Earthing a generator

[All_at_Sea]

I'm installing a Fischer Panda generator and want to know if l need to earth the unit, and if so where to?

The unit is going in a aft deck locker, so not near the main engine. If l need to l could take a wire to the stern gear, but do l need to?

 

[Lon nan Gruagach]

First and foremost is to make sure that the generator earth wire is connected to your 240V distribution earth wire.
Since the generator has 240Vac inside it then its case must be connected to its earth wire.
You should(must) also check that the neutral wire is connected to the earth wire at the generator.

Now, since you have just made an earth neutral short you must make sure that generator neutral and shore power neutral cannot be connected so use a 2 pole change over switch or equivalent on the 240V selector (and be darned sure it is break before make)


After that you are good to go with what ever earthing system you want to use, totally isolated or with galvanic isolator, bond everything together or isolate them all.

 

[rogerthebodger]

I'm installing a Fischer Panda generator and want to know if l need to earth the unit, and if so where to?

The unit is going in a aft deck locker, so not near the main engine. If l need to l could take a wire to the stern gear, but do l need to?

No point in connecting any part of the generator chassis to ground but you need to connect the mains neutral generator connection to the system mains earth if you have a permanent mains electrical installation which include a RCD.

This has been discussed several times in the past so try to do a forum search.

 

[All_at_Sea]

I'm putting in a crossover switch into the system and the mains circuit has a rcd/breaker in line so the genny current will have to go through this as well when turned on.

 

[superheat6k]

All power sources should be earthed with the neutral connected to earth at the source.

For shore power the earth - neutral link occurs at the shore supply transformer. If you have a generator the earth should connect to the neutral BEFORE the isolating breaker from the generator, so when the generator is not connected and providing the supply the earth link is disconnected from the rest of the neutral by the neutral line isolation.

The RCD should sit after the isolation / selector breaker so it protects regardless of supply - shore / inverter / generator.

As to whether you connect the 240v earth to your bonding is a subject of some discussion. I am of the camp that feels it should be connected, but many on here do not. If you do bond I would take it to the same common connection point used by the rest of the 240volt system, e.g the engine block. I would run a piece of 4 or 6mm2 cable for this purpose, and separate to the starter motor negative.

Finally and of significant importance is that the generator should be isolated in such a way that a full disconnection of shore power and / or inverter supply occurs before the generator supplies the AC power. It is absolutely essential that the generator must not try to connect to an AC supply supplied by another source. If your generator were to connect to a live AC source it would almost certainly be out of phase synchronisation and speed and would instantly wreck the generator and possibly damage the supply wiring at the same time.

 

[MengWalton]

Take it from me who works on ships with D/G's of 25MW make sure you don't connect the generator to the busbars(system) whilst shorepower is still on as it will be out of phase and well it will get intresting........ Make sure your switch is break before make

 

[nigelmercier]

I have found the most simple way is to totally isolate the generator, treat the boat as the appliance, and simply plug the standard output into the shore power inlet when needed. No joining of earth or neutral required.

 

[Lon nan Gruagach]

I have found the most simple way is to totally isolate the generator, treat the boat as the appliance, and simply plug the standard output into the shore power inlet when needed. No joining of earth or neutral required.

I think you are referring to generators that are fitted with standard sockets. hard wired ones offer the link as an option (some supply configurations use it differently)

 

[All_at_Sea]

I have found the most simple way is to totally isolate the generator, treat the boat as the appliance, and simply plug the standard output into the shore power inlet when needed. No joining of earth or neutral required.

In a way that is what l have done. I have taken the wire from the shore power 'in' to a crossover switch. The original input from this now becomes the common feed to the ships supply and l have added the generator to the other input on the crossover. HOWEVER within the crossover box all the earths are connected together and l wonder if this is the bit that people are worried about? So far l haven't connected the genny yet so now is the time to get the wiring right.
In wiring the genny to the crossover l have a junction box so l could easily connect the genny earth to the neutral here if that is what is required, but like Nigel l was trying to keep things simple.....

 

[rogerthebodger]

First and foremost is to make sure that the generator earth wire is connected to your 240V distribution earth wire.
Since the generator has 240Vac inside it then its case must be connected to its earth wire.

I have a problem with this as if there is a short inside the generator where the 240VAC live shorts to the case the whole earthing system could be live and a high current would flow in the earth wire only and thus not through the live and neutral wires and there through no protection device RCD overload or fuse.

In my generator / inverter setup I do not have any generator or inverter case connection to system earth which I still am not quite happy with.
On my generator I have been trying to think of a way to shut dawn the generator if there is an internal short in the generator maybe by using a current relay in the earthing line to kill the generator engine in some way.

You should(must) also check that the neutral wire is connected to the earth wire at the generator.

Non of my off the shelf generators including my Honda suitcase generator has that as supplied which IMHO is a fundamental design fault.

 

[RichardS]

Non of my off the shelf generators including my Honda suitcase generator has that as supplied which IMHO is a fundamental design fault.

Why would that be necessary if the generator has a plastic case and plastic controls?

Richard

 

[rogerthebodger]

Why would that be necessary if the generator has a plastic case and plastic controls?

Richard

Its only my suitcase generator that has a plastic case the frame is steel and the recoil starter is not all plastic the choke lever is metal as is the fuel tap.

Both my other generators have the normal steel tubular frame.

But anyway there should be a way for any domestic power supply device (generator / inverter) to be shut down is an electrical fault occurs. The generally do have a shutdown for low engine oil but not for generator electrical faults.

 

[nigelmercier]

... within the crossover box all the earths are connected together ...

I don't see a problem with that.

However I do see a problem connecting earth to neutral in the absence of a real protective earth bond, so for those who insist on this please enlighten me.

 

[rogerthebodger]

I don't see a problem with that.

However I do see a problem connecting earth to neutral in the absence of a real protective earth bond, so for those who insist on this please enlighten me.

IMHO the neutral to earth connection at the power supply device is to provide an alternate path for any leakage current from the live circuit to return back to the neutral without passing through the RCD thus there would be an imbalance in the currents flowing in the 2 connection to the RCD thus the RCD would trip.

Generally a real protective earth bond is to provide and alternate path for the leakage to flow back to the power supply device incase the wired earth is compromised. If anyone is standing on a non insulated ground and the wired earth is compromised the leakage current would flow through the ground to the earth spike and thus back to neutral on the power supply.

Now in a GRP boat you are standing on insulated surface and if there is no earth bonding ther cannot be any leakage current through the GRP structure back to the neutral/earth connection.

On a metal boat like mine the situation is quite different as my hull is conductive, even my pushpit and pulpit are electrically connected to the hull. It only my engine that is isolated from the steel hull

Pls tell me if that answers your question?

 

[nigelmercier]

IMHO the neutral to earth connection at the power supply device is to provide an alternate path for any leakage current from the live circuit to return back to the neutral ...

But one would hope this path was already incorporated in the generator without the need for an inelegant solution.

 

[rogerthebodger]

But one would hope this path was already incorporated in the generator without the need for an inelegant solution.

Yes you are correct but non of the 3 portable petrol generators I have don't have an earth to neutral connection so end up being a floating supply and if no E to N connection there would be no RCD protection.
It would be interesting if the more modern inverter generators have this and or RCD's fitted to the generator control panel instead of just current overloads like mine.

 

[Lon nan Gruagach]

I have a problem with this as if there is a short inside the generator where the 240VAC live shorts to the case the whole earthing system could be live and a high current would flow in the earth wire only and thus not through the live and neutral wires and there through no protection device RCD overload or fuse.

In my generator / inverter setup I do not have any generator or inverter case connection to system earth which I still am not quite happy with.
On my generator I have been trying to think of a way to shut dawn the generator if there is an internal short in the generator maybe by using a current relay in the earthing line to kill the generator engine in some way.


Non of my off the shelf generators including my Honda suitcase generator has that as supplied which IMHO is a fundamental design fault.

If the fault is within the generator then, without earthing, the case will become live, if the case is earthed then the high currents will remain inside the case and externally earth will remain earth, neutral may become a weak opposite of live and live will brown-out. Sure, some generators have no protection against internal faults and they will die a horrible smoky death.

 

[nigelmercier]

Yes you are correct but non of the 3 portable petrol generators I have don't have an earth to neutral connection so end up being a floating supply ...

Just like an isolating transformer then.

Job done.

 

[VicS]

Just like an isolating transformer then.

Job done.

One conductor should be bonded, to create a neutral, to the boats internal eearthing system , which will inclde the DC negative unless the DC system is isolated and the hull of a metal hulled vessel.

This daigram show the genrl idea of earth bonding the output of a generators and the secodary winding of an aisolating transfomer

Anyone installing an AC system or adding istems such as a generator or inverter should consult ISO 13297-2014

 

[Lon nan Gruagach]

One conductor should be bonded, to create a neutral, to the boats internal eearthing system , which will inclde the DC negative unless the DC system is isolated and the hull of a metal hulled vessel.

This daigram show the genrl idea of earth bonding the output of a generators and the secodary winding of an aisolating transfomer

Anyone installing an AC system or adding istems such as a generator or inverter should consult ISO 13297-2014

Are all the little black dots GIs?