ECN Forum Forums General Topics of the Trade General Discussion Area ammeter readings on 240

when i measure the amps on my A/C, i get 14 amps drawn on each hot leg of the 240V circuit. Now my question is, would that combine to be a total of 28 amps of drawn power, thus requiring at least a 35 amp fusing, or is it only truley drawing 14 amps at 240, therefore only needing 20 amp fuses to protect it?

No it's 14 amps. You'll need to use a breaker designed to protect 240V loads (handle strapped together and such) at 20A or a pair of fuses at 20A if code allows it (which I'd doubt), assuming the wire is the right size for it.

[This message has been edited by wa2ise (edited 09-15-2005).]

There is no reason to be using an ammeter to determine the breaker or conductor size on any air conditioner.

Read the nameplate follow it exactly.

If it happens to be a window AC the factory installed plug will tell you all you need to know.

thanks for your response wa2ise. I'm a little suprised with your response iwire. I do have reason to be using the ammeter, and was hoping to get a bit more clarification on how to read it on difering voltages, as I was suprised that the fluke T5 came with no instruction manual.

sysrq no need to be surprised, it is not code compliant to size your circuit based on the ammeter readings.

The NEC spells out specifically how to size the circuit and it has to do with the label.

An ammeter is for troubleshooting, not circuit sizing.

Bob

Sys, this is a fundamental part of electricity. If you have a 240-volt load, and the current is 14 amps in each hot, that's a total of 14 amps, and there will be no neutral current (and likely no neutral at all).

The same amount of electrical power (watts) supplied at 120 volts would require 28 amps. Since volts x amps = watts (by definition), if you halve one, the other doubles, and power remains the same.

Lower current (and the resulting reduced need for conductor current capacity) and less voltage drop are why higher voltages are used for larger loads. After all, insulation is cheaper than conductor.

Sysrq, you can download the instructions and safety sheet at the link below.
http://us.fluke.com/usen/products/ProductManuals.htm?cs_id=3395(FlukeProducts)&category=ELT(FlukeProducts)

Note that the instructions are only in the use of the meter and will be of little if any help in understanding circuits, or current flow.

Roger