What Dost Thou Mean, o OSG?

[NickD]

Section 3.3, Fault Current Protection.

"When a CU to BSEN60439-3 or BS5486art13 or a fuseboard having fuselinks to BS88-2 or BS88-6 or BS1361 is used, then fault current protection will be given by the overload protective device. For other protective devices the breaking capacity must be adequate for the prospective fault current at that point."

I don't understand what this is getting at in the first sentence. Which overload protective device is it talking about? If it means the fuses/MCBs, then that seems to say the same (obvious) thing as sentence 2. If it isn't, what device is it talking about? Cut out fuse?

 

[Richard Burns]

If you have a CU to those BS's or you have a board which has fuses to those BS's, the devices in the board are in place to provide overload protection however they also provide fault current protection.
If you have circuit breakers / RCBOs in a board not to the first two BS then these only provide overload protection unless the breaking capacity is suitable for the PFC.
This is the difference between protection against overload and fault current being identified.

 

[NickD]

Is the guide saying then that if the requirements of sentence 1 is met then fault protection is unconditionally met regardless of magnitude of PFC and the breaking capacities of the protective devices? Surely not?

 

[NickD]

Pretty sure I've seen a BS5486Pt13 CU with 3036 fuses in it which can't be trusted to break a 1.1kA fart.

 

[Richard Burns]

Is the guide saying then that if the requirements of sentence 1 is met then fault protection is unconditionally met regardless of magnitude of PFC and the breaking capacities of the protective devices? Surely not?

I think there was something in the OSG saying that the maximum fault current to be found (outside large cities) was 16kA and that CUs to BSEN60439-3 are rated to that level. BS1361 etc. start their breaking capacity at 16kA I think. Therefore they are saying that since the PFC will not be above those levels then those devices will protect against fault current.

Pretty sure I've seen a BS5486Pt13 CU with 3036 fuses in it which can't be trusted to break a 1.1kA fart.

BS3036 fuses is another matter all together sine they have very low breaking capacity, but presumably they are saying that the board as a whole could safely break this level.