RCDs in Series

[perfo]

I've done a bit of research on here and this subject has come up a few times but not quite like this . I have a house (not unusual there) and a garage/workshop some 15m away. I have an RCD protecting the house circuits and the SWA cable feeding the garage /workshop and then another in the workshop CU. Reading up on this, it appears this is a no no under the regs and you should never have two RCDs in series. The problem of two in series is both trip when you get a fault at the garage end, so if I get a trip in the workshop I also trip the house. This could be cured by taking the RCD out at the garage end and replacing with an MCB. Problem is I'm not always on site (in the house ) when the garage is in use so it would be a problem if the house trips. How can I get around this one?
A thought I’ve had is to put another earth electrode in at the garage end but if I do this would I connect it to the neutral in the garage CU???
Thanks.

 

[ban-all-sheds]

How can I get around this one?

Leave the RCD in the garage CU and don't have the cable supplying it on an RCD in the house.

A thought I’ve had is to put another earth electrode in at the garage end but if I do this would I connect it to the neutral in the garage CU???

No.

Why would you want to connect the neutral to an earth rod? What would it achieve, apart from permanent earth leakage and the RCD never staying on?

 

[ericmark]

Forgetting Part P.
The idea is each RCD is three times smaller than one before with a lower and lower delay time. In practice the time is a problem as once you have a 30ma 40ms RCD then even using a 10ma RCD still has a 40ms time.

There are two specials. One has a warning meter built in and does not trip until between 90% and 100% of the rated milliamp instead of the normal 60% to 100% so making it more likely that a second RCD will trip first. The other is an auto resetting RCD but at £300+ each not a cheap option.

With 1A at 10 second dropping in stages 300ma at 5 seconds then 100ma at 1 second and finally 30ma at 40ms when a guy put a nail through the cable it still tripped the lot. So there is no way to be sure one RCD will always trip before another but likely it will.

Depending on earth system and type of consumer unit fitted it may be possible to remove the RCD in the house and replace it with RCBO's instead and feed the garage with a MCB. Even if it requires changing the consumer unit likely cheaper and better than the auto reset type.

However returning to Part P the costs of LABC charges likely will mean you are better employing a registered electrician to do the work.

As to the rules well it does not say you must not put two RCD's of same type feeding each other in fact you have to do just that with caravans and boats. It says the design should minimise unwanted tripping.

It is in the main down to cost. And without knowing if your existing consumer unit will take RCBO's hard to say how much. But as already said likely cheaper to not DIY if you want to follow the rules.

 

[JohnW2]

Leave the RCD in the garage CU and don't have the cable supplying it on an RCD in the house.

That presumably assumes that the SWA goes all the way to the house CU and/or that any part of the cable run which is not SWA is otherwise exempt from needing RCD protection?

Kind Regards, John.