Can anyone tell me what the cable carrying capacity of 20mm conduit is?. The conduit is PVC coated galvanised steel with an internal diameter of 17mm. I need to know how many single core conduit cables (1.5mm or 2.5mm) I can run in parallel (I assume this is based upon max current carrying capacity of each core).
There's a table in the IEE On-site guide, but I've lent mine to someone. The limit is based on what you can pull in to the conduit without risk of damage, and IIRC, it depends how long the section of conduit between access points is and how many bends you are pulling round.
There will also be the issue of derating the current capacity of the conductors due to grouping.
Some of the cable factors and conduit factors info is on the TLC web site here
Indeed. The Cg factors are here
When they talk about conduit diameter in these tables, do they mean outer diameter of conduit or inner diameter? I plan on using PVC coated galvanised steel which I suspect will have a smaller internal diameter than plain PVC.
In practical terms, it depends on how long a run you have. But for any reasonable length of run, you'll only get one 2.5 mm TC&E cable to easily go down a 20 mm conduit. I'd be using one a lot bigger (32mm or more) & get the cables pulled through more easily & a lot quicker. And of course, all cables pulled at the same time, else one cable will rub the other
I find the practical limit to drawing them through is the two sets of three single core needed for a ring main feed and return to a socket outlet and that only if you feed them all through together. It might be possible to get more down a completely straight run, but mine always have an elbow or two.
Colin Bignell
True enough, but the O/P was asking about singles rather than T+E.
My mistake. This makes it worse, as there's a lot more insulation involved with singe core as it has to be double insulated. You'd be lucky to get three single cores in one 20 mm conduit, unless it's really short.
O/D.
I've never come across PVC-coated steel conduit. Is this tube you plan to use a recognised electrical conduit type to a relevant British or International standard? If not it's doubtful whether you'll comply with the wiring regs (BS 7671), in particular Reg. 133-01-01 requiring good workmanship and _proper_materials_ and Reg. 511-01-01 requiring compliance with standards.
Also remember that when wired with 'singles' metal conduit is an exposed-conductive-part (see definitions) and must be earthed, regardless of whether or not it is also being used as the circuit protective conductor. The insulation provided by a thin PVC coating should not be relied on. It is also important that electrical continuity is maintained through all joints, which is why only threaded joints or "substantial mechanical clamps" are allowed [Reg. 543-03-06].
Not in conduit, it doesn't. Single conduit wire (6491X or 6491B) with only basic insulation is perfectly allowable, and indeed quite normal, in conduit. If the conduit is metal it must be earthed, even if a separate circuit protective conductor is provided in the wiring.
Also insulated and sheathed cables (6181Y) should not be described as "double insulated" since they are not considered as being of Class 2 construction - see Reg. 471-09-04 in BS 7671. However metal conduit wired exclusively in such cable, including ordinary T&E (6242Y), does not need to be earthed [471-09-04 again], except where Reg. 522-06-06 (iii) applies - i.e. to provide protection for cables buried in walls being run outside of the "safe zones".
"nightjar .uk.com>"
Ok from working out the capacity I think I'm going to need 25mm diameter conduit to be on the safe side. Incidently, does the conduit have to be steel lined (its going to be buried mostly under a patio) or can it just be standard flexible PVC conduit? The steel lined one I've found is here:
Ah, flexible conduit and an underground application - two things you hadn't mentioned before. What is it you're trying to do?
You shouldn't use flexible conduit underground unless it's a type specifically designed for such use. Nor is it very sensible to be using single conduit wire underground. Better to use SWA cable, which can be buried directly, or a sheathed cable such as ordinary T&E or Hi-Tuf in substantial plastic service duct.
Ah so PVC coated galvanised conduit (as above link) won't cut it then? My interpretation of the regs was as follows (taken from TLC site) "Any suitable cable enclosed in conduit or duct which gives at least the same degree of mechanical protection as an armoured cable."
The reason for using single core was that at the end of each run I will have multiple circuits I need switching (deck lights, LED lights etc) which in one case requires upto 4 seperate switched lives in one run.
I was told since the conduit was galvanised & PVC coated it would be waterproof (& rustproof) therefore ok for underground use.
Hi-Tuf in
"Any
First scratch of the pvc will say goodbye to the waterproofing as the various salts in the soil will locally disolve the zinc then the steel in double quick time. I would echo the SWA or Hi-Tuf suggestion, or consider putting normal solid pvc rigid conduit inside some other protection such as 100mm soil pipe with both the conduit and the soil pipe having glued joints.
AWEM
You can get multicore SWA, e.g.
replying to Andrew Mawson, Adam wrote: What about simply concrete around the pvc, like done in USA or Caribbean? Although, there is a place somewhere that lists the rating of pvc schedule 40 as being the same in six inch concrete as buried at two feet
A blast from the past - 2007 !!!!!!
Andrew
Yes Home Owners Club crappy message sorting strikes again. It actually is on the page OK but people are not expecting the year to change. Why they have not fixed the message sorting to include the year is beyond me. If the admins are reading this on that web interface to usenet, please fix it now or we will pur molten lead into your server bay. brian
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