Electrical issues

[The Book of Sail]

During a recent survey, I received the following finding on my 2002 Hunter 356, "Under Generator power, every outlet shows reverse polarity. Ground neutral voltage is up around 31 volts. When the generator selector (circuit breaker) at the switch board is engaged the neutral and busses are supposed to be bonded together and the the neutral and ground busses ARE NOT supposed to be bonded together onboard when the selector is in the shore supplied power position." The boat has a Westerbeke 3.8KW generator installed.

Today I made measurements of the voltages at the AC Power Panels under the following conditions:

I have concerns about the fact that the polarity is inverted prior to switching on the generator breaker on the AC Panel, and that in general, the neutral to ground voltage is high and variable depending on load. I did not see negative polarity at the outlets, just a high ground to Neutral voltage.

Wondering if anyone has seen anything similar, or if this appears indicative of any issues. All the AC power loads appear to operate normally under generator power, but I do want to address this from a safety perspective..

 

[jviss]

if this appears indicative of any issues

Well, yes!
(By the way, the image you posted is not visible).
It seems the generator is wired-in incorrectly.
My understanding is that the neutral (white) and safety ground (green wire) should be tied together at the generator. If the rest of the boat is wired correctly, this will be open when the generator is disconnected, with the safety ground still connected to the engine, i.e., DC negative.
Your problem might be as simple as the neutral and line (black) being swapped at the generator.
I recommend you get a qualified marine electrician to check it out, unless you are skilled, experienced, and certain of what you are doing with electrical systems.

 

[Ken Cross]

I wonder if the wrong type generator selector is installed. Is it a single pole switch or multi-pole?
Is this boat new to you, or had recent work done in this area? If not, start looking for corrosion issues in the ground and safety ground wiring.
Ken

 

[uncledom]

There should be a relay to bond the Neutral and Ground when ever the Generator runs. This should also happen if you have a proper Inverter. It should happen within the item that is currently powering the boat with AC power as it is NEC rules to have them bonded at the source of power. There is NO polarity on AC power. Hence the name Alternating Current.

 

[uncledom]

One way to tell if there is a problem is to test between Hot to Neutral, then Hot to Ground, the Neutral to Ground, and finally each leg to what ever should be earth ground, such as the engine block, and record all the readings.

 

[dlochner]

There is NO polarity on AC power. Hence the name Alternating Current.

There are 2 was to look at this. Yes, there is no polarity in AC in the same way that DC has a positive and negative, there is polarity in how AC circuits are wired.

The hot wire (the black wire on AC circuits) should always be on the same side of the plug and circuit. The neutral (white wire) should be on the other side. This is important because at some point in an AC circuit the ground (green wire or bare wire) will be tied together. I'm more familiar with land based AC wiring than boat based, so I won't venture a guess as to where the Neutral and Ground should be connected on a boat with a generator or inverter.

If the Neutral and Hot wires are reversed, 2 wire AC devices will still run, but, the case won't be grounded that can lead to electric shocks. AC outlets are color coded, the darker connection is for the hot (black) wire and the lighter colored connection for the neutral (white) wire. Green is for the ground (bare copper in house wiring).

 

[uncledom]

The Ground and Neutral are to be bonded ( connected together) at the "source" of incoming power. This would be on the secondary side of a transformer such as an isolation transformer, at the incoming service for the marina, or when disconnected from shore power at the generator or the inverter. The OP seemed to be commenting on not being able to see the reversal with his meter and I was trying to take a simple path to explain why. The biggest issue I have heard so far is that there is a potential (voltage) between Neutral and Ground. That is an easy path to electrocution.

 

[Stu Jackson]

AC outlets are color coded, the darker connection is for the hot (black) wire and the lighter colored connection for the neutral (white) wire.

Yes, the screws in the back of receptacles are two different colors. IIRC, the larger slit in the plugs is the HOT.
Reverse Polarity:

There are three A.C. wires: black (hot), white (Neutral) and green (ground).

ON SHORE the neutral and ground are tied together. NEVER on a boat as part of the shorepower AC system. It's pretty simple. Inverters and generators should do this inside the equipment.

The AC and DC green grounds are connected on a boat.

Reverse polarity is when the HOT and NEUTRAL are reversed, usually at the dockside by, as Maine Sail has written, Darrryl & his other brother Darryl. It is rarely wrong on a boat unless the PO has snafued his own work.

Reverse polarity is measured between the neutral and ground wire ON THE BOAT with the neon glow lamps with the 25K ohm resistors. However, what they are telling you, regardless of how this is done, is that you have the HOT and NEUTRAL reversed. That's why we recommend that everyone just go down to their ACE hardware store and buy one of those simple plug-in testers. That avoids any confusion about RP. F'rinstance, in our boat we have THREE RP lights, two are indicating NORMAL and means everything is OK. When the third light comes on: PROBLEM!!! Confuses some people. SOME FOLKS ONLY HAVE ONE LIGHT SO WHEN IT COMES ON IT MEANS a PROBLEM.

 

[uncledom]

ON SHORE the neutral and ground are tied together. NEVER on a boat. It's pretty simple.

Not exactly true. Read my previous post. I'm sure I was hitting send just before you and you didn't have the info.

 

[jviss]

There is NO polarity on AC power.

That's certainly true, but the expression "reversed polarity" is commonly used to mean that the neutral and line are swapped.

 

[jviss]

he larger slit in the plugs is the HOT.

Whoops, that's incorrect. The larger slit is neutral. Smaller one is "hot," or line.

 

[Ron20324]

This thread has more holes than a wheel of Swiss cheese.

 

[Bill Roosa]

check your ground at the generator. It may just be loose or corroded.
As for reverse "polarity" aka hot and neutral reversed, about the only thing that can cause that is the selector switch. The genset has to have a hot, neutral, and ground. Make sure the connections are correct at the genset, the selector switch, and then to the AC buss

 

[Bill Roosa]

It is probably illuminating to pull the cover on your house breaker box. You will see ALL the white and ground wires connected together "at the source" This happens for shore power at the breaker box for the dock and not on the boat. For all sea power sources the neutral and ground are also connected "at the source" aka in the inverter or genset.
and if you don't understand AC electrical you should get a pro. even 20 amp service can light a fire pretty fast or worse kill you. My dad was an electrician and the safety rule he drilled into me was "always keep one hand in your pocket when working on live wires." keeps the current from crossing your heart.

 

[LloydB]

You are at the point where what you don't know can kill you. Buy two hours from a marine electrician to find out what is wrong. Also purchase a reverse polarity tester and ask them how to use it in the future when needed. Save a zinc and a zap for thirty bucks if at a new port.