IET logo
 
IET
Decrease font size
Increase font size
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
1 2 3 Next Last unread
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 02 May 2014 11:24 AM
User is offline View Users Profile Print this message



geov

Posts: 190
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
User is offline View Users Profile Print this message



daveparry1

Posts: 6239
Joined: 04 July 2007

7/029 lives and 3/029 for the earth.
 02 May 2014 05:14 PM
User is offline View Users Profile Print this message



geov

Posts: 190
Joined: 22 February 2004

Cheers Dave.
 02 May 2014 05:46 PM
User is offline View Users Profile Print this message



mikejumper

Posts: 1746
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
User is offline View Users Profile Print this message



napitprofessional

Posts: 380
Joined: 08 March 2008

Approx 3 and 1.3 square mill respectively, at a guess.
 02 May 2014 09:39 PM
User is offline View Users Profile Print this message



maltrefor

Posts: 121
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
User is offline View Users Profile Print this message



maltrefor

Posts: 121
Joined: 01 November 2009

But didn't 7/.029 T & E cable contain a 3/.036 earth conductor ?
 03 May 2014 08:18 AM
User is online View Users Profile Print this message



perspicacious

Posts: 7244
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
User is offline View Users Profile Print this message



phantom9

Posts: 690
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
User is offline View Users Profile Print this message



daveparry1

Posts: 6239
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
User is offline View Users Profile Print this message


Avatar for Legh.
Legh

Posts: 3498
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

-------------------------
Why do we need Vernier Calipers when we have container ships?

http://www.leghrichardson.co.uk

"Science has overcome time and space. Well, Harvey has overcome not only time and space - but any objections."
 03 May 2014 12:11 PM
User is offline View Users Profile Print this message



phantom9

Posts: 690
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
User is offline View Users Profile Print this message



daveparry1

Posts: 6239
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
User is offline View Users Profile Print this message



geov

Posts: 190
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
User is offline View Users Profile Print this message



phantom9

Posts: 690
Joined: 16 December 2002

But why? Just put nearest metric size. What difference does it make?
 03 May 2014 10:37 PM
User is offline View Users Profile Print this message



daveparry1

Posts: 6239
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
User is offline View Users Profile Print this message



phantom9

Posts: 690
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
User is online View Users Profile Print this message


Avatar for leckie.
leckie

Posts: 1872
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
User is offline View Users Profile Print this message



normcall

Posts: 8144
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
User is online View Users Profile Print this message



Jaymack

Posts: 4668
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

1 2 3 Next Last unread
Topic Tools Topic Tools
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.