reverse polarity

[josefa]

I bought a Coleman generator for my boat. When I hooked it to the external power outlet on the side of the boat and started the generator, I got a reverse polarity light on the boat battery charger breaker panel. How do I correct the reverse polarity?

[Verytricky]

First check the generator with a test plug. The three light system is simplest and easiest. Then test your ships electric system with the same tester.

Often the need for live and neutral to be in their correct place is not understood, and the thought is - as it is alternating currrent - it has no actual meaning...

But test first before you change anything!

[Frosty]

Originally Posted by Verytricky;

Often the need for live and neutral to be in their correct place is not understood, and the thought is - as it is alternating currrent - it has no actual meaning...

Please continue.

in out --in out, thats ac isnt it? alternating? whats the difference?

[Verytricky]

Originally Posted by Frosty

Please continue.

in out --in out, thats ac isnt it? alternating? whats the difference?

My point exactly. People dont understand, and dont really care.

You will find that for the majority of appliances, if you swap over live and neutral there will be little effect on the running of the appliance. However, when things go wrong with the appliance, then you can have a fatal incident. Also, there are several types of equipment designed around live being live and neutral being neutral, and this equipment will fail when you wire it incorrectly.

Live is trip switched or fused, and neutral is linked to ground. If a failure occurs, Neutral dumps to ground, and live trips or blows the fuse. Reverse this and neutral trips the fusebox, but live continues to zap the person/object.

Three way light switches for example ( like top and bottom of stairs on one switch ) incorrectly wired can bypass the fusebox in the case of electrocution unless you have a RCD fitted.

Incorrect wiring actually increases the electromagnetic field generated by the wiring - which is a harmfull thing to people and animals and stuff.

[Frosty]

Earth leakage trips are duall poll, or should be.

Here in Thailand we only--(and have always had) two pin plugs. EVERY appliance sold is two pin??

Twin and earth wire for instance is not available. Only now is earth wire Or (third wire to them) is being fitted by request.

What equipment then is polarity sensative.

[josefa]

Thank you for the answer. I noted that when the generator is running and the reverse polarity light is on, all the lights and other equipment on board operate except for the battery charger. Why is this? Are battery chargers wired to not operate with reverse polarity?

[marshmat]

Lighting is generally not sensitive to polarity.
Anything that uses a low-voltage, low-current rectifying power supply- such as laptop computers, cellphone chargers, and other portable electronics- is usually (but not always) designed so as not to be sensitive to polarity.
Most devices that utilize AC motors or heaters, have a high inductance, or modulate/change the AC waveform in any substantial way, must be connected with the correct polarity. Needless to say, this is why such devices when equipped with 2-prong plugs (in North America at least) have one fat and one skinny prong, so you can't reverse-polarize them by accident.
The only way to know for sure whether a device is polarity-sensitive is to check its manual or call the manufacturer.
A battery charger, which has a large internal step-down transformer, could very well be sensitive to polarity. If so, it may be designed to disconnect itself in the event the polarity is reversed.
The "test plug" described by verytricky is a cheap, durable and nearly foolproof device to see if it's wired incorrectly. The device looks like a fat, bulbous plug with no cord, and three coloured lights. Plug it in, it lights up, look at the label to see what error matches the colours that come up. Start at the generator plug, and work your way out from there until it reads something other than "Normal".

[Frosty]

Again everything here is 2 pin, we generally have everthing that the rest of the world has if not more, therefore I an at a loss as to what is polarity sensative.

Unless it is the American way of conecting thier negative (although its not) to earth.

Not everybody does this. Its always easy to tell if we have an American boat in the Marina!! they blow the trips.

I dont have earth on my boat and I have just about everything that there can be, generators ,smart chargers,washing machines, computers and microwave.

I wired the whole boat from srcatch. Earth on a boat is risky if the earth cable isnt working, faulty , disconected. If your earth system is fastened to your Dc bonding system (which some people recomend) you will be your neighbours earth for him.

The only argument I have ever heard of an appliance being polarity sensative was that of a battery charger. This is because it uses the posative to rectify to DC. MOST work iether way but some good ones require (but not necessary) to be sensative to polarity.

There was a mention of getting a shock from a faulty appliance. Most equipment today is plastic bodied, infact Just about every thing is,

I am told that to tell the difference between the pos and neg you need an osciliscope.

[Frosty]

To answer Josefa question.

If your talking about a portable gen that when pluged into the boat you get an incorrect polarity light on , then change the live and neutral wires in the plug from the gen.

The boat should not be conected to shore at this point!!!! If it is it should be isolated with dual pole switching equipment. (Thats just a posh word for a switch with switches live and neutral at the same time.

[marshmat]

I am told that to tell the difference between the pos and neg you need an osciliscope.

You can tell which lead is which using an ordinary multimeter. Ground one probe (either to the ground terminal of the receptacle or another grounded object, such as a metal water line) and measure the VOLTAGE at each terminal of the receptacle individually, with no load plugged in. The voltage between ground and neutral will be on the order of a few hundred millivolts (the losses in the neutral line between the receptacle and the earth point at the utility's main junction box); the voltage between ground and live will be the nominal RMS line voltage.

The neutral wire should never be connected to earth/ground on board the vessel; this connection is made only at the on-shore distribution panel.

A standard small boat AC installation, as I understand it, has three leads- hot, neutral and ground- coming through the shorepower plug. Onboard the boat, once you're past the galvanic isolation transformer, hot/live goes to the circuit breakers, neutral goes to a common bus bar, and ground goes to a separate common bus bar as well as being bonded to the hull. The hot, neutral and ground leads of the genset are connected to a dual pole switch allowing you to use genset or shorepower, but never both at once.

[Verytricky]

Originally Posted by Frosty

Unless it is the American way of conecting thier negative (although its not) to earth.

Most of the world connects the 'earth' or ground to the 'negative' pole of an AC system. This is only for safety.

Originally Posted by Frosty

I dont have earth on my boat and I have just about everything that there can be, generators ,smart chargers,washing machines, computers and microwave.

I am not very clued up on boat electrics, but....
For safety - the negative pole is thought to be ground, so designers of electrical equipment such as microwaves, washing machines etc always use the negative pole to the chassis of their equipment, so as to provide a safe failure path in the event of electricity escaping. Not having this earthed in some manner would lead you succeptable to electrocution.

[marshmat]

Most of the world connects the 'earth' or ground to the 'negative' pole of an AC system. This is only for safety.

Land-based systems commonly ground the neutral at the building's main distribution box. This is normal and correct in most terrestrial AC distribution systems.
NEVER do this on a boat- on board the boat, the neutral is treated as if it were a live wire. If the neutral is connected to the boat's ground, some of the return current will go from the boat's ground, through the water, to the shore terminal's ground. Such setups tend to kill people who swim or fall between the boat and the dock. Only at the distribution box on shore can the neutral be connected to ground.

[Verytricky]

So you have to keep them as three seperate wiring systems?

What about when you are not connected to the land wire?

I have a generator that automatically connects neutral and earth - if that is on a boat is this dangerous?

Originally Posted by Verytricky

So you have to keep them as three seperate wiring systems?
I have a generator that automatically connects neutral and earth - if that is on a boat is this dangerous?

Yes.

Have a nice read here:

http://www.kastenmarine.com/corrosion.htm

and here:

Regards
Richard

[gonzo]

110V AC is not alternating current. It is pulsating with a neutral reference. In the USA there is A and B lines,(plus and minus) which added up give 220V.