Adding fused 'spur' to radial sockets

[leezer3]

I've got a radial socket circut upstairs.
Best I can tell, this goes from the CU to a junction box somewhere under the stairs, and then in a star shape to the 4 sockets connected to this circuit. I've only got one cable from the CU & each socket has a single cable, hence the radial & shape assumption?
(These are on the near and far walls of each upstairs bedroom)
I can't get much more than this without pulling the floors up.

Rooms are both 3.38m x 3.38m, so I believe I'm well under the size requirements. The star shape concerns me a little, but not overly?

Circuit is run in 2.5mm² cabling througout on a 20a MCB, with a single RCD in the board (Volex, will get full details if necessary)
I'd like to add a fused 'spur' to connect some model railway bits to in the front bedroom. I've got plenty of 2.5mm² cable, which I intend on using.

Thoughts please peeps, particularly anything I've forgotten?

 

[echoes]

Any particular reason for thinking you need a fused spur? Is it just for some extra sockets?
Radial circuits can continue to branch in the same size cable without needing to fuse down.

 

[JohnW2]

Circuit is run in 2.5mm² cabling througout on a 20a MCB, with a single RCD in the board (Volex, will get full details if necessary)
I'd like to add a fused 'spur' to connect some model railway bits to in the front bedroom. I've got plenty of 2.5mm² cable, which I intend on using.

'Spur' doesn't really have much meaning in relation to a radial circuit, since such circuits are allowed to have 'branches'. Unless anyone else can think of something, I see no reason why it would not be permissible to run one (or more) sockets from one of the existing bedroom ones, and I can't see why it would need to be done as a 'fused spur' unless you have some reason for wanting that - just a direct connection with 2.5mm² cable should be OK.

Kind Regards, John.

 

[leezer3]

Any particular reason for thinking you need a fused spur? Is it just for some extra sockets?
Radial circuits can continue to branch in the same size cable without needing to fuse down.

It's more than I'm planning on running several transformers and a lot of other bits and bobs off this (8 plugs in two 4-ways), and some of the models are high value kit. Nothing directly requires it's own fuse, but I'm trying to avoid problems.
Edit:Total load is well under 13a at the minute, I've had everything plugged into a single 8-way before.


Adding an additional fuse/ isolator seems a good way to isolate everything, and hopefully keep any issues within the models bit.

 

[JohnW2]

It's more than I'm planning on running several transformers and a lot of other bits and bobs off this, and some of the models are high value kit. Nothing directly requires it's own fuse, but I'm trying to avoid problems.

You'll have fuses (of whatever rating you choose) in the plugs you plug into the new socket(s), so nothing much would really be gained by having a fuse in a fused connector unit (if that's what you were thinking of) as well. Any bit of 2.5mm² cable can take the full 20A allowed on the circuit if it has to.

Kind Regards, John.

 

[JohnW2]

Adding an additional fuse/ isolator seems a good way to isolate everything, and hopefully keep any issues within the models bit.

Ah, you added this bit after I replied! If you want that sort of isolation (in addition to switches on the socket(s), you could use a 20A switch, rather than a fused FCU, if you wanted.

Kind Regards, John.

 

[echoes]

Agree with John - no point in limiting your branch to 13 A - the fuse in the spur is to protect the 'downstream' cable only, and the 20 A MCB does this.

If a single point of isolation is required, then a 20 A ... abort! (I have just seen John's reply to this bit as well)!

 

[ban-all-sheds]

Do you plan to install 8 sockets supplied by the FCU, or two, and use 4-way strips plugged in?

The only benefit an FCU would bring would be a SPOC for all of the outlets, there are no "problems" or "issues" which could arise in the model kit for which the fuse in the FCU would be helpful, so if your plan is to use 1 or 2 plugged in socket strips then you might as well just use the switch(es) in the socket(s) they're plugged into.


//www.diynot.com/wiki/electrics:walls

 

[leezer3]

Either one or more likely a pair of double sockets to provide some future spares, along with the current set of 4-ways.
The primary thinking behind the fused spur is that it just lets me quickly and simply pull anything I've added in the models out of the equation in the case of tripping. Also, if the whole lot pulls more than 13a, that again points to a problem that requires solving sooner rather than later, and I'd rather know about it


Cables would end up being run at about 5cm depth in trunking in the horizontal yellow safe zone.
Only other thought I have is that the exising cables come in vertically. It doesn't state that using two of the safe zones is bad, but I suppose I could drop under the floor temporarily.

 

[JohnW2]

Either one or more likely a pair of double sockets to provide some future spares, along with the current set of 4-ways.
The primary thinking behind the fused spur is that it just lets me quickly and simply pull anything I've added in the models out of the equation in the case of tripping. Also, if the whole lot pulls more than 13a, that again points to a problem that requires solving sooner rather than later, and I'd rather know about it

It's obviously up to you, and what you feel is the most convenient - there's nothing wrong with any of the options that have been discussed. As for your last comment, it would probably take best part of 20A to blow a 13A fuse, and it's pretty unlikely that a problem in your kit would result in an unexpectedly high current, unless there was a short somewhere (in which case the 20A MCB would deal with that).

Cables would end up being run at about 5cm depth in trunking in the horizontal yellow safe zone.
Only other thought I have is that the exising cables come in vertically. It doesn't state that using two of the safe zones is bad, but I suppose I could drop under the floor temporarily.

I stand to be corrected, but don't think there's any problem with using both vertical and horizontal safe zones.

Kind Regards, John.

 

[echoes]

The 13 A fuse in the proposed FCU will not discriminate with the 13 A fuse in either of your 4-ways in the event of a fault or overload - either may blow. At least a fuse popping in the 4-ways will give you an narrower indication of where a fault is.

The fuse in an FCU is there for one reason - to protect the spur's cable against fault or overload, and at 13A would not offer much protection to your kit anyway.

You are very, very unlikely to overload the circuit with low-power transformer fed equipment. If you want protection for you kit, then the 3 A or smaller fuses in the individual plugs will discriminate better and provide the protection you want.

I do take your point about a single point of isolation, and a 20 A DP switch would be my preference (may even live extravagantly and get one with a neon).

 

[ban-all-sheds]

The primary thinking behind the fused spur is that it just lets me quickly and simply pull anything I've added in the models out of the equation in the case of tripping.

As would a switched socket.

Also, if the whole lot pulls more than 13a, that again points to a problem that requires solving sooner rather than later, and I'd rather know about it

There are fuses in the plugs of the multi-way strips....

Cables would end up being run at about 5cm depth in trunking in the horizontal yellow safe zone.

Too deep, unless the wall is over 30cm thick - maximum depth for horizontal chases is ¹/6 the thickness of the leaf. (Unless you have sufficient structural engineering expertise to say otherwise).

See 10.1.2 of this:

Only other thought I have is that the exising cables come in vertically. It doesn't state that using two of the safe zones is bad, but I suppose I could drop under the floor temporarily.

Vertical chases are better. Can be deeper, and require less making good.