Ring Final Circuits & Correction Factors

[Silly Sausage]

Something I've wondered about for a while...
If you had both legs of a RFC, in say T&E or singles, running in the same conduit, so basically touching, would you need to apply the appropriate correction factor for grouping?

 

[Silly Sausage]

Any takers on this?
Or am I just being a complete numpty?

A

 

[Jimmyb]

I was all told @ collage that you dont as it one circuit but i dont really agree with it but tbh ive never worried about when they are arranged in this way

 

[Silly Sausage]

Cheers J
It's what I was thinking, one of those things that gets swept under the carpet.

 

[Engineer54]

So you think it would be better to class them as 2 separate circuits??? For Gods sake WHY???

 

[DavidJ91]

If there is more than one single-core cable in conduit, I would think the grouping factor DOES apply as there are multiple cables in the same enclosure (same run of conduit) together. With six single-cores all in one enclosure, the factor would be 0.57.

BUT - How big would this conduit be? It'd have to be big enough to leave room for heat dissipation.

Sorry if I'm sounding like a know-it-all and I'm sure you're more experienced than me, I'm just trying to learn this too as I've been doing this kind of stuff in theory.

Thanks for posing the question
Helps me learn about specific, rare scenarios

 

[Deleted member 26818]

If there is more than one circuit in the conduit, then yes apply group correction factors.
If however, ther is just the one circuit, the RFC, then there is no group to correct for.

 

[Silly Sausage]

So you think it would be better to class them as 2 separate circuits??? For Gods sake WHY???

That was the point of my question, do you treat them as separate circuits?
I need to read up on ring main theory a bit more, or get out a bit more often and stop asking daft questions and wasting everyones time on ElectriciansForum.

Cheers...

 

[telectrix]

not a daft question archy, everyone on here did not know things until they asked or were taught, or sometimes found out the hard way, as the hedgehog said, climbing off the bog brush.

 

[Engineer54]

That was the point of my question, do you treat them as separate circuits?
I need to read up on ring main theory a bit more, or get out a bit more often and stop asking daft questions and wasting everyones time on ElectriciansForum.

Cheers...

Archy,

A final Ring Circuit is and always has been ''One'' circuit. What i can't quite fathom out is why you think it is 2 circuits or should be treated as such??

Davidj91,

I think your getting confused with conduit ''Fill Factor'' and Grouping Factors, they are not the same!!!

 

[pushrod]

Must admit this is something that has occurred to me before as i know grouping factors are for separate circuits, but in the scenario where you have say a ring dropping down from the first floor to a ground floor socket in a bit of conduit so that you have both legs in the same conduit - that counts the same as just one leg running in conduit - doesn't seem to quite add up in my mind (more current flowing and less space for the heat to dissipate into).

 

[Silly Sausage]

It's probably what I was thinking, 2.5mm about 20Amps, times 2 on a 32A breaker, if they were any where near max capacity the breaker would trip. One circuit! Choz E54.

Next grouping question...

I've done PIRs in hotels and seen like at least 6 inch diameter bundles of T&E (2.5s power rings, 1.5s lights etc) from 24 or 36 way TP boards going off into the ceiling, then obviuosly splitting up to feed each bedroom, according to "THE LAW BS7671" you'd have have a derating factor of 0.6 or whatever. I don't fail it though because I think the chances of any of them cables being fully loaded is minimal. Am I right?

 

[Engineer54]

Must admit this is something that has occurred to me before as i know grouping factors are for separate circuits, but in the scenario where you have say a ring dropping down from the first floor to a ground floor socket in a bit of conduit so that you have both legs in the same conduit - that counts the same as just one leg running in conduit - doesn't seem to quite add up in my mind (more current flowing and less space for the heat to dissipate into).

So what's so different taking the same senerio you mention above, with being say in the middle of a radial circuit? Still have the same amount of wires in the conduit drop!!! and the load will be the same too....

 

[pushrod]

So what's so different taking the same senerio you mention above, with being say in the middle of a radial circuit? Still have the same amount of wires in the conduit drop!!! and the load will be the same too....

just seems odd to me that you could have double the length/amount of cable in one conduit, and in another you have half the length, and yet they count the same.

 

[Engineer54]

It's probably what I was thinking, 2.5mm about 20Amps, times 2 on a 32A breaker, if they were any where near max capacity the breaker would trip. One circuit! Choz E54.

Max capacity, (taking nothing else into consideration) would be limited by the 32A breaker...

Next grouping question...

I've done PIRs in hotels and seen like at least 6 inch diameter bundles of T&E (2.5s power rings, 1.5s lights etc) from 24 or 36 way TP boards going off into the ceiling, then obviuosly splitting up to feed each bedroom, according to "THE LAW BS7671" you'd have have a derating factor of 0.6 or whatever. I don't fail it though because I think the chances of any of them cables being fully loaded is minimal. Am I right?

That's not what the O/P was talking about, he was talking about the 6 wires accociated with a single ring circuit.

As you were conducting the PIR, it would be up to you to access the loading on the various circuits you are inspecting/testing. Many forget mind, that grouping factors are based on FLC, which will rarely apply in all cases in the real world of things.