earth bonding to additional consumer units

[sparkattack]

Hi, when you are confronted with 2 or more consumer units on each system what is the requirements for the earth bonding to incoming supplies such as water and gas? do they go to an earth block and then to each and every consumer? cheers guys

 

[fletchflash]

relevant size PEB to main earth terminal (earth block), then main earth to each CU. if in same property

 

[SLIPSHOD & SLAPDASH]

And the earth block in the existing c/u could be designated the main earth terminal so all you need is a link of the correct size (normally 16mm for domestic) to the second board.

If its a fairly modern unit the cables will fit. If its old you will struggle to get large terminated and a additonal block may have to be used

 

[Sidewinder]

Utilise a BEMT - Building Earth Marshalling Terminal.

i.e. a seperate external earth terminal designate this as the main earth and "distribute" from there, common in LARGE installs.

 

[green-hornet]

+1 ^

makes everything easier to disconnect when testing as well.

 

[sprocketflup]

Utilise a BEMT - Building Earth Marshalling Terminal.i.e. a seperate external earth terminal designate this as the main earth and "distribute" from there, common in LARGE installs.

Would there be any special requirements for it Sidewinder? Could you use say a five way Henley block?

 

[Ash]

I bought a stacking kit for stacking two MK boards and it came with a 6mm earth cable to join between them.

Is this acceptable?

 

[Sidewinder]

Sprocket,

IF a 5 way Henly could take all the connections then it should be OK in principle.

Ash,

IMHO ONLY IF the 6mm could carry the possible fault currents as per 7671.

 

[Ash]

Based on that CCU, the pfc was 1.47kA

so can you confirm if I did this calculation right

√(1470sq*0.4)/160

came out as 5.81

so 6mm would have been fine if I'd chosen to use it?

 

[Sidewinder]

Ash,

More info please especially at this time of night! Guinness

 

[sparkattack]

does 3 phase require larger earth bonding as opposed to standard single phase supply?

 

[Sidewinder]

Depends!

Sorry!

 

[Ash]

Ash,More info please especially at this time of night! Guinness

lol, sorry

i based it on

S = √(I2*t) / k

I2 was the pfc of 1.47kA squared times disconnection time of 0.4 (this was what I wasn't sure if I got right) / k value that came out at 160degrees on the chart

 

[Sidewinder]

Was this Ph to E or Ph to Ph?

Would this matter?

Sorry forgot to say, your I^2 value

 

[Ash]

you got me confused now, but I would go with Ph to E if I understand you correctly

 

[Sidewinder]

OK, just making you think!

I can't anymore too tired will look more when I have a chance sorry.

Was up late last night and early this am!

 

[Ash]

I enjoy a good challenge like this

 

[Larnacaman]

Ash,

That 6mm cable is just a bonding cable between the 2 CUs. You will still need to connect a correctly sized Earth cable to the supply tails to each CU from the EMT.

SparkAttack,

No, Bonding cable sizes follow for either single or three phase installations. As does the main earthing cable size, which is dependant on the cable size of the supply cables...

 

[spinlondon]

Might be helpfull if you told us the earthing system, TN-C-S, TN-S or TT?