3 Farm buildings

[mattmoo1974]

Hi iv been asked to wire 3 farm buildings.
The sub mains have to be RCD protected, Do i 300ma Main swt first ccu rcbo's
100 Ma second and use rcbo's and 30ma main swt and mcb's ccu?
Any suggestions would be helpful iv red the green book and me head is hurting lol i could use a 100 ma upfront but this would mean a lot of walking if it trips,im after good discrimination.

Also its a 300 meter run to the last shed with a 5Kw load @ the end, and 22amps required mid way. So im getting a bit confused with VD(not the disease)

I'm after helpful suggestions not a ribbing

 

[mattmoo1974]

Sorry i forgot tot mention the Main intake is in shed 1 if you didn't guess and daisy chain along.

 

[JD6400]

So have you got one distribution point with 3 sub mains going out or is it one distribution point with just one sub main going to shed 1 then shed 2 and again on to shed 3 ?
Sorry if it was obvious in your first post , but this Bison grass Polish vodka is taking its toll !

 

[mattmoo1974]

Haha iv had a few as well
Yes first Shed in the intake and then to number 2 then onto number 3 shed
Its not split just daisy chaining along

 

[Taylortwocities]

Repeat after me

You can only achieve discrimination of RCDs by using time delay not current as the discrimination factor.

Think about this:

You have a 300mA RCD at the source
a 100mA at the DB and a 30mA RCBO protecting a circuit.

An earth fault occurs on the end circuit.

Which RCD will trip first?


Answers on a postcard please......
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The RCD that will trip first will be one with the fastest trip time depending on where the AC sine wave happens to be.
It could be any, or all of the RCDs that trip. It depends.

The only way to properly achieve discrimination is to have a series of time delay RCDs with the longest trip time at the source and the shortest at the end point.

 

[JD6400]

I would start with a 100-300ma s type up front , personally i will only go tt even if there has been a metal gridded floor installed !
Is there no way of running separate subs ?

 

[JD6400]

Repeat after me

You can only achieve discrimination of RCDs by using time delay not current as the discrimination factor.

Think about this:

You have a 300mA RCD at the source
a 100mA at the DB and a 30mA RCBO protecting a circuit.

An earth fault occurs on the end circuit.

Which RCD will trip first?


Answers on a postcard please......
v
v
v
v
v
v
v
v
v
v
v
v
v
v
v
The RCD that will trip first will be one with the fastest trip time depending on where the AC sine wave happens to be.
It could be any, or all of the RCDs that trip. It depends.

The only way to properly achieve discrimination is to have a series of time delay RCDs with the longest trip time at the source and the shortest at the end point.

Not always !
Have a look at thread that was up on Friday about a time delay going out first , i will try and find it's name if i can focus long enough .:17:

Edit ; But yes it would obviously normally be the case !

 

[JD6400]

It was " 100mA delayed RCD tripping before the 30mA at DB. TT system "

 

[Taylortwocities]

Zubrowka rules!
But I'm on Taylors LB Port (what else?)

I will consider your input after a snooze..............

 

[JD6400]

To be honest I'm about to bow out now for the same reason !:stuart:

 

[Knobhead]

I with I had been on the booze, there may have been a chance of understanding the first paragraph of gibberish!

 

[mattmoo1974]

Everyone else seemed to understand it, Tony! and they've been drinking! My apologies if it was that hard to work out. Maybe you need a drink to chill out a bit!


I'm after helpful suggestions not a ribbing <<<<<<<<<<<<<<<<<<<< It's sad that I had to put this request on the end of my question, but you always seem to get someone who is more interested in having a pop rather then helping! Thanks you for all the helpful suggestions...