220V two wires, why? 1

[2571]

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

 

[itsmoked]

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

 

[jraef]

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

 

[2571]

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

 

[maximka]

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.

 

[maximka]

Neutral and ground are very often the same.

 

[Skogsgurra]

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

http://www.gke.org

 

[Skogsgurra]

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

Gunnar Englund

http://www.gke.org

 

[itsmoked]

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

 

[rbulsara]

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.

 

[jraef]

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

 

[Skogsgurra]

2571,

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

Gunnar Englund

http://www.gke.org

 

[itsmoked]

And nothing but the truth!


Gads that reminds me, I have jury duty..

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[2571]

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

 

[TheBlacksmith]

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.

 

[Skogsgurra]

That is also true!

Gunnar Englund

http://www.gke.org

 

[jraef]

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

 

[Skogsgurra]

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

Gunnar Englund

http://www.gke.org

 

[jraef]

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

 

[Senselessticker]

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.