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#218419 - 04/18/17 02:55 PM Re: Why cables look like they do **** [Re: C-H]  
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,400
Vienna, Austria
Stranded wire is only any good if your devices and connectors are rated for the use of stranded wire without ferrules or other terminals. Most designed for the central European market aren't, so using stranded building wire introduces additional labour costs. Coarse stranded wire as is common in Scandinavia is only used for sizes of 10 mm2 and larger here. In Germany cables up to 16 mm2 have solid conductors! I hate to imagine working with them, solid 6 mm2 is annoying enough in tight spaces!

AFAIK Britain and Norway are the only countries in Europe that still allow reduced-size earth conductors smaller than 16 mm2 and the only two that commonly use bare earth conductors in building wiring (Ireland started requiring full-sized isolated earth conductors a year ago I think but I'm not sure if that's already affected actual wiring practices).

Then there's the divide between flat and round cables for building wiring - the UK, Norway and a couple of Eastern European countries predominantly use flat, the others round cables. Not much harmonisation there to see.


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#218439 - 04/26/17 09:36 AM Re: Why cables look like they do [Re: Texas_Ranger]  
LongRunner  Offline
Member
Joined: May 2015
Posts: 47
Albany, Western Australia
16mm2 solid core?! eek That's about 4.5mm in diameter of solid copper. Those Germans must be out of their minds!

In Australia our multi-core fixed cables have full-size earths up to 2.5mm2, then 4mm2 cables have a 2.5mm2 earth, 6mm2 through 16mm2 have earths two sizes smaller (2.5mm2 through 6mm2), 25mm2 through 70mm2 have earths three sizes smaller (6mm2 through 25mm2), and 95mm2 and up have earths four sizes smaller. (Given that the size steps get relatively smaller as the absolute size goes up, it's actually 25mm2 that gets the proportionally smallest earth there.) All modern versions have insulated earths, though bare earths can be found in older buildings.

We also get the options of flat or circular cables, the latter having tougher sheathing (usually coloured orange) and available in either 450/750V or 0.6/1kV ratings (up to 6mm2, above which it's 0.6/1kV exclusively). The flat cables are rated 450/750V (older versions were 0.6/1kV) and go up to 16mm2. Also worthy of mention are "twin active" flat cables (with red and white cores) commonly used for switch drops, and "SDI" (single-core double insulated) which contains just a single insulated and sheathed core (most often with red inner insulation, but occasionally also black or white). SDI is usually rated 450/750V up to 16mm2, and 0.6/1kV for 25mm2 and up. (Are cables similar to SDI used in other countries?)


#218452 - 05/03/17 10:42 AM Re: Why cables look like they do [Re: C-H]  
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,400
Vienna, Austria
Yep, apparently Germans are a bit masochistic! I recently saw a picture of what looked like a terminal box inside a lamppost and someone commented: "Ever tried wiring three 5G16 mm2 solid conductor cables into one of these?" and several others chimed in sympathetically.

I rarely have to work with larger cables so I'm not entirely sure but I think from 25 mm2 and up you can go done one size with the earth (and neutral), so 25/16, 35/25 etc.

Flat cable was and to some extent is used in most Eastern Bloc countries as well as in Norway, the UK and Ireland, although Ireland seems to have switched to round German style NYM a few years ago. Then there's ribbon cable, three, four or five solid conductors with fairly thin conductor isolation and an even thinner outer sheath, with only a small bridge of sheath between the conductors. Sort of like zip cord but with a lot more space between the conductors. It's used in new brick and concrete construction and can be glued or nailed to the raw brick walls and plastered over. Round cable or conduit usually requires trenching walls or pre-installing conduit in the forms while ribbon cable doesn't. The Germans mostly use NYIF with rubber sheath and that deteriorates wuite badly and crumbles if you try to work with older wiring. The Austrians had PVC-sheathed but always preferred conduit anyway. These days ribbon cable is rarely used and outrageously expensive (two to three times the price of round). Due to the thin sheath it mustn't be used anywhere near metal and combustible materials.

SDI seems to be a British thing mainly. In Germany it's commonly used for equipotential bonding and the likes, obviously with a yellow/green conductor.

I've never seen any equivalent to twin-active cable here, either the blue conductor is used as an active instead of neutral or a cable with more cores is used. Some Germans simply use 5-core (4+earth) by default.


#218461 - 05/06/17 05:26 AM Re: Why cables look like they do [Re: Texas_Ranger]  
LongRunner  Offline
Member
Joined: May 2015
Posts: 47
Albany, Western Australia
Curious, isn't it, how countries can differ so drastically in at what point reduced-size earths are allowed (in British 2C+E and 3C+E flat cables, the 1mm2 is the only one that actually has the same-size earth, everything larger has smaller earths). And I believe some European rules may even demand a larger earth in smaller cables (or singles in conduit)? Would sure be interesting to know how they worked them all out. wink (Flexible cords pretty much anywhere seem to all have same-size earths.)

I can understand keeping cables away from sharp metal, but any metal? That one's new to me. With a restriction like that, it's a wonder they still bother making it at all, especially given such inflated pricing. crazy

Having double insulation on an earth wire seems a bit unnecessary too. And it's possible to get British 2C+E (and prior to 1966, 2-core without earth) with two brown (modern) or red (older) wires, but most electricians there seem to just use the normal kind (brown+blue now, red+black historically) and over-sleeve the "neutral" core.

Last edited by LongRunner; 05/06/17 05:26 AM.

#218478 - 05/09/17 06:44 PM Re: Why cables look like they do [Re: C-H]  
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,400
Vienna, Austria
If you'd ever seen NYIF you'd know why it has to be kept away from anything that could damage the flimsy rubber sheath! I've seen rolls that were so badly mangled on the shelf in the store that I wouldn't buy them at any cost!

http://c.heimwerker.de/fa/_processed_/csm_stegleitung_detail_ef635d81a7.jpg

1 mm2 is considered too small for fixed wiring in all European countries except the UK and Ireland as far as I know, on grounds of insufficient mechanical strength. In Austria it was banned soon after WWII if it was even legal after 1938 (introduction of the German regs. in occupied Austria).

I've never heard of up-sized earths being required, only suggestions that they might be a wise idea in some very specific applications. e.g. data centres.

Not having any exposed earth wire in boxes does make some sense to me and I assume that's the whole point of isolated earth conductors. The British require sleeving, which adds unnecessary labour costs, probably exceeding the manufacturing costs of fully isolated earth wires. Ireland started requiring full-sized isolated earth in 2013 and seems to have switched from T&E according to British Standard to NYM according to German DIN VDE.


#218535 - 06/03/17 11:09 PM Re: Why cables look like they do [Re: LongRunner]  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,217
SI,New Zealand
Originally Posted by LongRunner

I can understand keeping cables away from sharp metal, but any metal? That one's new to me.

With any large sort of cable running next to or through metallic surfaces, you end up with induced and eddy currents, respectively, especially over long runs.
This is why things like cable trays/ladders are equi-potentially bonded together and earthed.
With respect to cables making entry to equipment, these days, especially where high frequency drives are concerned, you must use an EMC type cable gland, not just the normal nylon one.
I've investigated numerous stray voltage problems, where this has been put down to Eddy currents flowing in metallic parts of the installation, caused by the lack of bad screening/wrong gland used.


Let's face it, these days if you're not young, you're old - Red Green grin

#218536 - 06/04/17 06:02 PM Re: Why cables look like they do [Re: C-H]  
Texas_Ranger  Offline
Member
Joined: Dec 2001
Posts: 2,400
Vienna, Austria
With this type of cable the sole concern is mechanical damage though. The main fear is that non-bonded steel like studs or wire lath could be energised by a damaged cable. It's really only designed to be embedded in plaster on a brick, block or concrete wall or ceiling. I'd say the outer sheat is maybe half the thickness of comparable cables or even less and it's rubber, a type of rubber that doesn't have all that much tensile strength and cuts easily. I've seen rolls of that wire on a store shelf that I wouldn't have used any more because the sheath looked so badly chafed!

This picture should give you an idea what I'm talking about:
http://cdn-reichelt.de/bilder/web/artikel_ws/C600/NYIFJ315.jpg

In new construction the cable is either nailed or glued to the rough walls before plastering.
https://upload.wikimedia.org/wikipedia/commons/7/7f/Stegleitung.jpg


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