There are some simple rules to follow. The only problem is they may be
difficult to implement in some cases.

Rule #1 For safety reasons, all AC systems need to have the neutral and
ground tied together.

Rule #2 The neutral and ground must be tied together at ONLY one place.

Rule #3 If you are connected to shore power, without an isolation
transformer in your vessel, the neutral and ground will be tied together at
the shore-side service panel.

Rule #4 If you are connected to shore power, as in rule 3, you MUST NOT
have the neutral and ground connected together aboard your vessel.

Rule #5 If you have an AC generator, of any voltage, the neutral and ground
should be connected together at the generator.

Rule #6 If you have a true isolation transformer on board with the shore
power connected to the input and the output feeding the loads on your
vessel, then you have created a 'separately derived system'. In this case,
you would connect the neutral output of the transformer to the vessel ground
to satisfy Rule #1.

Notice Rule #4 says you must not have neutral connected to ground aboard
your vessel and Rule #5 says they should be connected together. This is
where it gets tricky. The easiest way to not break either rule is to have a
two-pole circuit breaker for the shore power and another one for the
generator. Each of these breakers disconnects the 120 volt hot lead AND the
neutral lead from it's source. These breakers must be mounted together with
a mechanical slide that will only allow one of the breakers to be ON at a
time. The output of these breakers supply the hot and neutral to all
on-board loads. By only having one breaker ON at a time you keep the
grounded neutrals apart and satisfy all the rules. An added benefit is you
also keep shore power and your generator output separate. If your shore
power is 120/240 volt and your generator is the same, then the two breakers
would be three-pole units. Each breaker would disconnect both hot leads and
the neutral from it's source.

If you have an inverter/charger and a generator on board then the whole
thing gets a lot more complicated. You still have to follow all the above
rules. There are various ways to do this, some simple, and some complicated.
Trace Engineering, now Zantec, will send you a relay switching diagram if
you ask for it.

If your single-phase generator is set up to put out two voltages, such as
120/240 volts, then the zero volt center tap IS the neutral and the only
lead tied to ground. If a single-phase generator is set up to produce only a
120 volt output then the neutral is the zero volt output and again is the
only wire connected to ground.

If you have a three-phase generator, one of the output leads will be
connected to ground. If a three-phase generator has a neutral output, it is
connected to ground. If, and only if, a three phase generator is wired so as
to NOT have a neutral output, then any ONE of the hot legs is grounded. This
is the ONLY time a hot wire would be grounded. This is a very rare type of
connection and would always be designed by an experienced marine electrical
engineer.

Most of my experience is with shore-based heavy industrial electrical
systems, process control systems, and remote off-grid power systems. I have
never seen a 60-0-60 volt generator. Nor have I seen equipment that is
designed for 60 volts AC. I have seen generators of 120-0-120 volt and three
phase generators of various higher voltages. My Northern Lights 5.5Kw marine
generator can be wired to provide either a single 120 volt two wire output
or 120/240 volt three wire output. Perhaps our questioner meant a 60 Hz 120
volt system where 60 refers to the frequency of the alternating current and
120 refers to the voltage.

Rusty