ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat Box
Recent Posts
HVDC Greece to Crete
by gfretwell - 08/02/20 08:11 PM
310.15 (B) 7 Feeders
by HotLine1 - 07/31/20 02:29 PM
What would be the ideal solution?
by Fleppin - 07/21/20 12:42 AM
NESC question
by gfretwell - 07/16/20 04:17 PM
Code Violation or just not good Practice?
by HotLine1 - 07/16/20 03:03 PM
New in the Gallery:
Facebook follies, bad wiring
FPE in Germany pt.2
Who's Online Now
1 registered members (Scott35), 13 guests, and 16 spiders.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 3 of 5 1 2 3 4 5
Re: Extension cords #134314 11/04/02 11:31 AM
Joined: Aug 2002
Posts: 1,691
SvenNYC Offline

Don't the large round ungrounded plugs have notches and contours cut out in them to bypass the ground contacts on Schuko and French sockets?

I have a high-intensity photography lamp that has such a plug (my mom brought it over from Germany when she moved here).

The plug is a 16-amp two-pin ungrounded (with the thick pins) and even has a fuse in it!! Go figure. [Linked Image]

Test Equipment:
Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement
Large Selection of Test Equipment For Electrical, HVAC, Test & Measurement
Re: Extension cords #134315 11/04/02 11:39 AM
Joined: Sep 2002
Posts: 1,497
C-H Offline OP
>Don't the large round ungrounded plugs have
>notches and contours cut out in them to
>bypass the ground contacts on Schuko and
>French sockets?

Yes and no - double insulated appliances have these plugs. Not used on the extension cords, as it would make it possible to connect an ungrounded trailing socket to a grounded wall socket.

Re: Extension cords #134316 11/04/02 03:22 PM
Joined: Dec 2001
Posts: 2,485
Texas_Ranger Offline
An add-on: They're called contour plugs and used instead of Euro plugs on appliances that draw more than 2.5A. They came up along with the first Schuko receptacles in the 1950ies. Many old radios and tape recorders have them. Euro plugs came much later.
I haven't seen anything but photo lamps with a fused plug. My old 1000W Super 8 movie light has that too.
The ungrounded plugs I was referring to are completely round and have small pins, just like Europlugs, but unsleeved.
Plus the pins were partially split in halves, so if the plug lost contact you just bent them apart and that was it.

Re: Extension cords #134317 11/04/02 03:52 PM
Joined: Sep 2002
Posts: 1,497
C-H Offline OP
Were the holes in ungrounded sockets smaller too?

(Full size (4.8 mm) solid pins on our ungrounded plugs. I've seen old ones with sleeves, but it's not used today)

Re: Extension cords #134318 11/05/02 12:59 PM
Joined: Dec 2001
Posts: 2,485
Texas_Ranger Offline
It depends. Wall outlets had the same holes Schuko receptacles have (nice for inserting contour plugs, but allows plugging in Schuko plugs), the ones used on extension cords have smaller holes, thus accepting only ungrounded and Euro plugs.
The pins of our old plugs were solid the first 5mm where they emerged the case, then they had a small slot. It looks as though they'd been partially cut in halves from the tip with a very thin saw blade. Cheap types didn't have that feature, they tend to slip out of most sockets (remember, all of them are older than 20 years now, they're pretty likely to be worn out at least a little bit).
Oldest sockets I've seen are from the beginning of the 20th century or maybe even earlier, were made of brass and white porcelaine, lokking pretty much like the one posted on the "old electrical parts" thread some time ago. These were usually wired with surface-mount 0.75 sq. mm cord, 2 single sheathed wires twisted around each other, put on porcelaine or glass insulators. If I'm ever going to see such an installation I'll take pictures, maybe I even have some (I think I took a pic of a light switch from 1924 with some cord)

Re: Extension cords #134319 11/05/02 07:10 PM
Joined: Aug 2001
Posts: 7,520
pauluk Offline
The pins of our old plugs were solid the first 5mm where they emerged the case, then they had a small slot. It looks as though they'd been partially cut in halves from the tip with a very thin saw blade.

Many types of British 2 and 5A plugs were similar. If a plug was a loose fit in an outlet, you could just pry the pin open very slightly to improve the contact.

Re: Extension cords [Re: Trumpy] #219227 04/05/18 07:55 AM
Joined: May 2015
Posts: 76
LongRunner Offline
As old as this thread is, I have to correct Trumpy on Australia/NZ extension cords:

Under official definitions, there are no (legal) "light duty" extension cords here; by "light duty" flex we mean H03VV-F (circular) or H03VVH2-F (flat), and their dimensional equivalents in AS/NZS 3191. Those only go up to 0.75mm^2, so they can't be used under the regulations for Aust/NZ extension cords (no doubt abrasion resistance is also a factor); therefore, no company here manufactures trailing sockets to fit H03VV-F (much less H03VVH2-F).

For ordinary-duty extension cords (as used in homes or offices), we of course use H05VV-F or the equivalent thereof. Heavy-duty extension cords here mainly use a flex (also specified in AS/NZS 3191) with the same dimensions as H07RN-F, but usually in PVC. "Extra heavy duty" isn't actually a type of flex with still thicker insulation, but just means a heavy-duty flex with 1.5mm^2 (or larger) conductors.

Otherwise, Trumpy is correct that 1.0mm^2 is the basic conductor size (for 10A); with 1.5mm^2 for 15/16A (and it can also be used to reduce voltage drop in longer 10A leads, of course). All legal versions are earthed, too.

The basic type of extension cord here has just a single socket; compared to many other arrangements, this is very sensible, and would be close (as far as reality allows) to fool-proof if it wasn't for the existence of the unprotected double-adaptors ("piggyback" plugs - common on some extension cords - also create the exact same hazard, just in a cosmetically different form).

Re: Extension cords [Re: C-H] #219233 04/12/18 08:20 AM
Joined: Dec 2001
Posts: 2,485
Texas_Ranger Offline
Yes, I suppose some updates are in order, although most of the posters on this thread are gone now.

1) Italy and France seem to be the only countries that have plugs that are compatible with Euro plugs but have a higher rating (6 A in France, 10 A in Italy). That's what sometimes ends up on cheap hairdryers, although I've seen at least one 1500 W hairdryer with a plug clearly marked "2.5 A 250 V". We also have one with a truly strange plug, the pins are exactly the same thickness as on a Euro plug but considerably shorter - I need to replace that one as soon as possible!

2) VDE now requires all extension leads (except those that only accept Euro plugs) to be 1.5 mm2 or larger, apparently there were too many issues with overheating 1 mm2 power strips.

3) There are extension leads with contour plugs and mating sockets that have plastic "walls" in place of the earth scrapers that should in theory exclude Schuko/French plugs but in reality they break easily. I'm not sure if they even comply with Austrian and German regs but they're sold. Usually they're undersized too, 1 mm2 and up to 20 m long. Fairly popular among contractors of Eastern European descent.

4) Earthing arrangements in Hungary, Slovakia and the Czech Republic (actually that deserves its own thread but I'll quickly comment on that here): some older places in Hungary have sockets for class-0 appliances but it seems they were banned for new work some time in the 60s or 70s. All earthed supplies seem to be TN-C-S with the PEN split near the supply fuses, although there might be TT supplies in rural areas. Old wiring is - scary enough - 1.5 mm2 Al in conduit or cable buried in the walls, in the 1980s they went up to 2.5 mm2 Al. Joints seem to be twisted and taped everywhere, even with newer copper mixed in.

In Czechoslovakia I've never seen a socket without earth, most houses seem to have been rewired at some point. However, all the older installations are TN-C, often wired with Al. A friend's apartment in Prague had 2.5 mm2 Cu socket circuits (two doubles per room) and 10 A lighting circuits wired with a wild mix of 1.5 mm2 Cu and 2.5 Al. I've also seen socket circuits with 4 mm2 Al. Aluminium wire seems to have been widely used in Europe during WWII due to material shortage but most, if not all countries behind the Iron Curtain continued using it into the early 1990s. Apparently in Latvia Al wire was readily available in DIY stores in the early 2000s.

Finally a note on pre-Schuko sockets and plugs (i.e. un-earthed for class-0 appliances): the original design was 6 A with split 4 mm pins and 4 mm holes on the sockets. Later, a 10 A design with 4.8 mm solid pins and corresponding holes on the sockets was introduced. Apparently 10 A plugs were fairly common in Germany but rather rare in Austria but most, if not all new sockets from the early 1950s onwards were 10 A. New installations were required to be fully earthed by 1958 with a transitional phase (for buildings already in planning or under construction) until 1960 but un-earthed sockets were sold as replacements or for extensions of existing installations well into the 1970s. Leftovers could be found in older stores as late as 1990.

A brief explanation on class 0 and un-earthed sockets: class-0 appliances are designed like class-1 appliances with only one protective layer between live parts and exposed metal casings. They were only to be used in "isolated rooms" with no exposed earth potential, e.g. earth wires from either mains wiring or radio/TV aerials, metal water, gas or central heating pipes, stone floors etc. The reasoning was that under these circumstances people could not possibly receive a fatal shock from a faulty appliance since there is no path to earth for a current to flow. This is the main reason why those old plugs don't fit Schuko sockets but vice versa - in an isolated room a class-1 appliance without earth is no more dangerous than a class-0 appliance. In some countries isolated rooms were used much longer than in Austria and Germany, e.g. in Sweden until 1994.

Last edited by Texas_Ranger; 04/12/18 08:35 AM. Reason: Added last two paragraphs
Re: Extension cords [Re: C-H] #219234 04/12/18 01:07 PM
Joined: Apr 2002
Posts: 7,191
HotLine1 Offline

As I am 100% not familiar with wiring and devices on the other side of the pond, your post was interesting.

Re: Extension cords [Re: Texas_Ranger] #219235 04/12/18 02:17 PM
Joined: May 2015
Posts: 76
LongRunner Offline
Well, I've already done some real load tests with cords of my own (a few of which I've described in a previous thread on this forum). (I probably ought to assemble a cleverer arrangement than convection heaters for future tests, though, in order to maintain slightly lower room temperatures during Australian summers grin.)

So, on the basis of those: For cords up to about 10m long, then, our 10A through 1.0mm^2 appears reasonably safe (although up to 25m is permitted, which will be somewhat worse). But 16A through 1.0mm^2 for 20m sounds like a meltdown waiting to happen, if the user isn't thinking. frown
On the occasion when you need a still-longer cord, then, I would go with a thermally protected extension reel, and/or upsize the wires another step (e.g. 1.5mm^2 for 10A, 2.5mm^2 for 15/16A).

While laid straight, though, the flexes themselves seem to cope well enough with 13A through 0.75mm^2, or 16A through 1.0mm^2 (or 20A through 1.5mm^2 etc.).
I strongly suspect that (most of) the true problem behind the VDE's "upgrade" was related to the inconsistent quality of terminations (which is no doubt severely exacerbated by penny-pinching). But although thicker wires may well keep borderline terminations a bit cooler and survive for a little longer, I've clearly seen signs of localized overheating even inside appliances that do it 'by-the-book' with 1.0mm^2 for 10A (or even lower current) -- and usually while the appliance itself still works. crazy
(For obvious reasons, space heaters are among the foremost victims...)

Page 3 of 5 1 2 3 4 5


2020 National Electrical Code
2020 National Electrical
Code (NEC)

* * * * * * *

2017 Master Electrician Exam Preparation Combos
2017 NEC Electrician
Exam Prep Combos:
Master / Journeyman


Member Spotlight
Posts: 46
Joined: May 2007
Show All Member Profiles 
Top Posters(30 Days)
BigB 3
Popular Topics(Views)
268,149 Are you busy
202,610 Re: Forum
191,044 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.3