Water heater question.

[Dairyspark]

Hi guys,

So I do a lot of work in agricultural settings and currently doing a new large dairy unit. 50 or 54 point rotary with everything from cooling compressors to vacuum pumps and beyond. Now my question comes in the form of this

The plant water heater is huge, it contains 3 x 6kw elements which consists of 3 x 2kw each having a phase and one common neutral, does that make sense?

Now all the elements are linked together so L1 of element one is linked to L1 of element 2 and then to element 3 so each phase has effectively 6kw attached to it and all the neutrals are just linked together.

Now my understanding of this is each phase will draw 26A and since they are all returning down one neutral line does that mean that it’s getting 78A back down the neutral? Now if this is correct then surely that’s absolutely no use to anyone as I’d have to supply it with a 16-25mm² cable to carry the neutral current. Surely this is a terrible design?

Am I being stupid and not understanding basic electrical theory or is this the most ridiculous water heater know to man

I have attached a picture of the offending water heater to show the size of it

Cheers
Bobby

 

[Geoff1946]

Assuming that they are all switched on simultaneously the load is balanced and there won't be any neutral current.

 

[Dairyspark]

Yeah they all come on together. I assumed since it was effectively 3 x 2kw elements lumped together you’d get neutral current

 

[Dairyspark]

Assuming that they are all switched on simultaneously the load is balanced and there won't be any neutral current.

Aw so is it basically like a Star point

 

[binky]

Aw so is it basically like a Star point

yes, a bit hard to get your head around but it does work.

 

[Fleeting]

How have you come to the conclusion of 26A per phase.

 

[Dairyspark]

How have you come to the conclusion of 26A per phase.

Each phase has 3 x 2kw elements attached to it so in my mind it was simple P=I/V

I = P/V 6000/230 = 26.08A
Which then let to me thinking each phase passing it’s current back through a common neutral which left me with 78.26A to return down the neutral line, but now that it all works out as a balanced 3 phase load there is no neutral current.

However does that mean I’d say one of the elements sections (2kw) fails will that then unbalance the load on all three elements and cause the high neutral current or only on one of the elements and the other 2 are still balanced?……am I making sense?

 

[johnb2713]

However does that mean I’d say one of the elements sections (2kw) fails will that then unbalance the load on all three elements and cause the high neutral current or only on one of the elements and the other 2 are still balanced?……am I making sense?

It would be neutral current of the failed element i.e. 2kW