Multi-Core Clamp Meter

Does the clamp meter need to go round all three cores, Boss, or are three meters needed for measuring one core each?

Instead of passing three cores through one meter, you could simply measure the neutral current instead.

http://en.wikipedia.org/wiki/Clamp_meter

Are the three cores three different phase conductors or the same phase?

Do you have a link to the clamp meter model you are talking about?

Megger MMC 850 Multi core clamp meter is the name of the meter Iam talking about and it can measure the current of neutral and the phase wire with out even seperating them.In conventional clamp meters current will be zero if both neutral and hot wire are in the clamp meter but in this case it will show both currents.For 3 phase it will also be the same.How it works Iam not clear,any one has a better idea???

Straight from Megger's website, the data sheet on the MMC 850 clamp meter, third paragraph, first page.

Unlike conventional clamp meters, the MMC850 has a complex array of Planer magnetic sensor coils to calculate the current flowing in the conductors of multicore cables with either 2 or 3 cores, and in either flat or round section cable, up to 100 A.

http://www.megger.com/us/products/ProductDetails.php?ID=656#View%20MMC850_DS_en_V02.pdf

Also available is an animated demonstration showing exactly how this is done (same link).

http://www.megger.com/us/products/ProductDetails.php?ID=656#View%20MMC850_DS_en_V02.pdf

Quick question, why didn't you try the Megger website?

The first thing I did was to go to megger website but some how I didnt find the animation thanks

but how it senses the distance between the cores ? any idea ?

The MMC850 meter is designed for round or flat cables (2 or 3 core). In this configuration the outer diameter of the cable and the distance between the conductors inside the cable is fairly constant (due to cables being designed and made to standards).

It is likely the special red jaws allow the meter to measure the overall cable diameter and the meter electronics do the rest by estimating from data tables the distance between the conductors based on the cable overall diameter (a 5% accuracy is mentioned in multi core cable mode meaning it is far less accurate than single core cable mode where position of the cable is not important).

Settings on the meter also likely fine tune the reading for the different cable types.