ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades Extra Low Voltage connectors - what do you use?

After seeing this for sale on the UK Ebay:
http://cgi.ebay.co.uk/12-V-SOCKET-C ARAVAN-CAR-MOTORHOME...

and this

http://cgi.ebay.co.uk/3-WAY-SOCKET-MAINS-CO- AX-12V-POINT-CARAVAN_...

I was reminded that outside of Australia, there exists no standard ELV plug and socket. We've been fortunate to have this:

This 402/32 plug and socket configuration has been around since the existance of the 12 and 32V home lighting plant which were common in rural areas until the 1960's. Now, there's been a resurgance in the popularity of this connector with solar/wind installations, caravans, boats, 4WD etc. Despite this, I have seen the horrifying installations where standard 240V 3 pin connectors have been used. (I remember as a young kid about to plug a 12V CB radio into the mains because there was a 240V plug on it but the owner came rushing over in a panic just in time).
But what of other countries? As far as I can tell it seems that various forms of mains plug and socket are often used. The Ebay example looks awfully like a polarised 120V socket. Pity the poor 12V appliance should it find it's way near a 120V outlet, though admittedly it isn't terribly likely given this socket is for sale in the UK.
Over in the US, it seems people with 12V wired homes simply have used the standard 3 pin 120V plug and socket.
Some Japanese vehicles of the 1960's & 1970's had a 2 pin outlet in the glove box into which one could plug the supplied trouble lamp which was fitted with a standard 120v plug. Again, one wonders how many got plugged into the mains in areas where that configuration is used for the domestic 120V supply.
The other issue, apart from the electrical destruction, is that 12v appliances often have the case connected to negative, so imagine what happens when the ELV appliance is plugged into the mains and the user touches it.
Surely an attempt needs to be made to standardise on a connector that does not resemble anything used for the mains.
As a final note, there has been a recall of portable generators sold in Australia during the 70's for this very reason...the 12V socket is remarkably like an Australasian 240V socket without the earth pin. http://www.energysafety.wa.gov.au/energysafety/media_include/unsafe_generators.pdf

While the common cigarette lighter socket is probably the next best thing where the 402/32 socket can't be obtained, it does suffer from poor reliability at high currents. But please...no mains plugs for 12V gear!

[This message has been edited by aussie240 (edited 09-21-2006).]

{ Edited to tidy up links }


[This message has been edited by pauluk (edited 09-23-2006).]

That is very interesting. Here in the states our 12Volt connector, used on generators, is similar to the Australasian 240V mains connector. Conversely the Australian Clipsal ELV connector is similar to our 120 or 240 volt 20 amp connectors

[This message has been edited by IanR (edited 09-22-2006).]

You took the words out of my mouth Ian!

From my memory of the US too.

UK 12V accessory socket in a caravan (trailer)for a TV etc., is as Ian describes.

Cheers,

Ian

Cigarette lighter plug is definitely most common in vehicles.
Solar installs used some kind of plug with a somewhat NEMA-like pattern but incompatible. It's been taken out of production though I think.

Other than that I've seen all kinds of ugly stuff... Swiss ungrounded plugs (next to Swiss receptacles feeding 220V AC), BS 1363 plugs,...

The assortment of 12-volt connectors found in campers, motorhomes, and caravans here does make things a little complicated at times.

There are about five types commonly found:

1. The standard cigarette lighter style.

2. The smaller DIN connectors which are similar in appearance to a cigarette lighter plug but smaller. Not so common as other types.

3. The two parallel, flat-blade plug as in the first eBay link above.

4. Another flat-bladed plug which is very similar but has the blades set at a slight angle to each other (not as much as an Aussie 240V plug or a U.S. "crowfoot" plug though).

5. The 3-pin 2-amp BS546 plug/socket, as was once common for 240V lighting outlets in homes. The original L and N pins are normally positive and negative respectively, with the original earth pin being unused.

Note the various plugs and adapter leads available here:
http://www.towsure.com/default.asp?t=476



[This message has been edited by pauluk (edited 09-23-2006).]

I've got a "power strip" unit that comes out of my 50 Amp (13.8VDC) PSU used for all of my Ham gear, this thing uses shrouded 30A individual Banana plug type connectors.
Each socket has a fuse associated with it (ie: 2 per "output").
As far as the Regulations go here, the plug must be of such configuration that it is impossble to insert an ELV plug into a Mains voltage outlet.

While we are on the subject of dedicated plugs, Aussie, have you ever seen plug/socket arrangements with the round earth pin (usual P-N pins) actually used in an installation?.
Reason I ask this, is because this system was bought in to prevent dedicated computer circuits, being taken out by some idiot plugging a 2.4kW heater into the wall next to the computer sockets.
(The circuit having been made "Computer Only" and being wired and protected accordingly {16A MCB and 1.5mm2 cable}).

{Sorry about the thread-jack, Aussie}

Yes, I have. Actually, you reminded me that I've seen the round earth pin plugs used on ELV. One was a 12V powered house, and by the awful voltage drop evident my guess is the GPO's were wired as they would be for 240V; ie. 2.5mm TPS feeding them...not good for a few amps draw at 12v at the other end of the house. Another ELV installation where I actually used them was in my school science lab. We had round earth pin GPO's around the room and when electrical experiments were done we were supplied with the round earth pin plugs fitted with short leads and banana plugs. In an adjacent room was a crude DC supply which I would now guess was simply a tapped transformer feeding a rectifier without any filtering or regulation.
One guy I know uses them to run his 110V vintage radios. Why he chose to do this I can't imagine when the two pin sockets are available here.
At my work we have some isolation transformers so fitted. They are used for a light dimmer/phase control demo so the students can observe the waveform on a CRO.
The other place I've seen them was in a hotel room. There was a light switch on the bedside table which was fed into the room wiring via the round earth pin socket.
My understanding was that this type of plug and socket was originally intended for lighting circuits. One wiring book I have from the 1970's specifically mentions this. In fact I wired up some of my garage lights thus, only because I had the fittings looking for a use.
These days with so many high current appliances now fitted with plugs that have no earth pin the usefulness of the round earth pin plug would be less than it once was.

The plugs with the round earth pin and the conventional flat P and N pins are used extensively for the connenction between HID lamps and their ballast boxes. You probably won't see many of these in an industrial setting, but those shops that sell indoor gardening equipment have plenty of them. The lampshades typically come with a flex with a REP plug on one end, and the ballast boxes have the matching socket.
While this eliminates the confusion that arises when the lamp is plugged into a 230V socket without the ballast, it does little to stop the ill-informed trying to run 600W or 1000W lamps from 400W ballast units.