RFC in Steel Conduit

[Tuttle]

I plan to install steel conduit (used as cpc) in a garage / workshop. I intend to run the conduit in a complete loop around the garage, i.e. starting at one point, going around all four walls and then back to the point at which I started. I want to do this because it makes wiring easier, i.e. lighting goes one way round, sockets go the other way round, but there is some overlap of lighting and socket wiring at the far end, which is why the conduit is in a loop ... I think that this is ok.

I plan to run both legs of the RFC together to make sure there can be no current imbalance, which might cause eddie currents, but is this strictly necessary? Could the RFC cabling be run around the conduit in a loop, going in one end of the conduit and coming out the other end. I think that in theory the currents in the L & N of each leg of the ring should be the same, but I'm wondering if this can be relied on in practice, e.g. a high resistance joint in either the L or N could cause a current imbalance between L & N in each leg of the RFC.

I think I will run both legs together to avoid this possibility, but I was wondering what others thought about this.

 

[Pete999]

Are you an Electrician?

 

[Tuttle]

Are you an Electrician?

Yes, but I don't use much steel conduit

 

[camerabloke]

Why do you want to use steel?

 

[telectrix]

just run conduit to furthest point. with the rFC stagger the outlets. i.e. 1,3,5, on 1 leg and 2.4.6. on the other, to ballance the load. or do it in a 4mm radial.

 

[Tuttle]

just run conduit to furthest point. with the rFC stagger the outlets. i.e. 1,3,5, on 1 leg and 2.4.6. on the other, to ballance the load. or do it in a 4mm radial.

Thanks, that's what I plan to do.

I still end up with the conduit in a loop though because my lighting circuit goes the other way round (or I have to use larger conduit to run it all together), which is what started me thinking.

 

[Pete999]

just run conduit to furthest point. with the rFC stagger the outlets. i.e. 1,3,5, on 1 leg and 2.4.6. on the other, to ballance the load. or do it in a 4mm radial.

Thats two radial aint it Tel? you need to link 5 and 6

 

[telectrix]

OK, smartrarse. . back to OP. use a 4mm radial, then you have loads of room in a 3/4"! conduit for both circuits . a tad more in this new-fangled metric crap.

 

[Tuttle]

OK, smartrarse. . back to OP. use a 4mm radial, then you have loads of room in a 3/4"! conduit for both circuits . a tad more in this new-fangled metric crap.

Maybe, but I've got an 8-way grid switch for the lights, so quite a lot of 1.5mm cores in places. I think it would be easier to run the lights one way and sockets the other, to avoid the switch wires, but the socket circuit does run pass the supply to the last couple of lights at the far end, which is why I end up with conduit in a loop.

Are you saying that the conduit shouldn't form a loop, or just suggesting alternatives?

 

[MDJ]

Maybe, but I've got an 8-way grid switch for the lights, so quite a lot of 1.5mm cores in places. I think it would be easier to run the lights one way and sockets the other, to avoid the switch wires, but the socket circuit does run pass the supply to the last couple of lights at the far end, which is why I end up with conduit in a loop.

Are you saying that the conduit shouldn't form a loop, or just suggesting alternatives?

Sounds like a right balls up to be fair, an 8 gang switch and ring main in one conduit? make sure you use plenty of soap.

 

[Tuttle]

Sounds like a right balls up to be fair, an 8 gang switch and ring main in one conduit? make sure you use plenty of soap.

Only if I end up with too many cables at any one point, surely.

What I've got in mind fits in with the conduit capacity tables.

 

[telectrix]

just wondering why an 8 gang switch. 1 for each downlight?

 

[MDJ]

Only if I end up with too many cables at any one point, surely.

What I've got in mind fits in with the conduit capacity tables.

I still struggle to see how the lighting and ring main will pass each other in the tube and you will have met regs regarding factors, sounds like you need a 2x2 glav trunking running around at high level and conduit drops, may be worth replanning the whole scheme to be honest, or perhaps you can explain your thoughts about how you intend to wire this so we can understand a bit more about your design.

 

[MDJ]

just wondering why an 8 gang switch. 1 for each downlight?

I am wondering when he said garage whether he meant a car garage owned by Vauxhall or ford and not his own little workshop LOL

 

[Tuttle]

just wondering why an 8 gang switch. 1 for each downlight?

Yes, one for each florescent fitting. Maybe a bit over the top but allows any combination of lights to be switched on.

 

[telectrix]

i'd switch them in pairs then. so only a 4 gang switch. K.I.S.S. is what my old man taught me.

 

[MDJ]

How big is this garage?

 

[Tuttle]

I still struggle to see how the lighting and ring main will pass each other in the tube and you will have met regs regarding factors, sounds like you need a 2x2 glav trunking running around at high level and conduit drops, may be worth replanning the whole scheme to be honest, or perhaps you can explain your thoughts about how you intend to wire this so we can understand a bit more about your design.

Ok, ring is 4 x 2.5mm -> 4 x 30 = 120 cable factor
This needs to run past the supply to last two lights which is 3 x 1.5mm (N + 2 switched lines) -> 3 x 22 = 66 cable factor
That's a total cable factor of 186 (the ring does not need to run past the grid switch)

20mm conduit allows 10m for 1 bend, 5m for two bends and 2.5m for three bends.

I could just keep the two conduits running in each direction separate, they would pass / run along side each other at the far end, but given that all the cables there would fit in one conduit I thought that wouldn't be necessary.

Go on, I know I've probably set myself up for a fall now :army:

 

[MDJ]

Fair enough Tuttle if you have gone to the trouble of calculating everything then it may well be fine, to answer your question, feeding the ring from one end of the conduit and then out the other is fine, or wire it as Tel mentioned, one leg to odd sockets one to even sockets and link between the last 2, that is what I normally do, either way it is fine.

 

[telectrix]

maybe not a fall, but a bit of over complication. still, a slong as it complies, it's you job at the end of the day, so do it as you think fit.