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Old 01-15-2010, 09:53 AM   #1
1Garageman
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Question How to tell how many amps are being used on a circuit

We just moved into our house about 2 months ago. I am starting to do some electrical work and add some things. I was wondering what is the best "meter" or device to use to tell how many amps are being used on a circuit?

I'd like to be able to take a circuit meter and just plug it into a wall socket or hot wires and see how many amps are being used? I need to add some wall plugs and lights into certain parts and would like to just add on and not have to put in a new circuit for that just yet.

Thanks guys!
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Old 01-15-2010, 09:59 AM   #2
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Default Re: How to tell how many amps are being used on a circuit

Put a clamp on amp meter on the wire near the circuit breaker. Be sure whatever is on that circuit is turned on, if a fridge is on the circuit the amps will change as the fridge is running or in the defrosting cycle, same with other appliances that run intermittently. They do sell equipment that will monitor and record usage over a period of time but they're usually expensive, I do recall a "As seen on TV" thing-a-ma-doodle that supposedly does this for a cheap price.
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Old 01-15-2010, 10:20 AM   #3
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Default Re: How to tell how many amps are being used on a circuit

Another question, If I test the amps with an amp meter of a 15amp or 20amp breaker, what is the maximum safe amount of amps it should read?
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Old 01-15-2010, 10:43 AM   #4
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Default Re: How to tell how many amps are being used on a circuit

I believe its 80% of its rated capacity, but a twenty amp breaker can safely hold twenty amps. You can do VA calculation and the NEC has specs for continuous loads versus non-continuous but I would just add new breakers where needed if you have the space.
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Old 01-15-2010, 10:45 AM   #5
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Default Re: How to tell how many amps are being used on a circuit

You shouldn't be consistently using more than 80% of the rating of the breaker. You may exceed that % temporarily, such as a motor starting.

For example, a 15 amp circuit shouldn't exceed 12; a 20 amp circuit shouldn't exceed 16.
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Old 01-15-2010, 10:47 AM   #6
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Default Re: How to tell how many amps are being used on a circuit

If you want to check an appliance at a time, a Kill-A-Watt plugin meter will do the trick for $20.

For complete branch circuit mesurement, the clamp-on amp meter is the easiest solution.
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Old 01-15-2010, 10:52 AM   #7
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Default Re: How to tell how many amps are being used on a circuit

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Originally Posted by lametec View Post
If you want to check an appliance at a time, a Kill-A-Watt plugin meter will do the trick for $20.

For complete branch circuit mesurement, the clamp-on amp meter is the easiest solution.
ya I think I would really like to get a clamp on meter and do some testing. I have a lot of wood working tools in the garage, plus my air compressor and stuff. Then in the basement I have a lot of computer stuff and hope to do some more things later on.

If I get a "clamp-on amp Meter", can I just hook it up to any hot wires on the circuit and it will tell my how many amps are being used on the circuit? Or just how many are being used from what ever is plugged into it?

Basically do I need to go to the breaker box to test the amps, or just any hot wire that is hooked up to the circuit anywhere??

Sorry for all the questions guys!
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Old 01-15-2010, 11:05 AM   #8
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Default Re: How to tell how many amps are being used on a circuit

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Originally Posted by 1Garageman View Post
If I get a "clamp-on amp Meter", can I just hook it up to any hot wires on the circuit and it will tell my how many amps are being used on the circuit? Or just how many are being used from what ever is plugged into it?
The amp meter will only tell what current is being drawn on the wire you put it on and only for whatever is turned on (lights, computer, TV), or is running, there are times certain units are not pulling a full load, other things to consider are loads like a hair dryer or toaster that pull a lot of current but are not used a lot. There are also NEC requirements about having dedicated circuits for certain areas that you are not supposed to add onto. You don't want to add onto something like a sump pump that might lead to a flood.

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Originally Posted by 1Garageman View Post
Basically do I need to go to the breaker box to test the amps, or just any hot wire that is hooked up to the circuit anywhere??
The best place is the circuit breaker box because it's at the end of the line, if you do it elsewhere you might miss something.
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Old 01-15-2010, 11:15 AM   #9
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Default Re: How to tell how many amps are being used on a circuit

Hi Garageman,

The clamp-on opens up to surround just one conductor (usually hot, but many times you can clamp around the neutral if it's not shared by another branch and it's easier to get to). It will tell you the current through that one conductor. Clamp-ons are nice because you don't have to disconnect anything if you can get to the individual conductors. To measure total amp draw, you need to open up the panel and find the feed conductor (and be especially careful ... ). For individual circuits, just clamp around individual feed (black or red) from the various breakers.

You can also buy or make a splitter device for measuring individual loads without opening up the panel. The homemade 120V kind usually has a plug on one end, three separate wires (white, black, and green) about one-foot long each, and a receptacle on the other end. This allows you to get the clamp-on around just the hot conductor, where that's impossible to do with a cord that has all 3 conductors inside.

The kind you buy do the same thing, but are molded plastic and usually have a 1:1 and a 10:1 section so you can measure smaller currents and cost about $15. They are called "line splitter" or sometimes "accessory". It looks like this:

http://www.texsoinstruments.com/ac-c...ource=googleps

The clamp-on just clamps around either the 1:1 or the 10:1 bars on the side.

-- Tom
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Old 01-15-2010, 11:20 AM   #10
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Default Re: How to tell how many amps are being used on a circuit

Thanks a ton for your help guys. I am trying to find a good cheap priced, if that possible amp meter now. Wonder if HarborFrieght has any that are decent? Like to keep it under $40.
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Old 01-15-2010, 12:26 PM   #11
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Default Re: How to tell how many amps are being used on a circuit

A number of electric utilities these days have those Kill-A-Watt (or similar) devices available to lend out to their customers for free, you may want to check it out with your utility company. Free is always good.
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Old 01-15-2010, 01:56 PM   #12
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Default Re: How to tell how many amps are being used on a circuit

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Originally Posted by 1Garageman View Post
Thanks a ton for your help guys. I am trying to find a good cheap priced, if that possible amp meter now. Wonder if HarborFrieght has any that are decent? Like to keep it under $40.
In my opinion Harbor Freight doesn't have anything decent. Out here there are a lot of amp meters on craig's list, many of them new quality brands, for really good prices. Just had an Ideal digital multimeter/ amp meter for $45 new in the package. You could step up to a new Fluke meter on sale for around $100 and it will last you a lifetime.
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Old 01-15-2010, 02:25 PM   #13
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Default Re: How to tell how many amps are being used on a circuit

I sue this one: http://www.sears.com/shc/s/p_10153_1...p+on+amp+meter
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Old 01-15-2010, 08:54 PM   #14
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Default Re: How to tell how many amps are being used on a circuit

Some public libraries have Kill-A-Watt meters you can check out. They will tell you how many KwH your appliance is using. Not sure if they will show actual amp draw at any given moment, never used one.

Sears has lots of different clamp on amp meters and other types of meters. Don't get one with a really huge loop, it is just that much more difficult to get around a wire in a crowded panelboard, something like this would be a good choice of an all purpose meter...................



or this.........



getting down into your price range somewhat..........



Here is the Kill-A-Watt meter



This AC line separator makes it real easy to clamp on an amp meter loop and measure current on one particular device or appliance. I've seen this elsewhere on the internet, Home Depot or somewhere, but cannot find it elsewhere right now. Pic doesn't show it, but it has a female receptacle in the end opposite the plug. You unplug the fridge (or whatever) and plug in this device, then plug the fridge into this. You have places to probe for voltage and a way to clamp on an amp meter. Here is the Extech web site lots of good test equipment and the splitter, and instructions, etc.



I've taken the flat ribbon cord of a dryer that has the grooves between the wires and split them with my pocket knife and pulled them apart and clamped the meter around the neutral or one or the other of the hots when troubleshooting dryer problems.

Charles

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Old 01-15-2010, 10:51 PM   #15
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Default Re: How to tell how many amps are being used on a circuit

Love my clamp on ammeter. I've learned tons about what my heat pumps/water heaters/steamer/stove/ etc are up under various conditions using it. I clamp it over the hot wire leading into the breaker, carefully......

I also made a device for plugged in equipment. I bought a short block heater cord (all snow climate folks should know what that is ) carefully cut the outer sheath exposing the hot/neutral/ground wires. I just clamp the ammeter around the exposed hot wire with a device plugged in. Very helpful I've found.
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Old 01-15-2010, 10:58 PM   #16
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Default Re: How to tell how many amps are being used on a circuit

Quote:
Originally Posted by 1Garageman View Post
We just moved into our house about 2 months ago. I am starting to do some electrical work and add some things. I was wondering what is the best "meter" or device to use to tell how many amps are being used on a circuit?

I'd like to be able to take a circuit meter and just plug it into a wall socket or hot wires and see how many amps are being used? I need to add some wall plugs and lights into certain parts and would like to just add on and not have to put in a new circuit for that just yet.

Thanks guys!
I use a Fluke 189 which can also monitor over time, but it's limited to 10A, if you need more the price goes up quite a bit I think..
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Old 01-15-2010, 11:01 PM   #17
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Default Re: How to tell how many amps are being used on a circuit

If you're that interested, you can also just get panel mount ammeters off of Ebay and mount them in a box near the panel... They make digital ones that will show high low and average, etc. too. Some are straight through feed, some just tap on a coil that you put on the wire. More money and work initially, but it's sure easier than taking the panel lid off every time..
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Old 01-15-2010, 11:02 PM   #18
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Default Re: How to tell how many amps are being used on a circuit

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I use a Fluke 189 which can also monitor over time, but it's limited to 10A, if you need more the price goes up quite a bit I think..
It's not like a 189 is just really cheap, either... there's some pretty cheap clamp-ons that will do peak hold and average.. I get past the 10a limit on my DMMs with a Fluke 80I current probe..
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Old 01-16-2010, 04:29 AM   #19
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Default Re: How to tell how many amps are being used on a circuit

I personally don't really like the digital clamp on meters....

I'll take a Simpson clamp on any day....for the stuff I do, I don't need to know the current down to the ma....I'm looking for pulses....it's had to see that with the digitals....

So...if you find a Simpson "Amp Probe"....go for it....
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Old 01-16-2010, 06:01 AM   #20
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Default Re: How to tell how many amps are being used on a circuit

I have to agree with John. I like the analog meters also so I can "see" those spikes. I have a 1X and 10X meter attachment. Some digital meters have peak hold functions but I like the old swinging needles.

If I need to read down to the mA than I have all the patch cords and equipment I need to use my digital meters or my old analog meter.

I also have a Kill-A-Watt meter like Charles shows in post #14.
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