A Simple Question - Phase / Neutral

Thanks redfred, very comprehensive answer, and GA from me

through follow up and GA

Hi,

This is Vishal (vish_al210). I am replying off my desk and hence have not logged in.

Thank you very much for the explaination.

I am an Embeded electronics engineer.

Please ignore S2. That was just to reference the question.

I do understand what you have stated but my question still stands.

With S2 removed and The load connected to the neutral how can the the two ends of the switch S1 be defined when the switch is open.

Is there a proper definition for Phase and neutral.

If the return phase is not grounded can it called neutral or is it to be referenced as Phase2.

Either case how should the two points of the Switch on the circuit be referenced. Please help me here.

with regards,

Vishal....

+919940131329

i am getting some faint inkling of what you want...maybe wrong, you have to tell me...

i would say

• Terminal 1 of S1 is connected to LINE
• Terminal 2 of S1 is connected to terminal 1 of LOAD2
• Terminal 2 of LOAD L2 is connected to NEUTRAL (which may or may not be earthed)

S2 having been eliminated.

Is this what you mean?

Yes Mr. Sridhar.

You have got my question right.

I have gone through 4 years of engineering course in Electrical and Electronics (2000-2004) and I find it shameful to ask.

I do know the concepts, the safety standards and design regulations and that if the potential at any point is varying w.r.t to the ground line it is phase. In a two wire system we may have a Phase and Neutral or Phase 1 ans Phase 2 (if neither is tied to the ground.)

The question I am ashamed to ask is:

If the switch is open (S1).. (S1 and S2 were only put in to make clear to all what the question was. But it only seems to have complicated things and left lot of them confused.)

re-iterating... if the switch S1 is open then can it be said that one end of the switch is connected to the Phase line and the other end of the switch is connected to the load end at ground potential or at Phase2 potential.

This is not while dealing with schematics or wiring diagrams. I was just verbally explaining the connection and said the same stated above. I got cornered .. and was told that I was wrong as the switch cannot be connected across phase and neutral as it would be a direct short. I tried explaining that I did not mean a switch parallel to the load but one in series. But under the given configuration the potential at the two ends of the switch will be of Phase1 and that of Phase 2 as long as the switch is open. Well once closed there is no potential (other than trace marginal voltage) difference across the switch.

I would really like to know what is the correct engineering terminology (not reference names or numbers of Schematics or wiring diagrams) of referencing the open end of the load (either side of phase or neutral) with refence to the supply lines. What potential does it carry??? Because after 14 years of schooling, 4 years of engineering and 6 years of feild/design work if I am not able to properly name this meagre point of reference then there must really be something wrong with me nad my understanding of the education.

And can someone please correct me with the definition of phase and neutral if the same mentioned in my original post is wrong.

Vish,

I think that you should say: S1 is connected between the Line and the Load. This should be enough to define it's status and duty.

I hope this satisfies.

No no ... going by the calibre of your posts, your education is certainly not wasted. Please get your self-esteem up .. only you can do it to yourself. Do not let yourself down because of some stupid fellows who just want to pull your chain.

Coming to your (still open) question, what i would say is : Switch S1 is in the LINE side of the load, and the neutral is connected to the other side of the load, thats it

Any complex schematic can be reduced to this i believe.

Now that your post has attracted some of the best brains of CR4, i am sure you will get a better answer .. let's wait.

I see a couple of questions from this post. I am glad S2 has been removed. From the standpoint of identifying the TWO sides of the switch 'S1", we have to designate ONE side a name and then the other side of the switch a different name. This way we know from a schematic point of view what point we are referencing.

Since the switch provides a "Make and Break" function for the Source (hot) side of your load, the 'Make' side would be the actual line source leading right up to the input terminal side of the switch. The 'Break' side of the switch is the only side that actually breaks the source OFF of L2. Call the make side S1m and the break side of the switch S1b.....just an idea! I would not reference the return side of your LOAD as phase 2. It is the 'identified' ground wire in the circuit(return). Hope this helps..

With S2 removed:

• The wire from the source to S1 is called the "Line" conductor, sometimes called the "Phase" conductor. Its potential with respect to ground is always at line voltage.
• The wire from S1 to the load is called the "Switch Leg". Its potential with respect to ground is dependent upon the position of switch S1.
• The wire from the load to the grounded side of the source is called the "Neutral" conductor, also known as the "Grounded" conductor. Its potential with respect to ground is always zero.

Note: As PWSlack mentioned with British Standards, the US National Electric Code(NEC) also prohibits independent switching of the neutral conductor.

this type of questions are reasonable if you are a student as it is quite natural at the beginning of your electrical course. It is explained clearly above. switches are provided in phase only. There is rules and standards to use color codes for phase and neutrals.

Dear Sir,

Your quetion is the best if you are a student of Logic & not engineering.

I assume that the practice is to provide solid connection after the load ( You can

see two fuse links in a single phase main switch of which one is wired to suit the

load & other has solid copper plate on the nuetral side so only the line fuse blows).

For Three phase connection there will be a solid terminal for the neutral ( except

for change-over-switches which are 4 pole type).

Manroop.Chennai.

It's simple the way I look at it...
Doesn't matter which side of the load you touch, if you get a shock it's Live (phase).
If you don't it's Neutral (lucky).

Actually it's a great question, with important safety implications (there's 'cat' in the middle of that word...did you see it eh? eh?)

Id probably call it something like 'Live but connected through (or via) a load' if I was explaining it to someone.

It's a good illustration of why we generally switch Live rather than switching Neutral. (I've heard of both in commercial Laundry equipment)
Del

A simple question-phase/neutral? I agree with a) and b) almost, the wording a little different but it will work. If indeed this circuit is single phase.. either 240 v-50 hz, or

120v-60 hz. One line is high potential (hot) and One line is the identified ground return line (neutral). The LOAD requires both potentials acting on it for the LOAD to work or perform! Normally you would install a switch only in the HOT side of your load.

There are only a few exceptions in the NEC code, but I am not sure about the other

country codes out there. It is hard to provide a simple answer with few details of the concern.... Mark

British Standard 7671 does not allow switches in the neutral wire on safety grounds.

You are complicating the issue. With only S1, one side is indicated as Live side. The other side will be called the load side.

But then, no indication is required on the switch itself since it is reversible (connection wise).

If One of the supply phases (or end...) is grounded, you should use only S1 for safety ( isolate the load when open, and trip a circuit breaker if a fault develops...)

If no end is gounded, then S1 & S2 should be there and linked mechanically for best practice. And you do not need to baptise them with any names except indicate where they are connected to (like L1 and L2 if these letters are used somewhere else on the supply lines...ex: transformer outputs(?)).

For single-phased AC power feeds (whether there is more than one phase or not), the wire with sinusoidal power on it is called the 'line' wire and the voltage it carries is 'line voltage'. The 'neutral, wire is called 'neutral'.

For multi-phased AC power feeds, phases much be distinguingished from each other. This is typically done by calling one phase 'L1', a second 'L2', and a third one 'L3'. Not all phases need be there, and they don't have to be called L1, L2, L3 .. they could just as easily be called L-A, L-B, L-C. To avoid confusion, the same convention should be used at a given facility.

As concerns control switches: in single-or multi-phased systems, it's good practice to connect them in series upstream of the load, where 'upstream' means closer to the line wire L and 'downstream' means closer to neutral. That you, just like kvsridhar said, won't get power on the upstream terminal of switch S2, which could shock an unwary electrician. (He ought to know better than working on an electrical circuit without first opening and locking a protection switch or breaker that powers that load, but we're all absent-minded at time; putting all switches on the 'line' side ensures that an electrician doesn't assume that there's no power on the upstream side of switch S2.)

Note that the above concerns CONTROL switches, which are used to turn a load on and off. For PROTECTION switches, that is switches/breakers/whatever that open automatically when there's a fault in the circuit (short circuit, short to ground, overload, etc.), the North American convention is to have a single relay contact (that is, a switch inside a protective relay) upstream of control switches where S1 presently is (here we define S1 as a control switch), which cuts off line power, but not neutral, to the control switches and the load. The European convention, however, is to cut off BOTH the line and the neutral. In that case, a protective switch upstream of where S1 is, and one downstream of where S2 is, are needed.

I'm not sure if the European convention requires that both switches be contacts within the same protective switch/breaker/whatever, but generally speaking it's good practice to have them so.

Cheers! DZ