March 6, 2005
There are 3 important things to know about electricity in Mexico:
1. Few homes are wired with a "3rd wire". In the US, its color coded green and it provides the grounding for your appliances. Not having a ground wire is a personal safety issue. In the event of a storm your appliances will not be protected. In addition, sensitive equipment (like computers) may not work properly without a ground.
Not only do you need a ground wire, but you also need a "tierra" - a physical ground. This is usually a metal pole driven deeply into the ground. A good local electrician can install these for you.
2. Electricity in Mexico is not as consistent as it is in the US. Power outages occur more frequently as do variations in the current. To protect sensitive equipment the best solution is to us an online UPS (see below).
3. Warranties for products purchased in the US will generally not be honored here in Mexico. In fact, if you read the warranty card itself, you will almost always see that it only covers usage in the United States. This is something to consider before you purchase an expensive electrical item in the US. Further, many appliances sold in Mexico have additional circuitry built in to handle the variation in voltage (voltage regulation). As an aside, warranties for cars purchased outside of Mexico generally aren't valid in Mexico.
Below is a more detailed and technical discussion for all the geeks. Permission was given to post it by George Culver.
Power quality can be degraded by the following types events:
Blackouts (no electricity) Brownouts (voltage is less than 100 volts) Temporary over-voltage (certain times of the day, week or year) Long-term over-voltage (consistently too high) Transient over-voltage (minor such as electrical noise) Transient over-voltage (major such as lightning strikes) Line frequency irregularities (should be exactly 60 cycles per second)
Blackouts result from failure in the power grid or at your local electrical service. The solution is to have automatically starting emergency generators or to utilize battery-backed-up Uninteruptible Power Supplies (UPS) UPS units are highly recommended for users of computers whose work is important to them. They will allow the computer to continue to operate for a period of time after a power failure. The length of time that they can provide power is determined by the physical size of the built-in battery. Some UPS units also provide voltage regulation and Transient Voltage Surge Suppression.
Brownouts result from more power being used in some part of the power grid than it was designed for. The result is referred to as Voltage Drop. Heavy industrial users of energy sometimes use more electricity at one time of the day than at other times of the day. Commercial and residential air-conditioners are also used more at certain times than others. To provide for peak usage like the examples above, the power company may adjust the voltage at the substation higher than normal. This can result in some customers receiving electricity at too high a voltage while others are receiving too low a voltage depending on where they are situated on the power grid. Voltage regulators and UPS units can correct both high and low voltage situations automatically. There at a least a half a dozen different types of both regulators and UPS units with varying degrees of protection for equipment.
Temporary over-voltage results from neighboring electrical power consumption being lower than the system was designed for. The result is less voltage drop. The solutions again are voltage regulators, and/or UPS units.
Long-term over-voltage results from poorly designed electrical grids. The voltage is set high near the substation with the knowledge that it will have dropped by the time it gets to the end of the line. Those nearest the substation receive electricity at a higher voltage than those at the end of the power distribution line. The solution is to install an additional transformer at the point of electricity usage. One type of transformer that is often suitable is known as a buck/boost autotransformer. It provides the ability to lower or raise the voltage depending on how it is connected but provides no regulation or surge suppression.
Transient over-voltage (minor) is best known by computer users; When the computer hardware "locks up" or quits working or when data is corrupted often it is a result of these very short lived voltage spikes. This is the only power quality event that a TVSS (surge suppressor) can provide protection for. The plug-strip type units or other small plug-in type of suppressors can block the minor voltage spikes before they get into electronic equipment. They can not however block huge voltage spikes that result from lighting or crossed high and low voltage distribution lines. The most common type of TVSS sold in stores utilize MOV components that are slowly eaten away by either numerous small spikes over a number of years or by one or more big spikes. If there is any discoloration or burnt smell or appearance on the TVSS unit they should be discarded.
Transient over-voltage (major such as lightning strikes) can be prevented only with large building mounted surge suppressors or lightning arrestors. Yes, the closer you are to towers, the more the risk. Lighting more often strikes the tallest structure around. Lightning discharges at very high voltage sometimes reaching millions of volts. When the lightning strikes a metal tower, the current goes down the tower and into the ground and travels through the ground by the path of least resistance. As it travels through the ground, voltage potential differences are created between different points in and on the earth. Since the electrical system is grounded (connected to the earth) at various points, damage to electrical equipment can result. When lightning strikes a power line the result is more direct: suddenly where there was once only 120 volts now many thousands of volts exist for a few seconds before everything is vaporized. Small TVSS units will simply explode also. Fortunately, strikes such as this are rare.
Line frequency irregularities are of little concern to most users of electricity.
Solutions:
1. One type (probably the best type) of UPS that includes regulation is an "online" UPS. This means that the 120 volt output is constantly fed from the battery. The input voltage, whether it be a little high, a little low or exactly 120 volts just charges the battery. Consequently, the output voltage is independent of the input voltage. The type of UPS that offers the least regulation is referred to as a standby UPS. The electronics contained within only kick-in when the power fails. I'm not sure which retailers sell online type UPS units. I know that they can be found on the internet though.
2. I don't believe that the electrical system on the top floor is more susceptible to lightning damage since all of the building wiring in a tall building comes up from underground. However, any wires, cables, and other metal structures on the roof could be struck.
3. During lightning storms, remain inside and stay off of the terrace.
4. If lightning strikes a tall, steel-reinforced concrete building the current will probably travel on the outside steel-reinforced shell down to the ground.
5. I don't think that either Mexico or the U.S. have regulations requiring lightning protection on residential buildings. I know that the U.S. National Electrical Code has no such requirements. On mission critical buildings such as airport control towers and airport terminal buildings lightning protection is usually provided. The forms of protection that I have seen have included roof mounted copper cable formed in a ring around the perimeter of the roof together with one or more cables extending down to 10 ft. driven ground rods interconnected with a buried grid of copper cables extending under and beyond the building foundation. Another form of protection on industrial buildings that I have seen are large lightning arrestors installed in the basement nearest the point of entrance of the electrical supply wires. David's suggestion to disconnect everything if lightning storms approach is a very good idea.
If you are confused between the difference between voltage regulation and surge suppression, try these sites:
http://en.wikipedia.org/wiki/Surge_suppressor
http://en.wikipedia.org/wiki/Voltage_regulator
If you have a problem with inconsistent voltage, you need some type of regulation like a UPS, but as George mentions above this is generally not a concern. If you want protection from lighning or other storm related power surges, then you need a surge protector.
Its possible for a unit to provide some level of both, but the problems are unrelated. To get real voltage regulation, you will probably need an expensive (and heavy) UPS. To get surge protection, purchase a properly rated (in Joules) protector.
Many of the better model surge protectors allow you to attach your electrical appliance AND a cable or phone line as well. Here is good site on the details:
http://www.aarp.org/learntech/computers/howto/Articles/a2003-03-13-surgeprotectors.html
Pay attention to the part about you get what you pay for in the above article. TripLite and UPC are the only companies with written insurance policies for their surge protectors. While these policies may not apply in Mexico, at least these companies stand behind their products, they have been throughly tested, and have good technical documentation.