Previous in Forum: Heating with Wire   Next in Forum: Defintions: Voltage, Current, Power
Close
Close
Close
21 comments
Rate Comments: Nested
Anonymous Poster #1

Neutral Grounding

08/07/2012 4:00 AM

I brought a Diesel generator 3 ph 4 wire 380v 60 Hz. The neutral terminal was connected to ths ground bus. I connected the 3 phases with neutral to different single phase loads. I connected the neutral/ground bus of generator to earth and distribution board ground also to the same earth point. When I energise the generator main breaker is tripping. Why?

Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#1

Re: Neutral grounding

08/07/2012 4:17 AM

Simple: when the generator is energised, the main breaker is experiencing a current that exceeds its trip setting.

As the installation cannot be seen from here, get a qualified local electrician to check the system and eliminate the fault that the breaker is proving is there before trying again. Has the installation had an insulation and continuity proving test before energising, for example <rhetorical question - NNTR>?

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Reply
Anonymous Poster #1
#2
In reply to #1

Re: Neutral grounding

08/07/2012 6:21 AM

The generator breaker is tripping when the neutral of the generator is connected to ground or earth point. if i remove the grounding of the neutral it is fine. But as you know it is better to hold the neutral at earth potential to have uniform single phase voltages on all the 3 phases.

Megger and continuity test have been done before enegising and it is fine.

Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#3
In reply to #2

Re: Neutral grounding

08/07/2012 6:59 AM

Please describe the breaker and its rating(s).

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Reply
Power-User

Join Date: Nov 2011
Posts: 131
Good Answers: 5
#10
In reply to #2

Re: Neutral grounding

08/08/2012 3:57 AM

It is preferred to use TNCS type earthing system with seperate PN and E conductor. Generator neutral should be connected to earth electrodes directly which should be different from electrodes of equipment earth bus. However, they may be interconnected at the electrode terminal end to bring down the overall earth resistance. You may like to monitor the neutral current of the generator by providing a neutral CT and use a earth fault relay for generator protection. This relay will not sense the unbalance current of the single phase loads.

Reply
Anonymous Poster #1
#11
In reply to #10

Re: Neutral grounding

08/08/2012 4:17 AM

Thanks for the suggestion.I agree . Any how i have a question again. what difference it makes if the generator neutral grounding and distribution board ground is common. pls can you explain me in detail.

Reply
Power-User

Join Date: Sep 2008
Posts: 196
Good Answers: 6
#13
In reply to #11

Re: Neutral grounding

08/08/2012 11:21 AM

Are you sure what the "root cause" for the generator load breaker trip actually is?

It may not be due an overload condition at all and it very well could be that the machine has ground fault protection on-board which is tripping the load breaker via the "shunt" trip circuit due to improper ground/earth connection(s) or other fault(s).

You really need to de-energize the system and check wiring continuity for correct connections and for any earth/ground fault conditions with a VOM.

Once the conductor continuity is verified you need to meggar the conductors and system at the rated voltage of the generator to eliminate and/or identify any insulation failures/faults.

If you are not thoroughly competent with performing these procedures, seek professional electrical help.

Reply
Power-User

Join Date: Nov 2011
Posts: 131
Good Answers: 5
#15
In reply to #11

Re: Neutral grounding

08/09/2012 1:14 AM

If the generator neutral grounding and the distribution board grounding is common then there will be current in the neutral bus both in case of ground fault and unbalance in single phase load. Thus it will be difficult to differentiate between the two and trip the circuit breaker only in case of ground fault.

Hence the neutral should be isolated from the earth bus and should be connected to earth only at one point near the generator and no multipoint earthing should be provided. This can be done like this - the generator neutral should be branched out at the terminal box, one branch should be connected to earth electrodes and a CT should be provided in this circuit, the other branch will be connected to the neutral bus of the distribution board. With this type of neutral bifurcation, the CT will sense only the ground fault current and not the unbalance current in the circuit. Hope I have cleared your doubt.

Reply
Guru

Join Date: Jun 2010
Location: srilanka
Posts: 2725
Good Answers: 5
#16
In reply to #15

Re: Neutral grounding

08/09/2012 1:26 AM

I have seen reputed manufacturer connecting neutral to generator metal work.

__________________
pnaban
Reply
Anonymous Poster #1
#19
In reply to #15

Re: Neutral grounding

08/12/2012 8:05 AM

i wanted to have separate earth point for the Ground-cum-neutral bus of generator. you are right. if we separate the ground-cum neutral earth point from the DB earth point , it should be ok.

thanks for the clarity.

Reply
Associate

Join Date: Nov 2007
Posts: 53
Good Answers: 1
#4

Re: Neutral Grounding

08/07/2012 11:12 PM

Get yourself a clamp on current meter and measure what is going on

__________________
Clintb3252
Reply
Guru

Join Date: Jun 2011
Location: Phnom Penh
Posts: 4019
Good Answers: 102
#5

Re: Neutral Grounding

08/07/2012 11:17 PM

Does the main breaker still trip if the single phase branch circuit breakers are open(off)?

Is this a back up for a mains connected installation or a standalone generator?

Is the distribution board ground also neutral bonded?

Can you table a sketch of your installation please?

__________________
Difficulty is not an obstacle it is merely an attribute.
Reply
Participant

Join Date: Apr 2012
Posts: 1
#7
In reply to #5

Re: Neutral Grounding

08/08/2012 2:01 AM

Isollate the load from grid this may be the couse

Reply
Guru

Join Date: Jun 2011
Location: Phnom Penh
Posts: 4019
Good Answers: 102
#8
In reply to #7

Re: Neutral Grounding

08/08/2012 2:10 AM

Could be......

Need OP's input here.

No need to guess if we have all or at least more information.

__________________
Difficulty is not an obstacle it is merely an attribute.
Reply
Guru

Join Date: Jun 2010
Location: srilanka
Posts: 2725
Good Answers: 5
#6

Re: Neutral Grounding

08/08/2012 12:54 AM

Don't connect neutral/ground bus to earth but use it as neutral. At the load end use an earth electrode for grounding/earth. Tell us whether it works now.

__________________
pnaban
Reply
Anonymous Poster #1
#12
In reply to #6

Re: Neutral Grounding

08/08/2012 4:21 AM

Then it becomes ungrounded neutral system. In that case if there is any fault, the other phase voltages will rise. i want to connect the generator neutral to ground point, so that even in case of fault other phase voltages are held at their normal value.

Reply
Guru

Join Date: Aug 2007
Location: London England.
Posts: 583
Good Answers: 10
#9

Re: Neutral Grounding

08/08/2012 3:28 AM

Ground the frame of the generator and connect the neutral to neutral in the dist board, if the supply to the distribution board or mains switch is fed by an armoured cable earth to that, but if it isn't an underground cable then you need to put in an earthing spike.

Bazzer

__________________
When I die I'd like to go peacefully in my sleep like my dad,not shouting and screaming like his passengers.
Reply
Participant

Join Date: Mar 2007
Posts: 3
#14

Re: Neutral Grounding

08/08/2012 9:28 PM

I brought a Diesel generator 3 ph 4 wire 380v 60 Hz. The neutral terminal was connected to ths ground bus. I connected the 3 phases with neutral to different single phase loads. I connected the neutral/ground bus of generator to earth and distribution board ground also to the same earth point. When I energise the generator main breaker is tripping. Why?

Disconnect the neutral from the ground at the generator. If its ok, then one of the phase loads is connected to a local ground and wired the wrong way!

__________________
Rthe16th
Reply
Commentator
Engineering Fields - Power Engineering - Projects Engineer

Join Date: Aug 2008
Location: Tanzania- East Africa
Posts: 71
#17

Re: Neutral Grounding

08/11/2012 2:28 AM

, you may need to go back to the basics.

What is the capacity of the generator,what is the load.when the generator is running. is the utility power isolated effectively.

do you have a dedicated earthing for the genset.

is your genset earthing effectively seperated from the rest of the earthing pits...i.e 6/7 meters apart.

sometimes obvious issues are left unattaended

regards

SAK

__________________
A wise person will understand more from a Foolish question than what a Fool will understand from a Wise Answer
Reply
Guru

Join Date: Jun 2011
Location: Phnom Penh
Posts: 4019
Good Answers: 102
#18
In reply to #17

Re: Neutral Grounding

08/11/2012 9:14 AM

is your genset earthing effectively seperated from the rest of the earthing pits...i.e 6/7 meters apart.

Huh?

Care to provide a model. citation or personal anecdote to support this?

__________________
Difficulty is not an obstacle it is merely an attribute.
Reply
Commentator

Join Date: Mar 2011
Location: off the beaten track, not quite whoop whoop nor humptydoo
Posts: 57
#20

Re: Neutral Grounding

08/25/2012 1:09 AM

The MEN connection in the generator is pretty standard from what I have seen of many sets coming into Australia from overseas. Apart from the standard questions about competencies and qualifications, you need to be aware that once you change the manufacturer's design you become personally liable for any damage caused when/if things go BANG. These same gensets have the MEN conductor running through the earth leakage relay's toroid. Is it the circuit breaker or the earth leakage relay tripping?

For myself I am still attempting to work out how to manage the liability issues as they conflict with the Australian Standards that state the MEN must be in the main distribution board...anyone? (& my apologies for hijacking this thread)

From post 2: The generator breaker is tripping when the neutral of the generator is connected to ground or earth point. if i remove the grounding of the neutral it is fine. Which cables are you disconnecting exactly - the MEN in the genset, or from DB earth bar?

Drawings would be extremely useful right about 15 days ago

__________________
Everything works out in the end, just not neccessarily how you want
Reply
Guru

Join Date: Jun 2011
Location: Phnom Penh
Posts: 4019
Good Answers: 102
#21
In reply to #20

Re: Neutral Grounding

08/25/2012 3:47 AM

The requirement for E-N bonding inside the genset is dependent on whether or not an RCD device is installed.

Have a look at section 5.2.2 and ensuing paragraphs.

__________________
Difficulty is not an obstacle it is merely an attribute.
Reply
Reply to Forum Thread 21 comments
Copy to Clipboard

Users who posted comments:

Anonymous Poster (4); Bazzer Englander (1); Bogere (1); Chook (1); Clintb32 (1); debata07 (2); pnaban (2); PWSlack (2); ruidasilva (1); SAK (1); SHOCKISCAN (1); Wal (4)

Previous in Forum: Heating with Wire   Next in Forum: Defintions: Voltage, Current, Power

Advertisement