Testing For 240V

[Dr. Spa]

I'm putting this up as many people don't seem to understand 220v electricity in the USA. It's a locked thread (you can't5 reply to it).

This is a reprint you can see here;

http://www.rhtubs.co...110-testing.htm

Electricity. Something we can't live without, and something sometimes difficult to understand. Lets start with the basics of voltage. For all intents and purposes, there's only two voltages spas operate on (in the USA), 120 volts and 240 volts. Even then, these voltages can be described slightly differently. 120 volts can be called 110v, 115v or 120v. For all intents and purposes the three numbers are interchangeable and mean the same thing. As to why the different numbers are used, there are many "opinions". My favorite is that it's an east coast / west coast thing, with different sides of the country having slightly different voltages... the most believable is that in North America the utility companies are required to supply 120 volts, +/- 5%, and various things causing normal voltage drops will decrease this further. While obviously each is a slightly different voltage, in reality an "electrical appliance" will run just fine as long as the voltage is within +/- 10% of what it's rated for.

120v is achieved by combining 120v from one wire, with a neutral wire. "240 volts" is achieved differently and can be a bit confusing to understand. Unlike 120v, 240v does not use a neutral wire, but instead uses two 120v wires in combination. But, not just any 120v wires. As electricity moves through wires, it alternates back and forth, think of it like sawing wood. To obtain 240v, two 120v wires are used, in which the electricity is alternating in opposite directions in each wire. Think of it like a two-man tree saw, where the electricity being pushed through one wire, while it's being pulled through the other wire. This pushing/pulling action is continually changing direction. In the US the direction changes 60 times a second.

This image shows the ONLY way to properly test the voltage at the heater. With a properly

working system (controller), testing for voltage between the two terminals will give a reading of 220v.

If electricity is only flowing to one terminal,

the voltage reading will be ZERO.

Testing for voltage, as show above, tells very little. It will tell you if there's "some"

voltage going to the heater, but will NOT verify there's correct voltage.

This is where many people get confused. From the last image, and this, it can "appear"

that there's 110v going to each terminal of the heater. IN FACT, electricity is simply

traveling THROUGH the element and being read at the "dead" terminal.

An AMP meter clips onto ONE wire going to the heater, and if the heater is getting

proper voltage, the AMP meter should give the correct reading for amps being

used. If the AMP meter reads zero, the heater element is probably bad.