Testing the voltage output of House Lights
- Thread starterShawncfer
- Start date
Lights don't put out voltage. They take in electricity and put out light 
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Are you wanting to measure the supply voltage to the lights? Or you can measure the current drawn by the lights. The latter is best done with a clamp meter, the former is done by contacting one probe of a regular DMM on each of the supply wires to the lights. But chances are you can figure the voltage out by looking at the circuit that supplies them.
.Are you wanting to measure the supply voltage to the lights? Or you can measure the current drawn by the lights. The latter is best done with a clamp meter, the former is done by contacting one probe of a regular DMM on each of the supply wires to the lights. But chances are you can figure the voltage out by looking at the circuit that supplies them.
shiben
Well-Known Member
The voltage on a light is listed. For most applications, its 120, for others, it requires a transformer or a bunch in series, such as an MR-16 or something, or higher like in an ML, which might run on a higher voltage, again, which will be listed. Alternatively, you can test the resistance, and, knowing the wattage, calculate the volts required to make it happen for a given current using V=IR, but that would require knowing the current draw of the device, which would be a value those who make the light would assume you could calculate given the wattage, and assuming you know how much voltage is being supplied.
If your trying to test the voltage coming out of your house outlets, as per the instructions, set your meter to V(AC), stick the probes into the appropriate parts of the socket and test away. Dont touch anything thats "hot", as it will hurt.
Edit: While I was writing, other good points were made.
shiben
Well-Known Member
Also, strictly speaking, Voltage in a static situation is a measure of electric potential. See: Voltage - Wikipedia, the free encyclopedia
What are those appropriate parts?
The reason Im asking is because I have some house lamps that are burning out way to fast, like after a week from replacing them. And I've been very careful of not touching them with my fingers, and always using gloves. So I was thinking maybe its getting to much power? Could that be a reason?
shiben
Well-Known Member
Electrical Power has 2 parts, Volts and Amps. See: Electric power - Wikipedia, the free encyclopedia
It COULD be a voltage problem, so if your getting well over 120V or well under, that might be the problem. Otherwise, there could be a fault in the line, or something similar, and if thats the case, only a real electrician would be able to tell.
As for what are the correct bits to test, I have a feeling the ToS would prohibit me from explaining this to you over the internet. If we were hanging out next to each other, I could show you how to do it, but we are not.
Some fun electrical facts for you to think about:
100 mA (a 1/10th of an Amp) is considered enough to kill a human, by irreversibly disrupting your heart.
Line current before the breaker trips is 20A
Significantly below that level, you will not be able to control any of your muscles, which is why a Taser, which outputs over 50,000V upon firing, dropping to under 10,000V when it makes good contact with your body, works the way it does.
Even if you are exposed to under a lethal current, it can still cause severe burns and possibly kill you through other unpleasant ways, such as burning your insides, and disrupting your heart.
The majority of deaths from electrical causes are not caused by electrocution, but arc flash and burns. Burns are very painful and not a whole lot of fun. Do not say well, I have been shocked by my home system before, so I will stick my hand in THIS.
Update: Looking at Electricity for the Entertainment Electrician and Technician, by Richard Cadena, I have some more fun facts:
at 30 mA of current, no one can let go of whatever current carrier they are grabbing
a current of 10 mA to 60 mA can cause you to have serious trouble breathing, and if no one is there to kick you off the conductor (only way to do it safely short of cutting the current off, is a boot to the body to remove you from the source) you will die of suffocation, which really sucks, I am told.
Do not play with things unless you know how not to die while doing it. Its not hard to do right. I see you are an undergraduate, so head over to the engineering or physics department of your college, and you can probably have them explain to you more than you ever wanted to know about your DMM. I would say the EE people are less likely to explain why your multimeter is not quite as good as their very fancy whatsit that cost more than your and your parents house, but the EEs are often similar.
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Everyone is correct in advising you to have someone show you how to meter properly. I am not a fan of the "stick the probes into the socket" method because you are metering where the load is supposed to be instead of metering the circuit with a load attached.
As for your houselight issue, I am going to assume that these are connected to a dimming system. (If not, ignore this post) Dimmers chop voltage (this has been covered in many threads) and thus you do not get a true sine wave of power, even at full. Many cheap DMMs are only designed for reading a true sine wave and can get confused and produce false readings when they read a dimming circuit. The way to avoid these false readings is to use a true RMS (RootMeanSquare) meter. This type of meter is a bit more expensive (see the "my meter is better than yours" discussion to which Shiben was referring) but it will average the readings it gets on a circuit that doesn't have a true sine wave and give you a more accurate representation of voltages on that circuit.
The other thing to check here, and I am sure is what lead you to ask the question of how much power you are getting at each circut, is what lamp you are using and is it rated for the voltage that is being provided to it. I would suspect that, unless you have an electrical problem, your lamps are not rated for the voltage being supplied to them (ie.: 115V lamps being fed 120V) and are being overdriven and exhausted faster. A simple(er) check might be to compare lamps that you are using in the other sections of your houselights that are not experiencing this issue and make sure that they have the same voltage rating.
I'm envisaging this to be an installation where 10+ fixtures are on the same circuit / dimmer... At that point, the extra load will not make the same amount of difference as a single fixture.
When you have your dimmed circuit at 100% - since that's what we care about in this instance, the difference between a true rms meter and a bog standard sinusoidal calibrated meter is going to be 1 or 2% I expect. So in this case, I don't see there being any great requirement for a true reading meter...
Fear is a great motivator for protection of the species. But knowledge can serve to allay fear. To that end, see Fluke's Electrical Measurement Safety Program, and order the free CD.
While waiting for it to arrive, see 10 dumb things smart people do when testing electricity.pdf , as well as the other Safety Application Notes.
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Refer to page 2 of the pdf Derek linked. It is my interpretation that a dimmer rack is a Cat III source and thus, if you are metering an outlet less than 10m from that dimmer you need a minimum of Cat III rating.
Just an FYI Fluke has an ABCs of electrical measurement safety article too as part of their educational partnership program. In case you don't want to wait for the video. It covers voltage spikes, new safety standards, transient protection, understanding categories, independent testing, tool tips, arc blast and electric shock, work safety, how to evaluate a testers safety rating and a lot more in just 7 pages.
