Electrician Jobs Rfc for a newby confirmation please guys

[Gary latto]

Hi guys still studying hoping to take exams this year at aged 54
Question is when doing continuity of rfc to confirm if a ring is complete .
Is they a table/chart for maximum ohms readings allowed etc I understand how to do the test etc and figure of 8 so hopefully just some confirmation.
Tia guys

 

[telectrix]

if your refer to end-end readings, there is no max. stipulated, but bear in mind (r1+r2)/4 = R1+R2, thus giving rise to Zs values compliant with 0.4sec. diss. for the MCB. generally accepted that a RFC (32A in 2.5mm) should not cover a floor area > 1oo sq.m.

 

[Gary latto]

Thanks telectrix makes sense cheers
Another quick one if you don't mind.
how do you go about if items are still plugged in and can't get to unplug ie built in appliances with no means of isolation without removal of appliance.
I'm assuming would get different results between phase and neutral lines ? Tia

 

[Dustydazzler]

I was always taught end to end is a commissioning test , so in theory nothing should be plugged in at this stage.
If appliances are plugged in and been live you are way past commissioning an installation

 

[Gary latto]

Hi was thinking if you were looking at adding say extras outlets then u want to check it's a rfc so for checking then and would probably have something probably plugged in

 

[Richard Burns]

For a confirmation of an existing ring I would say that in general just measuring the end to end continuity of the ring conductors would show that it is a ring of some sort.
To check it is a compliant ring, such as at initial verification, would require the crossover figure 8 measurements but if this had been done at the original installation if the conductors are still continuous it is unlikely to have changed, unless you can tell there have been major changes.

However even if you were to measure the crossover line and neutral resistances with a connected load on the ring it would only lower the measured resistances slightly.
The load would be in parallel with the resistance you are measuring but would be at least an order of magnitude higher or greater and so the effect on the actual measured resistance would be negligible.
For example even a load drawing the full 32A of a ring would be a resistance of about 7Ω and so on a, say, 0.7Ω ring resistance would then make it 0.63Ω so a 0.07Ω difference at the worst case.

 

[richy3333]

And, there won't be any appliances plugged in for your practical tests

 

[FatAlan]

Never too old Gary. Are you signed up to the Trainee section?

 

[Gary latto]

Hi fatalan no mate I'm not should I and how or where do I do that ? Cheers

 

[Pete999]

Just post to Admin for access. Westward 10, Leesparkykent, Sparkychick will be able to help I'm sure.