance.