2 Pin Convention

[johna]

Is there a wiring convention when using 2 pin plugs and sockets with different sized pins? Should the larger pin be positive on negative? I have consulted O'Connell's Marine Electrics but it does not help can someone look in the 12Volt Bible for me please.

 

[theduke]

for what its worth i always wire the large as positive,using the premise that the supply should have the least resistance, and that the negative is the earth . as long as you always use the same format once you have decided which you prefer you wont reverse feed anything

 

[trev]

I've always considered the large pin to be positive.

Trev

 

[sonarbell]

Think you will find, large pin is negative as this is where all the current comes from.

 

[Strathglass]

I would agree with sonarbell
On most DC power systems the negative side of the supply is normally the common line and is usually grounded. It is better that the lowest impedence is present in the common line. Thus I consider that the thicker pin should be used for the negative feed.
Iain

 

[boatmad2]

with referance to hooks law what flows into a circuit must flow out again.
so barring any shorts both pins should carry the same currant

 

[ccscott49]

I agree with the duke, it doesnt really matter as long as you always wire it that way. The current will be the same in both pins, ohms law.

 

[Guest]

I think that with DC the current will flow from negative to positive. This is called "conventional current". However, the size of the pins shouldn't matter much as long as you aren't drawing huge amounts of current through this for running an electric fire!

 

[Bergman]

Hooks Law talks about springs and elasticity.

Don't think its relevant to this question

Maybe Mr Kirchoff may be of more use.

In the absence of any convention it matter not which pin is +ve and which -ve so long as all plugs and of course all sockets are wired alike.

 

[ccscott49]

Conventional current passes from pos to neg, electron flow is neg to pos.I think, going back to my aircraft and vehicle artificer days.

 

[johna]

While I agree with you it doesn't matter if you have all your equipment wired the same way, the question came up because I wired a cigar lighter socket to such a plug so that I could use my handheld in the cockpit. (New boat this year) I had wired the positive side to the larger pin and no GPS. Investigation indicated larger socket wired to negative on boat. Thus the post was my instincts correct or is the boat correct?

 

[Bergman]

Sorry to hear that, real bad luck.

I am surprised that the GPS didn't have reverse connection protection.

It does however demonstrate the point. Vital that BOTH plugs and sockets are wired to same convention, clearly your GPS was not.

Not clear why you want 12V plugs and sockets. Could you standardise on cigar lighter sockets, -ve outer +ve inner.

Only plug-ins I have are a fan and an inverter - both on cigar lighter plugs.

You would need to be a bit careful if fiting one in cockpit - don't mix well with water.

Hope you don't lose any more kit

 

[chippie]

I agree with Bergman, these days, most 12v equipment comes with a cigarette lighter fitting. If you dont have too many 2 pin outlets why not consider changing them to the more modern fitting and reduce the risk of error.

 

[johna]

Sorry if I gave the impression that the GPS was blown. No it is OK now I have changed the polarity of the plug to suit the socket on the boat. It just did not work first time with my use of the large pin as positive. From the replies there is still no definite convention as far as I can see. Does anyone have the 12Volt Bible?

 

[Trevor_swfyc]

Agree I also connect positive to the large pin, but when you buy a plug or socket do you get any instructions, no so can I assume there is no convention. The size is nothing to do with current flow but to ensure it will only fit one way. While you may have your own convention on your own boat what if someone borrows your prize bit of kit with plug that fits there socket, they plug it in but have large pin negative.
When I take any electronic gear onto another yacht I always take a meter to check the polarity before I plug it in.
It appears that because its only 12v the attitude is very lax with regard to regulation.
This reminds me of an incident at work many years ago with 240 volt sockets and plugs some sockets had a keyway and some the key. Likewise some plugs had keyways some keys. You can guess what eventually happened accidently in a rush I plugged a keyway plug into a keyway socket the chassis of the heating mantle became live and gave me one hell a jolt. The company blamed me for not being observant but by the following day they were all removed and corrected so such an accident could not happen again. Fortunatly safety has moved on considerably since then?
Has anybody who has puchased one of the 2 pin plugs referred to ever got any instructions with it regarding correct polarity ?
Trevor

 

[ccscott49]

I have six or seven of these plugs and sockets on board, all mine are pos on the big pin, I find it easier to remember, big=power/positive, works for me anyway, maybe we should start our own convention on this, so at least all of us use it! Then we can tell everybody else. I did replace all the old ones I had, as they were equal sized pins! Now that is confusing! They did have nice chromed blanks, rather than the cheapie plastic ones they have now.

 

[Lynette]

Yes ... Big pin = positive.

On every boat I've been on and checked. Probably no harm done wiring it the other way, as long as you are consistent, and don't ask anyone else to fix your wiring.

 

[bedouin]

The one I purchased recently was marked with the fatter pin as negative.

 

[philip_stevens]

This is the way I have connected mine - in the same way that the big terminal on "post" batteries is the positive.

Yet just above this posting Bedouin says that one he has bought, has the big pin marked as negative.

As others have said, if its your own boat, so long as all are connected the same - no problems.

Still, it's confusing to say the least. No electrical manual (that I have) shows which way around they should be connected.

regards,
Philip