3 X single phase showers

[David Rann]

I've been asked to price 3 X 7kw showers. There is a three phase board about 40 meters away. Can anyone see an issue with 40 amp three phase MCB with 10mm four core swa to a sub board then 3 X 32 amp rcbos for each individual shower.

Cheers

 

[David Rann]

Flogged?

 

[David Rann]

Flogged?

 

[Pete999]

Will you be using shower priority contactors ?

What is a "shower priority contactor"?

 

[Pete999]

Will you be using shower priority contactors ?

What is a "shower priority contactor"?

 

[Andy78]

What is a "shower priority contactor"?

Pre made units that can limit the amount of current drawn by only letting one shower be energised at a time.

For clarity, I'm not saying one needs to be used, but was asking if one was being used as I've never fitted one and would be interested if one was.

 

[David Rann]

I thought that in a three phase supply that if you have 32 amp running on each phase then they would be balanced and you would have nothing down the neutral?

 

[Pete999]

Pre made units that can limit the amount of current drawn by only letting one shower be energised at a time.

For clarity, I'm not saying one needs to be used, but was asking if one was being used as I've never fitted one and would be interested if one was.

As would I, as would I.

 

[Deleted member 26818]

I thought that in a three phase supply that if you have 32 amp running on each phase then they would be balanced and you would have nothing down the neutral?

They don’t balance out over the single phase part.
They only balance out over the 3 phase part, once the 3 neutrals are connected together.
Even then, they only actually balance if all the phases have the same loading at the same time.
As a rule of thumb, double the single phase load to determine the CSA of the neutral for the 3 phase part.
So if each phase will be feeding a 7kw shower, that makes 14kw.

 

[Pete999]

Flogged?

Urban Dictionary: Flogged - https://www.urbandictionary.com/define.php?term=Flogged

 

[westward10]

Phasor diagram anyone.

 

[David Rann]

They don’t balance out over the single phase part.
They only balance out over the 3 phase part, once the 3 neutrals are connected together.
Even then, they only actually balance if all the phases have the same loading at the same time.
As a rule of thumb, double the single phase load to determine the CSA of the neutral for the 3 phase part.
So if each phase will be feeding a 7kw shower, that makes 14kw.

So why on a 100amp supply do we have 25mm tails and neutral?

 

[Deleted member 26818]

Phasor diagram anyone.

Too complicated for me.
Have enough trouble just posting text.

 

[David Rann]

So a 100amp three phase board could have potential 300amp flowing down the neutral so why is it 25mm then?

 

[David Rann]

They don’t balance out over the single phase part.
They only balance out over the 3 phase part, once the 3 neutrals are connected together.
Even then, they only actually balance if all the phases have the same loading at the same time.
As a rule of thumb, double the single phase load to determine the CSA of the neutral for the 3 phase part.
So if each phase will be feeding a 7kw shower, that makes 14kw.

Yes so the neutrals will be connected at the sub board?

 

[Pete999]

Yes so the neutrals will be connected at the sub board?

If all the showers are the same loading, no need for a N Make them 4oo Volt showers job sorted, engage brains. Hypothetical scenario