Wiring A 3 Pole 12v Switch

[fishfoxey]

I am looking to wire an on off switch into the 12v supply on my fridge ( to stop me accidentally leaving it on ). The switch is a 3 pole switch , can someone please have a look at the attached pic and confirm if this is the correct way to wire it in . Thx

[Vaughan]

Short answer - No!

 It looks as though you have a SPDT switch (single pole double throw) so you only need one of the throws.

The black wire is the return, and does not connect to the switch.

The best way is to test the switch with an ohm-meter to see what happens, but you can't do any harm, with a DC circuit!

Just try out the terminal positions until you find one that works.

 

An electric fridge will cut off automatically when it gets below 12 volts, in order to protect its motor.

[gancanny]

totally agree with vaughan,    i would like to add, going off a problem i had with the same type of switch,

 one of the outer terminals has a very fine wire which is only there to power the tiny light in the switch, it is not heavy enough to carry the power your fridge needs,  make sure you get the correct terminal

[fishfoxey]

26 minutes ago, Vaughan said:

Short answer - No!

 It looks as though you have a SPDT switch (single pole double throw) so you only need one of the throws.

The black wire is the return, and does not connect to the switch.

The best way is to test the switch with an ohm-meter to see what happens, but you can't do any harm, with a DC circuit!

Just try out the terminal positions until you find one that works.

 

An electric fridge will cut off automatically when it gets below 12 volts, in order to protect its motor.

Thanks , more complicated than I thought then lol

[Oddfellow]

Whichever way you look at it, that's wrong, sorry. 

You only need to switch the positive or negative line. Only one cable runs through the switch. Your diagram will generate an immediate short which, if there's no fuse, will burn the cables out quickly and cause a fire in the worst possible case. 

If you have no fuse in the circuit, you absolutely need one. And fridges have a big load requirement in general, so ensure that your switch and all cables are more than adequate to carry that load else you may have many other problems. The biggest issue with electric fridges is poor cabling which can't handle the current draw which causes the fridge to not work properly. 

Cables should be crimped and not soldered and poor joints will cause failures. 

If you're not sure, get a professional to do it. 

[fishfoxey]

Thanks, although I am only looking at doing it myself as seems difficult to find available marine electricians currently 

[WherryNice]

Do you have a picture of the switch? Show the terminals on it if possible as there are different types. As already said you only need to switch either the live or the earth not both(I would do the live personally). 

I would imagine that most boatyards could tackle this for you btw.

[Oddfellow]

19 minutes ago, fishfoxey said:

Thanks, although I am only looking at doing it myself as seems difficult to find available marine electricians currently 

I'd say you need to be careful then and really understand what you're doing before you cut any cable. If you don't have the proper crimp tool, don't do it and also make sure you have the proper sized crimp terminals as well. If you have to remove strands from the wire or double the wire up to fit a terminal, it's the wrong size and may cause further problems down the line. 

I've seen some truly awful wiring done in my time, some down-right dangerous. People often think that 12v isn't dangerous and that's true only to the point of not getting a big shock off of it in certain circumstances. The danger lurks in bad cable, switch and connection choice and festers over time, growing with every new engine vibration. 

Incidentally, who installed a fridge without an external switch anyway? Very bad practice.

[Meantime]

Definitely not the right way to wire the switch up, but going back to basics you say;

16 hours ago, fishfoxey said:

( to stop me accidentally leaving it on ).

Most fridges have an off switch as part of the temperature control. If you turn it fully one way it will normally click off. Surely adding another switch isn't going to stop you from forgetting to turn the fridge off? However that leaves me to think that your worried about leaving the fridge on when you leave the boat for a long period as in when you go home. Surely you have a main battery isolator and you remove the key, or turn this off when leaving the boat for long periods? and the fridge should be wired after the battery isolator so that it is also turned off when you leave the boat?

Apart from other stuff I might do when leaving my boat to go home, I have the rule off six. I have four battery isolators which all get the key removed, turn the gas off and close the raw water seacock. Other things might get done depending on the time of year and how long I'm intending to leave the boat, but those six things are the absolute safe minimum when going home from the boat.

52 minutes ago, WherryNice said:

As already said you only need to switch either the live or the earth not both

I would never switch the neutral and never the earth which in effect are one and the same thing. The back of most fridges is encased in metal which will be connected to the negative of the fridge. If you switch the negative, you only need any other piece of earthed or negative metal or wire to touch the chassis of the fridge and the fridge is turned back on again.

[Oddfellow]

21 minutes ago, Meantime said:

 

I would never switch the neutral and never the earth which in effect are one and the same thing. The back of most fridges is encased in metal which will be connected to the negative of the fridge. If you switch the negative, you only need any other piece of earthed or negative metal or wire to touch the chassis of the fridge and the fridge is turned back on again.

Can we please use the correct terminology. There is no earth or neutral line on your boat's low-voltage DC system. These terms relate primarily to AC mains in this context and must not be confused and should not be interchanged. 

The DC system has Positive and Negative; possibly, hopefully,  a ground though this isn't as common as it perhaps should be and can be very complicated.  

In a car, we might consider that we have a positive or negative 'earth' because the car is made of metal, we can use the whole of the vehicle to conduct the negative of the power circuit. On the vast majority of boats, this will not be done. Positive and Negative are carried in their own cable conductors. Sadly, the use of the word "earth" is technically incorrect again. 

This brings me to the point of accidentally turning the fridge back on by connecting a negative piece of metal to the chassis if you're switching the neutral line rather than the positive. Given that there should not be any stray cables laying around anyway, the chances of this are low. Yes, electrics are all about "potential", but it's perfectly legitimate to fuse and switch either the negative or positive lines. Generally, we consider the that we should only do this on the positive because we consider this to be the power "feed" or "supply". Again, this is technically incorrect. Ions actually travel from the negative terminal of the battery to the positive terminal in a circuit and not the other way which is how we generally think of it. In practice, it make little or no difference. What you need to ensure is that there is a "standard" across the whole of the DC circuits so that confusion isn't introduced when you have to troubleshoot an issue.  

As a point of note, I hold a British Marine Electrical Technician (BMET) certificate.   

[Oddfellow]

59 minutes ago, Oddfellow said:

This brings me to the point of accidentally turning the fridge back on by connecting a negative piece of metal to the chassis if you're switching the neutral line rather than the positive. Given that there should not be any stray cables laying around anyway, 

See, even I made the same mistake here. Negative not neutral. 

[floydraser]

Just my two pen'orth: Have you considered fitting a fused panel with all the switches together so you switch them off at the same place? 

The 140 miles between my boat and I is a motivator for a few memory aids due to the consequences of forgetting something. I always use a printed sheet and when leaving, go through it and say out loud what I'm doing, pilot style.

Forecabin: Close hatch, lights off, tidy up. Galley: Gas off, water heater off, louvres closed, etc. (fridge switch is in a cupboard on the afore mentioned panel). Lastly as I close the door: "Behave yourself and I'll see you later".

[Oddfellow]

3 minutes ago, floydraser said:

Just my two pen'orth: Have you considered fitting a fused panel with all the switches together so you switch them off at the same place? 

I would never advocate merging or combining fuse/switch panels. If you already have such a panel, great, but never add one if you already have a fuse panel elsewhere for the same reason it's bad practice to add a fuse hidden away behind, say, a fridge. whilst you have another fuse panel somewhere else - when there's a fault, you have to trace everything and a long-forgotten fuse behind something will make that process hard. Keep all things alike in the same place. All fuse panels together; all main circuit switches together. 

Also, as I said earlier, a fridge needs a decent current and some fuse panels won't have switches capable of the load. One of the best ways to switch such a device is with a relay where you let the relay deal with the heavy load and use a low-amperage switch to energise the relay. 

There are many dos and don't to marine electrics but mostly in terms of safety. Most boat owners have just about enough knowledge to rig something to make it work but with little regard to safety, long-term operation and troubleshooting. It's not dangerous 'cos it's only 12v, right? Have you ever seen cable insulation melt because some tool has put in a big fuse because the right sized one kept blowing? 

 

 

[floydraser]

33 minutes ago, Oddfellow said:

I would never advocate merging or combining fuse/switch panels. If you already have such a panel, great, but never add one if you already have a fuse panel elsewhere for the same reason it's bad practice to add a fuse hidden away behind, say, a fridge. whilst you have another fuse panel somewhere else - when there's a fault, you have to trace everything and a long-forgotten fuse behind something will make that process hard. Keep all things alike in the same place. All fuse panels together; all main circuit switches together. 

Also, as I said earlier, a fridge needs a decent current and some fuse panels won't have switches capable of the load. One of the best ways to switch such a device is with a relay where you let the relay deal with the heavy load and use a low-amperage switch to energise the relay. 

There are many dos and don't to marine electrics but mostly in terms of safety. Most boat owners have just about enough knowledge to rig something to make it work but with little regard to safety, long-term operation and troubleshooting. It's not dangerous 'cos it's only 12v, right? Have you ever seen cable insulation melt because some tool has put in a big fuse because the right sized one kept blowing? 

 

 

I assumed the OP doesn't have a panel fitted or the original question would have been relating to it.

I still maintain it's a good idea not to have main switches dotted all around the boat where one or two could easily be forgotten about. So we would need a fused switch panel that does have switches rated high enough to handle anything likely to be fitted to a boat. Just need to check the specifications before we buy but I would think it's hard to find one which wouldn't handle a fridge.

[grendel]

1 hour ago, Oddfellow said:

I would never advocate merging or combining fuse/switch panels. If you already have such a panel, great, but never add one if you already have a fuse panel elsewhere for the same reason it's bad practice to add a fuse hidden away behind, say, a fridge. whilst you have another fuse panel somewhere else - when there's a fault, you have to trace everything and a long-forgotten fuse behind something will make that process hard. Keep all things alike in the same place. All fuse panels together; all main circuit switches together. 

which is why Water Rail will be getting a rewire in the not too distant future, the wiring is all over the place, the switch for the fridge is at the helm, the switch for the inverter is by the fridge, only half of the wiring is labelled, we have lamps and fittings and switches that no longer do anything, and as dave said, the stupid battery isolator that potentially allows you to flatten all the batteries at the same time,

[annv]

Hi Foxey Just to add what Vaughan said use only 50 amp wire, use crimp spade connectors or screw connectors dip bare ends of wire in Vaseline to stop corrosion problems before crimping/screwing, the switch needs to be rated at 25/30 amps or more, the wiring should go straight from battery switch via a fuse to the fridge, only switch the live pos wire from supply, fridges are very sensitive to low battery volts. John 

[grendel]

26 minutes ago, floydraser said:

So we would need a fused switch panel that does have switches rated high enough to handle anything likely to be fitted to a boat

nowadays easier to have and fit the correct rating of circuit breaker, nothing worse than having a fuse blow and not be able to find the correct replacement (which is when a bigger size will be used.)

[floydraser]

7 minutes ago, grendel said:

nowadays easier to have and fit the correct rating of circuit breaker, nothing worse than having a fuse blow and not be able to find the correct replacement (which is when a bigger size will be used.)

Of course, sorry, I'm a bit behind the times!

[WherryNice]

3 hours ago, Oddfellow said:

Can we please use the correct terminology. There is no earth or neutral line on your boat's low-voltage DC system. These terms relate primarily to AC mains in this context and must not be confused and should not be interchanged. 

The DC system has Positive and Negative; possibly, hopefully,  a ground though this isn't as common as it perhaps should be and can be very complicated.  

In a car, we might consider that we have a positive or negative 'earth' because the car is made of metal, we can use the whole of the vehicle to conduct the negative of the power circuit. On the vast majority of boats, this will not be done. Positive and Negative are carried in their own cable conductors. Sadly, the use of the word "earth" is technically incorrect again. 

Ah, sorry my mistake, here in my corner of the motor trade we say Earth or Ground rather than negative but I take the point and will use negative on boats in future

[Oddfellow]

33 minutes ago, annv said:

Hi Foxey Just to add what Vaughan said use only 50 amp wire, use crimp spade connectors or screw connectors dip bare ends of wire in Vaseline to stop corrosion problems before crimping/screwing, the switch needs to be rated at 25/30 amps or more, the wiring should go straight from battery switch via a fuse to the fridge, only switch the live pos wire from supply, fridges are very sensitive to low battery volts. John 

Screw connectors should not be used to create electrical connections on boats. It's part of the wiring regs in the BMET scheme. They damage the stranded wire, cause pinch points that vibrations then break.  Additionally, very few are remotely suitable for damp marine environments and corrode horribly over time resulting in poor connections and a total inability to disassemble without just cutting the wires. 

 

[annv]

Hi That's why i use Vaseline and many boats only have screw connections.John

[Oddfellow]

27 minutes ago, annv said:

Hi That's why i use Vaseline and many boats only have screw connections.John

Vasseline will not stop damage to the cables.
This is the principal reason these types of terminal blocks should not be used.  Just because "most" boats only have screw connectors does not make it right. I would argue "most" is inaccurate too. Boats from the 70s and 80s would commonly have screw terminal blocks. By the 90s, practices were changing. I removed many of these blocks from fleet when time allowed as I knew how difficult fault finding could be with them. 

You can buy terminal blocks that have a crush plate in them so that pressure is applied more evenly to the cable than just a screw base, but these aren't decent substitute for a good crimp. 

The best crimp terminals are the uninsulated ones with a separate boot. Insulated ones are all too oven badly crimped and come loose. There's also some absolutely awful, cheap nasty insulated crimp terms out there that I wouldn't dream of using. 

Like most such things, a little knowledge can get you some of the way but doing it properly is where properly trained and experienced pros are needed. 

 

[rightsaidfred]

This is not a subject I would normally get involved in as I am not technically proficient but before we get to involved in semantics lets not forget the majority of broads boats predate most regulations and very little was ever standard.

Fred

[gancanny]

i would bet the OP did not expect this responce to his question  

[Oddfellow]

8 minutes ago, rightsaidfred said:

This is not a subject I would normally get involved in as I am not technically proficient but before we get to involved in semantics lets not forget the majority of broads boats predate most regulations and very little was ever standard.

Fred

There are no regulations that are enforceable other than the BSS which is pretty pants for electrical safety. This is about best practices using the knowledge that we have today and not just doing things as they did 20/50 years ago because it worked then.

If we can justifiably say that, for instance, screw terminal blocks should not be used to terminate cables because we know that it damages them, would it not be better to use terminals that we know are substantially better and ultimately safer?

Of course, anyone can do anything they like on their boat and see whether it passes a BSS next time or causes damage in the first place. As someone who holds a marine electrical installation certificate, I felt it was better to counter some of the advice given here by people who aren't professional in these matters.