Advice on generator earthing

[Davisonp]

Hi, I am looking for some advice.

I have been asked to quote for an installation where a generator will be used to supply occasional power to an installation that is not connected to the grid.
The IET says a floating earth generator needs to be modified to connect earth and neutral if more than one item of class 1 equipment may be connected. That is not practical as the installation will probably be in use long after the generator is changed, so the earth to neutral connection needs to happen in the installation to accommodate changing generators.
My current plan is to have a 16A CEEForm inlet to the fixed installation with the neutral earth link in the CEEform inlet, but there are two ways to provide the earth neutral link.

1. Take the earth for the installation and connect it to the neutral and earth from the generator.
2. Take the earth for the installation and connect it to the neutral from the generator only.

Option 1 means that all the earth is connected to neutral from the generator through the entire installation.
Option 2 will leave the earth between the generator and CEEform inlet as supplied by the generator, and the earth from the inlet onwards with earth connected to neutral.

There is also the option of leaving the connecting of earth and neutral until the small consumer unit, but I believe the sooner the better for this link. Am I correct?

Regards

 

[GEOFF S]

Hi

What type of installation is it?

Cheers

 

[Davisonp]

Hi

What type of installation is it?

Cheers

Hi,

It’s a farm building, demolished and a rebuilt on the same footprint as a wooden insulated structure that is intended to be used a communal area for youth camps.
It has a larger meeting area and two rooms with bunk beds for up to 8 leaders.
The building is over 500 meters from the nearest electrical supply, so they want to have a generator providing a small amount of power (probably 1Kw) for recharging phones, laptops etc. for when the building is in use. No kettles or anything requiring that sort of power according to the customer.
Lighting has been requested as LED, and as 12V LED strip will run directly off a 12V car battery, I have suggested they use a couple of solar panels they already have but are not using to recharge the car battery leaving the lighting system a completely independent 12V system with no connection to the generator output.

I hope this helps

Thanks

 

[HandySparks]

Depending on how often it's used, they might be best charging phones off the battery via the usual 12V to 5V USB car chargers plus maybe a low power inverter for laptop chargers. Then they won't have to have the generator running all night just for a small charging load. Could perhaps use the generator as a backup charger for the battery in case of extended periods without sun. Many small generators have a 12V output for battery charging.

 

[Deleted member 26818]

Option1 is pointless.
Use option2.

 

[davesparks]

What type of generator are they planning on using? The poor thing probably won't like all that electronic loading without a bit of resistive load to ballast it.

 

[Davisonp]

What type of generator are they planning on using? The poor thing probably won't like all that electronic loading without a bit of resistive load to ballast it.

Interesting. I have not considered the type of loading. Do you have any suggestions for a suitable resistive load?
I have assumed the generator purchased would have enough headroom for it not to be a worry. Would that bypass th issue?

The client has not spoken about the actual generator. I have suggested they consider an inverter by preference, or an AVR generator as a minimum specification. I would hate to think what a fake apple charger would do with an unregulated slightly unstable power supply.

 

[davesparks]

Interesting. I have not considered the type of loading. Do you have any suggestions for a suitable resistive load?
I have assumed the generator purchased would have enough headroom for it not to be a worry. Would that bypass th issue?

The client has not spoken about the actual generator. I have suggested they consider an inverter by preference, or an AVR generator as a minimum specification. I would hate to think what a fake apple charger would do with an unregulated slightly unstable power supply.

If you aren't supplying the generator or advising on the type to get then don't worry about it, but then you also cannot know what to do with the earthing arrangements can you?

A genuine apple charger probably won't fare much better than the fake one.

 

[Davisonp]

If you aren't supplying the generator or advising on the type to get then don't worry about it, but then you also cannot know what to do with the earthing arrangements can you?

You can set up the earthing so it does not matter what type of earthing the generator has, the RCD downstream will work. You can even set it up so a floating earth generator will still be floating up to the start of the fixed installation, then you connect neutral and fixed installation earth creating a TN-C-S System.

 

[Davisonp]

A genuine apple charger probably won't fare much better than the fake one.

Interesting, I would have expected a good quality transformer to have a better tolerance.

 

[davesparks]

You can set up the earthing so it does not matter what type of earthing the generator has, the RCD downstream will work. You can even set it up so a floating earth generator will still be floating up to the start of the fixed installation, then you connect neutral and fixed installation earth creating a TN-C-S System.

It does matter what type of earthing the generator has! If someone connects a generator with an earthed centre tapped output to it or if they connect a generator with an internal N-E link then you have a problem.

 

[davesparks]

Interesting, I would have expected a good quality transformer to have a better tolerance.

Transformers will be fine with it, but electronic switchmode chargers as found in these chargers may not be.

 

[Davisonp]

It does matter what type of earthing the generator has! If someone connects a generator with an earthed centre tapped output to it or if they connect a generator with an internal N-E link then you have a problem.

Sorry, I do not know what a “earthed centre tapped output” is, however I still struggle to understand how this will affect the installation as the generator earthing stops at the Ceeform connector into the installation, and from there, it is only the live and neutral of the generator that continue into the installation, the neutral being split to provide an earth before the consumer unit.

 

[Deleted member 26818]

The whole point of this exercise, is to provide an earth for the generator.
If the generator already has an earth, then you don't need to provide one.
Hence my earlier post, that option1 is pointless.

 

[Davisonp]

The whole point of this exercise, is to provide an earth for the generator.
If the generator already has an earth, then you don't need to provide one.
Hence my earlier post, that option1 is pointless.

I agree, the more the discussion goes on the more it appears option 2 is the only way forward, especially as it now appears option 1 may cause significant problems to some design of generator.

I am always keen to understand fully and learn from more experienced electricians. I hope to understand the problem Davesparks sees with generator earthing.

 

[Davisonp]

Sorry, I do not know what a “earthed centre tapped output” is, however I still struggle to understand how this will affect the installation as the generator earthing stops at the Ceeform connector into the installation, and from there, it is only the live and neutral of the generator that continue into the installation, the neutral being split to provide an earth before the consumer unit.

Actually, thinking about “earthed centre tapped output” this morning (a slow week for work) I suspect this may be what I have read about known as “V-O-V” generators, and those should not be used for domestic standby or similar installations. My understanding is that in V-O-V generators, the neutral actually has potential, and is NOT tied to 0v like a normal star point. If that is the case, then regular RCD’s will not work and the installation will not be suitably protected.
I would think an inverter generator will not have this output configuration, but I do not know if AVR output generators may still be V-O-V. I believe the clients need to confirm in writing that the wiring of the generator they buy is not a V-O-V configuration before purchase.