Neutral cable

[SkyWalker]

Basic electrical question here guys,

Current draw on a neutral wire?

I thought there should be no measurable current draw on a neutral, in theory, but i have been clamping some neutrals just out of interest and on a few sites i found some neutral wires with measurable neutral current draw? one site had like 15A ish on a blue box DX condenser?

how much if any current should we pick up on a neutral be it 3 phase or single phase? if none then why does some kit have it?

I asked a sparky friend but he didn't know why?

[mad fridgie]

"Single phase" the neutral and live are the "SAME"

[NoNickName]

On a single phase, as mad fridgie said, the current that flows in the live, also flows in the neutral. Infact, differential magnetic switches (AKA leakage breakers) measure the "difference" of current between live and neutral and if different, they trip.
On a three phase power supply there is current flowing in the neutral when there is any unbalance between the loads on the lives.

[Quality]

On a three phase power supply there is current flowing in the neutral when there is any unbalance between the loads on the lives.

Yes there could potential but please explain the current in neutral between what unbalanced lives
It may be a description I don`t understand what you mean ?

[coolstuf]

Yes, listen to NNN, he is expert on neutral!

Sorry, I could not resist

[monkey spanners]

Yes there could potential but please explain the current in neutral between what unbalanced lives
It may be a description I don`t understand

Say you had a 5hp comp pulling 6 amps per phase and two single phase fans a 1.2 amps each then you'd have 6A, 6A, 8.4A on the lives and 2.4A on the neutral i think

Though in the real world it is rare for the currents on different phases to match as the supply volatage are not usually equal.

Jon

[SkyWalker]

Thanks guys, I have never really considered clamping a neutral in the past, only making sure it is connected.

So the current draw on the three phase system I saw is due to unbalanced loading of the 3 phases. The only thing causing a big imbalance could be the compressor, fan Motors x2 are small relatively speaking and everything else is control, I will double check supply voltage on all three lives next time I'm there make sure there the same, if a comp is unbalanced is this a sign of electrical breakdown or mechanical failure?

[SkyWalker]

That makes great sense monkey spanners thank you, would this only be the case if the fan motors where single phase? If so could we state that neutral amp draw should equal total single phase load of the condenser? Because if there where only three phase motors we wouldn't need a neutral connected? BUT if there is a neutral and a three phase motor is unbalanced this can cause amp draw on the neutral. (sorry for double posting)

[monkey spanners]

If the three phase is unbalanced there won't be any current on the neutral as the motors don't have a neutral connection.

This is my understanding of these things but i'm no expert!

Jon

[Gingerair]

Interesting..
Is there any advantage/disadvantage in not having a neutral connection at all in a unit ?

Ginge..

[Quality]

If the three phase is unbalanced there won't be any current on the neutral as the motors don't have a neutral connection.

This is my understanding of these things but i'm no expert!

Jon

thats what I tried to explain

[chilliwilly]

Interesting..
Is there any advantage/disadvantage in not having a neutral connection at all in a unit ?

Ginge..

Most modern industrial plant/machinery, not always including fridge and aircon is wired with just three phase and earth/ground, and no neutral 380-415 volts UK and EU, 470 volts USA and CA, for power applications such as larger motors and heating loads. And the control circuits tend to be 110-120 volts wired from the secondary side of a reduced low voltage multi tapped transformer, and 110-208-240-270-380-415-480 volt primary. When imported to North America, the control circuits can be connected directly to the residential voltage supply (120 volts) with a neutral, or the primary of the control transformer any industrial voltage as it is in the UK and the EU.

This is typical of plant machinery that is either exported or imported from the USA or CA. And means that no adjustments to the control wiring is needed when used in either Continent. But selection and choice of power loads may need to be considered for the line voltage. Even the modern control components such as contactor coils and sensors are dual frequency rated.

The reduced low voltage system has two wiring configurations. A split twin legged circuit centre tapped secondary (55-60 volts to earth/ground and 110 volts between each leg). With only one of the legs switched and the other acting as a neutral, but isn't a neutral by definition because it remains live/hot, but is treat as a neutral but with more respect. Or a twin legged circuit with an earthed/grounded leg (0 volts, and the other leg ungrounded/earthed 110 volts to earth/ground), with the live leg switched and the grounded/earthed leg unswitched.

Star/Wye and delta/mesh connections don't require a neutral, because any one of the three load total currents, will in turn flow through the load via the other two phase non peaking voltage lines, and in turn will flow back through the load via the other two phases that are 120 degrees out of phase with each other, to the generator/power plant. Then each of the phase currents will repeat the the same process.

However in some cases the resistance of the windings of three phase motors, and the resisistance of some other three phase loads, are not always equal in value. This can cause phase current imbalance when voltage is applied, and in some cases when a neutral is connected to heating loads, it will have out of balance current flowing through it. Therefore in some certain cases neutrals are connected as a remedy, to star/wye connected motors (especially rewinds), where the windings are not equal in resistance and the line voltages differ by 15%+. As this can cut down on vibration, excessive noise, and potential burnouts. And also maintain the operation of heating loads when one of the phase voltages is either low or missing.

[NoNickName]

thats what I tried to explain

Ok, let's put it this way: three single-phase loads distributed on three phases do need neutral.
That doesn't mean the current is flowing in it.

Most modern industrial plant/machinery, not always including fridge and aircon is wired with just three phase and earth/ground, and no neutral 380-415 volts UK and EU

Not necessarily true. I design equipment with three lives, plus control circuitry supplied between one live and neutral (actually just after an isolation transformer, but it's merely a 1:1 transformer).
For example an air conditioner with three phase compressor and a single phase fan and remote condenser are designed with 4-wire power supply (+PE).
In this case a current flows in the neutral back to the line transformer.

[chilliwilly]

Ok, let's put it this way: three single-phase loads distributed on three phases do need neutral.
That doesn't mean the current is flowing in it.

Not necessarily true. I design equipment with three lives, plus control circuitry supplied between one live and neutral (actually just after an isolation transformer, but it's merely a 1:1 transformer).
For example an air conditioner with three phase compressor and a single phase fan and remote condenser are designed with 4-wire power supply (+PE).
In this case a current flows in the neutral back to the line transformer.

Not always including fridge and aircon.

I have also designed electrical circuits for various wiring systems and machinery, that include countries like the UK, USA, and CA. And have done for over 30 years for various editions of wiring regulations/codes. I also include a neutral, on request from the client, but they don't always request it due to the RLV system thats compatible with the worlds electrical wiring systems.

The wiring system that your refering to, will have to be adjusted if used in North America due to their wiring system. Otherwise it will be similar to the RLV system, exept the 240 volt will consist of two phases of a three phase feed (120-208-240 volt, the 240 volts has an ungrounded neutral) residential/small commercial loads.

And when switched will contraveine the NEC and the CEC definitions of a dangerous voltage, in both cases is 30 volts (UK 49 volts). So when one of the live/hot legs is switched, there still remains an ungrounded leg with 120 volts present to earth/ground. As opposed to the 110-120 volt to earth/ground circuit that will switch the live/hot leg, leaving the grounded leg at 0 volts, and in compliance with wiring regulations/codes.

A control circuit supplied from a multi tapped transformer, is a much more versatile system than a 240 volt to earth/ground single phase and neutral circuit. If you just work with the electrical system in refrigeration, you may never see or use the system. Until somewhere like North America order Italian refrigeration/aircon equipment from you. Then you will have no choice but to implement it.

[NoNickName]

I don't get it. I produce units declared with power supply 400-415/3/50+N+Pe or 400/3/60+N+Pe.
You want it? Good, here it is.
You don't want it? See you next time.

That's entirely off topic though against the question of the OP.
He's asking whether there is current flowing back to the neutral. The short answer is yes, and I explained why.
You don't have the neutral in your appliances? That's entirely your business.

[r.bartlett]

It's a pain when there is no N present as you end up using the Earth as a netural to run your vac pump etc!

[chilliwilly]

I don't get it. I produce units declared with power supply 400-415/3/50+N+Pe or 400/3/60+N+Pe.
You want it? Good, here it is.
You don't want it? See you next time.

That's entirely off topic though against the question of the OP.
He's asking whether there is current flowing back to the neutral. The short answer is yes, and I explained why.
You don't have the neutral in your appliances? That's entirely your business.

Then your units will not work Globaly without adjustments to their control wiring. Especially in the USA and CA.

I didn't say your work was wrong, I said the RLV control circuit system with a multi tapped transformer, was more versatile than a standard phase and neutral control circuit.

The RLV system has been common in the UK and the EU for some 30 years or more. And is accepted as the basic norm in control circuits found in industrial plant and machinery, and not as a bespoke requirement. Not because of safety issues but for versatillity issues. And sometimes this versatillity will include fridge and aircon, unless of course the work order doesn't specify it. As this seems to be the case with your work experience, no disrespect intended to you, but maybe one day you will be asked to implement it.

And if you don't do any electrical work on any other systems except aircon and fridge, you will be unlikely to see it, unless you have worked on, or have been requested to design for the North American wiring system.

I also posted my thoughts and experiences on neutral connections with polyphase/three phase systems. Which were not off topic, and had everything to with electrical principles and the systems available. And if there is no neutral connected in a three phase system, then current cannot flow through it. But will flow back to its source other ways, so whether or not a neutral is or isn't present, is everbodies business, not just just mine.

Good enough? See you next time!

[frank]

And have done for over 30 years

Geez Chilli.....did you start designing at the young age of 14?

Your profile ages you at 45

[chilliwilly]

Geez Chilli.....did you start designing at the young age of 14?

Your profile ages you at 45

Started at 11 years old actually, my mates dad was an old school electrician and radio and tv engineer. In the days when they had tv and electrical repair corner shops. My mate knew quite a bit about it and he always mended our tv set that was about 10 years old back then. I took an interest in both electrical and electronics, and when I got into my teens, I used to give them both a hand in their workshop and out on site.

Later on I used to twag school and work with them both on domestic/residential rewires, and in the mills and foundries in the town where I grew up. When I got to 16 years old his dad retired and sold up, and my mate joined the Army. So I kept myself busy whenever I could but with no money to start a business, but plenty of electrical knowledge with no qualifications, and no job. And I was exploited for some years after I can tell you, not just doing electrical work. The rest is history.

[mikeref]

Good on you Chilli. Think i was playing cricket or up to no good at that age, however next time i come up against a rock and a hard place, i'll call on you.. Mike