Max zs for 400 v 3 phase

[oneflashbash]

Hi

I'm after some advice on the max zs for 3 phase 400 v circuits.

Do I use the tables 41.2 - 41.4 in the regs as these are for 230 v or do I calculate them for 400 v .

Also I know the calc for type 1,2,3 and b,c,d breakers but what about bs 88 as the tables only go up to 200 amps and are also 230 v

Thanks in advance

Matt

 

[Doc Hudson]

Hi I'm after some advice on the max zs for 3 phase 400 v circuits.

Do I use the tables 41.2 - 41.4 in the regs as these are for 230 v or do I calculate them for 400 v .

Also I know the calc for type 1,2,3 and b,c,d breakers but what about bs 88 as the tables only go up to 200 amps and are also 230 v

Thanks in advance

Matt

Zs is the earth fault loop impedance, between a line and earth. Tables 41.2 - 41.4 in the regs are for a Uo of 230v. Uo is the nominal rms line voltage to earth. I think you will find that the typical three phase is still 230v with respect to earth from each of the phases. The 400v you refer to would be U 'Voltage between lines'. unless you have some specialised supply I don't think the line to earth voltage (Uo) is going to be 400v

Doc H.

 

[Andy™]

Hi I'm after some advice on the max zs for 3 phase 400 v circuits.

Do I use the tables 41.2 - 41.4 in the regs as these are for 230 v or do I calculate them for 400 v .

Also I know the calc for type 1,2,3 and b,c,d breakers but what about bs 88 as the tables only go up to 200 amps and are also 230 v

Thanks in advance

Matt

maybe stick with experimenting with a 9v battery for a little longer?

 

[oneflashbash]

Hi Doc H

Thanks for the reply

The system i'm testing is a 690v beetween lives and 400v to earth on a water treatment plant.All the testing they require is megger testing 1000v and resistance R1+R2,Just need to check if the fuses and mcb's are correct.

Matt

 

[Andy™]

this gets even worse... your playing with 690/400v yet you done know what your doing. i hope this is not an EICR your doing, because your clearly not competant