RCD RATING VS. SERVICE FUSE RATING

[spud1]

Hi chaps

A Wholesaler told me me this week that the RCDs in the new '18th' split load boards have to be rated at 100a because the 100a service fuse is only means of upstream overcurrent protection. But I was once told that service fuses, although marked as 100A on the cutout label are actually only actually 80amp?

Any thoughts guys?

 

[Nigel]

Please bare with me here.....so assuming method 2, rccb is not less than main cut out fuse....is diversity then allowed over the mcbs?

No.

 

[Wilko]

My take of Reg 536.4.202 is if the manufacturer instructs 100A RCD for a 100A fuse, that's what's needed (from last sentence of Reg). Downstream of the RCD it's still ok to design using diversity factors so that 100A (in this case) is not exceeded. Or have I misunderstood?

 

[Baddegg]

That’s what I was getting at wilko.....but you word it better ha ha

 

[Deleted member 26818]

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[mattg4321]

You maybe right, but BYB 120.1 & 131.1 state blah blah blah.
Can anyone cite me an example of, in the last 10 or 15 years or so, where non-application of these new regs have caused a problem?

Being cynical, what with AFDDs etc, there seems to be a lot of finding and enforcing solutions to (virtually) non existent problems occurring here.

But if they didn't do that then how could they justify selling us more pointless books/courses and their own positions.

 

[spark 68]

The very first line of that reg 536.4.202 states the design current (Ib) shall not exceed the rated current of an assembly Ina having taken any applicable diversity/loading factors into account.

So even if you have a 100A incomer and a split-load board you are going to try and load balance a bit, aren't you ? apart from the usual US SO/DS Lights and DS SO.U/S lights a twin 63A split load board will comply on even a 100A main incoming fuse if you design it correctly.
Bear in mind this is the Ib or design current that is stated here.
Same as it always was but not necessarily stated explicitly in the regs, we knew this anyway, didn't we ?.