Installing 60Kva generator.

[samg2014]

Hi Everyone,

First post in a while. We are currently quoting for putting a 60Kva generator into a factory, this will be powering one machine only and will not be connected to the mains. It will only be used 3 times a week, this will free up some load from the main DNO supply.

I have searched some of the forum for anwsers, but still cannot get anywhere.



- Will i need to install an earth rod?
- I am going to put a 4 way MCCB panel board in, which will then feed the machine.

Help needed

 

[jackhammerJIM]

search the forum . try searching your regs book or call your scheme provider .

Yes it will require an earth rod ...

 

[Richard Burns]

You have an interesting and complicated situation there.
The interaction of two sources of power within the same location can cause a significant headache.
The generator would need to be set up as an independent supply to the machine, but the earthing and bonding arrangements may well mean that the independent generator and the DNO supply are connected via the earthing and so you need to ensure that a fault on the generator cannot affect the public supply.
You could start by reading section 551 on generators and perhaps reference the Special location in GN7 for generating sets.
I think this is a complex installation and would need professional guidance and communication with the DNO to ensure safety.

 

[Ian1981]

Hi Everyone,

First post in a while. We are currently quoting for putting a 60Kva generator into a factory, this will be powering one machine only and will not be connected to the mains. It will only be used 3 times a week, this will free up some load from the main DNO supply.


- Will i need to install an earth rod?
- I am going to put a 4 way MCCB panel board in, which will then feed the machine.

Help needed

.
I installed power to a new build site compound recently and was advised by the generator supplier that the earthing arrangement was a tn-s system the neutral being bonded/linked to earth at the windings and anything over 10kva the chassis of the generator required connecting to an earth rod with a resistance under 200 ohms
However page 25 in the on site guide advises that you can't measure the resistance of the rod using an earth fault loop impedance tester as the rod doesn't form part of the earth loop.

 

[Deleted member 26818]

You have to use an Earth electrode resistance meter.

 

[Ian1981]

Hi Everyone,

First post in a while. We are currently quoting for putting a 60Kva generator into a factory, this will be powering one machine only and will not be connected to the mains. It will only be used 3 times a week, this will free up some load from the main DNO supply.

I have searched some of the forum for anwsers, but still cannot

get anywhere.



- Will i need to install an earth rod?
- I am going to put a 4 way MCCB panel board in, which will then feed the machine.

Help needed

i

Hi Everyone,

First post in a while. We are currently quoting for putting a 60Kva generator into a factory, this will be powering one machine only and will not be connected to the mains. It will only be used 3 times a week, this will free up some load from the main DNO supply.

I have searched some of the forum for anwsers, but still cannot get anywhere.



- Will i need to install an earth rod?
- I am going to put a 4 way MCCB panel board in, which will then feed the machine.

Help needed

Hi Everyone,

First post in a while. We are currently quoting for putting a 60Kva generator into a factory, this will be powering one machine only and will not be connected to the mains. It will only be used 3 times a week, this will free up some load from the main DNO supply.

I have searched some of the forum for anwsers, but still cannot get anywhere.



- Will i need to install an earth rod?
- I am going to put a 4 way MCCB panel board in, which will then feed the machine.

Help needed

You have to use an Earth electrode resistance meter.

yeah unfortunately very time consuming!

 

[jackhammerJIM]

Ian . I thought it was less than 20 ohms ?

 

[Ian1981]

Ian . I thought it was less than 20 ohms ?

On site guide suggests 200hms.
21ohms is usually the reading at the supply end earth electrode connected to the neutral or transformer end from the DNO in a normal TN earthing arrangement.
The generator supplier also stipulated 200 ohms.
As far as I'm aware bonding the chassis to an electrode is just referencing the generator to earth and nothing more.

 

[Wilko]

I did this method from OSG 10.3.5.2 a couple of weeks ago using Kewtech KT65DL and the earth kit. All good

 

[Richard Burns]

I am not sure that the OSG is totally relevant to the application of installing a 60kVA generator on a permanent basis.
This link to the HSE OC on Electrical safety may help you define the requirements for which you need to account, it is fairly old but the principles are still sound. Obviously the site conditions will dictate a lot of the requirements, but this may help.

 

[davesparks]

On site guide suggests 200hms.
21ohms is usually the reading at the supply end earth electrode connected to the neutral or transformer end from the DNO in a normal TN earthing arrangement.
The generator supplier also stipulated 200 ohms.
As far as I'm aware bonding the chassis to an electrode is just referencing the generator to earth and nothing more.

The DNO earth connection will be a heck of a lot less than 21 ohms unless they are having serious issues, I believe they consider anything over an ohm to be a 'hot' site these days!

200ohms is a very high value for the neutral to earth link for a TN-S supply, are you sure that you have this right?

True you cannot test it with an earth fault loop impedance test, but this should be blindingly obvious really as it is the earth reference of the supply you are testing, you need to use a earth electrode resistance test.

 

[PEG]

I would recommend speaking to your generator suppliers technical adviser,presuming it is new...
If the existing machines,and all it's associated parts,are earthed to the DNO's earth,you may have problems separating this,to it's new supply earthing arrangement,if needed,and may even have a potential,between the two.

There are ways around this issue,but they are normally reserved for larger institutions,with large budgets,and will definitely require liason with the appropriate DNO.

 

[Ian1981]

The DNO earth connection will be a heck of a lot less than 21 ohms unless they are having serious issues, I believe they consider anything over an ohm to be a 'hot' site these days!

200ohms is a very high value for the neutral to earth link for a TN-S supply, are you sure that you have this right?

True you cannot test it with an earth fault loop impedance test, but this should be blindingly obvious really as it is the earth reference of the supply you are testing, you need to use a earth electrode resistance test.

I'm well aware of what test instrument is needed to determine the resistance of the earth electrode.
200 ohm value is not the resistance of the neutral earth link it is simply a value give for a reliable connection to earth from the chassis of the generator to say its resonably connected to earth as the 200 ohm value max is what we would use on a regular TT earthing arrangement.
Guidance was sought from the generator supplier and through looking at the on site guide page 25 which talks about installing an earth electrode to reference a generator to earth only and to note we are not creating a TT system.

 

[PEG]

Hi,most,if not all of the literary journals quoted,are dealing with a situation where the generator is stand-alone,or a replacement,for DNO connection.

The example you quote,is for a separate supply,to run concurrent,and within the confines of additional equipment,supplied by the DNO.

This greatly affects advice given,in regard of earthing/bonding,etc.

Another way of considering this situation,is if,for example,you had a large industrial establishment,with a production area supplied via a dedicated TX,and the offices,supplied by a local TN-S sub-main.

Without expressed advice,you would not be mixing earthing arrangements,or supplies,and special measures would have to be employed,to ensure the set-up and risks,were available to anybody who may work on the installation.

The situation i mention,above,existed at a large local food processing factory,and some of their long-standing arrangements,included multiple warning posters,forbidding the use of extension leads,without permit.

Discounting institutions such as Hospitals,BNFL and MOD sites,the only customers i have dealt with,who have sizeable additional generator use,would be in construction,quarrying and scrap processing,where the equipment powered,is itself "stand-alone",usually outside any building or cover,and therefore does not suffer or impose,any influence,on a secondary source.

 

[davesparks]

I'm well aware of what test instrument is needed to determine the resistance of the earth electrode.
200 ohm value is not the resistance of the neutral earth link it is simply a value give for a reliable connection to earth from the chassis of the generator to say its resonably connected to earth as the 200 ohm value max is what we would use on a regular TT earthing arrangement.
Guidance was sought from the generator supplier and through looking at the on site guide page 25 which talks about installing an earth electrode to reference a generator to earth only and to note we are not creating a TT system.

It is the neutral to earth link, it is the link which references the neutral to the general mass of earth.
And yes it is not a TT system, it is a TNS system which you are creating.

200ohm is not the value we would use on a TT arrangement, that is a misinterpreted suggestion from the regulations on what may be a limit of stability in some situations.

 

[Ian1981]

It is the neutral to earth link, it is the link which references the neutral to the general mass of earth.
And yes it is not a TT system, it is a TNS system which you are creating.

200ohm is not the value we would use on a TT arrangement, that is a misinterpreted suggestion from the regulations on what may be a limit of stability in some situations.

The resistance of the installation electrode should be as low as practicable a value of exceeding 200 ohms may not be stable
Table 41.5 note 2 bs7671.
200ohms is the adopted figure used I would say!
If you want to be percise it is RA x Idelta N equal to or less than 50v which I'm sure you know this.
If I'm incorrect about the earth neutral link then hey I stand corrected

 

[Ian1981]

The resistance of the installation electrode should be as low as practicable a value of exceeding 200 ohms may not be stable
Table 41.5 note 2 bs7671.
200ohms is the adopted figure used I would say!
If you want to be percise it is RA x Idelta N equal to or less than 50v which I'm sure you know this.
If I'm incorrect about the earth neutral link then hey I stand corrected

When using an rcd for fault protection purposes

 

[davesparks]

The resistance of the installation electrode should be as low as practicable a value of exceeding 200 ohms may not be stable
Table 41.5 note 2 bs7671.
200ohms is the adopted figure used I would say!
If you want to be percise it is RA x Idelta N equal to or less than 50v which I'm sure you know this.
If I'm incorrect about the earth neutral link then hey I stand corrected

'May not be stable' that does not mean that it is a suggested value, maximum value or even that a value less than it is stable.
'As low as practicable' does not mean that you are aiming for a particular value, it means getting it as low as you practically can, which in most cases is a lot less than 200 ohms.

I do know about that calculation, but there are more factors to consider, for example if you read the instructions for a Schneider rcbo they state a maximum Zs for the protected circuit of 100ohms.

the generator as supplied will have a link which connects the star point of the alternator to the case of the generator, this is not a neutral to earth link as there is no connection to earth and it for small an IT supply. By connecting the star point to the general mass of earth it can be turned in to a TNS supply.

 

[Ian1981]

'May not be stable' that does not mean that it is a suggested value, maximum value or even that a value less than it is stable.
'As low as practicable' does not mean that you are aiming for a particular value, it means getting it as low as you practically can, which in most cases is a lot less than 200 ohms.

I do know about that calculation, but there are more factors to consider, for example if you read the instructions for a Schneider rcbo they state a maximum Zs for the protected circuit of 100ohms.

the generator as supplied will have a link which connects the star point of the alternator to the case of the generator, this is not a neutral to earth link as there is no connection to earth and it for small an IT supply. By connecting the star point to the general mass of earth it can be turned in to a TNS supply.

The 'calculation ' is from bs 7671 RA sum of resistance of electrode and associated cpc stating that the total resistance x by say a 30mA rcd cannot be greater than the recommended 50v touch voltage.
Ideally get the electrode as low as possible i never said there was a magic number to aim for other than what is recommended in the on suite guide, the NICEIC guidance for installations upto 100amps guide and note 2 from bs 7671.

Never seen rcbo instructions for Schneider rcbos I'll have to take your word on that tho it maybe the manufacturers guidance I fail to see if the resistance is greater than 100bohms has got to do with it as the max zs associated with an 30mA rcbo would be 1667 ohms!
Unless the rcbo won't work over 100 ohms in which case remind me never to use Schneider!

 

[PEG]

This thread has gone AWOL from the OP's original ask...