Split The Conductors For Easy Current Measurement
By Benjamen Johnson
In last week’s post on the Black & Decker Power Monitor, we talked about monitoring your power usage. If you want to monitor the power consumption of a single appliance the old-school way — with a clamp-on ammeter — try an AC line splitter like this one from Elenco.
The problem is, you can’t just clamp an ammeter over a power cord and measure how much juice the appliance is taking; you need access to a single conductor to measure the current. That’s where this tool comes in handy — rather than ruin a power cord you can just plug in the line splitter.
Elenco’s AC line splitter works for voltages up to 250VAC and currents up to 15A. Place the line splitter in between the device under test and the outlet. It internally splits off a single conductor so you can clamp your ammeter around it. For greater sensitivity it gives you an option to measure 10x the current. This particular line splitter also provides probe slots for measuring the voltage under load.
Look to pay about $10 to $15 for the Elenco AC line splitter.
AC Line Splitter [Elenco]
Street Pricing [Google Products]
Via Amazon [What’s This?]
December 3rd, 2008 at 12:55 pm
…or just use a short, flat extension cord and separate the insulated conductors.
December 3rd, 2008 at 1:38 pm
Thats what I suggested last week… I just don’t get why I’m going to spend $15 on a single purpose tool when I’ve got extension cords lying all over.
December 3rd, 2008 at 2:12 pm
I don’t understand why I should by a voltage tester when I can just stick my finger in the socket and see if I get shocked…
December 3rd, 2008 at 2:57 pm
Ben,
Ben there, done that. When I was 3 years old! Now I’m an Electrical Engineer. Go figure.
December 3rd, 2008 at 3:47 pm
This ain’t how you monitor AC power usage. It’s not even how you determine instantaneous AC power. When you measure instantaneous current, you find out what the instantaneous current is, and that’s about all. That can be real handy, and sometimes it’s exactly what you need to know, but it’s not monitoring power usage. It’s not even “monitoring” current, and knowing current and voltage alone will not give you power in an AC circuit. If you also know that it is a purely resistive circuit, it can. This technique can give you useful information, but it shouldn’t be confused with monitoring power. For that you need information over a period of time. You don’t pay for kilowatts– you pay for kilowatt-hours. This gives you neither kilowatts nor hours.
There are clamp-on meters that work for multiple-conductor cords. And a good line splitter, as the article says, does a number of things for you besides split the line. Toolhearty does have the best quick way of making a usable, field expedient line splitter in his flat-cord method.
And I’ve got a first-edition American Electrician’s Handbook from 1913 with all kinds of stuff about testing with your fingers.
December 3rd, 2008 at 4:09 pm
David Bryant: Good information, thanks. It would be fascinating to see some of those 1913 testing ideas; would it be possible to post some of them?
December 3rd, 2008 at 4:17 pm
David Bryan:
You are correct, it’s not really very straight forward monitoring power with a clamp-on ammeter. Unless you have a logging ammeter and make a few assumptions you’ve better off doing it another way.
I was more concerned with the comments in the Black & Decker Power Monitor post and wasn’t really thinking when I wrote the line about monitoring power.
I would like you to explain how you can get a clamp on ammeter to work over “multiple conductor cords” though. I’m assuming you mean a cord with current flowing in one direction on one conductor and the other on the second. If the two fields don’t cancel each other out you’re leaking current to ground somewhere and if you were using a GFI it would trip.
December 3rd, 2008 at 4:29 pm
Well, I’ll run through some of the topic headings:
90. Electricians often test circuits for the presence of voltage by touching the conductors with the fingers.
91. The presence of low voltages can be determined by “tasting.”
93. A telephone receiver in combination with one or two dry cells constitutes an excellent equipment for certain tests.
95. A telegraph sounder is sometimes used for testing.
96. An electric bell outfit for testing.
113. How to Make a Slide-Wire Bridge
119. Testing Cables For Insulation with a Telephone Receiver and Battery
That scratches the surface. There’s a bunch of tricks for determining DC polarity too.
I just found my “Modern Electrical Construction” from 1904, now I’ll have to look through that one.
December 3rd, 2008 at 4:56 pm
Benjamin– I don’t know how they do it. These days I am but a lowly recreational romex jerker, at best, for the most part. But the Megger model MMC850 is supposed to do it, and I think I’ve seen another one that will too. They say it’ll work for one, two, or three conductors. What a smart little machine it must be.
December 3rd, 2008 at 4:59 pm
David Bryant: I’m almost afraid to ask about #91 as it likely violates my rule which states: Fingers, sometimes; tongue, no way/no how.
December 3rd, 2008 at 5:04 pm
I’m not touching that one.
December 3rd, 2008 at 5:33 pm
David Bryan: My rule only applies to electrical and mechanical things.
December 3rd, 2008 at 5:44 pm
Wow, I have to eat crow twice for one post.
David Bryan, You are absolutely right, the Megger does measure current in multiple conductors, but you have to know the distance between the conductors. It uses the fact the fields don’t overlap completely to figure out the current. I’m surprised they can sell a consumer products that can measure the fields precisely enough to do this, let alone for $300.
Thanks, David. This is good. I’ll have to post about it in a while.
December 3rd, 2008 at 10:05 pm
To be fair, #91 did say “low” :-p
cl
December 4th, 2008 at 6:58 am
Re: #91
Who hasn’t “licked” a nine volt battery to see if it was good or not?
December 4th, 2008 at 1:41 pm
@PutnamEco:
That always reminds me of a story I heard about the early Li batteries. Executives were going through the labs, engineers were showing this new 9V lithium battery that would last years. An executive picked it up, stuck out his tongue, and before he could “test” it, the engineer grabbed it from his hand.
The engineer then took a small copper rod and shorted the battery terminals.
The copper rod evaporated.
Since it was an engineering sample, it didn’t have a current limiter in it in case of short circuit…
And, of course, there’s also the (true story of a Navy seaman managing to kill himself with a multimeter powered by a 9V battery (hint: your external electrical resistance is in the thousands of Ohms. Your internal electrical resistance is rather considerably less and tends to go through your heart).
December 5th, 2008 at 11:30 am
[...] Split The Conductors For Easy Current Measurement If you want to monitor the power consumption of a single appliance the old-school way — with a clamp-on ammeter — try an AC line splitter like this one from Elenco. The problem is, you can’t just clamp an ammeter over a power cord and measure how much juice the appliance is taking; you need access to a single conductor to measure the current. That’s where this tool comes in handy — rather than ruin a power cord you can just plug in the line splitter. [...]
December 5th, 2008 at 12:07 pm
Zathrus,
The killer 9 volt lithium battery sounds like a classic “friend of a friend story.” You know, the kind that starts, “A firend of mine told me about this guy he knew who…”
The only nine volt batteries that people test with their tongues are the little ones you put (are used to put) in radios. There is not enough current in them to melt anything, no matter what you do. a 9 volt battery is actually a package of 6 tiny 1.5 volt batteries. Thus, each battery has a very low current output, no matter what chemistry is used.
Further, lithium batteries do not have current limiters in them. No batteries do.
December 7th, 2008 at 3:13 am
I’ve read up on that Navy story quite a bit and I just can’t bring myself to buy it. There’s just something fishy about it, nautically speaking. The other one is just not how things work. I used to hear all kinds of whoppers at safety meetings. I’ve told a bunch of ‘em myself, usually involving death, evisceration, mutilation, etc. And I know some really ugly, sometimes improbable true ones. But if these stories help somebody be safer there’s something to be said for them. You’ll shoot your eye out, you’ll break your neck, you’ll atrially fibrillate yourself, if you don’t watch out.