Generator on Farm

[johnboy6083]

Far better to have one rod position and coupling the rods to give you the depth, rather than having 2 X 1 metre rods in 2 positions. Even better, to have the 2 rod positions each with 2 rods coupled together!!

What is important is to make absolutely sure your neutral point on the Genny is earthed via your rods, and not just bonded to the Genny frame.

When I said rods, I meant that a number of rods screwed together still constitutes one complete rod. I wouldn't advise only sinking one length.

 

[Engineer54]

When I said rods, I meant that a number of rods screwed together still constitutes one complete rod. I wouldn't advise only sinking one length.

Glad to hear that...lol!! I'm afraid i take all rods, to be these 1 metre things in the UK these day's... lol!!!

 

[Engineer54]

When I said rods, I meant that a number of rods screwed together still constitutes one complete rod. I wouldn't advise only sinking one length.

What i tend to do when supplying a TT earth for permanent and semi-permanent Genny's of a smaller size, is to position my earth rods diagonally approx a metre or so away from the the Genny mounting pad and run a 16/25mm bare copper conductor around the pad at around 50 to 60cm depth, linking the 2 rod positions.


Also, if the pad is substantual, with decent reinforcment, i'll also make arrangements to have to a section of rebar brought out of the pad and connect that to the earth ring. Or connect a short length of insulated earth conductor to the rebar prior to the concrete pour.

For larger stand-by, and prime power Genny's (750 KVA and above) the earth arrangement will be obviously be a good deal more involved but still based loosely on the above arrangement...

As i've stated before, i'm far more used to working with 3m 3/4'' earth rods, but nothing stopping anyone in the UK from coupling together 2 or 3, 5/8'' rods to get the depth, stability and decent Ra value

 

[Guybrows]

Had a look today and looks easy enough to run the cable using gurder clips to run the cable up and across along the steel frame of the milking parlor.

Going to do my cable calculations to get correct cable size.
The Generator(44kva) will be sitting on a concrete pad that has already been built and will be fixed down.
Where the generator is currently situated it has a bond from the frame to the steel structure of the building.

Am i correct in assuming that,

1. I will need to bond the frame of the generator to the steel frame as you can touch both at the same time

2. An earth spike shall be installed and connected to external earth connection on the frame of the generator and then check continuity between earth point and neutral connection at the generator.

3. Does the above then give me a pme at the cu that the generator is feeding thus i have no need for an earth spike at cu or the running of a separate earth from generator to cu, i'm guessing i should then do a ze at cu and get less than 20 ohms.

4. The cu has two supplies connected. the permanent generator that is getting moved being one and they also have a smaller generator that they use as a back up if the permanent generator goes down. Theoretically this allows for both generators to be supplying cu simultaneously. Is this allowed?

5. Does the installation need rcd protection or does it now become a pme/tncs system?

Thanks for all your help guys, really enjoying this one as its all new to me!

 

[poppypiesdad]

Can we get some piccys , when your not busy during the install


I would say that unless the two gennys can be synchronised then it would not be allowed , could be wrong ,
JAmie

 

[johnboy6083]

the genny should be bionded to any metalwork that is within reach.
The normal convention is to run a 4core cable (3ph) and an earth, or 5 single cores.
gennys may only be used together if it is possible to syncronise them together, to prevent strange voltages. If this is not possible then no, it will not be allowed.
the supply will only need RCD protection if the Ze/Zs values mean that the protective devices will not
operate within specified times.

 

[spark 68]

Theoretically this allows for both generators to be supplying cu simultaneously. Is this allowed?

Most definitely not!, they should be seperated by at least a changeover switch, or more usually by a changeover contactor/s, with the main Generator pulling in the contacts for one set (N/O) and the backup generator on the N/C set, these are often mechanically interlocked, and sometimes a timer (delay) set on the main control circuit.

It is wired this way so when the main generator is working it pulls the changeover contacts from the normally open position, and when it is not powered to let the backup genny come into play, it should be impossible for both to be connected at the same time (synchronised types aside), as you would be backfeeding either onto the dormant genny, or putting two un-synchronised supplies together.

Ps. I will do a drawing later, unless someone beats me to it

 

[Knobhead]

Running two generators in synchronous causes all kinds of problems with earthing. Only one should have the neutral connected and earthed to stop circulating currents. Get a change over switch, it will save all the problems of synchronisation unless of course you want the fun of setting up a syncroscope. Run as independent units the earths can be linked but bolted links should be put in so they can be totally isolated for testing, (which I’ve missed off the drawing. Bugger!)

View attachment 9018

 

[Guybrows]

Thanks for that drawing Tony. I thought that would be the case don't know how he's gona take that but if he doesnt like it id rather not do the job.

Im still struggling with the earthing arrangement im reading so much conflicting info and cant find anything solid.

Do I link earth neutral in the generator connection panel and run a 4 core swa to cu and have a tncs/pme system. Is the earth provided from the frame? Is that what is meant by floating earth?

Or do i have to install a earth spike and connect to the genarator. Would this mean i have to have Main rcd on cu?

Thanks

 

[Knobhead]

The best way is a solid connection from the neutral to earth. You must also earth the frame but do not rely on that as your neutral earth.

There is a lot of confusion regarding paralleled generators. Only one will have it’s neutral and earth contactors closed. This is usually the larger set.If just one generator is running it’s respective neutral and earth contactor will be closed.

Does your farmer want to run parallel sets? If he is then he’s in for trouble. Synchronising is the easy bit, load sharing, voltage and frequency control are a minefield. Hunting between set is a common problem.
View attachment 9025
It would be a good idea to fit a RCD

 

[andrew.w]

Hi, I was wondreing if anyone could help me, I installed a circit in a farm house this weekend. And when i was testing the property there was 100v live to earth and 100v neurtal to earth and 230v between live and neutral this property was supplyed by a small single phase generater oveusly then i could not test ze zs ect. i looked all over the gen and inside to find neutral earth link no joy as i dont really know what to look for. Any input to my question would be helpful thanks

 

[Knobhead]

Andrew you should have started a new thread for this, it just muddies the water for the original question.

But to your question, from what you say it could be a centre tapped generator. You need to find some information otherwise it’s pure guesswork on our part. Make, model, etc.
As a safety note, if it is centre tapped then all MCB’s and switches should be double pole.

 

[Guybrows]

He doesnt want to run paralell sets he just want one as a back up for the other so i ll fit a change over swithch.

I was thinking of running a 4core swa from main generator to change over switch.

A single earth connected to earth bolt on frame of generator going to change over switch. Neutral Earth linked in generator.

steel frame building Metal work bonded to earth bolt on frame of generator.

2 x sets of 2m earth rods connected to earth bolt on frame

This will then be a TNS?

I ll then do the same from the other generator and link the earths at consumer unit with removable bolt.

Hows this sound

Thanks a lot

 

[Knobhead]

Sounds good to me. Yes it will be TN-S.

 

[Engineer54]

He doesnt want to run paralell sets he just want one as a back up for the other so i ll fit a change over swithch.

I was thinking of running a 4core swa from main generator to change over switch.

A single earth connected to earth bolt on frame of generator going to change over switch. ......Neutral Earth linked in generator. See below

steel frame building Metal work bonded to earth bolt on frame of generator.

2 x sets of 2m earth rods connected to earth bolt on frame
No, ....connected to neutral point, then to frame Yes

This will then be a TNS?
Yes


I ll then do the same from the other generator and link the earths at consumer unit with removable bolt.
Bolts, ...separarate connections

Hows this sound

Thanks a lot

Question, ... will these genny's be located on the same pad foundation and close to each other??