Domestic supply on a farm

[Tony Way]

Hi all. - Sorry - bit of an essay below but would appreciate time taken to read.

Have been asked to look at wiring an extension on a farm house. Took a look and found the following:

Supply is 1ph via the 3ph supply on the other side of the stock yard. feed to house through a 1361 60/80A to 60A RCD (ancient and the test button doesn't trip it) throught a 60A semi enclosed into 10mm (I think - although the cable cross section is oval not round so not that easy to tell) SWA to the house and into a 100A Isolator into MCBs. Currently the Main Earth to the House is TN-S exported via the outer of the SWA.

The farmer is not about to rip up his stock yard and under the newish barn to run a 16mm SWA so I'm stuck with the 10mm. Therefore 60A max supply.

I need to replace the old RCD but can only find 63A which is outside the rating of the SWA. Any smaller and his 5 bed house is going to be short on Amps.

I'm thinking of making the house TT and only using the TN-S to protect the supply cable.

Any suggestions as to where I can get a 60A RCD and MCB (or RCBO)? OR any other solutions??

Many thanks

 

[bugsy]

Is the supply cable to the house ( 10mm t&e ) buried and in conduit.

 

[marksparky]

i think the supply cable is 10mm swa bugsy?? as long as ur armouring is correctly terminated ie earthed there would be no need to protect it with a rcd? u could terminate armoured cable into 60 amp switchfuse?

 

[monkeyelectric]

Hiya mate, an rcd is only for fault current not overcurrent so would have to be switchfuse or rcbo, and if it is 10mm and the start of the cable is over the other side of the stock yard you may have too much volt drop so will have to reduce the current anyway

 

[roukel01]

If it's TN-S does the supply SWA have to be RCD protected? Can't you use something like this?

 

[bugsy]

As markysparky said - I should have read the post correctly

Whats the length of run , Is it buried, whats the earth loop at the house DB, and max demand / design current

 

[Tony Way]

Hi All.

The SWA is buried under the stock yard and barn. RCD necessary because the farmer has already put one of the support posts for the barn through the SWA. and the way he swings his JCB around, I can't gurantee that a bucket won't go through it again. Fuse needed for over current protection to the cable in case of fault.

Run is about 40m and I've checked the vd already and is only 1.2%.

I like the 63A RCD put through a 60A fuse. Yes I was getting confused between cable protection (RCD) and over current protection(fuse).

Am I doing the right thing by putting the House on TT and leaving the cable protected by TN-S?

Thanks

Sorry didn't read the last post fully.

Haven't done earth loop for house yet. Design current with diversity only about 50A - I've convinced him he needs to change the 9kW shower for a 13A pump version.