Spur at point of origin

[pyrosym]

Just a quick question, I know you can spur a ring at the C.U. but can you do the same with a radial?

I have not seen it done that way on a 20A A3 radial.

It is only for a test rig I am putting together to train students testing so its not that important any thoughts?

 

[Deleted member 26818]

I love appendix 15.
The answer to your question is yes apparently you can spur off at the origin on a Radial just as with an RFC.

 

[malcolmsanford]

To be honest I have never been quite sure what is meant by a "spur" of off a radial circuit. I guess on a 4mm socket radial there could be a call for it, cost wise if you wanted to extend it and decrease the cost of cable down to 2.5mm

As for a 20amp 2.5mm socket radial, well unless you wanted to take say a light off of it, there is very little point in creating a "spur" and that is why in appendix 15 there is no mention of spurring at the CU, as there is no mention of spurring anywhere full stop.

As for what you plan there is nothing wrong with it. In essence your using the MCB/Fuse in the CU as a JB. It is still just one circuit, and as long as you utilize the correct size cable for the PD it is fine

 

[kingeri]

The way I see it, if you 'spur' off a 20a 2.5mm radial at the CU or anywhere else, it is not actually a spur, it is just a branch of that circuit. As malcolm points out, a 2.5mm branch off a 4mm 32a radial would in fact be a spur (hence can only serve one double socket)!

 

[Deleted member 26818]

Sorry Malcolm but if you look at page 426 in the BGB, it does actually state: "An unfused spur may be connected to the origin of the circuit in the distribution board".

 

[malcolmsanford]

That is mentioned on the 4mm 32amp radial Spin, I was referring to the 20amp 2.5mm (A3) one mate, that doesn't mention mention spurs at all.

 

[Deleted member 26818]

That is mentioned on the 4mm 32amp radial Spin, I was referring to the 20amp 2.5mm (A3) one mate, that doesn't mention mention spurs at all.

Oh yes I see what you mean.
If you notice, there is no mention of the two spurs on the 20A diagram.
That's because the spurs use the same CSA conductors.
Just as with the 30/32A diagram, ther is no mention of the 4mm² spur.
I guess they didn't consider it worth a mention, if the spur uses the same CSA as the rest of the circuit, as the CPD will provide protection.
Only fused and unfused spurs are mentioned because the CPD won't provide overload protection.

 

[kingeri]

You can't really have what I'd call an unfused spur off a 20a radial.....it's just a branch! An unfused spur would have to be run in 1.5mm², and we obviously wouldn't do that! If you see what I mean lol.

 

[Deleted member 26818]

You can't really have what I'd call an unfused spur off a 20a radial.....it's just a branch! An unfused spur would have to be run in 1.5mm², and we obviously wouldn't do that! If you see what I mean lol.

I wouldn't know about that.
I'm thinking bell transformers, smokes and door entry systems.
Often spured off in 0.75mm² or even smaller.

 

[kingeri]

I wouldn't know about that.
I'm thinking bell transformers, smokes and door entry systems.
Often spured off in 0.75mm² or even smaller.

You'd spur off a 20a radial in 0.75mm² without fusing down??????

 

[malcolmsanford]

Yes of course you can King, they are fixed loads and if you keep the distance below 3 mtrs

 

[kingeri]

Thanks malcom I'm being a bit of a retard I think

 

[malcolmsanford]

Thanks malcom I'm being a bit of a retard I think

Lol not at all mate, I think this NICEIC/ELECSA tie up is upsetting a lot of lads

 

[pyrosym]

Thank you all,
It seems like it will create debate among my students so I'm going to do it and see what they come up with on their EICR sheets. I'm going to spur off the breaker with a double socket and built in RCD just to make them scratch their heads a bit more as its already a sub.

kind regards all