3 phase 70 KVA generator

[Matt Crunden]

Hello

Does anyone know about installation of generators. I been asked to price for a 70 KVA gererator on a domestic property (MAD) and need to know more about it.

I have done a install before when I use to work for a company so I do understand that there is a change over switch which is mounted next to the main distrubution board which is linked to generator via control wiring.

I feel a little lost about earthing. Will the generator need to supply its own earth rod? as it is a TNCS system on the property

I understand there is BS50438 but the cost is £190 and we have not got the job yet any thoughts or things I should be aware of please

Many Thanks

Matt

 

[malcolmsanford]

Did you say domestic ......................good grief what do they have there !!!!!!! That is over 100 amps per phase if 3 phase and ni on 300 amps at 230.

Yes you will need to ensure you have total separation from the DNO supply which the ATS will give you, And you need to tie down the earth as well.

Have a read of section 551 of the Regs in general and 551.4.3.2 before you buy any other British Standards

 

[Knobhead]

The generator will have to have it’s own earth nest. You cannot rely on the DNO earth. (Jointers will not be happy with you if you do).
View attachment 12193
Are you using an ATS or manual change over?

70KVA! That’s not a house, it’s a bloody hotel!

 

[Matt Crunden]

Thanks for that I will have a read. The only thing I which has crossed my mind is in the ATS panel I will need RCD protection as I have SWA sub mains with no RCD protection from the main board.

On the installation they have 36 KVA 3 phase pump for the ground source heating. Also it is a big 8 bed house with swimming pool, hot tub , over 300 light fittings and enough outside lighting to put Blackpool to shame at Christmas time!

With regards to my price if I think I am allowing for the following

3 phase gererator and ATS panel

Cable to feed ATS panel from generator

Earth rod etc

RCD protection from ATS panel

any thing else I should look at???

Did you say domestic ......................good grief what do they have there !!!!!!! That is over 100 amps per phase if 3 phase and ni on 300 amps at 230.

Yes you will need to ensure you have total separation from the DNO supply which the ATS will give you, And you need to tie down the earth as well.

Have a read of section 551 of the Regs in general and 551.4.3.2 before you buy any other British Standards

 

[Matt Crunden]

I know we been working on it for 18 months and since all the rain they had problems with power cuts and sump pumps not working. They have basement with cinema room, wine cellar and gym. Had water in the floor sockets the other day as sump pump not working. So they decided to have back up generator which can run the whole house + the 32KVA ground source pump. Thanks for the diagram. Thinking of putting earth rod by generator and running them to ATS panel. cheers :army:

 

[malcolmsanford]

Matt I can't see why you would need to RCD the supply from the ATS switch to be honest, but I'm not fully up on the BS for generation. I can't seem to find this requirement in the BS 7671-2008

 

[Matt Crunden]

thanks no worrys

 

[Engineer54]

Where are you mounting this generator?? It really needs to sit on it's own plinth, with the generator frame sitting on vibration isolators. You'll really need more than just one earth rod location, it's normal for generator positions to have rod locations at 2 corners (diagonally opposed), and linked both sides with a suitable sized earth conductor. Use 2 X 5/8'' coupled together at each location. If the plinth is new, constructed on bare earth, you can also use any re-bar as an additional Ufer earth connected to the linking earth cables, or one of the rods... Don't forget to ''ensure'' you solidly ground your Generators neutral point position as well as the frame....

By the way Who sized this generator?? Remember if the generator is over rated on it's load, the engine can suffer significantly. Generators should have enough load to satisfy at least 65 to 70% of it's continuous rating.... Less than that, and an expensive auto load bank will need to be installed to compensate for the lack of load... lol!!!

It's going to be extremely difficult to isolate the DNO earthing system, not unless you purchase an ATS that separates the earthing systems, or include a separate N/O-N/C contactor to isolate them. Personally i can't see a problem using the DNO earthing system for the installation itself, just don't use it to ground/earth your generator!!!

 

[netblindpaul]

OP also please note the word Tony used to describe the earthing, "nest", on rod even double length is NOT enough.
E54 has suggested probably the minimum, you will need to refer to other BS's to get the design compliant, thus, you will need copies of them, unless the generator supplier will design the earthing and change over system for you...

 

[Matt Crunden]

Hello It is going to be mounted 15m away from the house. We have done a KVA rating for the house when the supply had to be connected. So it possible we can do a smaller generator and the house would be limited on power when on the generator. We have Ground source heat pump at 35 KVA ish so maybe a 50KVA could be better. I will put this to the the QS . Many Thanks

Where are you mounting this generator?? It really needs to sit on it's own plinth, with the generator frame sitting on vibration isolators. You'll really need more than just one earth rod location, it's normal for generator positions to have rod locations at 2 corners (diagonally opposed), and linked both sides with a suitable sized earth conductor. Use 2 X 5/8'' coupled together at each location. If the plinth is new, constructed on bare earth, you can also use any re-bar as an additional Ufer earth connected to the linking earth cables, or one of the rods... Don't forget to ''ensure'' you solidly ground your Generators neutral point position as well as the frame....

By the way Who sized this generator?? Remember if the generator is over rated on it's load, the engine can suffer significantly. Generators should have enough load to satisfy at least 65 to 70% of it's continuous rating.... Less than that, and an expensive auto load bank will need to be installed to compensate for the lack of load... lol!!!

It's going to be extremely difficult to isolate the DNO earthing system, not unless you purchase an ATS that separates the earthing systems, or include a separate N/O-N/C contactor to isolate them. Personally i can't see a problem using the DNO earthing system for the installation itself, just don't use it to ground/earth your generator!!!

 

[dichroic]

View attachment Earthing of generators.pdf

Hi Matt, Hopefully this may assist you with this.

Dichroic

 

[Marvo]

With regards to my price if I think I am allowing for the following

3 phase gererator and ATS panel

Cable to feed ATS panel from generator

Earth rod etc

RCD protection from ATS panel

any thing else I should look at???

I would be looking at an outhouse possibly with sonic attenuation built in, or as E54 suggested a decent slab at least. With a generator of this size separate fuel storage might be required. Can't help thinking this unit is way oversized even for Buckingham Palace. Do they really need to accommodate the GSHP in the back-up equation?

 

[johnboy6083]

View attachment 12354

Hi Matt, Hopefully this may assist you with this.

Dichroic

Ive just been reading this guide, and it suggests that the suppliers earthing facility cannot be relied upon for ADS, when the genny is in operation.
Now in my mind, this means that your earthing for the genny is required to be at TN levels (very very low on large gen sets), or MCCB's with residual earth fault protection are required. Can anyone add to this please, and point me to documentation?

Thanks

John

 

[johnboy6083]

Bumping this up!

 

[Guest123]

Bumping this up!

I've done a lot with gennys over the years and have gathered info from various sources along the way.

I'll e-mail you some PDF's if you want mate.

I think I still have your e-mail address, better PM it to me just incase though as the PDF's are too big to upload onto the forum.