TheBackShed.com

Forum Index : Other Stuff : 3 phase to neutral Loads.

Author

Message

Davo99
Guru

Joined: 03/06/2019
Location: Australia
Posts: 1585

Posted: 04:47am 11 Jan 2026

Copy link to clipboard

Print this post

I am trying to get some clarification on this as I get a lot of conflicting opinions so maybe the knowledgeable people I trust can give me a consensus.

With 3 phase power, if connections are from each live back to neutal for 3 single phase connections/ loads, What is the load Limit PER PHASE when all are used together AND if only 2 phases are in use?

Lets say the cables are 6mm / 32 Amp.

Is the power that can be pulled 32 A total across / divided by the 3 phasese or 32 per phase?

If only 2 of the 3 phases are being used, does that change the per phase load limit?

Again, I am talking specificaly each live to neutral for 230V, NOT phase to phase 415V.

I won't give anymore background to my thoughts and what I have been told which may confuse the question, I'll leave the question as that as I'm interested to see what people here say.

phil99

Guru

Joined: 11/02/2018
Location: Australia
Posts: 3004

Posted: 07:39am 11 Jan 2026

Copy link to clipboard

Print this post

The basic limit for a 32A 4 core + earth cable is 32A per phase, regardless of whether 1, 2 or 3 phases are drawing that current. The worst-case neutral current will be 32A. If the 3 actives carry the same current the neutral current is 0 as it is the vector sum of the active currents.

The exception is if the temperature is likely to approach the limit for the cable insulation.
There are de-rating tables that set a lower current in such situations.
Edited 2026-01-11 17:40 by phil99

Godoh
Guru

Joined: 26/09/2020
Location: Australia
Posts: 608

Posted: 02:59am 14 Jan 2026

Copy link to clipboard

Print this post

As Phil says the neutral current is a vector sum of the currents in the three phases.
As the phases are 120 degrees out of phase if the phase currents are balanced then the neutral current is zero.
Depending on how out of balance the phase loads are the neutral current will vary.
There are online calculators available to calculate the current, or you can go back to the old method of drawing up vector diagrams and working out the current from there.
pete

Print this page

To reply to this topic, you need to log in.