Moulded Case Circuit Breakers

[Les Macaulay]

Under what circumstances are type C cb's required?

 

[moose]

Type C are usually in office and the likes, B are usualy used in the home and D are for Slow breaking motors that type of thing.

 

[Les Macaulay]

Thanks for that, moose. If type c is fitted with an rcd pod to convert it to an RCBO, am I correct in saying that Table 41.3(b) isn't relevant re max Zs value of that circuit, so long as the RCD test proves satisfactory?

 

[Engineer54]

Point 1, an MCCB is not a MCB, and don't come in Type designated tripping curves..

Point 2, Any RCD protection on a TN system is classed as ''Additional'' protection, so therefore your primary ADS system should be in place and functionally conforming to the circuits requirement!!

RCD protective devices are not, cover-all get out of jail cards, to be used to cover up an inadequate ADS on new circuits...

 

[Les Macaulay]

That's the first time I've heard this. So Zs needs to comply with the disconnection times regardless of any RCD. Is there not the possibility that the rcd can be added because the Zs is too high for ADS?

 

[Engineer54]

Well why would you install a circuit, that didn't conform to the protective devices Zs requirements in the first place??

I'm sure that many here think it's perfectly legitimate, the problems come when the RCD fails to operate. You are literary putting all your trust on a not so reliable RCD component/element rather than as an addition to a solidly connected earthing system....