3 Phase wiring?

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#1

Originally Posted By: Kevin Blackwell
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I have look at some 3 phase wiring diagrams were the wires enter the service entrance.


I see three wires in a 3 phase connection my question is should there
only be 3 wires or 4 wires were the wiring enter the service entrance?

Thx Kevin from Houston,Texas preparing for pro.inspec.exam

#2

Originally Posted By: Charles Palmieri
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Kevin it would help if you could be a bit more discript regarding the circuit configuration.


That being said there are several types of three phase services but typically your concern seems on target. Most services for other than industrial applications (SOMETIMES) will consist of A four wire installation. That is, phase A, B, and C (UNGROUNDED OR HOT) with a fourth grounded conductor that has equal potential from it to the other three ungrounded conductors (refered to as the neutral) this fourth (neutral ) conductor provides common lighting voltages generally 120V or 277V depending upon the premisis requirements.

This does not exclude three wire installations with out a lighting voltage, or neutral conductor. There are times where a straight three phase (so to say) is brought to the premises without a neutral. This is common as a three phase delta supply and in many cases one corner will be grounded (yes it is a grounded phase leg).


Primary feed
If you are looking at a HIGH (above 600V) voltage entrance in the diagrams you may be viewing an installation that does not have a utility supplied grounded conductor and in that case only three wires would enter the premisis. In these cases you ususally have a customer owned distribution transformer and the end user will benifit (usually) by having primary metering. What is the voltage of the conductors that you are questioning

Hope this helps

charlie palmieri

#3

Originally Posted By: dbozek
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Kevin,


The 3 phase wiring you see depends on the voltage being utilized. For instance a 3 phase 208 volt system would be 4 wire, or in other words, 3 hots (phase A, phase B and phase C) and a neutral. On a 240 volt 3 phase system there typically would not be a neutral conductor...therefore a 3 wire system. 480 volts is a 4 wire system as well.

At times they may bring in 480 volts and then feed another disconnect and a transformer to make 120/208 volts. In this scenario the 480 volts may run equipment and lighting and the 120/208 volts would then be applied to run general office circuits, etc. Hope I didn't confuse you with this info.

A question for the HI's.....can there be 3 phase going into a single family home?

--
You cannot help men permanently by doing for them what they should and could do for themselves. Abraham Lincoln

#4

Originally Posted By: Greg Fretwell
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dbozek wrote:
Kevin,

The 3 phase wiring you see depends on the voltage being utilized. For instance a 3 phase 208 volt system would be 4 wire, or in other words, 3 hots (phase A, phase B and phase C) and a neutral. On a 240 volt 3 phase system there typically would not be a neutral conductor...therefore a 3 wire system.
...

...A question for the HI's.....can there be 3 phase going into a single family home?


If you do see 3 phase in a residential area it is as likely as not to be a center tapped delta with only 2 transformers. You also see that a lot in mixed use light industrial bay areas.
It is also called "red leg" or "wild leg" delta because the 3d leg is 208 to ground. The other 2 are 120 so you can feed single phase loads normally.
The advantage for the utility is they only need one extra transformer to give you 3 phase. The center tapped transformer is the standard pole pig you have for single phase. The other transformer may actually be smaller since they expect single phase loads.
#5

Originally Posted By: jpeck
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dbozek wrote:
A question for the HI's.....can there be 3 phase going into a single family home?


Down here, only on some of the older larger homes for their a/c's. Otherwise, not much on residential - down here.

--
Jerry Peck
South Florida
#6

Originally Posted By: gbeaumont
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Hi Dennis,


About the only time I see 3 phase up here is on older former Agricultural buildings, and very occasionally, supplying some part commercial buildings, if I know I am inspecting a building with 3 phase I take a reformed commercial electrician along with me. ![icon_wink.gif](upload://ssT9V5t45yjlgXqiFRXL04eXtqw.gif)

Regards

Gerry

--
Gerry Beaumont
NACHI Education Committee
e-mail : education@nachi.org
NACHI phone 484-429-5466

Inspection Depot Education
gbeaumont@inspectiondepot.com

"Education is a journey, not a destination"

#7

Originally Posted By: dbozek
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For the most part, same here. Only a select few older homes. First time I saw it I was a little puzzled as to why. Recently, I did a small job for one of the churches here and yep…they had it. It was kinda funny cuz they were going to throw this festival of sorts and they needed to bring out some power to run booths, etc and the deacon was worried he didn’t have enough electrical to do that. I told him he had enough to run the city icon_lol.gif

–
You cannot help men permanently by doing for them what they should and could do for themselves. Abraham Lincoln

#8

Originally Posted By: Charles Palmieri
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Kevin


I thought you were referring to diagrams you were studying for an exam prep.

are there three conductors entering the premises per the diagram??

is one of those conductors grounded at any point??