Options for new shower circuit

[flameport]

Other option would be split the tails and install a seperate shower CU with its own RCD and breaker in it

That is the only option.
The existing CU already has a single RCD for everything and does not comply, adding another circuit to it makes this worse.

 

[EFLImpudence]

is the rcd 63a rating what it can take under normal load or what it can successfully break? Or both the same?

You're getting confused.
The OP said it was an RCCB so 63A is its maximum CCC.

For MCB they obviously have different values but for RCD they don't mark the breaking capacity.

They do not break overcurrent -
though must be the same as MCBs to cope with short-circuit and fault current as do the cables.
Schneider are marked 10kA.

I'd have thought they'd need to break more than 63A because if there's a fault to earth that isn't enough to trip the MCB quickly, it would be nice if the rcd could break it first.

They don't limit the fault current but only need 30mA (or whatever the rating) to break an earth fault.

 

[John D v2.0]

You're getting confused.
The OP said it was an RCCB so 63A is its maximum CCC.


They do not break overcurrent -
though must be the same as MCBs to cope with short-circuit and fault current as do the cables.
Schneider are marked 10kA.


They don't limit the fault current but only need 30mA (or whatever the rating) to break an earth fault.

I'm not confused, I know it will trip on a Delta I of 30mA. And it will ignore over current that's balanced.
I'm not sure if you know what I mean by breaking capacity?

Basically any protective device or switch has a maximum current it can break. Over that current, an arc may form and the current may still flow as if the switch was still closed. Or the protective device may be damaged.
For mcbs they can only do 6ka typically. But the fuse in the supply will break more than that, but will let through a lot more energy hence why you use cat IV equipment there.
Anyway back to my original question, can an rcd break more than it's 63a value marked on the front? Or do we assume any faults over 63a would trip the mcb in time due to correct loop impedence. (No not you, the actual impedence)

 

[EFLImpudence]

Yes, I said about breaking capacity:
"... must be the same as MCBs to cope with short-circuit and fault current as do the cables.
Schneider are marked 10kA."

Although this for 61008s says only 1.5kA

The 63A is the (continuous) CCC but irrelevant to breaking capacity as others of 40A, 80A or 100A would have to be the same.

can an rcd break more than it's 63a value marked on the front? Or do we assume any faults over 63a would trip the mcb in time due to correct loop impedence.

As above, yes, a fault current will be hundreds of amps.
It would be unlikely that a fault current would be only 63A - an EFLI of 3.65Ω @ 230V.

 

[John D v2.0]

Yes, I said about breaking capacity:
"... must be the same as MCBs to cope with short-circuit and fault current as do the cables.
Schneider are marked 10kA."

Strange to use "cope" as a synonym for breaking capacity. What does breaking capacity mean in terms of a cable?

As above, yes, a fault current will be hundreds of amps.
It would be unlikely that a fault current would be only 63A - an EFLI of 3.65Ω @ 230V.

True but in that case the MCB is designed to break the circuit, so the RCD just has to avoid catching fire in that time. I can't think of any situation the RCD would be required to trip above it's rated current when the MCB wouldn't. Assuming a single fault. Hence my question.
Anyway you answered my question from the data table, just seems like Hager didn't write it on my RCDs!

 

[EFLImpudence]

Strange to use "cope" as a synonym for breaking capacity. What does breaking capacity mean in terms of a cable?

It's not a synonym for breaking capacity.

It means, with reference to the 63A rating, it deals effectively with the short-circuit current without damage - when not breaking, as does the cable - until disconnection by the MCB.

True but in that case the MCB is designed to break the circuit, so the RCD just has to avoid catching fire in that time.

Yes, the same as the cable.

I can't think of any situation the RCD would be required to trip above it's rated current when the MCB wouldn't. Assuming a single fault.

Do you not think the RCD will trip as well - or instead - with fault current of hundreds of amps?

 

[John D v2.0]

Do you not think the RCD will trip as well - or instead - with fault current of hundreds of amps?

I think you've gone round in a big circle and then back to my original question!
That was exactly my original question, but I think the data table you quoted saying 1.5kA answered it the "will it" but not necessarily the "why". Where's JohnW2 when you need him

 

[stillp]

Although this for 61008s says only 1.5kA

Why are they quoting the making and breaking capacities in kiloAngstroms, I wonder?

 

[EFLImpudence]

That's not making and breaking; it says surge current withstand without tripping for S types.

 

[stillp]

Oh yes, my mistake. So what are the units they've used?

 

[EFLImpudence]

I think you are right about Angstroms - the symbol anyway - just not for making and breaking current.