In this article I will discuss the digital clamp multimeter & why this little gem can come in handy, they are not commonly discussed and not everyone bothers to have One. For me, I wouldn’t be without One, its not a bit of kit I use on a regular basis, but they can tell you things most other bits of test gear cant.
What does it do
The clamp meter allows you to measure electric current flowing through a cable, the unit of measurement is the Ampere or as everyone calls it an Amp.
You may ask why do I need to know this as the most commonly used term is voltage or volts (V). To try to keep this simple if you look at the fuse box in your house then all the circuit breakers or fuses are rated in Amps
As seen above there is B32 & 20A, these indicate how much current can safely flow through the wires attached to the fuse (RHS image) or miniature circuit breaker (MCB) (LHS).
If the current flowing through the circuit or cable is exceeded (goes above the rating in Amps) then the MCB will trip or the fuse will blow, this is designed to prevent cables melting & fires starting.
Sometimes however circuit breakers can go faulty and trip for no apparent reason, they can be reset but will often keep tripping, if this is the case then you need to see if the current flowing in the cable it is protecting has exceeded its rating, or is the current flowing well below the trip rating.
This is where the digital clamp multimeter is invaluable, it allows you to see graphically on an LCD display what current is actually flowing in real time.
From this you can quickly determine if the load on the cable is too great, causing the breaker to trip off or the fuse to blow. If the current is lower than the rating and the breaker keeps tripping off then you have a faulty breaker, it has become too sensitive and is tripping off when it shouldn’t be.
In the case of the re-wire fuse, you would need to check if the correct rating of fuse wire has been fitted, if it has then the fault lies elsewhere, the same for the MCB, if the current flowing through the circuit is too great then there is something on that circuit drawing too much current and should be investigated to find the cause, something for a future post.
How to use
The digital clamp meter is possibly One of the easiest tools to use, as the name suggests it has a clamp like part usually brightly colored. The clamp is spring loaded and is normally opened by a lever on the side of the meter, squeezing this inwards will open the clamp.
In this case the clamp or hoop is yellow as is the lever on the left side, to take a current reading you will need to access the inside of a fuse box or consumer unit. Extreme caution is required as you will be exposing yourself to LIVE parts, only attempt this if you are confident and have enough knowledge of what you are looking at and are about to do, I cannot stress this enough !
To take a reading, switch the meter on and select the highest Amp setting, you will require a meter that can read up to about 200 Amps ac (for domestic readings).
Select a single cable that comes out of the breaker or fuse and open the clamp and allow the clamp to close around the conductor. Once the clamp has closed around the cable you will see a reading on the digital display, this indicates the current flowing through the conductor.
All meters will vary so spend some time reading the manuals that are supplied with the meter to gain familiarization first.
Some clamps differ in that they dont have a closed loop, they are slotted and dont require a full loop or hoop to read current flowing, these tend to be more expensive but really only do the same job, just a little more convenient to use in tight fuse or distribution boards.
Above is the slotted type made by FLUKE, these are more expensive, but they are a good quality product. As you can see the cable is between both of the sides of the slot and a reading is shown of 2.8 amps flowing, it might be 28 amps as the image is not too clear, but it does show the meter in use.
How much to spend
This really is down to the individual, for me I have Two clamp meters and both were inexpensive, both have provided years of trouble free testing and have been invaluable to me and without one would have meant a lot more work to simply prove the current flowing through a device or through a cable or circuit.
Final words of caution
Please remember, to use a clamp meter you will be working on LIVE cables, if you are not confident & competent then DO NOT attempt to undertake current or voltage readings. Electricity does not take prisoners, it has no prejudices, and doesn’t care who it comes into contact with or who it kills, electricity will kill you !