Another odd fault, you decide..

[JohnW2]

Ze was 0.09 when measured today, and this sub board and socket isn't very far from mains, so may be in luck!

You might be in luck, then! what is the CSA of the extension lead cable?

Intellectually speaking, it would be nice to wait until (if) the problem recurs before changing to a Type D. If not, as I said, you'll probably cure it with the Type D without ever having any insight into the 'why'. However, expediency, rather than intellectual satisfaction, may well be the name of the day!

Mind you, a D40 is a bit 'frightening' since it needs 800A for a magnetic trip - one might even argue that it's 'hardly worth having'! What upstream OPDs are there?

Kind Regards, John

 

[flyingsparks]

Ze was 0.09 when measured today, and this sub board and socket isn't very far from mains, so may be in luck!

You might be in luck, then! what is the CSA of the extension lead cable?

Intellectually speaking, it would be nice to wait until (if) the problem recurs before changing to a Type D. If not, as I said, you'll probably cure it with the Type D without ever having any insight into the 'why'. However, expediency, rather than intellectual satisfaction, may well be the name of the day!

Mind you, a D40 is a bit 'frightening' since it needs 800A for a magnetic trip - one might even argue that it's 'hardly worth having'! What upstream OPDs are there?

Kind Regards, John

Flex is a 4mm. Don't forget the c40 is on the submain to the sub board, and then there is a c32 feeding the socket.

800 A is fair frightening, your right, I hadn't looked up that figure! Upstream of that is a 100A MCCB and then the 200A MCCB main switch and then 200A main supplier fuses.

 

[JohnW2]

Ze was 0.09 when measured today, and this sub board and socket isn't very far from mains, so may be in luck!
Flex is a 4mm.

By my reckoning, that's 0.09Ω for the Ze plus 0.19Ω for the extension lead which, at 0.28Ω is already above the 0.23Ω maximum for a D40, even before you add in anything else in the installation.

Don't forget the c40 is on the submain to the sub board, and then there is a c32 feeding the socket.

OK,if it were a D32 protecting the circuit, then you could go up to 0.29Ω, but it sounds as if you may well be over that with the extension lead. Also, if you changed that to a D32 but left the C40 in circuit, the latter might still trip. However, I suppose that if the D32 were satisfying the disconnection times, you could go up to a D40 for the other one, even if Zs was too high for that one, itself, to achieve satisfactory disconnection times.

800 A is fair frightening, your right, I hadn't looked up that figure!

40A x 20 = 800A

Upstream of that is a 100A MCCB and then the 200A MCCB main switch and then 200A main supplier fuses.

To be clear, what do you mean by 'MCCB'?

Kind Regards, John

 

[DaftPunk]

MCCB is a moulded case circuit breaker as found in panel boards and typically used to supply submains etc.

 

[JohnW2]

MCCB is a moulded case circuit breaker as found in panel boards and typically used to supply submains etc.

Thanks, but I now see that I wasn't clear about what I was asking - what is an MCCB functionally - magnetic, thermal or (like MCBs) both?

Kind Regards, John