Use RCD for 130m cable run to outbuilding?

[PEG]

Let us hope the OP can get equally good advice from his "sparkly"...sounds bright enough

 

[Ewok]

Interesting to see all the different options and solutions - hence posting on here. I wanted a bit of background knowledge so I have some idea of what my sparky tells me is a good solution

 

[westward10]

The cable to the outbuilding would be protected by an MCB, lets say its 32A. If there is an earth fault on the cable the MCB should trip, but the earth fault current will be restricted by the impedance of the earth/ROD at the house and, and that is never going to be enough to trip a 40A MCB.
So an RCD is needed to provide this protection. Its not for personal protection, so 100mA fits the bill, but it needs to be time-delayed or an earth fault in the outbuilding could trip both the remote 30mA RCD, and the 100mA RCD at the source end.

How have you come to the conclusion a 32A device will trip but a 40A will not? This is all dependent on the magnitude of fault current which we do not know.

 

[westward10]

SWA is a cable used as an alternative to RCD protection and for situations where RCD protection is not acceptable.

Eh?

 

[Deleted member 26818]

Where cables are concealed in walls, the options are to bury the cable at a depth greater than 50mm, use an earthed sheath cable such as SWA, install the cables in earthed conduit or trunking, provide mechanical protection sufficient to prevent penetration by drilling or nails or to run the cables in prescribed routes and provide additional protection by means of a 30mA RCD.
For cables concealed above ceilings and below floors, where the cables pass through joists or battens, the same options are available, excepting the option to run in prescribed zones with 30mA RCD protection.

Hence my comment.

 

[westward10]

Where cables are concealed in walls, the options are to bury the cable at a depth greater than 50mm, use an earthed sheath cable such as SWA, install the cables in earthed conduit or trunking, provide mechanical protection sufficient to prevent penetration by drilling or nails or to run the cables in prescribed routes and provide additional protection by means of a 30mA RCD.
For cables concealed above ceilings and below floors, where the cables pass through joists or battens, the same options are available, excepting the option to run in prescribed zones with 30mA RCD protection.

Hence my comment.

Not sure the 130m run will be concealed in walls.

 

[Deleted member 26818]

Not saying it will be.
Just saying, that SWA is a cable which is used where RCDs are not allowed.
So is fine to use without an RCD.

 

[westward10]

Not saying it will be.
Just saying, that SWA is a cable which is used where RCDs are not allowed.
So is fine to use without an RCD.

Give an example please of where rcds are not allowed.

 

[mrloy99]

Hospital..sèe special locations 710 operating theatre.

Oops ancient post soŕry

 

[Rpa07]

Don't worry @mrloy99 - far more ancient threads have been revived. Some have needed an obligatory dust off. Late September is concidered recent!
Ps how are you getting the accents on your letters in your post?

 

[mrloy99]

Don't worry @mrloy99 - far more ancient threads have been revived. Some have needed an obligatory dust off. Late September is concidered recent!
Ps how are you getting the accents on your letters in your post?

 

[mrloy99]

Sorry fat lìngèring fingers.

 

[Rpa07]

You are making lingering sound like lingerie! I'm going to change my keyboard setting too!

 

[Rpa07]

I've decided not to mess!