Quick question planing to install a 4.5kw water heater do I need to run the earth back the the main distribution board. Or can I safely run it back to the earth rod which is behind the bathroom any way so a lot closer

You should run back to the board if at all possible. But a local rod will be infinitely safer than no rod at all.

 

Do bear in mind that if you get a nearby lightning strike, whilst unlikely, there could be considerable potential between the two "earths", possibly enough to cause a flashover and resultant nasties.

 

Australia specifically forbids multiple ground rods, even if interlinked, for just this reason.

i agree with previous post also to keep in mind might be to ensure suitable input power source  as there seems to be only a live/neutral supply at the moment is it also suitable  for upgrade/new heater?  maybe worth a thought

So crossy I didn't mean install a new earth rod behind the bathroom. The existing earth rod for the mains is already behind the bathroom. 

 

So what  I meant is it ok to run a new cable to the existing earth rod or is it better to have only one cable coming off an earth rod.

37 minutes ago, outdoorbloke said:

So crossy I didn't mean install a new earth rod behind the bathroom. The existing earth rod for the mains is already behind the bathroom.

So what  I meant is it ok to run a new cable to the existing earth rod or is it better to have only one cable coming off an earth rod.

Ah, now I understand.

 

Under UK regs it wouldn't be allowed with the concept of a MET (main earth terminal) where all grounds are marshaled.

 

Personally I would still run back to the board, but in reality with only a single rod I see no real issues.

 

As others noted, do ensure the existing cable is man enough. 4.5kW is about 20.5A, just OK on 2.5mm² and a 20A breaker but anything smaller will need to be replaced.

Another option would be to connect to the roof steel assuming that is convenient to do.

Was planning to run a 4mm cable in case I want to upgrade later existing earth from mains is a 6mm back to the rod.

 

Reason I was going to run the earth direct to the rod is because I am yet to find 3 wire 4mm and it's a pain to run an extra cable.

42 minutes ago, outdoorbloke said:

Was planning to run a 4mm cable in case I want to upgrade later existing earth from mains is a 6mm back to the rod.

 

Reason I was going to run the earth direct to the rod is because I am yet to find 3 wire 4mm and it's a pain to run an extra cable.

Pain is relative I suppose, but running an extra cable is not difficult.  And, in my opinion, 2.5mm² is more than enough to run as a ground.

2 hours ago, bankruatsteve said:

Pain is relative I suppose, but running an extra cable is not difficult.  And, in my opinion, 2.5mm² is more than enough to run as a ground.

Yup. Reduced section protection is common in the UK. Finger in the air says it will be fine if the run isn't too long.