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Tool Talk Discussion Forum

voltage drop accross 60 watt light bulb?

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frankiee

12-14-2006 15:08:37




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Maybe a bit O/T but it does involve proper use of a multimeter.
I I had a 60 watt bulb which was lit and put my voltmeter accross it in parallel to measure the voltage drop.
How many volts would the voltmeter read.
120 voltage




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MarkB_MI

12-15-2006 02:42:58




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 Re: voltage drop accross 60 watt light bulb? in reply to frankiee, 12-14-2006 15:08:37  
The voltage DROP is generally measured across the wiring, not across the load. Here's how to figure your voltage drop:

Remove the light bulb and turn on the switch to it. Turn off anything else on the same circuit. Measure and record the voltage at the light socket.

Now install the bulb and measure the voltage again. Subtract the second reading from the first. The difference between the two readings is your drop. It will probably be less than a volt, but that depends on wire gauge and distance from the panel.

You'll probably need a meter with at least 4-1/2 digits to get a meaningful measurement, if your wiring is good. Most cheap meters only have 3-1/2 digits, if that.

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banjo

12-14-2006 18:17:25




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 Re: voltage drop accross 60 watt light bulb? in reply to frankiee, 12-14-2006 15:08:37  
if the switch is on wouldn't it read 0 volts.



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John T

12-14-2006 19:01:35




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 Re: voltage drop accross 60 watt light bulb? in reply to banjo, 12-14-2006 18:17:25  
If the switch is on and assuming???? Alllll is working n wired correct, almost alllll ll the voltage in that series circuit consisting of the wire n the switch n the light bulb will appear across the bulb, i.e. near 120 volts, near the available line voltage (Line to neutral) back at the distribution panelboard, which is also near the secondary voltage available from Line to Neutral outside at the transformer LESS the voltage drop across the wires to the house.

Yall take care now

John T

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John T

12-14-2006 18:05:11




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 Re: voltage drop accross 60 watt light bulb? in reply to frankiee, 12-14-2006 15:08:37  
Frankie, The EXACT answer depends upon the available line voltage back at your panelboard LESS whatever voltage was dropped across the branch circuit which fed voltage to that bulb LESS the voltage dropped across a light switch if one were used. HOWEVER assuming a relatively short run of wire in the branch circuit and it was of say 12 or 14 gauge wire at relatively low amps and the light switch was in good condition (little resistance across its contacts) ALMOST ALL THE VOLTAGE AVAILABLE AT THE PANEL would be droped across the bulb with very little voltage drop across the wiring and switch. i.e. the voltage drop across the bulb would be very close to the line voltage at your distribution panel which should be around 115 to 120 VAC. Kirchoffs Laws describes this sort of stuff, its very basic n fun stuff to work with.

John T

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Jerry (KS)

12-14-2006 17:07:35




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 Re: voltage drop accross 60 watt light bulb? in reply to frankiee, 12-14-2006 15:08:37  
I think the only way you would see a voltage drop a single light would be if the light bulbs were wired in series....like the OLD type Christmas tree lights.



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tech4

12-14-2006 15:37:32




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 Re: voltage drop accross 60 watt light bulb? in reply to frankiee, 12-14-2006 15:08:37  
And a 100 watt bulb will also read line voltage or a 25 watt bulb the same. You are reading line voltage which should be near 120 volts.



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Sam#3

12-14-2006 15:15:19




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 Re: voltage drop accross 60 watt light bulb? in reply to frankiee, 12-14-2006 15:08:37  
It will read the line voltage. Should be close to 120v.



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