Science Buddies: "Ask an Expert"

How do you use a multi-meter to measure the amps being used from a 120V, 15 amp AC wall outlet, like what the Kill A Watt does?

Kill A Watt - P3 P4400 Kill A Watt Electricity Usage Monitor . . . amzn.com/B00009MDBU

Reviews on the Kill A Watt make it sound like it's a piece of junk, and will probably break within a year of use, so I'd rather put the money toward a better multi-meter than the one I have, one that can measure amps.

Here's what I'm thinking:

Question 1: It seems like the multi-meter would have to be able to handle 15 amps (that's what the house has at the circuit breaker), but it seems like they only go up to 10 amps. Any idea why?

Only going up to 10 amps would restrict some of the things that I'd like to test, such as a space heater, that uses 12.5 amps at its highest setting.

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I think you'd have to get a couple of leads coming out of the wall outlet (forget the ground, there's nothing on the multi-meter to attach to) - probably get them by taking apart an unusable, damaged extension cord . . . but, you'd want it to be 12 gauge (that's what the house is wired with), and I don't have one that heavy duty.

Question 2: How about this, do it by modifying / cutting one of these 12 gauge, 2 foot extension cords:

2 ft. 12/3 STW Extension Cord with 3 Outlet Lighted Power Block - Yellow, $12.97
http://www.homedepot.com/p/YELLOW-JACKET-2-ft-12-3-STW-Extension-Cord-with-3-Outlet-Lighted-Power-Block-Yellow-2882/204667724?N=5yc1vZc4neZ2bcpq3Z1z0tu05

. . . leave the plug head on, leave one foot of wire, and trim back the wire, to expose 3/4" for wire leads

Next, connect a 12 gauge white wire, with a couple of alligator clips on each end, to complete the neutral side.

Then, put the multi-meter on 10 amps, and connect it from the hot side of the wall outlet wire, to the hot side of the 14 gauge extension cord plug . . . this would be to a 25', 14 gauge extension cord, that I'm currently using to power my computer . . . I put it on an extension cord, to free up wall outlets in this room, for a ceramic space heater, 12.5 amp max . . . Reason: You don't want to use an extension cord on a space heater (it's a fire hazard), you want to plug those directly into a wall outlet, so I went the other way . . . power on the equipment, and see how many amps it's using

Be careful not to touch any of the exposed metal, as this will cause a shock. Keep the leads raised up so they don't touch anything, like the carpet.

Update:

It occurred to me that if I'm very careful with an Exacto blade, I could cut off, maybe, a 6" section of the jacket, around the center of the 2' yellow extension cord.

I would leave all of the wires intact, except for the hot wire . . . I would cut that, trim back 3/4" for the leads, and then put the multi-meter in between, with alligator clips.

I would then use the intact socket on the other end, to plug in the 25' extension cord.

This would make it a little safer.

As you've noted, even most good meters meant for casual use top out at 10 amps. To do this, you'd need to buy one better suited to higher currents. Besides, this is *seriously dangerous*.

A much safer way is to use an inductive current meter. They typically have a spring clamp that you open and clip around a single current carrying wire. If you split out the hot side of your power lead, you just clip the thing on the black wire. They look like this: http://www.amazon.com/MASTECH-MS2108A-C ... B009CNYJG2 but many companies make them. The problem though is that you have a 3-conductor cable and it's still pretty risky to cut it apart to separate out the black wire. To work around that, the meter industry came up with the "AC line splitter" which looks like this: http://www.amazon.com/Extech-480172-AC- ... B0000YHN9W . You plug that into the wall, plug your item under test into it and then clamp the meter in the loop. Easy peasy.

What you are proposing with cutting leads, using alligator clips and trying to be careful not to touch anything with the exposed metal is a recipe for disaster. Don't do it.

I will take a look at that, thank you!

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Another idea:

Crimp a couple of these on to the 12 gauge wire of the extension cord:

Ring Terminal Vinyl 8 AWG Stud 1/4 In. 5/Clam
http://www.homedepot.com/p/Tyco-Electronics-Ring-Terminal-Vinyl-8-AWG-Stud-1-4-In-5-Clam-CPGI-8-52041-3-5/202204324

. . . Ring terminals seem like they'd make a better connection than Spade terminals, with alligator clips from the multi-meter

. . . I don't readily see these Ring terminals for 12 gauge, but 8 would work

. . . I'm not sure how the heat shrink ones work, no big deal

sludge7051-x - Inexpensive multimeters of the type used in most of the Science Buddies experiments will not measure AC current. They will measure AC and DC voltage and DC current from milliamps to an ampere, and often have a separate input for a 10 amp range, but that is strictly a DC function. As HowardE explained, a clamp-on inductive meter is necessary to measure AC current. These are relatively inexpensive, as are the multimeters I described in general. to operate, the clamp-on jaws are placed around only one of the conductors. If placed around both, or say the AC cord, the reading will be zero as the the currents in the two conductors will cancel any reading out. Often, these meters are sold with an adapter that can be described as a short extension cord between your wall outlet and your load, but with a separation between the conductors. You can make one yourself from a short extension cord by carefully splitting a short length, only a few inches would be needed. Be careful not to cut the insulation in such a way as would expose the copper wire. Another way of measuring current is to measure an AC voltage across a low resistance load and use Ohms Law to calculate the current. This has some dangerous aspects, as you would have to break the AC wiring path and insert a sampling load resistor of perhaps a fraction of an ohm and measure the voltage drop across the device.

Rick Marz

. . . Inexpensive multimeters of the type used in most of the Science Buddies experiments will not measure AC current

Yes, this is the kind I have. I got an analog one first, to tell if batteries were good or not (it didn't need a battery to do this, I liked that feature, no dependence on batteries). I then thought it would be cool to have a digital readout (easier to read, and more accurate), I got one of those, and it's what I've been using

. . . clamp-on inductive meter is necessary to measure AC current . . . to operate, the clamp-on jaws are placed around only one of the conductors. If placed around both, or say the AC cord, the reading will be zero as the currents in the two conductors will cancel any reading out.

Ok, yes, I see, that's what the AC splitter is for

. . . Another way of measuring current is to measure an AC voltage across a low resistance load and use Ohms Law to calculate the current. This has some dangerous aspects, as you would have to break the AC wiring path and insert a sampling load resistor of perhaps a fraction of an ohm and measure the voltage drop across the device.

Getting kind of complicated . . . plus, if I were to do that . . . might as well just take my idea above with the modified 12 gauge extension cord . . . and secure the cut open part to a 2 x 4, along with a switch . . . I would put the hot wire on the switch, and have a 12 gauge solid core wire coming out the other side, maybe 1" . . . that would make things safer . . . then I'd have to see if they have a multi-meter that can do 15 amps

The AC splitter and clamp-on inductive meter seem a lot easier and safer, though

It looks like the clamp meters have been around since 1950 . . . http://www.ebay.com/gds/Your-Guide-to-B ... 248/g.html

It looks like the clamp on meter won't replace my multi-meter, it has a different focus of use.

It doesn't look like the clamp on meters automatically come with the AC splitter.

I see that this multi-meter will measure up to 20 amps, and it's only $29.22 . . . http://www.ebay.com/itm/LCD-Digital-Dis ... 3f38ab1143

. . . but maybe that would be a little dangerous with the exposed hot wire LOL, or, I could just get a pair of rubber gloves to wear while I was doing this.

The inexpensive meter you identified will measure up to 20A of DC, but only 10A of AC. There were specifications at the bottom of the page that explained each of the ranges in detail.

If you were completely familiar with safety procedures and could guarantee that you didn't nick any wire when you separated out the black line from an extension cord, you could make your own line splitter. I love your enthusiasm and interest in the subject, but I fear that you don't have the experience with high voltage (high compared to batteries) to start cutting into power cords safely. The commercial line splitters can be found for well under $10. You could also ask an adult who works in the trade to make you one from a power cord. Electricians I know would be thrilled to help you learn about this stuff safely.

The clamp meters almost always take lead connections and do most of the measurements that standard meters do. I have a Fluke clamp meter that will measure both AC and DC current with the clamp. It will also measure voltages up to 600V and AC or DC current to 10A with the leads. These clamp meters may not have the audible continuity or transistor checking features, but are still perfectly usable meters without the clamp.

Seriously, what you're suggesting (cutting into cords and exposing 120V wires) is seriously dangerous stuff. The fact that you knew about the rubber gloves suggests you know this. Please be safe and make your measurements safely. 120V from the wall is not something to fool with.

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. . . The inexpensive meter you identified will measure up to 20A of DC, but only 10A of AC . . .

Ok, yes I see that now, I just took a quick look at the dial, I should know by now that you can't do that:

DC Current (A) 20uA, 200uA, 2mA, 20mA, 200mA, 2A, ... 10/20A
AC Current(A) 20uA, 200uA, 2mA, 20mA, 200mA, 2A, ... 10A

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If I go to the Fluke web page, and see what they've got, from high to low, I see:

Fluke 88V/A Automotive Multimeter Combo Kit . . . http://en-us.fluke.com/products/digital-multimeters/fluke-88v-a-digital-multimeter-kit.html#features

It says it does 20 A for up to 30 seconds

Fluke 88VA Series V Deluxe Automotive Multimeter Kit, $436.49 . . . amzn.com/B0002SRIMI

They don't make it easy to find the lowest price one you can get that does 20 amps.

Do multi-meters just come in 10 or 20 amps, then you have to go to the clamp-on inductive to go higher?

Would that be the price range for one that does 20 amps, a little over $400?

Are high amp multi-meters mostly used in the automotive industry? What's on a car that's uses more than 10 amps? Maybe there's something on trucks.

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. . . If you were completely familiar with safety procedures and could guarantee that you didn't nick any wire when you separated out the black line from an extension cord, you could make your own line splitter.

I could do it. We had a flood on 2006. I got a book on electrical at the home improvement store, and figured out how to re-wire some of the 12 gauge down there. I moved outlets around, and installed some fluorescents. It was a little scary at first, and I wired a switch wrong once, but I got used to working with the wires, and most of the things you do are pretty simple. So, there was something good that came out of the flood, I learned electrical!

I have an Exacto, and some wire cutters. Just put the wire in the appropriate half-circle, or one that would cut it carefully, and not cut off any of the strand wires.

Mounting the extension cord on the 2x4, I could use electrical tape to cover up any exposed copper, and just have the ring terminals exposed for the alligator clips.

I could use some smaller pieces of wood to get the ring terminals 3/4" above the 2x4, to make clear connections.

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. . . The clamp meters almost always take lead connections and do most of the measurements that standard meters do.

I haven't looked into these yet. Do they all measure in the range of 0 to 20 amps? . . . Something tells me that they go a lot higher, though, right?

Who uses clamp-on meters, mostly? Electrical contractors, running the high power AC lines to new housing?

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. . . Seriously, what you're suggesting (cutting into cords and exposing 120V wires) is seriously dangerous stuff. The fact that you knew about the rubber gloves suggests you know this. Please be safe and make your measurements safely. 120V from the wall is not something to fool with.

I know to be extra careful, and to turn off power at the circuit breaker when necessary.

Would any pair of rubber gloves work, like ones you use to clean the shower? These can be thick, or thin.

If thin, would that be enough to prevent a shock? . . . or do you really need thicker gloves to be safe, specifically made for electrical work?

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Considering there's a perfectly good option (a cheap clamp meter and a line splitter), I'm not going to agree that there's any need for you to cut into a power cord. I've stripped the jacket off a cord and made a line splitter in a pinch and that's at least better than cutting and exposing copper. I can't stress strongly enough how easy it is for you to fry yourself playing with live 120V.

Clamp meters typically read up to 600A. In a car, the alternator typically charges around 10 amps or less. When you start a car though, a starter can draw 200 amps. Depending on what you're trying to debug it can be handy to read the starting current. Not all clamp meters read DC amps though - that's often a feature you pay extra for. Meters that allow greater than 10A with the test leads are rare. I have a $600 Fluke, 4 1/2 digit lab grade handheld that only reads up to 2A. Automotive meters that can go beyond 10A often do that with an external shunt - a low resistance hunk of metal that you attach between red and black. The meter reads the voltage across the resistance and calculates the current.

I'm impressed that you did all that electrical work. At least you got a book to get you started. Safety is something best learned by watching someone experienced though - I hope you have a chance to work alongside an experienced electrician someday and see how a pro does it.

Electrical gloves are rated in dielectric protection. Most of the rated ones are good to at least 1000V. The trick though is that a tiny tear in the gloves will compromise them. Besides, it's always better to not handle the live portion of the circuit if you can avoid it.

At the risk of sounding like a broken record (or a defective MP3 for those of you who have never seen a record skip), please get yourself a line splitter and a clamp meter. There's no reason to start hacking up 120V cords.

Howard

sludge7051-x - You could also go with a very inexpensive Harbor Freight model.

http://www.harborfreight.com/digital-cl ... 96308.html

Rick Marz

. . . I can't stress strongly enough how easy it is for you to fry yourself playing with live 120V

In my experience, you just get a good shock, if you're on the second floor of the building (you're far from the ground). There could be a serious problem, though, if you're in the basement, standing barefoot on the concrete . . . and even more serious if the concrete has water on it, or if you're standing in a pool of water there. Don't work on the circuit breaker in those conditions.

. . . Clamp meters typically read up to 600A. In a car, the alternator typically charges around 10 amps or less. When you start a car though, a starter can draw 200 amps.

Wow, a lot!

. . . Meters that allow greater than 10A with the test leads are rare. I have a $600 Fluke, 4 1/2 digit lab grade handheld that only reads up to 2A. Automotive meters that can go beyond 10A often do that with an external shunt - a low resistance hunk of metal that you attach between red and black. The meter reads the voltage across the resistance and calculates the current.

I wonder how often you'd need one of these to fix a car. Probably just if you need a new alternator.

. . . I'm impressed that you did all that electrical work. At least you got a book to get you started.

Thanks. The flood became the reason for me to learn it. I would have otherwise stopped at how to wire table lamps, and how to do the UL knot.

. . . Electrical gloves are rated in dielectric protection. Most of the rated ones are good to at least 1000V. The trick though is that a tiny tear in the gloves will compromise them. Besides, it's always better to not handle the live portion of the circuit if you can avoid it.

Good info, thx!

. . . At the risk of sounding like a broken record (or a defective MP3 for those of you who have never seen a record skip), please get yourself a line splitter and a clamp meter. There's no reason to start hacking up 120V cords.

Yes, that's what I'm going to do. I'll let you know what happens.

. . . You could also go with a very inexpensive Harbor Freight model [$11.99] . . . http://www.harborfreight.com/digital-clamp-meter-96308.html

I went to see what kind Radio Shack had ($34.99), because I have a coupon . . . http://www.radioshack.com/radioshack-true-rms-digital-clamp-on-multimeter/2200172.html#&tab=tab3

It gets bad reviews. It seems like I need to get a more expensive one, if I want to get good readings, and have it last a while.

This is what I got:

Amprobe ACD-10 PLUS Clamp Meter for Precision . . . http://www.amprobe.com/amprobe/usen/Clamp-Meters/Multimeter-Clamps/AMP-ACD-10-PLUS.htm?PID=73064
Amprobe ACD-10 PLUS 600A Clamp Multimeter . . . http://amzn.com/B003Z7UQJA

Amprobe ELS2A AC Current Clamp Accessory - AC Current Clamp Accessory . . . http://www.amprobe.com/Amprobe/usen/Accessories/Other/AMP-ELS2A.htm?PID=73229
Amprobe ELS2A AC Line Splitter . . . http://amzn.com/B001DPR0FE

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Here's what I found:

Specification from the device . . . V . . . A

UPS BATTERY SIDE
modem, fiber optic . . . 12.000 . . . 3.000
HP mini-tower . . . 12.000 . . . 0.300
answering machine . . . 6.000 . . . 0.350
monitor . . . 12.000 . . . 3.333
Sub-Total . . . n/a . . . 6.983

UPS AC SIDE
speakers . . . 12.000 . . . 0.700
light bulb (29W) . . . 120.000 . . . 0.242
Sub-Total . . . n/a . . . 0.942

Total . . . n/a . . . 7.925

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The above is what's on the main UPS that I use, which is an:
APC, BE550G ... 550VA, 12V, 4.6A, 330W . . . 4.6A will handle what I need, based on what I measured (below)
VA to amps calculator - it looks like the UPS is Single Phase . . . http://www.rapidtables.com/calc/electric/va-to-amps-calculator.htm
I have a second one of these UPS's for other computer equipment (described below)

Before I had measured the actual amps used, and knew the logical thing to do,
I got two 14 gauge, 25' extension cords - one for each outlet - one for each UPS plug (described above)
14 gauge is rated for 15 amps
. . . my circuit breaker box is 15 amps
. . . so the outlet isn't going to put out more than 15 amps
. . . the outlet is wired with 12 gauge NM-B, which is rated for 20 amps
. . . at this time, I thought that two extension cords would be good, and make things run cooler (fail)

The guy at the home improvement store said that I should be using a 12 gauge extension cord
12 gauge is rated for 20 amps . . . he didn't know my situation, or how many amps I would be running

Knowing what I know now, what I should have done was . . . I could have gotten:
a.) just one 12 gauge extension cord, and a power strip (with surge protection, can't hurt, right?)
. . . they have 12 gauge, 25' extension cords
. . . with and without a lighted end . . . with 1 or 3 end plugs . . . respectively
. . . the lighted end makes it more expensive
. . . I think that a power strip would work better, though, because the UPS plugs are angled, and, I could put more things on the extension cord if I wanted
b.) just one 14 gauge extension cord, and a power strip (with surge protection, can't hurt, right?)
. . . this is how I ended up re-configuring it

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02/05/15 For my primary UPS, reading what the above uses, with my clamp meter:
. . . the amps initially go up to 1.7 . . . then settle down to 1.28 - 1.35

Why is so little electricity used, if the amps for everything add up to 7.925? This really surprised me.

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02/05/15 For my other UPS (AC Side), with only a few things plugged in (powered on, individually)
laser printer (idle) . . . 00.05
scanner (idle) . . . 00.02
alarm clock . . . 00.001
. . . I use the battery side when making backups to external hard drives

This surprised me, too, how few amps these things use.

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02/05/15 Other:

the space heater - Lasko Ceramic CC13652
http://www.laskoproducts.com/electronic-ceramic-heater-with-warm-air-motion-technology-model-cc13652/
Watts: 900 / 1500
BTUs: 2,560 / 5,118
Amps: 7.5 / 12.5
. . . in Standby . . . 00.08 - 00.11
. . . on High . . . it initially goes up to 15.00 . . . then settles down to 11.50 - 11.75
. . . on Low . . . it goes to 6.25 - 6.35

oscillating fan . . . 00.32
the wall outlet, ACV = 122.7

I think you made a wise meter choice. Thank you for not slicing open cords.

As a caution, UPS manufacturers used to suggest that you not use any active surge suppression with a UPS. The cheap MOV type isn't a big deal, but the surge suppression circuitry in the really good strips wastes energy that you don't want to waste coming from the battery. besides, the UPS had plenty of surge suppression already and any more is a waste. The MOV technology is pretty harmless though, and arguably not very effective anyway.

In the end, the final number is that your setup uses maybe 1.5 amps at 120V. That's about 180 watts, or 0.18 kW. The range of electric rates is generally about 5 to 15 cents per kWh in the US. So if you leave your equipment on for 24 hours, you'll use 0.18*24 or 4.32 kWh which costs between 21 and 65 cents per day (depending on the rates where you live).

In your math, you said that the monitor was drawing 3 amps and your modem was 3 amps as well. That can't be at 120V. If what you meant was that it was rated for 3 amps at 12V, that's only 36 watts. Remember that if you ignore any conversion losses, a 12V adapter putting out 3 amps only needs 0.3 amps at 120V to do that. I think your numbers may be mixing up low voltage (12V) DC and the 120V wall power.

Howard

. . . I think you made a wise meter choice

Thx!

. . . As a caution, UPS manufacturers used to suggest that you not use any active surge suppression with a UPS.

Yes, I wondered about that . . .

When I determined to get the surge protected power strip, my thinking was that it would take some of the surge, and lessen it for the UPS - but apparently this is not a good idea, due to how surge protection works

This seems similar to how a while back, I was putting one or two GFI's downline from another one on the same branch circuit. Someone mentioned this error, I read up on it, and now understand how one GFI will effectively protect all of them - but if you have more, then they can't work as designed. Instead, be sure to put a label on an outlet to let others know that it is GFI protected (and where).

I'll have to get a non-surge protected power strip for the end of the extension cord. Thanks for the tip!

. . . The cheap MOV type isn't a big deal, but the surge suppression circuitry in the really good strips wastes energy that you don't want to waste coming from the battery.

Is this MOV? . . . http://en.wikipedia.org/wiki/Surge_protector#Metal_oxide_varistor_.28MOV.29

The UPS is plugged into this surge protected power strip . . . which is plugged into the 14 gauge extension cord, and then to the wall, but . . . I will replace that, yes, but . . .

I see that I'm using 3 surge protected power strips, plugged into the UPS. They act as a power switch for:
1.) my desktop speakers (the power strip has a green LED for "on," these other two don't) - the power button on the speakers can break easily
2.) my modem
3.) my laser printer and scanner

Do you think this is a significant issue?

. . . besides, the UPS had plenty of surge suppression already and any more is a waste.

ok

. . . The MOV technology is pretty harmless though, and arguably not very effective anyway.

. . . In the end, the final number is that your setup uses maybe 1.5 amps at 120V. That's about 180 watts, or 0.18 kW. The range of electric rates is generally about 5 to 15 cents per kWh in the US. So if you leave your equipment on for 24 hours, you'll use 0.18*24 or 4.32 kWh which costs between 21 and 65 cents per day (depending on the rates where you live).

It cost me $1.10 per day last year, so that seems reasonable. I've read that the fridge uses the most electricity. It seems like the furnace fan would use a lot in winter.

. . . In your math, you said that the monitor was drawing 3 amps and your modem was 3 amps as well. That can't be at 120V. If what you meant was that it was rated for 3 amps at 12V, that's only 36 watts.

Yes, they're both on an adapter, so that would be DC.

http://en.wikipedia.org/wiki/Surge_prot ... _.28MOV.29

Yes, that's what MOV is. To connect to a UPS, it's okay to use one but you can also open the strip and chop the MOV out (power OFF, of course).

Using a strip for the power switch is just fine. There are quite a few decent strip without protection you can buy cheap. Using the three surge suppressed ones is okay if you have them. It's better to use unprotected ones if you've got them. The article you highlighted suggests they catch on fire when they fail but that's not likely to happen in a protected UPS socket.

. . . Yes, that's what MOV is. To connect to a UPS, it's okay to use one but you can also open the strip and chop the MOV out (power OFF, of course).

Interesting! - (this is a good topic question) - I've heard that the surge protection goes bad after a while, but never thought of how you can tell - In looking at this, I guess it's from the surge protection LEDs, but one of my power strips doesn't have one.

Also, maybe the LED isn't an accurate indicator. I think I read somewhere that you should just replace surge power strips after 5 to 10 years. That seems like a waste.

If the surge protection light goes out, it seems to me like you can you just it as unprotected power strip. Would there be any point to cutting out the MOV?

Why would you want to cut out the MOV, if using the power strip attached to the UPS? Because the surge LED would be off, and that saves on amps used by the UPS in a power failure?

Here's how I have my 4 power strips set up:

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1 - two UPS.jpg . . . http://i.imgur.com/OOB9M5x.jpg
. . . Here are my two APC UPS. UPS #1, on the left, is the main one for my computer. UPS #2, on the right, is for other devices.

2 - PS for UPS.jpg . . . http://i.imgur.com/HhvEFkE.jpg
. . . On/Off switch (red, lighted) . . . Surge Protection indicator (green, lighted)
. . . This is most recent power strip that I got for the two UPS's. When the green LED doesn't stay on, you know that surge protection is no longer working. I will have to replace this with a non-surge power strip.

3 - PS speakers.jpg . . . http://i.imgur.com/Eu8SA49.jpg
. . . On/Off switch (not lighted) . . . Surge Protection indicator (green, lighted)
. . . I use this as the power switch for these cheap desktop speakers. I had a pair of these before, and the power switch broke after a year, so this seemed like the way to make them last a lot longer. So far, it has worked. This power strip and a table lamp plug into that extension cord in the bottom left, which plugs into the AC side of UPS #1 . . . . Same thing here - When the green LED doesn't stay on, you know that surge protection is no longer working.

4 - PS modem.jpg . . . http://i.imgur.com/NhtiOKs.jpg
. . . On/Off switch (not lighted) . . . Surge Protection indicator (none)
. . . Sometimes you have to power off the modem, and power it on, to get the connection back. I haven't had to do that with this recent, new modem I got, but this acts as its power switch. I have is set up this way, from reading somewhere that you want to have everything plugged in, first, and then power it on - as opposed to pulling out the DC power supply in the back of the modem, and then putting it back in . . . As far as I can tell, there's no way to know if surge protection is working on this power strip, or not.

5 - PS other.jpg . . . http://i.imgur.com/tMEgowY.jpg
. . . On/Off switch (red, lighted - but not working) . . . Surge Protection indicator (red, lighted)
. . . This power strip plugs into the AC side of UPS #2. It acts as the power switch for the scanner and laser printer . . . . Same thing here - When the red LED doesn't stay on, you know that surge protection is no longer working.

Am I wrong on any of this?

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. . . It's better to use unprotected ones if you've got them.

Is that just because the LED would use some of the amps from the UPS if the power goes out? I don't think they use a lot. I've had the power go off in storms, and the UPS kept everything on perfectly, I didn't notice a thing.

. . . The article you highlighted suggests they catch on fire when they fail but that's not likely to happen in a protected UPS socket.

Do you need surge protection if lightning strikes somewhere, and causes a spike . . . Or is surge protection used when the power goes off for 10 minutes, and comes back on . . . Or if there is a brownout, where the power goes off for 1 to 2 seconds, and then back on?

This is all rather off topic, but-

MOV protection is spotty at best. A lightning strike nearby can easily cause a surge to blow through a cheap MOV protector. Your UPS already has better protection than that, so it's likely that the MOV in the power strip won't get a workout anyway.

In a breakdown of some cheap power strips, the LED is simply wired across the power and doesn't indicate anything. In some it may actually indicate that the MOV is working. An MOV is high (essentially infinite) resistance under normal circumstances and simply conducts when the voltage exceeds a threshold. I'm not sure how you wire an LED to indicate that this infinite resistor is ready to conduct. There may be a way, but I doubt that the LEDs are a reliable indication.

As several web articles have indicated, MOVs fail after a number of surges. One failure mode is to short out which would blow breakers, melt wires or cause fires perhaps. In a few cases where I needed a strip and all I could find were MOV protected ones, I just removed the MOV to eliminate that possibility.

Also, maybe the LED isn't an accurate indicator. I think I read somewhere that you should just replace surge power strips after 5 to 10 years. That seems like a waste.

Agreed. If the LED indicates that it's failed but the strip is okay, I wouldn't throw it out.

The way you've set up your power strips is fine if it's working for you. As you've noted, you can't ever really be sure whether the protection is working or not (and there's no way of testing it), or for that matter - whether an incoming surge might be bigger than the protection could have handled anyway. Plugged into the UPS, a strip may not see a surge because the UPS will have stopped it with its own circuitry.

Schneider Electric makes APC brand UPS systems and is one of the larger manufacturers of UPS devices for home use. This is what they say about it: http://www.schneider-electric.us/sites/ ... irect=true

This helps a lot. Thank you!

Here's how I re-did my 4 power strips, using a three-head splitter ($2.99), and non-surge power strips ($3.99 each, 125V, 15A, 1875W, overload protection):

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Per this page:
"Discounting network monitoring features, and sane rackmount compatibility, PDUs are essentially [non-surge] power strips."
http://serverfault.com/questions/371740/what-is-the-difference-between-a-pdu-and-a-power-strip-both-120v-15a

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21 - new PS.jpg . . . http://i.imgur.com/X7DPU84.jpg

22 - PS for UPS.jpg . . . http://i.imgur.com/VJPQYZR.jpg

. . . My connection from the extension cord to the two UPS's

. . . I'm just wondering about this now, could . . . "it [the three-head splitter] may compromise the ground connection, which the UPS needs in order to provide adequate surge protection."

. . . There's a "Building Wiring Fault" light on the back of the UPS. This would be on, if you used a 3-prong to 2-prong adapter to power the UPS at the wall plug, in a house that didn't have grounded electrical outlets - so, this seems to indicate to me that the UPS tests that the ground connection is good

. . . I think the three-head splitter would be better than a power strip, "In order for your UPS to get the best power available"

. . . I could get this other 14 gauge 25' extension cord for the other UPS, and run it to the socket, but I don't think that's necessary

. . . They say to plug in the UPS directly into the wall, but I can't do that, in this case, so this seems like the next, best way to go.

23 - PS speakers.jpg . . . http://i.imgur.com/98CXCw4.jpg

24 - PS modem.jpg . . . http://i.imgur.com/B8DuMyy.jpg

25 - PS other.jpg . . . http://i.imgur.com/YbvKzCU.jpg

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My UPS batteries usually last 5.5 years. I have previously just gotten the battery replaced, to save money buying a whole new UPS. I thought I could just keep doing this until something broke.

Since you mentioned MOV, though, now I'm thinking that the UPS's are not good, indefinitely.

It seems like you just want to replace the battery once - you can get 10 years out of a UPS - then you want to buy a whole new UPS, with a new MOV.

http://en.wikipedia.org/wiki/Surge_protector#Metal_oxide_varistor_.28MOV.29

I would expect that plugging a three head splitter or a power strip into the UPS would be fine from a ground standpoint.

As for the batteries, I often have to replace the UPS batteries after 2 or 3 years. I've never had one last 5.5 years and still have any useful life. APC recommends replacing the whole UPS periodically as well but I don't see any reason to do that if the old one is working. I guess if the unit failed a self-test and I repleced the battery and the unit still fails to power things, then I'd certainly replace it. Hopefully the surge suppression in a UPS is much better than a junky MOV. I have some UPS units that are standby UPS units with good surge suppression and two that are true UPS units that generate power constantly and only use wall power for battery charging. Those are much more expensive than your average computer store UPS units and there's no way I could afford to replace those for no reason.

Your setup sounds find as it is. As long as the batteries can power things long enough for your needs, I wouldn't spend a lot of time or money worrying about it.

Previously, I have known to replace the battery, when the light does something different (this from the manual, next). Usually, the LED is solid green:

LED . . . Replace Battery is in need of charging or is at the end of its usual life and must be replaced
Visual Indicator . . . Green/Red alternating LED - flashing
Audible Alarm . . . Constant tone
Action: UPS turned off with the power switch.

. . . and I get 5.5 years before it does this . . . so it must be good at 2 or 3 years - but how do I know for sure?

I know for my car battery, you have to take the car in, and put it on a machine to see if it has the CCA (cold cranking amps).

Previously, I was using the multi-meter to look at the volts on my car battery, but learned somewhere that:

Good volts doesn't mean that I have the CCA to start the engine.
You have to put the battery on the Carbon-Pyle tester, to see the CCA. It's better than the electric type of tester.
279 cold cranking amps (OEM battery)

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There is a lot to this. Part of what I found:

http://www.batterystuff.com/tutorial_battery.html

Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at 0 ° F for 30 seconds and not drop below 7.2 volts.
So a high CCA battery rating is especially important in starting battery applications, and in cold weather.
This measurement is not particularly important in Deep cycle batteries, though it is the most commonly 'known' battery measurement.

CA is cranking amps measured at 32 degrees F.
This rating is also called marine cranking amps (MCA).

Hot cranking amps (HCA) is seldom used any longer but is measured at 80 ° F.

Reserve Capacity (RC) is a very important rating. This is the number of minutes a fully charged battery at 80 ° F will discharge 25 amps until the battery drops below 10.5 volts.

An amp hour (AH) is a rating usually found on deep cycle batteries.
If a battery is rated at 100 amp hours it should deliver 5 amps for 20 hours, 20 amps for 5 hours, etc.
Buy the highest RC reserve capacity or AH amp hour battery that will fit your configuration.

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It must be the same for this battery. I wonder if it could be tested on that machine.

The only other way, which isn't very scientific, is to have all of my stuff plugged in and running, pull the plug, and see what happens - or just rely on the LED.

If that LED can tell you that the battery needs to be replaced . . . I wonder how that works, that you don't need a machine . . .

I wonder what device is monitoring the UPS battery, that a car battery doesn't have.

The bottom line is: when the power fails, how long will the UPS keep your stuff running? Every once in a while, plug the UPS into a power strip and turn off the switch (this kills the power and keeps a ground connection). How long does it last? Long enough? As long as you expect? Or does it seem to die quicker than you'd predict based on the load. If you'd predict it should last 20 minutes and it lasts 15, you're okay. If it lasts 5, you might want to change the battery.

And if the battery has any corrosion on the terminals or has any bulges, you definitely want to replace it.

Howard

. . . plug the UPS into a power strip and turn off the switch (this kills the power and keeps a ground connection)

Never thought of that, thanks!

My equipment uses 1.7 amps . . . how would I test to see how long it can sustain 1.7 amps? . . . let's say that it's 2 amps . . .

. . . it doesn't seem like a good idea to me, to have my hard drive spinning, and then the power cuts off, seems like it could damage it, so what else could I use? . . .

I could put the space heater on it, on Low, which uses 6 amps. If it stays on for 12 minutes, and then the battery dies . . . that's like 3 sets of 2 amps . . . 12 minutes divided by 3 = 4 minutes . . . so I could calculate that 2 amps would stay on for 4 minutes?

I think it's ok if the battery gets depleted like this, now and then, but I've never done it . . . So this test should be ok.

A 60W bulb uses .5 amps . . . V x a = W . . . 120 x a = 60 . . . a = .5 . . . I could rig up four 60W bulbs, which would use 2 amps, and see how long they stayed on.

Different topic: A 29W bulb uses .24 amps . . . How do they regulate how many amps a light bulb uses? I never took one apart. Is there a .24 resistor in there, in this case? Or a .5 resistor in a 60W bulb?

You don't have to let the computer actually die. The UPS will start beeping and throwing a hissy fit before it dies. Time until it's clear it won't last much longer (there may be a display on the UPS) then shut the computer down.

An incandescent bulb has resistance. The filament is a resistor - it glows because the energy dissipated by the resistor comes in the form of visible light and heat. The resistance does change as it warms, but you can measure the resistance with your meter. That's not true for LED lamps and fluorescents of course. LED lights might have a measurable resistance, depending on whether they are simply LEDs and resistors or have active circuitry inside of them.

Interesting, thanks!! I never thought of the filament as being the resistor.