Schedule of circuits - Lighting FCU on RFC

[Dartlec]

On a couple of recent EICRs I've run into FCUs on a RFC, then 1.5 or 1mm to several lighting points and would be interested how people would note this on the schedule?

On the most recent one there are 6 outside lanterns fed from an FCU on the socket circuit, with max R1+R2 outside of 4.5Ohm (Dodgy joints partly to blame I suspect, but didn't have time to further investigate).

Putting it as the highest reading on the main RFC circuit doesn't make it clear that there isn't a very poor connection on the sockets that should be investigated. It would also look as though the RCD is being used for fault protection on that circuit without further clarification.

Would you note the fused circuit as a separate circuit in the schedule list, noting 1362 as the OCPD (which means it's well under the 15.6 max Zs). If so, how do you make it clear which circuit it's fed from? I'm thinking of just listing it as "FCU Garden Lights fed from circuit x" - Seems overkill to consider it as another db with a second page of test results just for a fused spur.

 

[timhoward]

R1+R2 outside would be including the impedance of the fuse itself wouldn't it?

 

[Dartlec]

R1+R2 outside would be including the impedance of the fuse itself wouldn't it?

Good point - yes In this case it would because I didn't isolate at the FCU and test just the load leg. I guess if I was treating it as a sub board that would be the correct way to do it - with Zdb at the FCU and its own page - but that seems a bit OTT for a single FCU?

If this had been a spur to an outside socket and I got a higher reading, then I'd just put it down and move on, but because the cabling changes I'm just not sure how to detail it so that it's clear what is going on.

The max Zs outside would be well within the 1667 limit since there is an RCD, if that was considered to be offering fault protection - but anyone glancing at the sheet in the future may not be clear on what's going on, so I just wonder how others would note it...

In reality, the 1362 is providing fault protection for that part of the circuit and the RCD is offering additional protection.

 

[timhoward]

As I think about it the 13A fuse wouldn't really change it at all...sorry.
(What erroneously came to mind was I once carefully nulled a wander lead as 0.60 ohms, then measured some 10mm gas bonding at over 1 ohms. Nonsensical, was driving me nuts. Then I realised I'd accidentally picked up a probe from a different meter and it had a fuse in!)

To answer the question...
I'd probably loop test the end light, IR test the spur wiring, and just add additional notes that the outside lighting had appropriate basic and fault protection. In the same way I don't detail every fan, boiler and other accessory on a spur, as long as it appears to be safe and has appropriate protection I wouldn't lose sleep about it if it seems safe.

As you say, with different wiring with smaller csa it's equally misleading to record the Zs on the load side of the FCU as the highest measured Zs for the RFC.

However in this case I would probably add an FI regading the high Zs - quick and simplified maths suggests Zs of 4.5 ohms in 1mm T+E is about 120m of cable (assuming equal conductor sizes and Ze of 0 for quick mathematical convenience). I'd want to know Zs at the supply side of the spur as a starting point too.
So even though I completely agree additional RCD protection will save the day I'd want to mention something is up and it needs looking at.

 

[loz2754]

Maybe list it as a sub circuit on the line below the RFC?
So if the RFC was circuit 6, the FCU would be designated as 6A, "FCU fed from circuit 6 RFC".
At least all the information could then be entered on one schedule...

 

[Lister1987]

Note it in the condition of Electrical Installation box (and any reading you want to take), it's then recorded, referenced and you're not arsing with a new sheet or line on the test results

 

[ipf]

The FCU should be counted as one point of the RFC.
The subsequent lights are a subsequent circuit protected by the 1362 but, not really worthy of a second schedule sheet.
A second line, with explanation, is OK.
A good case for explanation in the notes.

I had a bit of a problem a few years ago where a mate had little choice but to extend kitchen lights from a FCU and another spark failed it due to slightly high Zs (RFC). He asked for help. I explained it's not ideal but it is a sub circuit. Fused down, smaller cable.