Just a thought on RFCs

[Pete999]

After reading a post yesterday regarding a Timber House Install, got me wondering, someone mentioned, can't remember who it was, and asked has anyone ever wired a RFC in 4mm2 cable, now I have never gotten involved in all this fancy Timber all insulated structures, so I asked myself the question, "if after all calculations", you came to the conclusion that normal 2.5mm2 RFC was, or did not meet the requirements after applying all the derating factors, you needed to install 4mm2 instead of 2.5mm2, how would you note the distraction from the, norm, would you just add a note on the certificate? describing what and why you had installed the circuit in this way. Just asking out of interest.

 

[Ian1981]

Think I mentioned it pete.
I wouldn't personally mention it as the reference method on the test sheet notes this,whether it be ref 101 or perhaps 103 for in walls should give someone an idea(an electrician perhaps) why it's in 4mm

 

[LankyWill]

Can't see why you would need to note it, as long as it's written in the csa size box on the eic.

 

[Octopus]

If the RFC isn't supplying the kitchen or utility maybe a 20A breaker is the way to go on the 2.5mm

That said, whats then to stop some muppet in the future installing a 32A breaker?

A very interesting subject...

 

[telectrix]

If the RFC isn't supplying the kitchen or utility maybe a 20A breaker is the way to go on the 2.5mm

That said, whats then to stop some muppet in the future installing a 32A breaker?

A very interesting subject...

then again, what's to stop some muppet replacing a 32A on a standard 2.5mm RFC with a 50A?

 

[Pete999]

Think I mentioned it pete.
I wouldn't personally mention it as the reference method on the test sheet notes this,whether it be ref 101 or perhaps 103 for in walls should give someone an idea(an electrician perhaps) why it's in 4mm

Yes thought that would be the best option, just interested that's all.

 

[Pete999]

then again, what's to stop some muppet replacing a 32A on a standard 2.5mm RFC with a 50A?

You mean one of the latest crop?

 

[Octopus]

then again, what's to stop some muppet replacing a 32A on a standard 2.5mm RFC with a 50A?

Bob the builder uses a populated board and any combination of connections and cables - nothing stops them!

 

[Ian1981]

Put it this way when I say to my boss I need 4mm not 2.5mm because of thermal insulation his face drops quite a bit
Then he sends someone else to do it who doesn't realise the effects of thermal insulation to cables

 

[Pete999]

Put it this way when I say to my boss I need 4mm not 2.5mm because of thermal insulation his face drops quite a bit
Then he sends someone else to do it who doesn't realise the effects of thermal insulation to cables

If that's the case then your Boss want's re educating, or giving up the job.

 

[Flanders]

Used 4mm for ring circuits with long runs on commersial installs and 2.5 mm for lighting circuits , makes connecting up click roses difficult though when you use 2.5mm , we just fill out the certs with the relevant details

 

[westward10]

See plenty of 4.0/4.0 ring finals doing PIRS.

 

[davesparks]

It's common on commercial specs to standardise lighting as 2.5mm minimum size and small power as 4mm minimum size. This is done to negate grouping factors and make calculations quicker and easier.

 

[Pete999]

See plenty of 4.0/4.0 ring finals doing PIRS.

Not disputing that Westy just wondered how people document it that's all.

 

[D00DY_T00DY]

then again, what's to stop some muppet replacing a 32A on a standard 2.5mm RFC with a 50A?

I'm smart and only put a 45A on mine
Better safe than sorry

 

[D00DY_T00DY]

Used 4mm for ring circuits with long runs on commersial installs and 2.5 mm for lighting circuits , makes connecting up click roses difficult though when you use 2.5mm , we just fill out the certs with the relevant details

After 4 years of house bashing those numbers just seem wrong to me D:

 

[davesparks]

Not disputing that Westy just wondered how people document it that's all.

Just record the cable size In the appropriate box on the schedule of test results.
If providing design paperwork with the installation then it would be recorded in there too, but that's almost certainly not going to be required, or done, for a domestic installation.

 

[Toneyz]

It's common on commercial specs to standardise lighting as 2.5mm minimum size and small power as 4mm minimum size. This is done to negate grouping factors and make calculations quicker and easier.

Used 4.0mm for RFC but not 2.5 for lighting yet guess you have to take consideration of terminal capacity /back box room

 

[westward10]

Used 4.0mm for RFC but not 2.5 for lighting yet guess you have to take consideration of terminal capacity /back box room

Large warehouses I have used up to 4.0 on the lighting terminated at 13A sockets. Fitting any more than one 2.5 at a Klix terminal is stupid as they do not terminate correctly.

 

[d.l.rob]

It's stated on p82 or p84 of bs7671 that every single leg of cable on a ring final circuit has to be able to manage 20A alone for the ref method it's Installed. P364 of bs7671 gives the current carrying capacities of twin and earth cable. A ring circuit wired with a ref method of 101 in 2.5mm won't achieve this regulation becaus it can't carry 20A so in that instance a 4mm twin and earth cable would be suitable. Hope that makes sense? This is a scenario when you would use a 4mm twin and earth to wire a ring circuit

 

[d.l.rob]

Read the question wrong sorry...

I would just put the cable size on the test sheet and be done with it

 

[Deleted member 26818]

I have been tasked with wiring RFCs in 4mm2 in the past.
I imagine it was more for volt drop than due to insulation?
Just note the CSA in the box.