-1
\$\begingroup\$

As per the title, this is a very specific figure. Is there a reason it's 127 instead of 120V or 130V?

\$\endgroup\$
  • 5
    \$\begingroup\$ Is there a reason you find the numbers 120 and 130 more natural except that they're easily expressed in "numbers of fingers I have on my hands"? This is not meant to be flippant, but if you ask "why not X", I expect a reason for expecting X. \$\endgroup\$ – DonFusili Sep 27 '18 at 14:23
  • 1
    \$\begingroup\$ @DonFusili, well yes, partially. Our entire counting system is base 10 simply because we have 10 fingers. That's why we refer to numbers that are multiples of 10 as "round numbers". Not only that, but a supplied voltage is always going to be +/- 5-10V around the nominal supply so again, 127V is very specific when compared to a "round number" of 120 or 130. \$\endgroup\$ – Darren Sep 27 '18 at 14:29
  • 2
    \$\begingroup\$ Don was providing a Socratic question... Anyways Saudi Arabia also has 127 volts as well. The reasons is just for convention. This question has the same answer on why we Americans have 120 volts instead of 127 volts or why the majority of Europe has 220 to 240 volts. The reason for our differences most likely has to do with the machines we make in our specific country that generate a specific voltage. \$\endgroup\$ – KingDuken Sep 27 '18 at 14:34
  • 1
    \$\begingroup\$ Sure, but electricity generation is mainly based on which one of the N working ones that is stable and mature enough a country decided to copy. I'd have understood this question better if your reasoning was "I'd expect it to be the same as the US in case they need to transfer power across the border". I don't see why someone would care about having a round number just for having a round number's sake. \$\endgroup\$ – DonFusili Sep 27 '18 at 14:34
  • \$\begingroup\$ Also, as an aside, I prefer that the people that have control over my electric supply don't have more problems with an interval centered on 127 than one centered on 120. \$\endgroup\$ – DonFusili Sep 27 '18 at 14:37
6
\$\begingroup\$

Saw this on another site https://www.electronicspoint.com/threads/127-volt-standard-voltage.164594/

Much, maybe all, of Mexico supplies single phase power via 2 phases from three phase power. In the US that is known in the power industry as "network power" and is usually 120/208 volts. Now 208 volts sucks. But to get 240 volts from such a configuration, you'd have to have 138.5 volts on line to neutral, and that is a bit too much for most things that want 120 volts. In Mexico they have chosen a compromise where the L-N voltage is just a little high (127 volts) and the L-L voltage is just a little low (220 volts).

Sounds reasonable. Haven't been able to find any search terms that yield anything better.

| improve this answer | |
\$\endgroup\$
  • \$\begingroup\$ Thank you very much for actually giving a reason instead of a facetious “why not?”. +1 and I will accept this as an answer in a day or two if no better answers come along. \$\endgroup\$ – Darren Sep 27 '18 at 18:10
2
\$\begingroup\$

The Mexican electrical grid is an unstable grid. It is not well maintained and is subject to highs and low of a frequent nature. 127 volts allows for the electrical distributor (CFE) to have greater flexibility in the power delivery. The 127 standard is slightly higher than the 120 standard for the bulk of the rest of North America but allows for variance of as much as 10% and still be within the confines of what is acceptable. For example: if the grid was set to 120 volts and an increase or decrease occurred of 10% (generally acceptable margin of error for power delivery on a single phase line) the allowance would only be to 132 volts or the low of 108. With 127 volt the variance is slightly more substantial - with an acceptable high of about 138 volt and a low of about 114. Generally the delivery system has a tendency to deliver over-voltage as opposed to under voltage and this 127 standard allows for a greater over voltage delivery with less concern of being outside acceptable parameters. In other words, it takes less work and energy to maintain a 127 volt grid than it does to maintain a 120 volt grid.

| improve this answer | |
\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.