Generator ground

[superheat6k]

Whereas the 'Neutral' conductor should be tied to Earth at the position of generation, ideally with the casing of the generator, with some portable generators the manufacturers connect the ground / earth to a centre tap on the generator windings.

This is done to reduce the electric shock risk to half the standard output voltage.

However, this means such a generator no longer has a 'Neutral' and 'Live', but rather two half potential 'Lives'. If the one nominated as 'Neutral' is then connected to Earth then half the generator winding will have become short circuited, which the generator will not like and the output voltage from the other nominal 'Live' side will drop to ~ half the normal output voltage.

It may not be easy to find out if a particular generator has a centre tapped earth, especially with a Inverter based generator, so sometimes it is better to cut the provided earth cable internal link entirely (if this is accessible) and then ground out the neutral to chassis earth without the original internal earth link remaining, the connected wire once cut should be properly insulated.

If the internal earth link wire is not accessible then this generator should not be used on a boat, where an earth bonded neutral is absolutely necessary, except perhaps for dedicated direct plugged in power tools, or similar.

 

[jdc]

Grounding the centre tap of a generator, giving 115V between live and around and 115V between neutral and ground, would be unusual, and I _think_ (but don't know for sure, probably PaulRainbow does) would contravene the UK and EU regs: ISO 13297 / 2020 is the applicable standard under the EU recreational craft directive as well as the UKCA equivalent, and it foresees connection of neutral to ground, and insists that it be done at the generator in most cases, see:

6.8 The neutral conductor shall be grounded (earthed) only at the source of power, i.e. at the onboard generator, the secondary windings of the isolation or polarization transformer, the shore power connection or inverter. The shore power neutral shall be grounded (earthed) through the shore power cable and shall not be grounded (earthed) on board the craft or:

a) for systems using an isolation transformer or polarization transformer, both the generator or inverter neutral and the transformer secondary neutrals may be grounded at the AC main grounding bus instead of at the generator, inverter, or transformer secondaries;

b) for systems using an isolation transformer or polarization transformer, or no shore power provision, both the generator or inverter neutral and the transformer secondary neutrals may be ungrounded provided double-pole protection and switching is installed.

In that section it mentions grounded neutral system (TN-S) and an isolated 230V system (IT), but doesn't seem to envisage a centre tapped system. Superheat6k is right to warn one off such a system!

 

[Refueler]

What you're saying seems contrary to what the manufacturer says in the manual

My 3kw Handy Gen has the ground bolt in the frame and manual says about connecting that bolt to a grounding stake into the actual ground. I read it and I ask myself where is the continuity ... if the ground around the Genny where its stood does not complete a circuit - what use is it ?

But on another item .. the summer guest mobile (which came from UK) down near the boats is wired as per UK ... in accordance with the standards for Caravan Parks / Mobile Home sites ... the metal frame of the mobile is connected to the Earth of the electrical supply. This caused a bit of a stir here as then the frame was found to be carrying a voltage .. not enough to be a problem - but it was there. My pal - who owns and runs an Electrical Installation Company came and checked it out ... he spent some years working in UK before so he knew what to look for ... the solution was a 2m iron rod driven into the ground behind the mobile and frame connected to it.

There's a reason its nicknamed : Electrickery !!

 

[rogerthebodger]

The OP spoke about a generator for his boat not a land insulation.

Most generator including one of mine used for load sheading are used in a land installation where the spec specifies a ground spike at the supply substation and at the residence where the power is consumed.

A GRP boats and cars and camper vans are isolated from the surrounding by the GRP hull and the rubber tires

So, there is a difference

This discussion is quite interesting

SmartGauge Electronics - To bond or not to bond - Hulls and electrical earthing

Ship grounding - How earthing works for different types of ships?

earthing systems on ships

 

[billskip]

Grounding the centre tap of a generator, giving 115V between live and around and 115V between neutral and ground, would be unusual,

This is normal practice when supply is 110v.per phase and 2 phase 220v supply is required in some countries. It creates a problem when 220v voltage protection units are required as they get standard imported 220v l/n units, when they then "trip" one side of your appliance is still "live" at 110v.
Also this causes a problem when 2 or 3 phase is distributed in a building it can and usually does feed 110v back into other phase through light bulb etc.
110/220v generators can be wired with centre tap.

 

[PaulRainbow]

The OP spoke about a generator for his boat not a land insulation.

Most generator including one of mine used for load sheading are used in a land installation where the spec specifies a ground spike at the supply substation and at the residence where the power is consumed.

A GRP boats and cars and camper vans are isolated from the surrounding by the GRP hull and the rubber tires

So, there is a difference

This discussion is quite interesting

SmartGauge Electronics - To bond or not to bond - Hulls and electrical earthing

Ship grounding - How earthing works for different types of ships?

earthing systems on ships

We don't have ships, we have boats.

 

[PaulRainbow]

Ref #21 and #22 and centre tapped inverters or generators....

Current standards (as pointed out) require the neutral and Earth eb bonded, they also require the Earth circuit to be "grounded" as in connected to the water. That for me means centre tapped equipment has not place onboard. I would refuse to fit such equipment. I'd also ignore suggestions of not fitting the Earth connection to the water.

As for the Honda generator that the OP is asking about, i specifically answered his question about that generator and i know that it is not centre tapped.