Why so many spurs? (Electrics)

Mickey666

onomatopoeia99 said:

Until a few years ago extending a ring was "notifiable work" so needed either an electrician that could self certify or paying LABC (over £400 round my way).  Adding fused spurs was not notifiable so could be done by a competent DIYer.  The wiring regs were subsequently changed to allow extending a ring as non-notifiable work.

This may be why there are many spurs.  It is why when I renovated my bedroom the extra sockets I added are on fused spurs, but when I needed extra sockets elsewhere a few years later I extended the ring (to BS7671 requirements - I live here so I don't want the place burning down with me inside, thank you very much).

What's wrong with a fused spur?  Indeed, what's wrong with an un-fused spur?  If they were in any way dangerous then they would not be allowed by the regulations, let alone not be notifiable work.

onomatopoeia99

Mickey666 said:

onomatopoeia99 said:

Until a few years ago extending a ring was "notifiable work" so needed either an electrician that could self certify or paying LABC (over £400 round my way).  Adding fused spurs was not notifiable so could be done by a competent DIYer.  The wiring regs were subsequently changed to allow extending a ring as non-notifiable work.

This may be why there are many spurs.  It is why when I renovated my bedroom the extra sockets I added are on fused spurs, but when I needed extra sockets elsewhere a few years later I extended the ring (to BS7671 requirements - I live here so I don't want the place burning down with me inside, thank you very much).

What's wrong with a fused spur?  Indeed, what's wrong with an un-fused spur?  If they were in any way dangerous then they would not be allowed by the regulations, let alone not be notifiable work.

Nothing, and I did not suggest there was.  The OP asked why there were so many spurs, not me.  I was providing a possible answer.

Mickey666

onomatopoeia99 said:

Mickey666 said:

onomatopoeia99 said:

Until a few years ago extending a ring was "notifiable work" so needed either an electrician that could self certify or paying LABC (over £400 round my way).  Adding fused spurs was not notifiable so could be done by a competent DIYer.  The wiring regs were subsequently changed to allow extending a ring as non-notifiable work.

This may be why there are many spurs.  It is why when I renovated my bedroom the extra sockets I added are on fused spurs, but when I needed extra sockets elsewhere a few years later I extended the ring (to BS7671 requirements - I live here so I don't want the place burning down with me inside, thank you very much).

What's wrong with a fused spur?  Indeed, what's wrong with an un-fused spur?  If they were in any way dangerous then they would not be allowed by the regulations, let alone not be notifiable work.

Nothing, and I did not suggest there was.  The OP asked why there were so many spurs, not me.  I was providing a possible answer.

Yes, but you also said. . . . 
 "It is why when I renovated my bedroom the extra sockets I added are on fused spurs, but when I needed extra sockets elsewhere a few years later I extended the ring (to BS7671 requirements - I live here so I don't want the place burning down with me inside, thank you very much)."
. . . which I interpreted as a warning against having so many spurs because you believed they would be a fire risk.

Do you really think the regulations would allow a configuration that is a fire risk?

grumbler

Only one unfused spur with one socket is allowed from each socket in a ring. If you need more, you have to use fused spurs.

What's wrong with an unfused spur (with many sockets)? - I have no idea. IMO, this restriction makes no sense, but we have to live with it.

Mickey666

grumbler said:

Only one unfused spur with one socket is allowed from each socket in a ring. If you need more, you have to use fused spurs.

What's wrong with an unfused spur (with many sockets)? - I have no idea. IMO, this restriction makes no sense, but we have to live with it.

It's all to do with cable ratings. 
A 2.5mm2 cable can easily carry 15A in almost all installation configurations.

A ring main can provide 30A because it is wired with TWO 2.5mm2 cables.  It's possible to overload a ring main by plugging in too many (say) electric fires but in such cases the 30A fuse/MCB will trip and therefore prevent the ring main wiring from overheating, with obvious potential consequences.

When a single socket is spurred off a ring main using 2.5mm2 cable, that cable will only support 15A but the circuit is protected by a 30A fuse/MCB.  However, the UK (almost uniquely in the world) uses fused plugs so any appliance can only draw 13A, which the 2.5mm2 spur cable can easily carry.

However, when a DOUBLE socket is spurred off a ring main using 2.5mm2 cable, it's possible for TWO appliances to be plugged into that spur meaning a potential 26A could be drawn, which would EXCEED the rating of the 2..5mm2 cable, leading to consequent overheating etc.  This is why a FUSED spur is specified for a double socket spur, so that the total current that can be drawn from both sockets cannot exceed 13A.

The objective of any installation is to provide sufficient sockets distributed among sufficient circuits such that overloading any circuit is highly unlikely in normal circumstances.

However, with a multi-socket circuit, it is ALWAYS POSSIBLE plug in more appliances than the circuit can safely support, which is why each circuit is protected with an appropriate fuse/MCB - to prevent cable overheating.

onomatopoeia99 was implying in their previous post.

grumbler

Yes, but AFAIK,

• it's more than 20A for 2.5mm2 cable, and the regulations say nothing about the cross-section of of a spur. Why can it not be thicker? Why can it not be a new ring (possibly, with one socket) connected to an existing socket without breaking the existing ring?
• an unfused spur can be a double socket;
• having a ring is just a recommendation, not a requirement. If so, if the existing sockets don't make a ring, then, essentially it's a long spur with many sockets.

Mickey666

grumbler said:

Yes, but AFAIK,

• it's more than 20A for 2.5mm2 cable, and the regulations say nothing about the cross-section of of a spur. Why can it not be thicker? Why can it not be a new ring (possibly, with one socket) connected to an existing socket without breaking the existing ring?
• an unfused spur can be a double socket;
• having a ring is just a recommendation, not a requirement. If so, if the existing sockets don't make a ring, then, essentially it's a long spur with many sockets.

1- cable ratings depend on many things and are quite conservative.  I used a figure of 15A to illustrate why a ring circuit can be rated at 30A because of the parallel wiring and without delving into the complexities of more precise cable ratings, but you're basically right.

As for using thicker cables, that would be fine from an electrical perspective but you try using 4mm2 to spur off a socket with two 2.5mm2 cables already connected.  It's a physical limitation issue.

2- An unfused double socket spur could load the connecting cable with 26A, so not really recommended.  I'm not sure if it is explicitly allowed.

3- Yes, no need for a ring circuit at all.  Most other countries I know about use radial circuits.  Also, typical usage patterns have changed over the decades such that most houses have very few high-power appliances to plug in around the house, like electric fires etc.  A radial circuit protected by a 20A fuse/MCB would be perfectly adequate.

These days, we really need far more sockets but much less power - hence the popularity 4-way multi-way socket strips.  I have about 10 devices plugged into socket strips in my study, all fed from a single wall socket.  All properly fused, so all perfectly safe as far as overloading is concerned.  Some would argue it's not ideal but who wants half a dozen double sockets in their walls?  Again, physical issues rather than electrical ones.   

onomatopoeia99

Mickey666 said:

onomatopoeia99 said:

Mickey666 said:

onomatopoeia99 said:

Until a few years ago extending a ring was "notifiable work" so needed either an electrician that could self certify or paying LABC (over £400 round my way).  Adding fused spurs was not notifiable so could be done by a competent DIYer.  The wiring regs were subsequently changed to allow extending a ring as non-notifiable work.

This may be why there are many spurs.  It is why when I renovated my bedroom the extra sockets I added are on fused spurs, but when I needed extra sockets elsewhere a few years later I extended the ring (to BS7671 requirements - I live here so I don't want the place burning down with me inside, thank you very much).

What's wrong with a fused spur?  Indeed, what's wrong with an un-fused spur?  If they were in any way dangerous then they would not be allowed by the regulations, let alone not be notifiable work.

Nothing, and I did not suggest there was.  The OP asked why there were so many spurs, not me.  I was providing a possible answer.

Yes, but you also said. . . . 
 "It is why when I renovated my bedroom the extra sockets I added are on fused spurs, but when I needed extra sockets elsewhere a few years later I extended the ring (to BS7671 requirements - I live here so I don't want the place burning down with me inside, thank you very much)."
. . . which I interpreted as a warning against having so many spurs because you believed they would be a fire risk.

Do you really think the regulations would allow a configuration that is a fire risk?

No, I don't, and you misinterpreted me. 

Mickey666

onomatopoeia99 said:

Mickey666 said:

onomatopoeia99 said:

Mickey666 said:

onomatopoeia99 said:

Until a few years ago extending a ring was "notifiable work" so needed either an electrician that could self certify or paying LABC (over £400 round my way).  Adding fused spurs was not notifiable so could be done by a competent DIYer.  The wiring regs were subsequently changed to allow extending a ring as non-notifiable work.

This may be why there are many spurs.  It is why when I renovated my bedroom the extra sockets I added are on fused spurs, but when I needed extra sockets elsewhere a few years later I extended the ring (to BS7671 requirements - I live here so I don't want the place burning down with me inside, thank you very much).

What's wrong with a fused spur?  Indeed, what's wrong with an un-fused spur?  If they were in any way dangerous then they would not be allowed by the regulations, let alone not be notifiable work.

Nothing, and I did not suggest there was.  The OP asked why there were so many spurs, not me.  I was providing a possible answer.

Yes, but you also said. . . . 
 "It is why when I renovated my bedroom the extra sockets I added are on fused spurs, but when I needed extra sockets elsewhere a few years later I extended the ring (to BS7671 requirements - I live here so I don't want the place burning down with me inside, thank you very much)."
. . . which I interpreted as a warning against having so many spurs because you believed they would be a fire risk.

Do you really think the regulations would allow a configuration that is a fire risk?

No, I don't, and you misinterpreted me. 

OK, but that's how it read to me.  Happy to be corrected with a clearer explanation though.

Ectophile

A double socket on an unfused spur is allowed.  In reality, a 2.5mm cable can carry 18A forever, and probably more than 21A for a short time, even buried in the wall.  There's an assumption that nobody is going two plug in two high-current appliances next to each other and then run them for long enough to melt the cable.

Anything more than one double socket needs a fused spur.