Questions like this will get answered faster in the wiring forum, and in future I strongly suggest you post there- but in any case the answer above is correct, but there are additional points and easier ways to think about it, no need to use a calculator, so  here goes.

In terms of the line current, which is what the MCBs will sense it matters not one jot if the load is connected delta or star so long as the load is balanced on all 3 phases - there will be no overall neutral current, and each line will carry 1/3 of the power.


If you wish you can faff about with 400V and factors of root 3, or you can realise that this is exactly the same as a single phase 3kW load 3 times.  So the current is the power divided by the single phase voltage 3000/230, so 13A. 

A 16 or 20A breaker would then be in order, as 13A is not a standard size. Depending on the cable length you may be limited by the cable current rating (and the nearest common size would be 2.5mm2 - the tables may suggest that for current handling, 1.5mm2 is OK and it is if you can avoid grouping it with other cables or embedding it in a wall on it's route, but nearly all real cable routes can not meet that requirement)*

On a longer run you may well be limited by voltage drop, and need something in larger cross section to keep the volt drop within limits..


Your choice of breaker should break all 3 phases, but breaking 3P and N is not incorrect, and is actually required if the supply is TT earthed

Best regards Mike.


* 6m will not have a volt drop issue, and if you can keep the cable cool, you can get away with 1.5mm2. Personally I'd suggest that 2.5mm2 is not a lot dearer, and remains the safe option in more situations - such as when someone adds more cables around it or boxes it in.


PS an immersion heater is not an example of an electrode heater - in the latter the water is live.

Questions like this will get answered faster in the wiring forum, and in future I strongly suggest you post there- but in any case the answer above is correct, but there are additional points and easier ways to think about it, no need to use a calculator, so  here goes.

In terms of the line current, which is what the MCBs will sense it matters not one jot if the load is connected delta or star so long as the load is balanced on all 3 phases - there will be no overall neutral current, and each line will carry 1/3 of the power.


If you wish you can faff about with 400V and factors of root 3, or you can realise that this is exactly the same as a single phase 3kW load 3 times.  So the current is the power divided by the single phase voltage 3000/230, so 13A. 

A 16 or 20A breaker would then be in order, as 13A is not a standard size. Depending on the cable length you may be limited by the cable current rating (and the nearest common size would be 2.5mm2 - the tables may suggest that for current handling, 1.5mm2 is OK and it is if you can avoid grouping it with other cables or embedding it in a wall on it's route, but nearly all real cable routes can not meet that requirement)*

On a longer run you may well be limited by voltage drop, and need something in larger cross section to keep the volt drop within limits..


Your choice of breaker should break all 3 phases, but breaking 3P and N is not incorrect, and is actually required if the supply is TT earthed

Best regards Mike.


* 6m will not have a volt drop issue, and if you can keep the cable cool, you can get away with 1.5mm2. Personally I'd suggest that 2.5mm2 is not a lot dearer, and remains the safe option in more situations - such as when someone adds more cables around it or boxes it in.


PS an immersion heater is not an example of an electrode heater - in the latter the water is live.