Halving Clamp Meter Reading

[MrAl]

Hello there,


This is another one of those "Anyone ever tried this" threads


Say we have a current clamp-on AC/DC meter that reads up to a max of 400 amps, but we want to read up to 550 or 600 amps or maybe even more.

It's well known that if you have a lower current to read you can wrap more turns around the clamp meter clamp, but here we want to read a higher current so we want to split the current.

Given two equal resistances in parallel the current splits exactly in half through each branch. So the idea is to use two heavy gauge wires connecting them in parallel using a careful technique and measuring the current in only one of those wires. Theoretically the current will be half of the total so 600 amps will read as 300 amps on the meter face.

Now i know this will take some care making good connections, no argument there. But since there can always be some random differences in the wire and connections, we would first measure the current in one of the wires, then in the other wire, then add the results. Later we would know how the current is actually splitting so we might not have to do this every time, but even if we did it may be for only one reading so it would not be too much trouble. So if we read 250 in one wire and 350 in the other then the total current is 600 amps, but for each measurement we could have gotten away with using a 400 amp max meter.

So, anyone ever try this measuring either one wire or both wires as above?

Also note that the higher current clamp-on meters are a lot more expensive than the lower current meters.

Thanks ...

 

[ronsimpson]

I understand your idea and think it is good. Yes you need to measure both wires and add the results. The two current paths do not need to exactly equal if you add them.

Small problem: The probe effects the current in the big wire. The probe is a current transformer and it will add a small amount of inductance and resistance to the wire you measure. You might be adding 0.001 ohms to the wire while the clamp is in place. If you had two clamp you could measure this effect. Put the first clamp on and measure the current. Then add/subtract the second calm while monitoring the first clamp.

Under normal conditions a m-ohm will not effect a 220V 400A service but a m-ohm will effect current sharing in a parallel strand of wire.

 

[MrAl]

Hello,

Yes, good points there. I expect to work with DC but knowing what will happen with AC is also a good idea. I dont have two clamp meters but i could borrow another one for the test.