Hi,

Both Charles Wing and Nigel Calder allude to connecting the neutral
and ground wire of AC generators at the generator. Both authors also
show alternator generators with a centre tap at 0v and the other two
conductors at +60/120v and -60/120v (giving 120 and 240v
respectively). The 0v centre tap I think is connected to ground, but
is one of the conductor wires really connected to the ground??? Both
authors have produced diagrams with no ground/conductor connection
shown. It seems a little odd - grateful for clarification.

TVMIA

"Rob" wrote in message
om...
Hi,

Both Charles Wing and Nigel Calder allude to connecting the neutral
and ground wire of AC generators at the generator. Both authors also
show alternator generators with a centre tap at 0v and the other two
conductors at +60/120v and -60/120v (giving 120 and 240v
respectively). The 0v centre tap I think is connected to ground, but
is one of the conductor wires really connected to the ground??? Both
authors have produced diagrams with no ground/conductor connection
shown. It seems a little odd - grateful for clarification.

TVMIA

Yeah like " I can't be bothered reading books or studying, would someone
please tell me in less than 25 words all about electricity. In particular AC
theory which can't be all that complicated since there are so many
electricians doing it. Not like it's difficult like real technicians who fix
TV's and things"

--
Regards ............... Rheilly Phoull

On 26 Dec 2003 01:19:31 -0800, (Rob) wrote:

Hi,

Both Charles Wing and Nigel Calder allude to connecting the neutral
and ground wire of AC generators at the generator. Both authors also
show alternator generators with a centre tap at 0v and the other two
conductors at +60/120v and -60/120v (giving 120 and 240v
respectively). The 0v centre tap I think is connected to ground, but
is one of the conductor wires really connected to the ground??? Both
authors have produced diagrams with no ground/conductor connection
shown. It seems a little odd - grateful for clarification.

TVMIA

120/240V gensets are, at least in the USA, set up like USA's
antiquated, unstandard AC power system, just like Tesla created it.

120V-------Neutral---------120V

The two 120V are out of phase (180 degrees), so if you connect from
120 to 120 you get 240 VAC to power big items. Our National Electric
Code requires the Neutral (center tap of the transformer secondary out
on the street) be a separate wire to carry the current from ground,
even though they are both connected together at the pole. There is no
60-0-60 power, here.

However, on ships, to reduce the voltage to ground reducing shock
hazards on 120V power systems, there IS a 60-0-60 system with a
center-tap-grounded power system. I used to serve on old Navy ships
that had this system. Not sure if they still use it on new ships,
now.

So, any 120/240 genset targeted at the US/Canadian market will have a
4-wire system, two 120V phases 180 degrees out of phase, a neutral
wire to carry the current to the center-tapped windings and a separate
ground which is the case of the genset and should be hooked to the
center tap of the genset's windings at the genset ONLY.

Hope this helps

Larry W4CSC

NNNN

Yeah like " I can't be bothered reading books or studying, would someone
please tell me in less than 25 words all about electricity. In particular AC
theory which can't be all that complicated since there are so many
electricians doing it. Not like it's difficult like real technicians who fix
TV's and things"

A particularly useful contribution - and I have been reading the books
- hence the question. If you have not got anything worthwile to say
that adds to the discussion, then don't bother cluttering up the
listing with your drivel.

On Fri, 26 Dec 2003 14:09:27 GMT, Larry W4CSC wrote:

On 26 Dec 2003 01:19:31 -0800, (Rob) wrote:

Hi,

Both Charles Wing and Nigel Calder allude to connecting the neutral
and ground wire of AC generators at the generator. Both authors also
show alternator generators with a centre tap at 0v and the other two
conductors at +60/120v and -60/120v (giving 120 and 240v
respectively). The 0v centre tap I think is connected to ground, but
is one of the conductor wires really connected to the ground??? Both
authors have produced diagrams with no ground/conductor connection
shown. It seems a little odd - grateful for clarification.

TVMIA

120/240V gensets are, at least in the USA, set up like USA's
antiquated, unstandard AC power system, just like Tesla created it.

120V-------Neutral---------120V

The two 120V are out of phase (180 degrees), so if you connect from
120 to 120 you get 240 VAC to power big items. Our National Electric
Code requires the Neutral (center tap of the transformer secondary out
on the street) be a separate wire to carry the current from ground,
even though they are both connected together at the pole. There is no
60-0-60 power, here.

However, on ships, to reduce the voltage to ground reducing shock
hazards on 120V power systems, there IS a 60-0-60 system with a
center-tap-grounded power system. I used to serve on old Navy ships
that had this system. Not sure if they still use it on new ships,
now.

So, any 120/240 genset targeted at the US/Canadian market will have a
4-wire system, two 120V phases 180 degrees out of phase, a neutral
wire to carry the current to the center-tapped windings and a separate
ground which is the case of the genset and should be hooked to the
center tap of the genset's windings at the genset ONLY.

Hope this helps

Larry W4CSC

NNNN

Larry,

Being totally unfamiliar with naval systems, the question Rob asked still
remains: Is the neutral (in a 60 - 0 - 60 system) connected to one of the
60 volt legs? Is it still coded white? I'm assuming that ground is always
connected to frame or earth ground in any system.
--

Larry
email is rapp at lmr dot com

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

On Sat, 27 Dec 2003 18:15:16 GMT, Larry wrote:


Being totally unfamiliar with naval systems, the question Rob asked still
remains: Is the neutral (in a 60 - 0 - 60 system) connected to one of the
60 volt legs? Is it still coded white? I'm assuming that ground is always
connected to frame or earth ground in any system.

I'm sorry but I really don't remember. The last ship I was on with
this was USS Everglades (AD-24) completed in 1952. I was on her from
1966-1969 and I'm WAY too old to remember details back THAT far,
now....

But, as I remember doing some wiring in our calibration lab, I don't
think there was a "neutral" in that system. The 120VAC was from one
wire to another and I don't think the center tap of it was connected
to anything but ship's ground, as we didn't use the 60VAC for anything
to that center tap.

Many ships have ungrounded systems, with ground fault monitoring. Single
phase panels are used (without the neutral bus), or three phase panels (120
volt delta). All circuits use 2 pole breakers. Common ground monitor is
lights from phase to ground, if the light is out the phase is grounded.

Pete Albright,
Tampa, FL

"Larry W4CSC" wrote in message
...
On Sat, 27 Dec 2003 18:15:16 GMT, Larry wrote:


Being totally unfamiliar with naval systems, the question Rob asked
still
remains: Is the neutral (in a 60 - 0 - 60 system) connected to one of
the
60 volt legs? Is it still coded white? I'm assuming that ground is
always
connected to frame or earth ground in any system.

I'm sorry but I really don't remember. The last ship I was on with
this was USS Everglades (AD-24) completed in 1952. I was on her from
1966-1969 and I'm WAY too old to remember details back THAT far,
now....

But, as I remember doing some wiring in our calibration lab, I don't
think there was a "neutral" in that system. The 120VAC was from one
wire to another and I don't think the center tap of it was connected
to anything but ship's ground, as we didn't use the 60VAC for anything
to that center tap.

Larry W4CSC wrote:

However, on ships, to reduce the voltage to ground reducing shock
hazards on 120V power systems, there IS a 60-0-60 system with a
center-tap-grounded power system. I used to serve on old Navy ships
that had this system. Not sure if they still use it on new ships,
now.

There was never a "60-0-60 system" on ships. Nearly every ship generates
3-phase power and for hotel services requiring 120VAC the phase
transformers are wired in wye-delta providing 3 conductors each of 120
volts between any two conductors. The voltage measured to ground would
be either about 87 volts or 70 volts depending on the phase which is
measured against the ship's ground.

When 120/208 power is required the phase transformers are wired in
delta-wye with a 4th neutral conductor connected to physical ground. Any
conductor measured to ground would deliver 120 volts single phase. The
voltage between conductors is 208 volts 3-phase. This is not commonly
supplied to "hotel" services as it is preferable to reduce shock hazard
via the lack of a grounded neutral and to avoid using the hull as a
current carrying ground.

Rick

In article ,
"PeteAlbright" wrote:

Many ships have ungrounded systems, with ground fault monitoring. Single
phase panels are used (without the neutral bus), or three phase panels (120
volt delta). All circuits use 2 pole breakers. Common ground monitor is
lights from phase to ground, if the light is out the phase is grounded.

Pete Albright,
Tampa, FL

"Larry W4CSC" wrote in message
...
On Sat, 27 Dec 2003 18:15:16 GMT, Larry wrote:


Being totally unfamiliar with naval systems, the question Rob asked
still
remains: Is the neutral (in a 60 - 0 - 60 system) connected to one of
the
60 volt legs? Is it still coded white? I'm assuming that ground is
always
connected to frame or earth ground in any system.

I'm sorry but I really don't remember. The last ship I was on with
this was USS Everglades (AD-24) completed in 1952. I was on her from
1966-1969 and I'm WAY too old to remember details back THAT far,
now....

But, as I remember doing some wiring in our calibration lab, I don't
think there was a "neutral" in that system. The 120VAC was from one
wire to another and I don't think the center tap of it was connected
to anything but ship's ground, as we didn't use the 60VAC for anything
to that center tap.






Pete is correct in that some on board wiring deletes the netral to earth
bonding altogether. In this situation you loose the fault current
protection generated when there is a fault from active to conductive
case of equipment. In this instance it is absolutely imperative to have
Residual Current Devices (RCD's) or GFI in NA parlance both on the shore
power inlet and the onboard generator. I just did an electrical survey
on a boat where this was the case. BTW downunder we have 240/408
single/3 phase 50 Hz systems.

John Proctor

--
John VK3JP