RCD requirements for TT?

[pc1966]

Is there a Type B solution that incorporates time delay or am I missing something obvious about the operation of different types of RCCB?

Not that I have seen. Doepke have a good range of type B (at a price!) but none are delay ones to mk knowledge.

Sorry if this is a stupid question, but I can't get enough of threads that raise issues specific to TT earthing systems.

No, it is a perfectly sensible question to ask!

 

[Ian1981]

Types of rcd in series
Images courtesy of BEAMA

 

[Ian1981]

Some EV manufacturers like Garo particularly stipulate this requirement, that a type AC cannot be upfront of their type A etc.
If also rcd manufacturers are telling you the same thing then that’s good enough for me.

 

[nicebutdim]

Types of rcd in series

That states that no Type S RCCB should be fitted upstream of a Type B or F, which obviously removes any issue of selectivity.

Would this be appropriate for a TT earthing system, given that disconnection may rely on electronics at a single point?

 

[Ian1981]

That states that no time delayed RCCB should be fitted upstream of a Type B or F, which obviously removes any issue of selectivity.

Would this be appropriate for a TT earthing system, given that disconnection may rely on electronics at a single point?

Not sure I follow?

 

[HappyHippyDad]

Types of rcd in series
Images courtesy of BEAMA

In your picture Ian, it shows a type A RCD upstream from a type B RCD. It then says a type A RCD should not be upstream from a type B RCD. I'm a little confused?

edit... No it doesn't! My error.

Although It does look like it is suggesting no upfront S type RCD if there is a type B RCD downstream (as there are no S type type B RCD's)

 

[nicebutdim]

It doesn’t, the paragraph above is for S types, the one below is for general rcd selection

My mistake, I was fixated by the diagram.

What I've been driving at is the fact that this discussion has highlighted that operation of Type S RCCBs may be impacted by DC earth leakage from devices that require protection of a Type B RCBO. As such I'm wondering if an upfront Type S RCCB could be rendered ineffective in such circumstances and, if so, what the most appropriate solution might be.

 

[HappyHippyDad]

My mistake, I was fixated by the diagram.

What I've been driving at is the fact that this discussion has highlighted that operation of Type S RCCBs may be impacted by DC earth leakage from devices that require protection of a Type B RCBO. As such I'm wondering if an upfront Type S RCCB could be rendered ineffective in such circumstances and, if so, what the most appropriate solution might be.

Higher rated type B RCD. E.g 300mA Type B? I can't imagine fitting one though!

 

[nicebutdim]

Higher rated type B RCD. E.g 300mA Type B? I can't imagine fitting one though!

I could stand to be corrected, but I believe that this wouldn't appropriately address the issue of selectivity as sufficient earth leakage could cause disconnection at either point.

 

[mattg4321]

So if you want to fit an EVSE on a TT supply with upfront S type you effectively can’t?