LV 3 pole ACB and Neutral

[zezo]

hi there ;
for LV 3pole ACB (without using external ct for Neutral)
1_how the breaker calculate the Neutral current is it the vector sum of L1+L2+L3
and what will be the different of the reading of N if we connect external ct for N.
2_ for ground fault function :
_what is the difference bet ground fault and Neutral protection?
_ how the ground fault function works as it must be external ct for N (for residual GF ) what is the eq of calculating lgf
is it like that (L1+L2+L3+N=Igf) ; then what should happen if Neutral external ct is not connected and gf function is activited; will it deal with neutral in the eq as N=0 so there is aground fault always and it should trip if the value equal to the adjusted value or what ? and does it mean for question no 1 the breaker is read ground current not neutral current but why the cb shows the reading of N although neutral ct is not connected and it may be a false reading ?
thanks.

[S-W]

Hello @zezo, thank you for your message, we'll come back to you with a reply soon.

[zezo]

Thanks; Iam waiting the answer🙂

[Gregoire_Brun · Accepted solution]

hello @zezo

As I know

1_how the breaker calculate the Neutral current is it the vector sum of L1+L2+L3

Yes
2_What will be the different of the reading of N if we connect external ct for N. 

The measuring is more accurate.

3_ for ground fault function :
_what is the difference bet ground fault and Neutral protection?

it depends of your type of network , some people can use the breaker just with one phase and neutral for specific application

Neutral measurment can be set with a different level of protection to control the unbalance of diferents phases,

Ground protection is to control if some curent flow true the earth 

so globaly when you dion't have external ct for neutral, it's a calculated value witch is use , with external ct , accuracy is more better because it's a real value using for the diffferent protections.

[S-W]

Thank you @Gregoire_Brun. @zezo, please let us know if you have further needs. Have a lovely day,

[zezo]

Thanks for your response;

But what about this part of question

how the ground fault function works as it must be external ct for N (for residual GF ) what is the eq of calculating lgf
is it like that (L1+L2+L3+N=Igf) ; then what should happen if Neutral external ct is not connected and gf function is activited; will it deal with neutral in the eq as N=0 so there is aground fault always and it should trip if the value equal to the adjusted value or what ? and does it mean for question no 1 the breaker is read ground current not neutral current

Thanks again.

[Gregoire_Brun]

Dear @zezo , clear ly it change the accuracy of the system 

With external CT it would be more precise . and if you need something more accuracy you must to switch with a Elcb protection system comming from VigiPacT offer