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220V two wires, why?

220V two wires, why?

220V two wires, why?

(OP)
Good afternoon,
  I've encounter a situation that I need help understanding. We have two parking lot lights that share the same 220V source. When trouble shooting the reason for them not being on  I had found there is only two wires. After asking a few other tradesmen why, there was no neutral I got the same responce "just because". If 120V circuit requires a neutral wire and 277V requires it, Why doesn't 208V or 220V? Is this normal or to code. What determines it the have a neutral or not?

Thank you in advance
2571

RE: 220V two wires, why?

A load needs a specific voltage. The power supply at any particular location consists of just a limited offering of voltages possibly, only one.  If the supply requires a 'neutral' to provide the load with its correct voltage then you need the neutral. If the supply can provide for the load's needs without a neutral then you don't need one.

Example: Facility has 208V 3phase.  This means (usually) that 120V can be supplied by using the neutral and a single phase line. Otherwise two phase lines are used to supply 208V.

If the lamp/load requires 120V use then neutral, 208V ditch the neutral.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: 220V two wires, why?

More specifically, "neutral" is just a reference point for the voltage. 220 lines are referenced to each other; when one is + the other is - so current has a path to flow. When you have only 1 "hot" line, the reference point for it is ground, but we don't like carrying current into the ground everywhere, so we make a "neutral" circuit that is referenced to ground at a common point for the entire service. In the case of your parking lot lights, you probably have a pole mounted transformer from the local utility that feeds you breaker panel. On that pole is a neutral grounding conductor going to a ground rod next to the pole. Some jurisdictions also require bonding the neutral to your service entrance ground as well, but nobody wants you to bond to ground at the load point, even though it would technically work. That just invites problems.

JRaef.com
Eng-Tips: Help for your job, not for your homework  Read FAQ731-376 pirate

RE: 220V two wires, why?

(OP)
jraef,
  Please exsplain yourself when you stated it just a reference point. reference to what? And how does a ground and a neutral differ. When I open a panel the green and white are all going to the same spot.
very curious.
2571

RE: 220V two wires, why?

In a 3-phase supply with Y configuration two voltages exist: phase-to-neutral and phase-to-phase. The phase-to-phase is 1.73 times the phase-to-neutral (example: 120 x 1.73=208). In Delta configuration only one voltage exists as phase-to-phase. In your case, you may have ether Y or Delta source, but your load (lights) needs phase-to-phase value. It is normal and fine with the code.

RE: 220V two wires, why?

Neutral and ground are very often the same.

RE: 220V two wires, why?

The difference between neutral and ground is that neutral is supposed to carry current. Ground is not supposed to carry current - except at faults when it is there a) to keep equipment potential at a safe level and b) to be a low impedance path for the fault current (so the overcurrent protection trips). Neutral and ground may seem to be the same thing to you. But they are not. And never mix them up if you are at all serious about code.

Gunnar Englund
www.gke.org

RE: 220V two wires, why?

The above post is an answer to 2751, not to maximka.

Gunnar Englund
www.gke.org

RE: 220V two wires, why?

To add to skogs responses; The neutral and the ground go to the same terminal block AT ONLY ONE LOCATION.  So the fact that you see the two going to the same block in your service panel doesn't mean; 'they are the same'.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: 220V two wires, why?

2571:

Let me rephrase what others have said. A single phase electrical equipment  requires its rated voltage between its two supply wires. It does not matter whether one of them is a neutral or both are hot wires. If a system happens to provide the rated voltage between one of its phase wires and a neutral, then the neutral is used. If a system can provide the rated voltage between its two hot wires, two hot wires are used.

For example  in USA, a common system is 208Y/120V, 3 phase, 4 wire, which will provide 208V between lines and 120V between L and N. In other countries there may be 400Y/230V system that wil provide 230 V(can be used for 220V equip) between a line and its neutral and 400V between lines.

There are many other configurations of voltage systems.

RE: 220V two wires, why?

Hmmm... more basic than my earlier post, huh?

Electricity has to flow from one place to another. In a battery it's going from + to - for instance. One side is the source, the other is the destination. We refer to this source and destination as having a difference in "potential", the potential for the electrons to flow from one place to another. The unit of measurement of that potential is the Volt. When electrons flow across that potential, we call the flow "Current" and the unit of measurement is the Ampere (amp). Work is done when current is allowed to flow across that potential, represented by  the heat it produces or the electromagnetic force it exudes. This work is the produce of the relationship between the Voltage and the Amperage (and Resistance) and we call that work Watts.

In AC, + and - are constantly changing, but that doesn't mean the current can flow, it still needs potential difference at all times.  In a US 240V 1 phase household system, you have 2 hot wires who's voltage (potential) relationship to each other is always 180 degrees apart, so like I said earlier, when one side is +, the other side is - and the current can flow across that potential difference as it should. When you have only 1 of those hot legs and you want to get some work done with it, you still need a place for the current to flow, some potential. It can always flow to "ground", essentially a zero-volt reference, because there is a potential difference between the hot and the ground.

The "Neutral" in that system is, as I said, at the same potential as the ground, but they (the utilities and safety organizations) don't want everyone hooking up their loads from hot to ground willy-nilly, so we create a current carrying path we call "neutral". It has insulated wires and is treated just like a hot wire, but for all intents and purposes is just that ground reference point so the potential energy in the hot wire has somewhere to flow.

In your panel, the ground and the neutral are connected at the panel. In my old hose in Seattle built in 1910, there is no connection there. It is made at the utility power pole. They had a conductor covered with a plastic sheath (it was wood up until a few years ago) coming down the pole going to a ground rod. As others said, the important issue is that the connection to ground is made at only one point. Otherwise, slight differences in the conductivity of the earth from one spot to another (salinity, moisture etc.) can cause ground currents to flow, and that has a host of other risks.

OK. I'm done.

JRaef.com
Eng-Tips: Help for your job, not for your homework  Read FAQ731-376 pirate

RE: 220V two wires, why?

2571,

You made us turn ourselves inside out. Please do accept what you read here. It represents the truth, the whole truth.

Gunnar Englund
www.gke.org

RE: 220V two wires, why?

And nothing but the truth!


Gads that reminds me, I have jury duty.. :(

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: 220V two wires, why?

(OP)
I would like to thank all of you for your responces now I truly have a clear understanding of what I'm seeing. I do appoligize for turning anyone inside out. It's obvious to me that all of you have the exspeariences I'm seeking and I'm looking forward to reading and learning more. Thanks agian for you time. I my case I have complete all of the college book work but I don't have a master electrician or even a journeymen to mentor and apply what I have learned. In many situation I'm left with have to figure out someone else mess. With many decision to be made if it happens to be right or wrong. So if you can find it possiable to be patient and understanding we all started somewhere.

thank you all
2571

RE: 220V two wires, why?

Just one final caution.  Electricity always follows the path of least resistance and can be unforgiving.  If through lack of experience, you create a situation where you become that path, it can kill you and it will hurt a lot while doing so.  If you are still unsure, find a qualified person; your life or the lives of others may depend on it.

RE: 220V two wires, why?

That is also true!

Gunnar Englund
www.gke.org

RE: 220V two wires, why?

Wise advice.
In golf they tell tou to "Be the Ball!"
In electricity you certainly DON'T want to "Be the Path!"

JRaef.com
Eng-Tips: Help for your job, not for your homework  Read FAQ731-376 pirate

RE: 220V two wires, why?

It is an old and well known saying that "there are no old and bad (read careless) sparkies".

Gunnar Englund
www.gke.org

RE: 220V two wires, why?

I've learned it in it's entire form:

"There are old electricians, and there are careless electricianss, but there are no old careless electricians."

Is that a common saying in other languages, i.e. Swedish? Or are there in fact old and careless Swedish electricians? You folks tend to live a charmed life up there.

JRaef.com
Eng-Tips: Help for your job, not for your homework  Read FAQ731-376 pirate

RE: 220V two wires, why?

Here is link which offers some very basic infomation on delta and wye systems coming off a transformer.  Check out the section on AC Circuits -> Transformers.  

http://www.sea.siemens.com/step/templates/lesson.mason?electricity:1:1:1

It is very difficult to quickly explain the black magic of grounding and the difference in neutral and ground to someone with minumal electrical knowledge.  However, the most basic fundamental understanding that one should know about a "ground wire" as opposed to a "neutral wire" is that the ground wire should NEVER carry electrical current except during a fault condition.    A neutral wire is intended to carry current.   

RE: 220V two wires, why?

The first time I read the NEC I was very confused until I realized that there was a significan distinction between "the grounding conductor" (equipment to earth ground) and "the grounded conductor" (neutral).

RE: 220V two wires, why?

Indeed!  Very confusing until you get it clear in your head.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: 220V two wires, why?

Quote:

Electricity always follows the path of least resistance and can be unforgiving.
That is not the complete story...it also follows all other paths.  It is these higher resistance paths that often ger us in trouble.
Don

RE: 220V two wires, why?

I was guilty of oversimplification, of course electricity follows multiple paths, it just that the human body has a low enough impedance to allow fatal levels of current flow if there is not a lower impedance path aka a properly conencted ground wire.

RE: 220V two wires, why?

I can't believe there are electricians out there who think that ground (that bit you stand on) is an effective conductor for the purposes of personal protection or that the neutral can be 'ditched' - I'd hate to wash my hands i his house just in case he'd wired up the tumble dryer.
Hasn't anyone heard of double insulated products? Perhaps they have never used portable hand held drills.
We (Europeans) always suspected that the US was the world's first equi-potential continental plane.

RE: 220V two wires, why?

Fieldbus,
Most of this discussion was theoretical in nature. Of course we have "double insulated" appliances and equipment and our neutral conductors are insulated, that is what separates them from ground conductors. But at the utility transformer or at the sevice entrance (depending on local codes), there is a connection from the neutral conductor to ground reference. It is not legal to use ground as a conductor here, I'm sorry that you interpreted it that way and as far as itsmoked's comment about "ditching the neutral", one could only do that IF the light fixture was designed and listed to be used without a ground connection, essntially what you would refer to as "double insulated". The OP mentioned that the installation only had 2 wires, the electrician told him that this was all that was required. The electrician would have been the one to take responsibility at installation to ensure that the fixture was listed to be connected that way, so if he said that was all that was necessary, he was probably correct (assuming you trust electricians).

I hooked up my own tumble dryer and I bathed my infant children in the stainless steel sink. We are not electrical barbarians!.  

JRaef.com
"Engineers like to solve problems.  If there are no problems handily available, they will create their own problems."   Scott Adams  
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