Rcd head scratcher

[Welchyboy1]

Farm job im at has a problem


three phase tt system comes into main barn area, three phase main distribution board (with 100mA s type 4 pole rcd as main switch) supplying barns and general farm buildings

Swa single phase supply to farm house(around 40meters away), supplied directly from meter side of distribution board on henly blocks to switchfuse/rcd

so house supply is totally independent from the barn supply

however everytime there is a fault on the barn distribution board and its main rcd operates it takes out the rcd at the farm house too

i havent been over to the farmhouse yet but i cant understand why it would be knocking out the rcd in the house?

any ideas?

 

[Darkwood]

Where abouts is the suppliers transformer ...is it close up a pole?
What kind of rcd's are they - are they modern type that measure inbalance between L/N?

Have you ensured all your customer side connections are sound and tight... check busbar tabs are on the correct side of any mcb, rcd and main switch terminal clamps.

 

[Pete999]

If the SP supply is taken from the load side of th e TP RCD the any fault on the SP supply will trip the TP RCD

 

[Deleted member 9648]

If the SP supply is taken from the load side of th e TP RCD the any fault on the SP supply will trip the TP RCD

He said it's on the mains side though.

 

[Darkwood]

If the SP supply is taken from the load side of th e TP RCD the any fault on the SP supply will trip the TP RCD

He's explained the set-up and the house supply is independent from the 3ph supply and straight off a henley block from the meter.

 

[Badged01]

As I read it Pete the house SP supply comes off before the 3P RCD so they should not effect each other. Which is the problem the OP is trying to get a handle on as to why they actually are!

 

[R G]

If theres a single earth stake in use for both barn and house , and all bonding is done at the house , it could be the Ze of the earth stake is higher resistance than the bonding at the house and fault currents are back fed to house , just a thought,,

 

[Badged01]

Beaten twice to the punch ......

 

[MDJ]

He said it's on the mains side though.

so it is a TT system, what is protecting the sub main to the house :lipsrsealed2:

 

[Badged01]

... and then beaten again with my next thought around the TT'ing set-up!

 

[Badged01]

Time to sit back and watch (read) you guys are just out thinking me! Far too fast for my simple brain processing ability ......

 

[Pete999]

Sorry lads too much red stuff missed that apologies for the assumption

 

[Darkwood]

This reads plain to me but a few are not reading the OP properly ...

At mains there is a 3ph board with 100mA rcd main switch
Also a 1 phase supply straight of the meter via a henley block to a sw/f + RCD ...lets assume 100mA

When a fault trips the rcd of the 3ph board the rcd IN THE house trips so assuming a 30mA is tripping in the house possibly 17th edition board.... can the OP confirm this!?


Edit confirmed in post 15.

 

[wozz]

he said henleys, switchfuse, rcd.

then i hear TP board and TT the first thing i think of, is the first (RCD) enclosure insulated?

 

[Welchyboy1]

so it is a TT system, what is protecting the sub main to the house :lipsrsealed2:

100ma sp rcd, at barn end, i haven't been into the house yet but from what the customer describes a 30ma rcd covering her whole cu and this is whats tripping out