Spur off a spur

[teddyward]

Hi there,

I am adding an en suite bathroom in my house. This involved removing a socket, which I relocated to the new stud wall within the bedroom. I think this socket was a spur as it just has a single cable going into it, I guess linked back to the ring main.

I would like to add another socket on the same wall, and within the bathroom I need to provide a fused supply for a Saniflo unit and also a shaver socket.

The more I read up about this, the more it seems unlikely that I can simply spur off the existing spur i.e. have the existing socket, the new socket, the saniflo and shaver running off the same spur - could anyone please confirm this?

Am I right in thinking that I really need to relocate the ring main, then bring 3 separate 2.5mm cables off the ring main to power these 3 new supplies?

Thanks for helping.

 

[PrenticeBoyofDerry]

If the circuit is a ring final (RFC) which will need to be confirmed.
You can not take more than one spurred socket outlet from a socket on the RFC.
Unless the you have created a 13A fused spurred connection (FCU) at the original socket on the RFC then you can take as many outlets after the 13A FCU as you wish but the load from the 13A FCU will be restricted to 13A.

For example

Untitled

• PrenticeBoyofDerry
• 29 Apr 2012
• 1

Also as some electrical work is within the bathroom all accessories must be zoned and IP rated correctly, with RCD protection. This is also deemed notifiable work, so you have a legal obligation to have the work notified to building controls.

 

[riveralt]

removed

 

[teddyward]

Thanks, for the info - really appreciated.

So, if I can determine that the existing socket is in fact spurred from the main ring, I can simply add a fcu between the main ring and the spurred socket, then go onto powering the other sockets from that spur?

Having read a little more into the shaver socket, it seems that the normal way is to run this off the lighting circuit so it would just be the 5amp fused unit for the saniflo and the other wall socket.

On the IP rated thing, the cable running into the bathroom would be under the floorboards which will be tiled. The supply for the Saniflo will be a unswitched 5a fused unit with a cable outlet for the flex. This will be mounted to an untiled section of dry lining which will then be enclosed within a box designed to hide the Saniflo, I will probably tile the box leaving a removable panel for access. Do you think I need to take any other precautions in terms of waterproofing?

One more thing, I assume I can't run the Saniflo from the lighting circuit?! If I could this would solve all my problems!

Thanks

 

[ericmark]

The English used to define what is a spur and what is a radial make it confusing. So I will try to explain.

The typical ring used in UK houses is protected by a 32A fuse and relies on having in the main two feeds to each socket so the power down each of the 2.5 mm sq cables is shared between the two cables.

Where a connection is made to this ring with a single 2.5mm sq cable one relies on the fuse in the plug to limit the power to 13A. Double sockets are allowed but not two single sockets.

Fitting a fused connection unit (FCU) will limit supply to 13A so there after you can have as many sockets as you want. Same as plugging in a 4 socket adaptor.

However we also use Radials as well as rings and often the radial will be supplied with a 20A fuse or MCB. If that's the case then you don't need a FCU you can just add more sockets.

Just to confuse further there is also a radial system using 4mm sq or 6 mm sq cable these are protected with same 32A fuse or MCB as a ring circuit. To extend these either a FCU or 4mm/6mm cable will be required.

So first question what size fuse feeds existing socket? Second question what size cable feeds existing socket? Do remember 2.5mm refers to cross sectional area of copper not diameter of cable.

But that's not the end. We also have to look at volt drop and loop impedance. What we have to ensure should there be a short circuit the MCB or fuse will open. There are three types of short circuit 1) Line - Neutral, 2) Line - Earth, 3) Neutral - Earth. The latter has very little protection but the first two have often two different devices. Line - Neutral is only protected by the MCB/Fuse and loop impedance is what decides if it will work correctly. Line - Earth should now be protected by a RCD but these did not exist with older houses.

Although you are not required to modify your house to comply with new regulations. Any new items added will need to comply. So any feed into a bathroom, or to socket (with some exceptions) or wire buried in wall (unless special cable) will need RCD protection.

So last question is a RCD already fitted?

When an electrician fits extras he completes a minor works or installation certificate and he has to measure the loop impedance etc and enter the readings. With domestic this is then sent where a bathroom is involved to either his scheme provider who in turn send it to the LABC or he pays the LABC a huge fee and deals direct.

The scheme provider or LABC then issue a completion certificate. This bit is law. Although you could also inform the LABC before starting and pay their fee you will need the meters to complete the minor works or installation certificate and also pay the LABC fee which does vary but over £100.

So in the main it's just not worth doing any DIY in a bathroom so what I have said is only for interest you are better off just getting an electrician who is a scheme member to do the work for you.

 

[PrenticeBoyofDerry]

So, if I can determine that the existing socket is in fact spurred from the main ring, I can simply add a fcu between the main ring and the spurred socket, then go onto powering the other sockets from that spur?

You can yes, ideally as close the RFC feed socket as possible and remember to use the prescribed safe zones or mechanical protection for any buried cable.
//www.diynot.com/wiki/electrics:installation_techniques:route
//www.diynot.com/wiki/electrics:installation_techniques:walls

Having read a little more into the shaver socket, it seems that the normal way is to run this off the lighting circuit so it would just be the 5amp fused unit for the saniflo and the other wall socket.

Shaver sockets can be run off the lighting circuits, again safe zones etc..

On the IP rated thing, the cable running into the bathroom would be under the floorboards which will be tiled. The supply for the Saniflo will be a unswitched 5a fused unit with a cable outlet for the flex. This will be mounted to an untiled section of dry lining which will then be enclosed within a box designed to hide the Saniflo, I will probably tile the box leaving a removable panel for access. Do you think I need to take any other precautions in terms of waterproofing?

Providing the accessory and enclosure are correctly IP rated for the location. It's the location that the equipment is in that is important.
Also again be aware of safe zones for cables, if the electrical connection is hidden, is there the relevant protection for the cable, as the route of the cable will be visibly unknown.

One more thing, I assume I can't run the Saniflo from the lighting circuit?! If I could this would solve all my problems!

A standard saniflo would require about 400-500 watts of output this would require 2-3A of current. (Manufacturers Instructions must be followed)
It would be advantageous to know what load demands are already existing on the lighting circuit, you would be allowed 66% load diversity of maximum load. So providing your lighting circuit is not already stacked up well above maximum load it should be.
But you must have RCD protection and follow the relevant legal requirements.