NEUTRAL CURRENTS IN 3 PHASE SYSTEMS – WHERE DO THEY GO TO – WHY ARE THEY DIFFERENT TO SINGLE PHASE?

At LearnElectrics we have often been asked about neutral currents in three phase systems and how they appear to differ from single phase systems.

Examples of questions have included …
In a balanced 3 phase system, why are there no neutral currents
If we have a neutral current in a single phase installation, then where has it gone in a three phase system
If there is no neutral current then how do things work?
And we will also introduce Kirchoff’s Law to show what is happening and how we can use this to show how balanced a system might be, what will happen if we add a piece of equipment onto the system.

To view all of our videos type in LearnElectrics all one word into the YouTube search bar.

This is video No.174 on our YouTube channel where we have videos on a wide range of electrical topics.

[DougStell]

Careful! The neutral current on a balanced 3 phase system is zero ONLY for linear loads, such as incandescent light bulbs. For non-linear loads, it can be 1.732 x the phase current. The NEC specifies either separate neutrals or a common neutral with 1.7 times the ampacity of each phase. I have seen neutrals on balanced fluorescent light systems burn. Doug Stell, MS(EE)

[danielteyehuago]

Wow! This is very informative, thanks for sharing it with us Dave. It worth it and the best tutorial on the topic for me.

[eugenepohjola]

Howdy. Great.
Usually the neutral current is no larger than a phase current. The neutral cross section may be the same as a phase cross section. And thicker than 16 mm2 copper the neutral may be half the phase, yet at least 16 mm2.
It should be noted though, that early age frequency converters generated so much harmonic reactive current in the neutral that it needed be at least 25 mm2. Best check the specs before commissioning.
And there is a situation when the neutral will carry more current than any phase. This will theoretically happen if there is a heavily inductive load on one phase and a heavily capacitive on another phase. Best be aware of this possibility.
Capacitive loads are rare though. The Code does not recognize this case. What could produce capacitive loads ? Over-magnetized synchronous motors will generate capacitive loading. Some "bulb-head" may think connecting a capacitor bank to a receptacle removes spikes and harmonics from the mains and delivers clean sine wave to one's HiFi system. It does. Yes. But best be aware of the possibility of strong neutral currents.
Regards.

[maxgiantbanana]

This Chanel is Killing The text book … the table explains everything about 3 phases and neutral…

[hunternixon]

So question. When you go to motor say in an industrial setting. That one motor would be a balanced load since the 3 legs are just connected to one device. Im a first year apprentice trying to understand thanks, hunter

[alexcurry]

In the video you say something like not all 3 phase systems require a neutral. Can you make a video about why and when a neutral isn't needed?

[khalidrash]

Hello
I am a follower of your lessons and a big fan of them. I hope that you will show videos explaining the method of calculating the power factor, as well as the correct way to calculate the main breaker, and whether it should be larger than the service provider’s breaker, equal to it, or less in size than it.

sincerely
Khalid

[timpullen]

Great explanation.
It's a mystery however that so many people in England use SAT and STOOD indirectly.

They are SAT is not correct English. SAT is past tense. They are SITTING is the correct English.

[VikramSingh-gphj]

नमस्कार सर आपका चैनल इलेक्ट्रिक हेल्प के नेम से हैं सर मुझे आपकी हेल्प चाहीये अगर आप हेल्प कर दोगे तो सर जो थ्री फेज जनरेटR
हैं 50 केवीए मे उसकी पर फेज की रेटिंग 70 एम्पायर हैं वो हमारे पास हैं।। ओर हम लाइट डेकोरेशन विवाह शादी के अंदर काम चालू किया है न्यू न्यू तो जैसे हम एक फेज पर 45 एम्पायर लोड डाल दिया ओर एक फेज पर 35 एम्पायर लोड डाल दिया ओर एक फेज पर 15 एम्पायर लोड डाल दिया तो कोई दिकत आएगी क्या सर कुछ लोग बोलते है partek फेज का लोड बराबर रखना होगा नही तो अल्टीनेटर जल जाएगा ये क्या सिस्टम है सर

[mAkills]

So out of 3 fellows any 1 fellow alternatively acts as drain pipe at any one point of time! My little brain says so!
FYI: After some tweaks I converted my single phase 240V variac into 2 phase 415V!

[damss]

How about if you have 2 power source like AC & solar power, Is it okay to have different grounding system for solar inverters that is neutral grounded to metal case/housing then TNS output? Of course has an input of AC TNS also...

[jmileshc]

Fantastic, thank you. Very much look forward to the balancing tutorial, coupled with PF issues & correction? possibly three tutorials there ;-)

[mohammedmoad]

Thinks so much for this explaine you are professor i wish if you can give me some books for electrical installation where i can download him thinks

[paulellam]

Crikey, best explanation yet on this topic, will watch a couple of times then attempt to write it down in my own words, which is how I then manage to soak it into the memory bank and be able to recall it at with understanding from then on. Brilliant narration and clear graphic representation, many thanks for providing this content.

[anthonyfindlay]

Thanks again Dave I appreciate the knowledge shared 🙏blessings.

[meandyna]

What happened when we lose neutral conductor in unbalanced 3 phase system?

[nodnarb]

I love this kind gentleman, and thank you for sharing this brilliant information. Thank you.

[STohme]

Excellent presentation of the topic for non expert in this area. Many thanks.

[hichamnabilnabil]

for the first time in my life i understand what happen realy and what neutral means ...thanks a lot

[enroute]

I have achieved what I want. Thank you🙏