Three pin plug wiring

[Fantasie 19]

OK guys - sorry for the dull question, but I can't find any guidance anywhere on this....

I need to re-wire a couple of my waterproof deck plugs - I guess they are the standard, screw down, waterproof, 3 pin (round pins) plugs.. one of the pins - the top one is bigger than the other two... can anyone tell me which is live, which is earth and which is neutral?

There are no markings (I can see) in the plug - and I've worn out google without success - are they laid out in the same way as a mains plug so the bigger pin is earth?

Told you it was dull...

 

[Leighb]

When talking about deck plugs, are you referring to plugs to connect mast wiring to the internal wiring?

If so it is likely that the large pin is for the common return (earth) usually a black wire. The other two will be for different masthead light circuits. Tricolour and Anchor light - say. They would be either both red or different, but you would need to trace the relevant wires and see which switch operates which circuit.

If you are referring to mains power, I guess it is the socket to connect the boat to shore power? In that case it is vital to ascertain which wire is connected to live and which to neutral. The large one is likely to be the earth as you suggest.

I am not an electrician however.

 

[TrueBlue]

Yes, it's the same as the more modern fused 13 Amp plug;
Big pin = Earth
Left pin = Neutral
Right pin = live.

However - off topic - that's for mains, and OK if your deck plugs are for 240v AC.

A lot of folks use 5 and (possibly) 15 amp round pin plugs and sockets for low voltage applications, so the wiring depends on what it's being used for. On my boat, I have
Big round central pin = common ground
Left pin = 12v
Right pin = 24v
There's some logic in it but not to any standard.
I found it difficult to get any acceptable marine / commercial system that fits in to how the stuff is used inside the boat.

 

[Fantasie 19]

Nope - good questions - these are plugs to connect mast wiring to the internal wiring..... in both cases it's single light cct's - one's a mast head, and one's a deck light...

The mast wiring is standard "land" type - but comes in two flavours - old style red/gr/blk for one, and newer blue/brn/g&y for the other...

 

[VicS]

Be warned that the three pin deck plugs with a screw-down ring usually, if not always, have the large pin earthed by the retaining grubscrew to the outer body if its metal. It should therefore be the negative pin on low voltage DC systems and the earth pin on mains systems.

Driplugs have plastic bodies which are not so connected.

 

[Fantasie 19]

Thanks VicS - yes there is a grub screw but I can't remember where it connects - almost certainly the big pin but I'll check and make sure it's on the big pin when I next go out to the boat...

 

[nedmin]

I would have thought that the large pin is negative and the other 2 are switched feeds from your deck and mast switches.Assuming we are talking about DC and not 240v AC.If you have a meter you should be able to prove which is which by switching ,say, the deck light on and check which 2 give you a voltage reading.Switch the deck light off and put the mast light on and do the same test.You will probably find then that the big pin is common to both to get the lights to work ie negative.If its 240v suggest you get someone electrical to sort it out.

 

[pvb]

It makes sense to use the larger pin for the negative, but basically it's only there to ensure the plug can only be inserted one way, thus ensuring that the right lights come on when switches are flipped.

 

[colvic987]

Hi, i had this problem two days ago on my deck gland plugs, the decklight had been playing up for months, what i found was that the deck plugs, is connected to a 3 core.

the common earth was blue,( larger pin ) and the other two were red,(2 smaller pins) they were the 12v feeds to the lights, one deck light the other was the steaming light. (1 for each)

 

[Spyro]

Nope - good questions - these are plugs to connect mast wiring to the internal wiring..... in both cases it's single light cct's - one's a mast head, and one's a deck light...

The mast wiring is standard "land" type - but comes in two flavours - old style red/gr/blk for one, and newer blue/brn/g&y for the other...

As you've discovered there is no such thing on a boat as standard wiring, Blue/brn /g&Y is almost certainly domestic wiring and was used because it was available. Lights on boats only need a live and an earth. use a muti-meter to find out what has been previously used. That set up could be done with one cable using a common earth and the two other wires for the live switched feed to each bulb.

 

[VicS]

Lights on boats only need a live and an earth

The OP is talking about low voltage DC navigation lights. they will have a positive and a negative. The negative may well be "earthed"

Red and black would be the most appropriate colours to use if buying marine cable for the purpose but if using domestic cable you are stuck with brown and blue.

I suggest if two circuits are run using domestic three core then brown for one circuit blue for the other and yellow/green for the common negative, but its just my suggestion.

 

[Fantasie 19]

Clearly not such a dull question after all!

Thanks chaps...

 

[Leighb]

I am far fom being an expert, but is it not a bad idea to use domestic cables in a marine environment, especially in a vulnerable area like mast wiring?

I would have thought they would be much more prone to corrosion, and possibly fracture due to vibration?

 

[VicS]

I am far fom being an expert, but is it not a bad idea to use domestic cables in a marine environment, especially in a vulnerable area like mast wiring?

I would have thought they would be much more prone to corrosion, and possibly fracture due to vibration?

Yes plain copper cables are prone to corrosion in the marine environment. That is why proper marine cable is tinned.

Its expensive so the budget level boat owner may choose to use ordinary domestic flex and replace any bits that become corroded from time to time.

I knew nothing bout the existence of tinned marine grade cables when I fitted out my boat 30+ years ago so it was all done with domestic stuff. Some has been replaced during the course of other work but so far none has actually failed due to corrosion.
Some of the original wiring remains in service. I reckon what's there now will see me out!

 

[Spyro]

The OP is talking about low voltage DC navigation lights. they will have a positive and a negative. The negative may well be "earthed"

.

you're quite right I just usually refer to the negative side as earth as it is all common. Other having no inboard engine when would it not be earthed?

 

[jsinger]

Hi, i had this problem two days ago on my deck gland plugs, the decklight had been playing up for months, what i found was that the deck plugs, is connected to a 3 core.

the common earth was blue,( larger pin ) and the other two were red,(2 smaller pins) they were the 12v feeds to the lights, one deck light the other was the steaming light. (1 for each)

So it doesn't matter which wire is connected to which pin (after the earth pin is connected)? It just determines which light is controlled by which switch? (I also have a deck light/steaming light in a single fixture.)

 

[wonkywinch]

So it doesn't matter which wire is connected to which pin (after the earth pin is connected)? It just determines which light is controlled by which switch? (I also have a deck light/steaming light in a single fixture.)

When colvic987 said he had the problem "two days ago", that was in July 2010 so the issue is now 5,207 days old ;-)

 

[jsinger]

When colvic987 said he had the problem "two days ago", that was in July 2010 so the issue is now 5,207 days old ;-)

The best info I've found on Google.

 

[rogerthebodger]

When colvic987 said he had the problem "two days ago", that was in July 2010 so the issue is now 5,207 days old ;-)

Give the guy a break he is a new user of the forum and found the thread using Google

His reply "So it doesn't matter which wire is connected to which pin (after the earth pin is connected)"

seems to relate to main referring to the earth pin can differ depending on the standards in his location.

In the UK it does matter which pin which wire is connected to in the 3-pin plug.

 

[Dellquay13]

Give the guy a break he is a new user of the forum and found the thread using Google

His reply "So it doesn't matter which wire is connected to which pin (after the earth pin is connected)"

seems to relate to main referring to the earth pin can differ depending on the standards in his location.

In the UK it does matter which pin which wire is connected to in the 3-pin plug.

It’s probably one of these deck plugs, low voltage about 5a max, or maybe a plastic variant.

As mentioned earlier one of the pins is larger to key it in one way only. Some people use that large pin as the 0v (or negative) pin, and use the other two pins for each of the 12v sends, but there isn’t a electrical ‘standard’ or officially right way to wire it.
If you are using 230v mains flex, it would be good practice to cover the brown, blue and green/yellow inner insulations with black and red insulation tape or sleeving, to show which is 0v and 12v for future reference.