sub main from a tt supply

[KEVINDOE]

Hi Guys,
I am running a s.w.a. sub main to a garage c.u., the supply is TT, The s.w.a will be buried for a few meters and then clipped direct before entering the garage.
The existing boured is 16th and has no free RcD ways, am i right in saying that a sub main should be protected if origin is TT ?

Thanks Jem

 

[telectrix]

henly blocks into switch/fuse, then SWA to garage CU with RCD/MCBs. 2nd rod at garage end . any water or services in garage ?

sorry just re-read post . thought you said no spare ways. but apparently you have spare non-RCD ways. then you can come off MCB. SWA doesn't need RCD at front end as it is mechanically protectd.

 

[KEVINDOE]

Yes telectrix, got spare non RCD way, final circuits will be 30ma protected at garage c.u. , no utilitys, perhaps im confused with a metal clad main c.u. situation ?

 

[telectrix]

think so. if metalclad CU in garage, need RCD at front end of SWA to prevent CU becoming live in case of fault.plastic CU, no need. suggested 2nd rod as that will improve your Ze on both house and garage. earth armour at both ends.

 

[Chr!s]

sorry just re-read post . thought you said no spare ways. but apparently you have spare non-RCD ways. then you can come off MCB. SWA doesn't need RCD at front end as it is mechanically protectd.

The circuit needs to comply with 411.3.2.4

 

[KEVINDOE]

ahh, thats where im getting the rcd thing from ....yes metal clad in garage

 

[Guest123]

SWA doesn't need RCD at front end as it is mechanically protectd.

It more than likely will on a TT system, unless you have a extremely good Ra of less than an ohm as the Zs will be too high for the MCB to achieve disconnection by itself

 

[KEVINDOE]

Time for a shuffle round in main c.u. i rekkon, squeeeeeeze an r.c.b.o in

 

[Guest123]

I'm surprised the existing DB doesn't have 1 x 100mA S type RCD & 1 x 30mA RCD if it is a 16th ed board on a TT system.......

 

[not clever]

100mA s Type on the distribution circuit/submain.

Just to quick for me Lenny.........

 

[Deleted member 9648]

An S type RCD will be expensive......If it's just a garage with the usual couple of sockets and lights I'd be inclined to 30ma RCD the distribution circuit from a separate henly blocked DB at the intake, and just use a normal main switch CU in the garage....depends whether cost is a consideration.

 

[JD6400]

I may have not have got this right but i think you have said the main supply is tt . If so how have you got any spare non rcd ways ! it's tt ?

 

[KEVINDOE]

Sorry dp, main 100 rcd removed to allow c.u. to be fitted as 4 way 3036 was there before, three rcbos on non rcd side 16th edition, imm, 2x lights.
i dont know who did the change, no certs provided, may have been d.i.y ?