Ok, so I'm still a bit confused about the characteristics of the various types of RCDs, i.e. AC/A/F/B. I've concluded that's because there are two classes of effects: a type of residual current that will cause a trip, and a type of residual current that will blind the device against other types of current it would normally trip on. I find that online discussions and 531.3.3 don't clearly distinguish these cases. Can anyone provide, or give a link to, a clear description of what each type RCD is designed to trip on, and what can blind it? For example, might a smooth DC residual current >6ma blind a type A? And if so, is that completely blind, or just blind against pulsating DC (AC still works)? Etc.
In particular, 531.3.3 says that type A will trip for pulsing DC imposed on smooth DC up to 6mA. Which I guess is a promise that it won't be blinded by smooth DC as long as its <6mA (and no guarantee about AC not being blinded). Type F has a similar note for 10mA. Then type B has a note that it will trip for pulsing DC imposed on smooth DC up to 0.4 x Idn. This seems to imply that even type Bs can be blinded by a large enough smooth DC added to a pulsating DC.
And there seems to be no provision for coordination. E.g. a downstream type B won't protect an upstream of any type "less than" B against residual DC currents which could blind it. So that 300mA fire RCD is stuffed.
It all seems to be a bit of mess, with the only logically safe arrangement being for every RCD to be type B.
How easy it is it to get blinding currents - e.g. could a fault in a cheap AA battery charger do the job?
In particular, 531.3.3 says that type A will trip for pulsing DC imposed on smooth DC up to 6mA. Which I guess is a promise that it won't be blinded by smooth DC as long as its <6mA (and no guarantee about AC not being blinded). Type F has a similar note for 10mA. Then type B has a note that it will trip for pulsing DC imposed on smooth DC up to 0.4 x Idn. This seems to imply that even type Bs can be blinded by a large enough smooth DC added to a pulsating DC.
And there seems to be no provision for coordination. E.g. a downstream type B won't protect an upstream of any type "less than" B against residual DC currents which could blind it. So that 300mA fire RCD is stuffed.
It all seems to be a bit of mess, with the only logically safe arrangement being for every RCD to be type B.
How easy it is it to get blinding currents - e.g. could a fault in a cheap AA battery charger do the job?
