Residential Electrical Overview: Comments invited

This is the overview for the Mexican Residential Electrical course, now at 22,500 words and probably 85% complete. Their standards are identical to the copy of the 2002 NEC I have with me. Anyone care to comment?
Anyone want to review the course material for accuracy?

                  Generally, a residential electrical system forms a large loop. Electricity:
  1. is supplied to the home through the service conductors, supplied by the CFE electrical power distribution lines;
  2. is distributed throughout the home by branch circuits; and 
  3. after passing through the home electrical system, some electrical current returns from the home to the                      CFE power distribution cables. No one seems to know where it goes after that. Please, PLEASE don't tell me "they return to the source" unless you can name the specific type of source and explain why electrons would go there.

Let’s take a closer look at each of these steps. A typical, properly designed, installed and operating residential electrical system operates like this:

**1. **Electricity is supplied to the home through the service conductors.
Typical modern homes are connected to the CFE power distribution system by the service drop (installed overhead), or service lateral (installed underground) through three service conductors. Two of these conductors are phase conductors, each one supplying the home with approximately 127v of electrical current. The third conductor is the neutral service conductor, through which unused electricity returns to the CFE power distribution cables.

Overhead service drop conductors enter a weatherhead that is installed at the top of conduit that encloses the conductors, protecting them from weather, abrasion or impact damage and prevents people from touching them.

As service conductors in a service lateral emerge from the ground, they also enter a conduit that serves the same purpose as that serving the service drop; protection for both the conductors, and for people.

The conduit enclosing the service conductors is attached to a meter housing, and the electrical current passes through the meter, which records the amount of electricity used each month so that CFE can bill the customer accordingly. From the meter, conductors carry current to a service panel, which is a metal box containing electrical components that distribute electricity to different parts of the home.

**2. ****Electricity is distributed through the home by branch circuits. **
Each branch circuit forms a loop that supplies electricity to a terminal point that fees a load, like a refrigerator, light, or receptacle. In modern homes, each branch circuit typically consists of three or four conductors, depending on the power requirements for that circuit. Each branch circuit contains one or two ungrounded (hot) conductors, a grounded (neutral) conductor, and an equipment grounding conductor.

**3. **After passing through the home electrical system, some electrical current will return to the CFE power distribution lines.
When electricity is consumed at a branch circuit termination (like when an electric light is turned on), a connection is made between the ungrounded (hot) and grounded (neutral) conductors in that branch circuit and electricity flows through the circuit. 127v of current will enter the light, some electricity will be consumed by the light, and the portion that is not consumed will flow back through the neutral conductor of that branch circuit to the service panel and from there to the CFE power lines on the neutral service conductor.

Before 1997 no standards existed in México to act as guidelines for the installation, maintenance and repair of residential electrical systems. Lack of guidelines or inspection by a neutral third party when electrical work has been performed has resulted in widespread poor quality work and unsafe electrical conditions in residential properties across México.

Although the electrical Normas Officiales de México (NOM)-001-SEDE have been available since 1997, neutral third party inspection of electrical work performed during home construction or major changes or repairs do not exist, and realistically, adherence to the Normas is at the option of the builder. Because electrical system installation that complies with the Normas may be more expensive, with no oversight, builders often surrender to the temptation to accept sub-standard workmanship and materials.

Neutral third-party – A neutral third-party is an unbiased person with no financial interest in the result of an inspection.

Home inspection is not inspection for compliance with the Normas. It is inspection for electrical system and major component defects and safety issues. Because the Normas were designed to help ensure safe electrical conditions, the purposes of the Normas and of home inspections are very similar, but General Home Inspections according to the InterNACHI México Standards of Practice are not designed to identify violations of the Normas. The Standards act as minimum guidelines that describe the portions of a residential electrical system that inspectors must inspect and report on. The extent to which each inspector exceeds the Standards is a decision to be made be each individual inspector. InterNACHI México requires only that the inspection reports of members comply with the Standards of Practice.

Residential electrical systems are designed in specific ways and have various devices installed to reduce the dangers connected with electricity, including electrical shock/electrocution and fire. Electrical installation methods, materials, and components have changed over the years as the understanding of electrical systems has improved and materials and components have become more sophisticated.
In the following sections of this course we will cover inspection of new and existing residential electrical systems, including the system and component configurations you should see, and common defective conditions.

I would take a look at this part:

The current flowing in a two wire circuit is equal in both the ungrounded and neutral conductors and alternating at 60 times a second. The way that it’s written it sounds as if the current is flowing out on the ungrounded conductor, some of it being used up and then some different amount is returning on the neutral conductor.

Oh. I thought that’s how it worked. Thanks for posting Robert!

Corrected version:

                 **1.    ****After passing through the home electrical system, some electrical current will return to the** **CFE power distribution cables.**

When electricity is consumed at a branch circuit termination (like when an electric light is turned on), a connection is made between the ungrounded (hot) and grounded (neutral) conductors in that branch circuit and electricity flows through the circuit. 127v of current will enter the light, and after passing through the fixture and bulb (the load) 127v of current will flow back through the neutral conductor of that branch circuit to the service panel and from there to the CFE power distribution cables.

I was told that this neutral shared between two adjacent services was not really a problem because voltages are lower in the neutrals. That’s not true if the ungrounded and grounded condutors are both carrying 120v (127v in Mexico).



No puedo entender esto

What’s depicted in the photo would be no different than a 3-wire, multi-wire branch circuit (MWBC) feeding two 2-wire branch circuits. In that scenario the neutral will not need to carry any current greater than the imbalance between the two circuits.

So if one were carrying 125v and the other 130v, the imbalance would be 5v and the neutral would only carry 5v? It wouldn’t carry the greater of the two- 130v?

The neutral is not carrying voltage as it is at ground potential.


Post #2 says ungrounded and grounded carry equal amounts of voltage. It’s prtetty well accepted that the neutral is a current-carrying conductor, so I don’t understand what you’re saying, Mike.

127v is standard here in Mexico.

voltage is not carried as it is pressure that pushes the amperage or current or to be exact electrons, The movement of electrons is measured in amperage, voltage is what pushes the electrons and does not flow or move

The above would be correct if you said amps instead of volts.

The neutral is carrying voltage.

A residential electrical system is a loop with ungrounded conductors as supply and grounded as return to the utility equipment (not sure exactly to what). If the neutral service conductor is fused and the fuse blows, electricity, current no longer flows, nothing electrical in the home works although the ungrounded conductors are still energized and so are the grounded up to the point of disconnection.

So on a normally-configured system (normal except for the shared neutral)… if the voltage can be as low as 5V on the neutral doesn’t that drastically reduce the operability of both the systems since flow back to the pole is severely restricted?

Why doesn’t current flowing back to the pole need as much motive force (voltage) as current flowing toward the loads in the home?

Kenton, you are to be commended for taking on this huge task. I know you’ve been working on it for what, a year or so? That said, I recommend you get Mike Holt’s “Basic Electrical Theory” book (INACHI has them available in the w/h I suspect, they sent me one as a gift a year or so ago) and read and understand the sections on Ohm’s Law, Kirchhoff’s Law and Chapter 14 and many of your questions will be answered. Listen carefully to Mike Whitt and Jim Port, they will not steer you wrong. Consider having them and/or someone like George Wells proof your course material (pay them if you have to) before “going to press”. Good work…keep at it, it will all come together.

Thanks Michael, I know you’re right. In the US it’s a lot easier to get by studying defective conditions and understanding some basics. Here, you never know what you’re going to see. The other courses aren’t too bad, but electrical is driving me crazy. I never before really felt the need to understand Ohms law and the other more challenging technical aspects of electrical inspection because most of us just recommend a specialist if it gets too complicated. We don’t install or design them…

It’s not uncommon down here to see three conductors go to three meters (for one house) —one of which will have a GEC and an electrode—installed on the outside of a boundary wall (so the meter reader doesn’t have to enter the property to read the meter). Then three conductors go to a fused disconnect enclosure with three fuses installed, there’s a mass of splices and double and triple taps (on both line and load sides of the fuse) and nothing is color coded.

Just found that out last week after 7 months here that usually one of the fuses is a usually fused neutral, meaning it’s a 2-phase system, except that down here if it’s got one phase conductor, it’s called single phase, two phase conductors makes it bi-phase and 3 phase conductors makes it tri-phase. Pretty crazy eh, to use logical terms when describing an electrical system that seems to have been installed by people with no electrical training.
One tap typically goes to a load center in the house which has it’s own grounding electrode, and another goes to the pool, which also has it’s own grounding electrode, if it’s grounded at all. Nothing is grounded at my girlfriend’s 4-year-old house including the pool and Jacuzzi (which I unplugged).

The house around the corner has one conductor only entering the Weatherhead!

Yours is good advice, and I hope that book is available in Kindle version.

That book has a lot of visuals that might not show up well on a Kindle. If you can’t get a hard copy from Nick then let me know and I’ll mail you my copy to keep. It might take a couple of weeks, you’re in Cuernavaca or somewhere like that, right?

Yep, Cuernavaca. Thanks Michael, I’ll get my hands on a copy.

Well, maybe I’ll take you up on your generous offer after all, Michael.
I’m at:

Kenton Shepard
Neptuno 200, #3
Colonia Delicias,
62330 Cuernavaca,

Phone: country code 52 777 154 5451

Written just like that

UPS is best since the postal service here likes to just chuck packages over the wall and comes closer to landing them in the pool each time!

Thanks Michael!

OK, I’ll try to get by the UPS store tomorrow morning and get it headed your way. I’ll get you the tracking number as soon as I have it.

The voltage drops across the load, because some of the ‘pressure’ is used, like a restriction in a water pipe. Current should stay the same. The measured voltage, and amperage, on a shared neutral can be zero, if the two energized lines use the same power AND are 180 degrees out of phase. Some loads have an inductive, or capacitive element that shifts the phase (timing) either forward or back, so the net result will be other than zero. As some of the flow goes forward from one line, flow is going backwards on the other line, canceling each other, if the phases are 180.
Not a sparky, so the terms I learned in college will be somewhat different. Plumbing terms are not exact, but help to visualize the unseen electricity.

Voltage = water pressure
Amperage = water volume flowing
Ohms = pipe resistance

You can have a small flow at high pressure, a large flow at low pressure, large short pipes equal low resistance (Ohms), thin long pipes equal high resistance.

Hope that helps

Switch = faucet
Drain = ground

Sparkies don’t be hatin for simple fyin

or I’ll be asking if you can calculate imaginary power loads and phase shifts