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New Service wiring
By storrence, Section Homebrewed Electricity Posted on Sun Jul 20, 2003 at 03:59:47 PM MST
Adding new electrical service in Brazil

I have a few questions about wiring we just had done for a new construction in rural part of Rio de Janeiro. I don't know if they do it here the same as in the rest of the world. I lived most of my life in the US and am used to 110/220v service. To describe what we have here: The main lines come to the edge of our property and have 4 wires. I'm assuming 3 wires for 3 phase and 1 for neutral. Each 110v I assume but haven't yet tested. But I think they use 126v here. We have the electrical box there on one of the line poles and then 4 separate wires are run underground for about 500-600 meters inside a hard plastic non rigid tubing that they also use here for water when it's run a long distance. Something that probably wouldn't pass code in other countries.
The meter box on the pole has a 40amp breaker that looks like it has 6 wires connected. I suppose the 3 hot leads.
I know this is 3 phase service but will I have any problem with running this distance?
Will I experience a voltage drop going this distance?
I haven't checked the guage of the wires but what would be the required guage for this type of service. Probably it depends on how much load I will be putting on it but our house is pretty typical. Probably less than what is typical in the US. We have a refrigerator a few water pumps, gas stove, electric washer and dryer. Single room airconditioner, A range of other devices like home stereo and about 6 computers. Oh and possibly an small electric water heater.
I am pretty sure with this type of service I would have 3 separate 110-120v legs and 3 separate 220-240v legs and 1 330-360v service. Am I correct or is there a way to test it? I have a multimeter.
Is there some sort of chart that shows the wire guage in relation to distance and load to know the correct guage to use?
Thank you!

New Service wiring | 7 comments (7 topical)

Re: New Service wiring (none / 0) (#1)
by zubbly on Sun Jul 20, 2003 at 08:33:39 PM MST

hello Storrence, it is good to read your posting. if things in your part of the world are the same as here in Canada, i think i know what you have. when you have a 3 phase service run to a residential dwelling, you have 3 208 volt lines with neutral. to get your 120 volt 1 phase service in your panel, you end up using 1 of the 208 volt lines plus the neutral. if you look at a star or sometimes called a wye connection, your 120 volt comes from one of the 208 volt lines and the star point ( the common connection where all three phases come together ). the voltage measured from line to star is always 58% of the incoming line voltage--120 volt. if you look inside your new panel in the house, you will see the three incoming lines plus neutral. the breakers or fuses will be connected ( zig zagged back and forth ) from all three lines to give you equal distribution on all three lines. put your volt meter from one of the three lines to the neutral, you will get 120 volt. also, if you are using an electric dryer, it should be 208 volt compatible. when you measure voltage across any 2 of the three lines, you will get 208 volt.

i hope this helps you!---zubbly

Re: New Service wiring (none / 0) (#3)
by storrence on Mon Jul 21, 2003 at 03:08:41 AM MST

Hello Zubbly!

Thanks very much for your help. I initially tried to test the voltage using my volt meter. It has a common connector and 2 + (1 that says 10A). I used that but accidentally put one of the hots on the neutral of the meter and another hot on the + of the meter and fried the fuse :-/ Well at least it wasn't the meter! I then did a test touching each wire with one hand and the other to the earth (they teach you this stuff in Brazil) :-) And found the common. Now today I will go test to see what the voltage is and report back.

Do you know how I can find a chart on the internet that would tell me what guage wire I should use for this distance to avoid any voltage drop? What are these charts usually called?

I know yesterday I did a test with a 110v light bulb and when I plugged it on 2 hots it was very bright and likely would have burned out in a minute. When I connected it to one neutral and one hot it worked fine.

Thanks again,
Steve

[ Parent ]

Re: New Service wiring (none / 0) (#4)
by zubbly on Mon Jul 21, 2003 at 06:46:59 AM MST

hello Steve, i am not sure what these charts are called, but any electrical distributor that supplies cable and connection supplies to your local electricians should be able to help you out here. i suggest following the code of your local electricity supplier to remain within code and insurance guidelines.

good luck-----zubbly

[ Parent ]

Re: New Service wiring (none / 0) (#2)
by ADMIN on Sun Jul 20, 2003 at 08:37:44 PM MST

Being not very fond of math myself, I look stuff up on a 10% loss chart, 5% loss chart, 3% loss chart, etc. The handiest ones I use here are in my Sunelco catalog. There are a few on the internet if you search Google.

I also have a nifty wire size/voltage/amperage/distance --> voltage drop calculator that was made by Onan in 1970 -- one of those cardboard slide rule things! It's great and I use it all the time. I don't think they still make them.

CHeers
DANF

Re: New Service wiring (none / 0) (#5)
by Matt on Mon Jul 21, 2003 at 07:26:49 AM MST

hi try this url it might be what you are looking for

http://www.elec-toolbox.com/calculators/voltdrop.htm

[ Parent ]

Re: New Service wiring (none / 0) (#6)
by storrence on Mon Jul 21, 2003 at 05:48:23 PM MST

Thanks Matt. It's not coming up now but I found quite a few on Google
http://www.google.com/search?q=voltage+drop+calculator&ie=UTF-8&oe=UTF-8

Using these calculators I'm wondering if we have sufficient gauge wire. I need to see the guage tomorrow. Hopefully they are using AWG or something else that these calculators work with. From what I'm seeing with these calculators I believe I have something like a 10 or 12 guage solid copper wire just from visually looking at it. If I plug that in to the calculator and also the distance which is about 1200 feet and just consider 110v service using one neutral and one hot it seems the voltage drop would be huge. Something like only 25 volts at the load if I was pulling 40 amps. I put in 40 amps because that is the rating on the breaker at the meter and probably would be what the average house would draw.

It seems the guage I would need according to these charts is 2/0 AWG to stay within a 5% voltage drop on a single phase 110v line. We have 3 phase with 4 wires (they tell me it's 3 110v lines and 1 neutral). I don't know if this makes a difference in these calculators so I just inputted it like it was 110v single phase since I will have that situation if I use 1 hot and 1 neutral.

[ Parent ]

Re: New Service wiring (none / 0) (#7)
by jubalearly on Mon Jul 28, 2003 at 04:27:29 PM MST

My rule of thumb is to go up to 100 ft. at the 60 deg C amp rating (20a for 12ga.) of the wire for 3% or less voltage drop, 1 phase. That's for normal residential wiring where you're allowed 5% total drop from the service entrance. It could put you a hair over 3% in some cases. Also, it's for 120v. For 12v, use 10% of that (10ft., 1 way).
Most of these formulas on the internet are for house wiring or DC applications. Note that DC wiring usually has higher amperages for ea. wire size (often 105 deg C rating) & therefore higher voltage drops. Residential wiring should never use more than the 75 deg C amperage rating (you can't get 90 deg C connectors) AC or DC. The NEC tells you how to allow for ambient or conduit (as opposed to "in air").
For long distances outdoors (underground or overhead) I prefer to use the more complicated formulas that work from the area of the wire (or the resistance per ft. - Ohm's law) and account for worst case environmental conditions (temperature, effect of conduit, etc.). The basic formula is

CSA = (kIL)/Ed

where L=distance in feet one way, I=amperes, Ed=voltage drop, and CSA is the required circular mil area. k is a constant, usually 22-24 for a complete circuit (copper, alum is 36-39)
The constant can be varied with load & temperature (like for those 105 deg C DC circuits use k=26-29). Being able to go down a size or 2 using underground ambients of 25 deg C is nice when your looking at several hundred feet of large wire. I've had fun talking to power company engineers - ask them what they use for underground or overhead & what they recommend.
HTH,
Russ

[ Parent ]

New Service wiring | 7 comments (7 topical)

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