Wiring amp multimeter

Measuring your way will get you track current. Measuring from a common terminal to all the commons connected together will get total current being supplied from the transformer.

Ron

I recommend a meter for each track feeder so you can see the current each power district is drawing.

Let's go back to the real question, before we add more answers than were asked.

It makes no difference whether you put the ammeter in series with the middle rail or the traction rail. You are using alternating current, and the meter doesn't care which rail you use, or what color the leads are. 

To find the current in any circuit, you need to isolate the exact component or circuit that needs to be measured. In your case, insert the meter as close to the track as possible. That eliminates any readings from other parallel circuit return wires.

RR Fan Ron is also correct in his advice. It is true that if you put the meter in series with a major wire that supplies all the "return" current from several different "hot" sources, you will read the total current being drawn from all those hot sides. But that's not what you asked, and it appears that you have a good understanding of how the meter should be used. Always remember to isolate the circuit.

Gun Runner also has a good idea: if you want to have a nice-looking control panel, use a separate analog meter in each track supply.  If you are just experimenting to see whazzup with current draw from various locos and passenger cars, then the digital test meter is the way to go.

Many digital meters have an internal fuse in the high current circuit. Are you using a digital or an analog meter?

Another option for Ad-hoc measurements of current around the layout, I use a clamp-on ammeter.  It doesn't require you connect the meter in series with anything, you don't disturb the wiring at all. 

Hard to go wrong with this one from Harbor Freight: 5 Function Digital Clamp-On Multimeter $12.99

Woo!  GR John, I think you've hit on what I will get myself for my birthday. (the big 65 on the 18th of March) Thanks for the lead!

http://www.harborfreight.com/7...ultimeter-98025.html

This one should in the tool box of every member of this forum. There's no excuse not to own one. If meters scare you, there are plenty of people here to help explain them.

I think you deserve two of them for the 65th!

If you're patient, the one you linked goes on sale pretty regularly for $3.99.

I don't believe this meter reads AC current.

Ken

Ken, you are correct.

I have 8 or 10 of these meters scattered around the house, shop, car, layout and ham shack.  They are good for many things, but they don't read AC current, and the lowest AC voltage scale is 200 volts, which is OK for coarse readings of track voltage, but not for detailed small-voltage analysis.  You can't beat the value, especially when they are on sale for $2.99 or $3.99 including battery.  (I have so many because it is almost cheaper to buy a new one than to replace the batteries!)

That's why I recommended the clamp-on.  It's a PITA to break the connection to read current anyway, so the clamp-on really earns it's keep.

Thanks guys for the replies.  Will use the hot side to read the draw from some older pw engines on an isolated loop.  Interesting comment re the common side.  Will check the draw from several "loops" sharing the common.

Thanks again