New earth bonding test

[Derlyn]

Thanks GCE.
2 reasons for my question. I'm on the earthing train at the moment and I'm adamant to understand as much as I can regarding earthing and bonding.

1. It's gonna be difficult to assign one ecc per slot on purchased populated db's. An 18 way db is supplied with an earthing terminal that has 6 to 8 slots max.

2. I'm struggling to understand what is meant in 6.11.4 by the words " conductors from more than one supply ". I have yet to find a db that has more than one supply.

[GCE]

I'm struggling to understand what is meant in 6.11.4 by the words " conductors from more than one supply ". I have yet to find a db that has more than one supply.

Could be a generator supply , inverter supply, Municipal supply on residential , all 3 or a combination - Add gridtie solar into the mix as well

On my little office I have Tesla powerwall , gridtie inverter and municipal supply on the same bus connection.

On bigger installations you could be running 2 transformers in parallel or a transformer LT supply into the main DB along with a generator that sync to mains on start up or switch off, so that you have seamless change overs.

There are also installations with 2 or 3 generators synchronized . You would run say 1 x 500KVA set and only bring the 2nd set in when you get to 400Kva to ensure you can get 1Mva and then a small 100Kva set for night time to run security etc .

There are a couple of combinations - You would not want to be in a sub station with a 500Kva transformer earth and genset earth on the same lug point . If you want to disconnect the genset earth you would need to remove mains earthing and get a whack in the process. If each was on it's own lug point that would not happen.

[Derlyn]

Thanks once again GCE.
Personally I have only come across systems with change over switches where there is only one supply cable to the db.

Anyway, without sabotaging this thread, how does one get by 6.6.1.1 with so many supplies on the busbar. Is there a multipole isolator that shuts off all the supplies or does each one go through its own isolator ?

[GCE]

Anyway, without sabotaging this thread, how does one get by 6.6.1.1 with so many supplies on the busbar. Is there a multipole isolator that shuts off all the supplies or does each one go through its own isolator ?

Basically each has it's own CB and then onto the main Busbar - With 2 transformers in parallel you generally have a bus coupler that will isolator the main busbar in the middle .

Label , Label and label again and also keys especially if you have "unlike" transformers ( 2 keys and 3 switches so only 2 can be on at the same time) . Have got to centers where phasing was never done correctly on installation and closed the bus couple to be able to open a transformer CB for servicing without dropping supply and the "bang" is real.
I have learnt not to trust others and check the phasing and direction now before closing.

[Derlyn]

Basically each has it's own CB and then onto the main Busbar - With 2 transformers in parallel you generally have a bus coupler that will isolator the main busbar in the middle .

Label , Label and label again and also keys especially if you have "unlike" transformers ( 2 keys and 3 switches so only 2 can be on at the same time) . Have got to centers where phasing was never done correctly on installation and closed the bus couple to be able to open a transformer CB for servicing without dropping supply and the "bang" is real.
I have learnt not to trust others and check the phasing and direction now before closing.

@ GCE

Thank you, brother.

Interesting. I am now in the slowing down stage and have concentrated my efforts on domestic installations for the last 13 years.
When I study the regulations, I think domestic installations and tend to forget that the regs cover the big stuff as well.

If it weren't for the fact that Lynette and I, in our advanced years, decided to put some young one's through school, I'm sure I would have been sipping sundowners on the banks of the Orange River somewhere by now.

Anyway, back to earthing now and thanks for the feedback. Much appreciated.