60947 Zs VALUE S

[driverman]

Guys. how do I find the Zs value for a 80A 60947-2 10Ka MCB? At this point in time I don't know the make. Is this a new number for MCB's? Does it make a difference with different manufactures? Cheers

 

[spark 68]

in your case In = 80 A, Type B= X5, type C= X10, type D= X20

so

230/(80 X10) = 230/800 = A =0.2875

0.2875 X 0.8 for temperature correction = max Zs of 0.23 ohms

In Amd 3 we apply a C min factor of 95% for max Voltage Drop so this would be 0.23 X 0.95, this is not really necessary at the moment though, but this will be reflected in the new Max Zs tables when Amd3 comes fully into force.

 

[Guest125]

Some of the gents on here have def got the knack of this theory malarky!!! I am very impressed. I always struggled with this in college. I watch this thread with admiration...

 

[driverman]

in your case In = 80 A, Type B= X5, type C= X10, type D= X20

so

230/(80 X10) = 230/800 = A =0.02875

0.02875 X 0.8 for temperature correction = max Zs of 0.023 ohms

In Amd 3 we apply a C min factor of 95% for max Voltage Drop so this would be 0.023 X 0.95, this is not really necessary at the moment though, but this will be reflected in the new Max Zs tables when Amd3 comes fully into force.

Thanks, I was about half way working it out, but would of been wrong. The readings that I have on various circuits protected by these MCB's are in the region of 0.54 to 0.68 which is higher than 0.23.
So, doing calcs using "B" type MCB, the Zs readings would be more acceptable, would they not?
0.58

 

[Geordie Spark]

60947 crossing the Border Bridge -->>> Rail Photoprints | V2 2-6-2 60800 - 60984 | 60947 Forth Bridge 210761 CR142

 

[driverman]

Some of the gents on here have def got the knack of this theory malarky!!! I am very impressed. I always struggled with this in college. I watch this thread with admiration...

Puts me to shame really, but, I have been out of the game for 20 + years! That's my excuse anyhow! But it's nice when steered in the right direction.

 

[trev]

ampage

Aaaaaaaaaaaaa!

 

[spark 68]

Applying it to fixed MCBs to 60947-2 will err on the side of caution as the manufacturers data will lead to a more accurate figure, and this may be slightly higher than this calc produces due to the way that standard is applied

In regard to this bit quoted, the manufacturers data may well allow a slightly higher max Zs, this is because of tolerances allowed in the 60947-2 standard, Shanky mentioned this a while back, I don't own the standard so cannot really add much more, but for instance a look at a manufacturers data sheet/trip curves may allow a type multiplier for C to be X7.5 instead of X10, the calc above works on the worst case of X10 in the absence of any hard data, hence erring on the side of caution.

 

[Geordie Spark]

Aaaaaaaaaaaaa!

Ye chokin' on yer dog there son??

 

[driverman]

Thanks, I was about half way working it out, but would of been wrong. The readings that I have on various circuits protected by these MCB's are in the region of 0.54 to 0.68 which is higher than 0.23.
So, doing calcs using "B" type MCB, the Zs readings would be more acceptable, would they not?
0.58

Just noticed, answer was 0.023 ohms not 0.23ohms...opps!

 

[spark 68]

You were right the first time lol, I had added an extra zero while typing, I have now corrected the earlier post

230/800 = 0.2875

0.2875 X 0.8 = 0.23

Sorry my Typo :mad2:

 

[driverman]

You were right the first time lol, I had added an extra zero while typing, I have now corrected the earlier post

230/800 = 0.2875

0.2875 X 0.8 = 0.23

Sorry my Typo :mad2:

No worries, thanks for your input. However after my concerns, it turns out that there is a 1000mA RCD upstream. Therefore max Zs allowed 50 0hms.
Could say that exercise this was a learning curve! lol.