Neutral current for tri-phased connection - Page 1
Forum section: electronics / general

author: kuon
author_rank: Regular Contributor
timestamp: March 10, 2022, 11:25:07 pm
content: I am working on a large 3d printer that I am designing that will use 2 1600W heaters for chamber and bed and the motors/electronic combined power is about 1200W max power.This is a total of 4400W or about 18A on 240V RMS.In my workshop I have 16A triphased CEE outlet, this outlet has 3L+N+PE (3 phase, neutral and earth).Everything is for 240V, (heaters, power supply...) so I plan to wire 1 heater to phase L1 + N, 1 heater to phase L2 + N and the rest to L3 + N.I want to be sure that everything is correct, and that also if my understanding of AC is correct, there will never be more than 16A on the neutral wire (N) at any time.

author: themadhippy
author_rank: Super Contributor
timestamp: March 11, 2022, 12:04:54 am
content: QuoteUnfortunately not,once harmonic currents start appearing the neutral can be carrying more than the phase conductor and in such cases a larger neutral is needed.However in this case i recon you'll be fine

author: dmills
author_rank: Super Contributor
timestamp: March 11, 2022, 10:47:45 am
content: As long as those SSRs are the zero crossing type and not trying to do phase angle control it will be fine, it is phase controlled 'dimming' that sometimes burns neutrals (As I know the Hippy knows well).

author: jonpaul
author_rank: Super Contributor
timestamp: March 11, 2022, 11:11:42 am
content: Most regulations limit a connection, socket or cable RMS current to derating perhaps 80 % nameplate, thus 16 A will not meet regs on 18 A connection.Finally the IEC CE flicker limite maynhe an issue.As compliance and safety is involved I would rely on a qualified compliance firm or engineer rather thank a few casual notes on general forum.Bon chanceJon

author: zeke.
author_rank: Contributor
timestamp: March 11, 2022, 03:38:56 pm
content: Well the system isn’t balanced because of your L3-N connection so you will have a neutral current + any harmonic currents.

author: bdunham7
author_rank: Super Contributor
timestamp: March 11, 2022, 03:57:33 pm
content: That should work fine. As long as your SSRs are ON/OFF, you won't have any more than 7 amps RMS on the neutral even if the control branch has a very low harmonic power factor, except possibly for inrush and surges. You might want to just use 1 10A 3PH circuit breaker in place of the 16A breaker, eliminating the single phase breakers unless there is some specific reason you need them.

author: themadhippy
author_rank: Super Contributor
timestamp: March 11, 2022, 03:59:29 pm
content: QuoteAlong with 101 other things,even the humble florry fitting can produce harmonics, but as i said in this particular case i wouldn't bother about it

author: kuon
author_rank: Regular Contributor
timestamp: March 13, 2022, 03:07:57 am
content: Thanks for your feedback. I had a feeling about the neutral carrying more current. I made my assumption using ideal AC, but of course, with a load this is different. Thanks for clarifying that.Also I'll replace the breakers with a single 10A 3 phase breaker.I asked my electrician and he said the neutral on those plugs is dimensioned to handle 23A. So I guess I'll be fine.