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 Topic Title: Imperial T&E Topic Summary: csa of earths Created On: 02 May 2014 11:24 AM Status: Post and Reply Linear : Threading : Single : Branch
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 02 May 2014 11:24 AM geov Posts: 278 Joined: 22 February 2004 Hi, bit of a blonde moment (yes, another one) - can anyone confirm the csa of the earth in the imperial equivalent of 2.5mm & 1.5mm T&E? Thanks. 02 May 2014 11:45 AM daveparry1 Posts: 7062 Joined: 04 July 2007 7/029 lives and 3/029 for the earth. 02 May 2014 05:14 PM geov Posts: 278 Joined: 22 February 2004 Cheers Dave. 02 May 2014 05:46 PM mikejumper Posts: 2022 Joined: 14 December 2006 Originally posted by: daveparry1 7/029 lives and 3/029 for the earth. As a matter of interest do you know what that translates to in new money? (approximately). 02 May 2014 07:21 PM napitprofessional Posts: 450 Joined: 08 March 2008 Approx 3 and 1.3 square mill respectively, at a guess. ------------------------- B. Eng (Hons) MIET 02 May 2014 09:39 PM maltrefor Posts: 125 Joined: 01 November 2009 01 May 2009 07:03 PM User is offline View Users Profile Send Private Message Print this message Paul1966 Posts: 1538 Joined: 21 December 2004 And the CSA conversions (rounded to 2 decimal places): 1/.044 = 0.97 sq. mm. 3/.029 = 1.29 3/.036 = 1.94 7/.029 = 2.90 7/.036 = 4.52 7/.044 = 6.45 7/.052 = 9.35 7/.064 = 14.52 19/.044 = 19.35 19/.052 = 25.81 19/.064 = 38.71 02 May 2014 09:48 PM maltrefor Posts: 125 Joined: 01 November 2009 But didn't 7/.029 T & E cable contain a 3/.036 earth conductor ? 03 May 2014 08:18 AM perspicacious Posts: 7672 Joined: 18 April 2006 1/.044 & 1/.044 3/.029 & 1/.044 3/.036 & 1/.044 7/.029 & 3/.036 7/.036 & 7/.029 7/.044 & 7/.036 7/.052 & 7/.044 7/.064 & 7/.052 I think you'll find that 1/.044 instead of being 0.97 mm2 to 2dp it should be 0.98 mm2 to 2dp from this to 7dp 0.9809857 mm2 In the same theme, I found a part drum of NTL sat cable whilst skip ratting and this was marked at 305 m but with a comment that the NTL contract allows this length to vary by +- 10% which I thought quite an amount. Regards BOD 03 May 2014 09:06 AM phantom9 Posts: 1443 Joined: 16 December 2002 Geov, Just out of interest, how does knowing this help you? I mean, BS7671 doesn't show any technical information relating to these sizes, and filling out test certs. with these sizes is meaningless because they don't translate to latest disconnection times or Zs max. Do you record these conductor sizes on your cert? 03 May 2014 09:36 AM daveparry1 Posts: 7062 Joined: 04 July 2007 Do you record these conductor sizes on your cert? I do on c/unit changes. 03 May 2014 11:34 AM Legh Posts: 3669 Joined: 17 December 2004 I think in this case that you record what you see as it can be translated into a close approximation of the coordination between cable size and protective device are likely to be. As the regs are not retrospective then an 'engineering decision' has to be taken. Legh ------------------------- http://www.leghrichardson.co.ukde-avatared 03 May 2014 12:11 PM phantom9 Posts: 1443 Joined: 16 December 2002 So you think that cable manufacturers work to hundreths of a millimetre for CSA? There is no guidance on using imperial sized cables in the current edition of BS7671 and as far as I am aware none since the cable sizes were discontinued. We only work with 1.0mm2, 1.5mm2, 2.5mm2, 4.0mm2, 6.0mm2, 10.0mm2 and 16.0mm2 in T&E so its really pointless recording CSA sizes to hundreths of a sq.mm on test certificates for imperial cable. Apart from being pedantic, and in the 0.05% that bother, what IS the point? I think that the metric versions of cables are (on a like-for-like basis of their imperial equivalents) smaller in CSA so recording the metric size is erring on the safe side. 03 May 2014 12:25 PM daveparry1 Posts: 7062 Joined: 04 July 2007 When I said I do record the cable sizes that are there I meant that if there's 7/029, 3/029 etc. there that's what I put in the box, I didn't mean that I go into details of the comparison between 7/029 and 2.50mm etc! 03 May 2014 09:15 PM geov Posts: 278 Joined: 22 February 2004 Originally posted by: phantom9 Geov, Just out of interest, how does knowing this help you? I mean, BS7671 doesn't show any technical information relating to these sizes, and filling out test certs. with these sizes is meaningless because they don't translate to latest disconnection times or Zs max. Do you record these conductor sizes on your cert? Yep, as per Dave. 03 May 2014 10:31 PM phantom9 Posts: 1443 Joined: 16 December 2002 But why? Just put nearest metric size. What difference does it make? 03 May 2014 10:37 PM daveparry1 Posts: 7062 Joined: 04 July 2007 In that case Phantom why not? What could be simpler than just putting 7/029 or 3/029 etc. if that's what's there just write it down! Of course it might be a problem for people without the experience to know what sizes imperial came in. 03 May 2014 10:41 PM phantom9 Posts: 1443 Joined: 16 December 2002 Exactly, Dave. Why would any electrician reasonably be expected to know what imperial sizes are? There is no requirement to record imperial sizes so just record nearest metric size. The point I am making is why bother when it has no relevance? 03 May 2014 10:50 PM leckie Posts: 2905 Joined: 21 November 2008 I agree with you phantom. I'm 57, and the imperial sizes are before my time. So by recording imperial sizes on a certificate, the only people able to have any idea about what they might mean are people just about to retire! Bit silly really. 04 May 2014 01:47 PM normcall Posts: 8361 Joined: 15 January 2005 It's a good job you youngsters never come across anything imperial. I suppose you rip out conduit, metal boxes and perfectly good/serviceable cable and switch gear just because 'it ain't in the book'. Why stop there? There are millions of 'obsolete' items out in the real world. Next time I see my customer who has a Jaguar XJ in his garage, I'll suggest he just gives it to me so I can drive it to the tip. ------------------------- Norman 04 May 2014 03:06 PM Jaymack Posts: 5075 Joined: 07 April 2004 Originally posted by: phantom9 Exactly, Dave. Why would any electrician reasonably be expected to know what imperial sizes are? It's a no brainer, would you be expected to know?, or at least to find out the different dimensions, they're easy to find out! There is no requirement to record imperial sizes so just record nearest metric size. You're showing your age! You probably just say that, because you can't be farced to find out the imperial sizes. Recording the fact that there are imperial cables in the first place, is a flag to indicate the probable age of the installation, and it demonstrates that one is aware of these, and that one ....... (not you), , have considered the ratings w.r.t. to the comparison table, which is at one's fingertips. The point I am making is why bother when it has no relevance? It obviously has no relevance to you, since you obviously have one leg shorter than the other ..... seeing the world as the leaning tower would. Regards
IET » Wiring and the regulations » Imperial T&E

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