To shunt or not to shunt (ammeter)?

[rogerthebodger]

Be careful here. One style of amp meter has a moving iron movement where the current goes through a heavy wire coil perhaps 6 turns which drag around an iron armature. Typical of old car amp meters reading + and - . Typically also non linear scale. It is conceivable that a shunt could be used with this type but it would mean a large current going through meter. So 200A 75mv shunt would not suit at all.
If OP has not bought the meter yet it is possible that it has a shunt bolted to the back of the (moving coil Mv) meter.In the form of a piece of sheet metal clamped under input bolts. This would have to be removed to use 75mv 200A shunt. But could in fact be used as the remote shunt by arranging a suitable insulating block for the shunt. use of a 200A shunt means at 200A 75mv will be dropped to drive meter. Which may mean 200A full scale so almost useless for OP typical current being measured. ie at 20 amps through 200A shunt you only get 7.5mv to drive meter to 20A mark FSD all very tricky ol'will

Yes I forget about the moving iron meter.

I mostly have digital volt meters with shunts usually 200Amp but mt bow thruster can draw 600 Amps and had had no issue with the over current for a short time and the digital meter just indicates over range.

I also do have some hall effect current drivers that also survive the over current when the bow thruster gets used and does not introduce any voltage drop

 

[Graham_Wright]

I don't bother with a shunt. Routing heavy duty cables to the meter (especially if it is in the cockpit), can be avoided.
The cables themselves have a resistance albeit small. I take connections from the source and destination of the cable and measure the voltage across it. It needs a sensitive meter but, if you measure the volts drop across the cable when it is carrying a reasonable current, you can choose one to suit. It may well be, in your case that removing the internal shunt in your meter will do the trick.

75 mv sounds pretty sensitive.