Why is my multitester showing less than 120V?

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Old 09-19-09, 01:18 PM
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Why is my multitester showing less than 120V?

I have a fan in my bathroom that is connected to a switch. Yesterday the fan stopped turning on when the switch is turned to "ON". I pulled out the switch and tested for continuity and the switch is fine. The two hot wires are unconnected at the moment since I removed the switch. I turned on the breaker and tested the voltage across the two wires. My multitester shows ~80V running between the wires. Shouldn't it be 120V, and if so, why would it be only 80V?
 
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Old 09-19-09, 03:04 PM
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It sounds like you are measuring across the switch legs. That doesn't tell you much.. It sounds like you are using a digital multimeter. Any reading below 100v may just be ghost/phantom voltage. If you open the fan you will probably see a plug and receptacle. Remove the plug. Reconnect the switch and turn it on. Measure voltage at the fans receptacle.
 
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Old 09-19-09, 03:21 PM
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When I went to quickly post, it said 0 replies. Then I see Ray beat me to it, by seconds.

He is right. Just thought you might not only like a second opinion. But since you called them 2 hot wires at the switch, when in reality the switch is just a bridge for the one hot wire to continue on it's way - it might pay to read up on basic wiring, as this could help you not only problem solve quicker, but be possibly safer as well, with some other future problem.

For just one little example, some people think the power has to come from the switch and go to a light, ceiling fan, or whatever. But in reality, the power may be right there in the box that the light or fan is over. And by turning off the switch, presuming you cannot possibly get shocked, you could very well get shocked, with one of these switched loop setups, even with the switch turned off, if you are working in that light or fan box.
 
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Old 09-19-09, 04:02 PM
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Originally Posted by ecman51` View Post
When I went to quickly post, it said 0 replies. Then I see Ray beat me to it, by seconds.

He is right. Just thought you might not only like a second opinion. But since you called them 2 hot wires at the switch, when in reality the switch is just a bridge for the one hot wire to continue on it's way - it might pay to read up on basic wiring, as this could help you not only problem solve quicker, but be possibly safer as well, with some other future problem.

For just one little example, some people think the power has to come from the switch and go to a light, ceiling fan, or whatever. But in reality, the power may be right there in the box that the light or fan is over. And by turning off the switch, presuming you cannot possibly get shocked, you could very well get shocked, with one of these switched loop setups, even with the switch turned off, if you are working in that light or fan box.
You're right in that I need somewhat of a primer on basics of wiring

What I'm confused about though is this. So the wire that's coming into the switch is hot and the switch is just a bridge (when it's turned to the "ON" position). If I remove the switch completely and put one test probe directly onto the wire that goes into the switch and the other test probe onto the wire that goes from the switch to the fan show 120V moving across the multitester?

I would assume that the multitester would act just like the switch in the ON position and complete the circuit, so 120V would be running across it. I'm probably completely misunderstanding though
 
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Old 09-19-09, 04:14 PM
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What you are doing is putting the meter in series with the fan. Your lucky the fan didn't work because the voltmeter was never intended to handle that much current. Of course it probably didn't run run because in a series circuit with two loads the voltage is divided between the two loads so the fan won't run because it is not getting full voltage... or the fan is working.
 
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Old 09-19-09, 04:48 PM
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Calavera. Ray is right.

A voltmeter is not used for testing in such a mannor. But, an ammeter is. An ammeter will record draw on either the hot or neutral lines when it's clamp is around either wire, singley. But wil be voided out if you try to clamp around both hot and neutral at once. I showed the master electrician I was with recently, my fairly new 'tinker toy' (I called it that as it looks like my big one, only a mini-version)amp meter I got cheap at one of the supply stores mentioned here fairly frequently.

Hopefully you enjoy this forum enough to read lots of the threads and maybe learn form what is said on many of them. There have been many threads started and post replies that show people how to trace problem wiring and how to troubleshoot.

Those bath fans have cheap motors that rely on a rotor with good bearings on each end, to hold the rotor true within the field. I have replaced so many of these home center bath fans over the years, it is not funny, in all the rentals. I have even rebuilt some of the motors to fit in other applications. If it is one of those 50 cfm varieties for like $10 or the 70 CFM variety for like $20...these things are cheap, with sleeve bearings, and fail.

And squirting lubricant in there may or may not help, for even the short term, but never works for the long term as the oil spins out. And if the bearing has slop, it's toast anyway. Only once, so far, on a better squirrel cage bath fan, was I able to drill a hole in the bearing cap and inject grease, then plug the drilled hole, and make this work. Why did I do that?: Changing out an entire bath fan from scratch is difficult.

But on those 50 or 70 cfm home center jobs, it is easy to only replace the motor housing from inside the ceiling box housing that is nailed or screwed in your ceiling. Only takes seconds to change them out! They just pop in! Then you just plug your bathfan motor cord back in.
 
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Old 09-21-09, 02:36 PM
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do you guys have any suggestions for either books or websites that will give me a good introduction to home wiring and electrical work?
 
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Old 09-21-09, 04:52 PM
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do you guys have any suggestions for either books or websites that will give me a good introduction to home wiring and electrical work?
Wiring Simplfied from Home Depot is one book to look for. You might also want to post that as a question over at Electrical - A/C & D/C - DoItYourself.com Community Forums. It gest more traffic then this forum.
 
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Old 09-21-09, 05:06 PM
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And after you get the book and a few of the others mentioned over there...just read through the forum when you have time. I think almost any question that can be asked HAS been asked over there...of course someone will prove me wrong w/i the next few days.

You can use the advanced search function and choose your forum to find book recommendations. If its working yet..there were problems a few days back.
 
 

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