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Testing 240 V outlets


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I picked up a two wire tester at the big box store that indicates 120v or 240v when inserted in a receptacle. I don't recall the proper name, but it tells me if the 240v clothes dryer outlet is actually 240v or if the strange looking wall receptacle is 120v or 240v -- usually installed for a window AC unit. I find it very useful.

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I use the device Paul does, and it costs less than ten bucks. I always let the customer know that the outlet was intended for a window A/C unit, is wired for 240v and that it should never be replaced with a nice, new shiny 120v outlet. I've actually discovered a couple of those in the past. All three lights on the tester illuminate.

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Originally posted by randynavarro

I'm assuming y'all are testing the 240v outlets if and when there isn't an appliance in the way?

95% of the time, there's always a dryer or oven (can't think of another household 240v appliance right now) installed.

Are you guys moving the appliances and unplugging them?


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I caught heat from a client recently because the clothes-dryer installation folks didn't bring a three-prong cord and said the existing outlet was no longer permitted. As far as I know, three-prong outlets are still legal, and its the installer's job to supply the appropriate cord.

Slight drift, but I also alert people that their plastic clothes-dryer ducts in unconditioned areas should be replaced, because the installers will refuse to connect a dryer to plastic ducting due to liability reasons. The usual "was permitted at the time of the house's construction" doesn't fly when Best Buy refuses to completely install someone's shiny new dryer.

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  • 2 weeks later...

I've spent thousands of hours with a digital multimeter in my hands trying to find why the radio goes off when the vehicle is put in reverse and other obscure problems. While analog meters are less likely to lie, both digital and analog meters are essentially too good for what we do and can produce data that while accurate is basically untrue due to the miniscule current the devices draw from a circuit.

A 120 volt reading means nothing at 2 milliamps the same way a battery can read 12 volts and not have enough juice to light a dome light bulb.

A wiggy draws a little current, has a dedicated singular purpose that will never lead to the question (your meter has an inductive ammeter, why didn't you use it?)

I offered that I use a wiggy to test 240 volt outlets. That statement is partially true; I most often test them by turning on the dryer or both sets of burners on the stove. Those are better tests that the wiggy or a Fluke 88 can perform.

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