3 Phase Immersion

Effects

So with a three phase immersion, does the neutral carry any current? Are these elements essentially balanced but there may be some out of balance current carried by the neutral?

stoneill

Always assume that neutral carries current.
Star system will have a neutral, delta systems will not.
There is a potential difference of 230v from phase to neutral.
This does not necessarily mean 0v-230v, it could be 10v - 240v.

Bruthal

If its always all 3 elements on, there would be little or no current. Nothing is 100% perfectly balanced, but it would be balanced enough that no neutral would be needed, even in star, if for example a 9kw element was consisting of 3 x 3kw elements, and all 3 would always be on together.

A neutral would only be needed if the 3 elements are not all going to be always on, as in, if just one or 2 of the 3 elements may be switched in at a time.

If a motor was connected in star, it would have no neutral to the star point.

2011

Effects wrote: »

So with a three phase immersion, does the neutral carry any current? Are these elements essentially balanced but there may be some out of balance current carried by the neutral?

+1 to Robbie

I would be surprised if there is even a neutral connection.

brightspark

Usually there just in case one of the elements fail open circuit

M cebee

Yes i connected a few years back
As said imo there would be a neutral in case 1 fails open

2011

If 1 fails then you will have 2 connected in series with line voltage (400V) across them. So they will still heat the water.

But I would of course connect the neutral if there is a connection for it.

M cebee

I cant recall
it wouldnt be critical anyhow

M cebee

Yes i think maybe they dont as 2 would heat at near full power anyhow

Bruthal

If one element fails with open circuit, the other 2 elements will just have 200v each, so a neutral still wouldnt be needed.

With the neutral in place, it would actually be less obvious that one element had failed, as the 2 remaining elements of the group would have full voltage.

Any 3 phase elements i seen had neutrals, as they were in the combi steam ovens i used to repair for a time, which could switch in each section individually.

Bruthal

M cebee wrote: »

Yes i think maybe they dont as 2 would heat at near full power anyhow

If there was no neutral, and 1 element fails, the elements will output half of the full power of all elements on.

If there is a neutral in place, it will be 2/3rds of full power. So they will get by better with the neutral in place alright, with one element failed.

Many would probably still run the neutral, even though its not really needed.

Effects

Thanks for the replies. I was asked about this by a colleague. I had assumed that there would normally be no current in the neutral. The elements are all on at the same time. It was a changover of a large immersion cylinder. I only disconnected it and someone else reconnected it. They were worried if the neutral would be carrying too high a current for the rating on the 3ph MCB.

Bruthal

Effects wrote: »

Thanks for the replies. I was asked about this by a colleague. I had assumed that there would normally be no current in the neutral. The elements are all on at the same time. It was a changover of a large immersion cylinder. I only disconnected it and someone else reconnected it. They were worried if the neutral would be carrying too high a current for the rating on the 3ph MCB.

If a neutral is connected to such an element fed by 3 phases, the highest current the neutral will carry is if 2 elements go off, or fail, and the neutral current will then be just the same as the phase current to the one remaining element. With 2 elements on, the neutral current will be less than 1 element`s current, and with all 3 working, the neutral current will be 0 amps.

The 3 phase element would also work with a single phase looped to all 3 elements, but in this case, the neutral current would be the 3 elements combined, just like 3 seperate single phase loads.