For Wirepuller

[richy3333]

You mentioned never having seen a domestic CU that had been wired entirely as RFCs. I just found these pictures. It was a DIY/homeowner self build. The far left circuit is the only radial - a feed to the shed!

 

[Deleted member 9648]

Lol.....having said I've never actually come across a lighting RFC I often hear people (usually non electrical who like to 'talk the talk') describing lighting circuits as 'lighting rings'.
I wonder how many of those circuits in that DB would test out correctly as rings? Be a long EICR test,I hate testing RFC's!

 

[Resu]

Ooh it would be interesting to see the other end of the cooker circuit

 

[Paul.M]

Ooh it would be interesting to see the other end of the cooker circuit

Lol, I did an EICR yesterday and the "cooker circuit" was a 2.5mm RFC for only 1 single socket. Waste of cable if you ask me.

 

[PEG]

Like it...if only that little 3A fuse,at the end of the boiler feed,knew how much weight he could put on...:icon12:

 

[Knobhead]

I take it this is in response to the “ring too long” thread where I stated I used rings for lighting.

I could guarantee the lighting rings or any circuit I installed would pass any test you could throw at them.

As said in that thread, I chose to over engineer just about everything. Through my job T&E cost next to bugger all. A few extra yards of cable made no odds to me.

 

[frontier219]

Lol, I did an EICR yesterday and the "cooker circuit" was a 2.5mm RFC for only 1 single socket. Waste of cable if you ask me.

Essentially a 5mm radial then!

 

[Paul.M]

Essentially a 5mm radial then!

NO, it is a 2.5mm RFC only serving a single 13A socket for a plug in cooker. A bit over the top when just a 2.5mm radial would have done the same job.

As for the lighting RFC topic, not a problem! Multi story car parks are wired like that and any other long run for the same type of install/building to save on cable. In a house, eeerrrmm I'm sure there is a reg saying that any RFC needs to be 2.5mm or greater???? I'll have a look at that in the morning. Either way is does not matter, it is just a Lighting RFC with switch drops and more of it to test. I cant see any problems with it.

 

[davesparks]

NO, it is a 2.5mm RFC only serving a single 13A socket for a plug in cooker. A bit over the top when just a 2.5mm radial would have done the same job.
it.

If it is only serving one point then it would be better described as a parallel feed or just 2 cables in parallel.

 

[davesparks]

Essentially a 5mm radial then!

Not really, it would be a radial yes but it would be formed from 2x 2.5mm cables in parallel which is not the same as a single 5mm cable. If you work out the ccc of 2x 2.5mm in parallel and compare that to the ccc of 6mm (or work it out for 5mm if you really want) you'll find it is very different.

 

[Paul.M]

If it is only serving one point then it would be better described as a parallel feed or just 2 cables in parallel.

Try and write that on a test sheet! I know what you mean Dave, yes you are correct that a single point of consumption in this case would class as a parallel path. How would everyone else test it if it came up? Is it a RFC if only one point is served or is it a Ring??? Well it is a ring at the DB regardless of how many points it serves???? (ok it is a parallel circuit, but it is not 5mm)

 

[Knobhead]

I’ve never found the “official” derating for a parallel feed. Years ago I was told 85% per cable. That tallies with the figure given in the NFPA-NEC.

 

[richy3333]

I take it this is in response to the “ring too long” thread where I stated I used rings for lighting.

I could guarantee the lighting rings or any circuit I installed would pass any test you could throw at them.

As said in that thread, I chose to over engineer just about everything. Through my job T&E cost next to bugger all. A few extra yards of cable made no odds to me.

Hi Tony.

The post comes out of that thread, but not specifically 'targeted' at you. I was looking for some other photos and came across these.

The customer was having a house built, lost his job and had to try and finish the house himself. He took advice from his old sparky he used when in England. He didn't know what qualifications he had, if any; but said he'd been an electrician, 'man and boy'. Not a Electrical Trainee on this occasion. The irony is that whilst he was trying to save money he's spent thousands extra on cable and accessories.

 

[Engineer54]

I’ve never found the “official” derating for a parallel feed. Years ago I was told 85% per cable. That tallies with the figure given in the NFPA-NEC.

Derating?? ...For what reason??

 

[davesparks]

Try and write that on a test sheet! I know what you mean Dave, yes you are correct that a single point of consumption in this case would class as a parallel path. How would everyone else test it if it came up? Is it a RFC if only one point is served or is it a Ring??? Well it is a ring at the DB regardless of how many points it serves???? (ok it is a parallel circuit, but it is not 5mm)

You test it as a parallel feed, the ring final tests won't be necessary on a single point.

If a submain is installed as 2x50mm cables is that a ring?

 

[Knobhead]

Derating?? ...For what reason??

Sorry the 85% is a typo, it should be 95%. (I had to dig my apprentice log book out for that.)

As you know I started under M&Q regulations working for a multinational. The central engineering department issued their own standards. I based it on that.

The first major install I was involved in had numerous 185mm[SUP]2[/SUP] 3c Al PILC-SWA parallel feeds to the MCC panels. I asked the designer why the cable was derated and was told it was central engineering policy. Considering they didn’t use the IEE CCC tables but up rated cables and issued their own standards I found it strange they would downrate anything!