Multi meter Low impedance input, input protection

[facosta]

I would like to measure mains power stray voltage between neutral and earth for an isolation transformer project. I do not own a multi meter with low impedance range but can overcome the problem by  jumping the multi meter's input jacks with a 10kohm resistor. If I probe between neutral and earth in the primary side  or between earth any of the terminals on the secondary side everything is sweet. If a make a mistake and probe between active and earth primary terminals or in between both secondary terminals, the resistor allows quite a bit of magic smoke to escape. How can I protect the resistor without using a beefy one? Would a PTC resistor achieve this goal? What protection multi meter manufactures use for this issue?   

[Simon]

in your case Id get a 7W resistor and do make sure your keeping stuff insulated.

[facosta]

Thanks Simon for your answer. Your solution is cheap and simple enough. Still trying to found another way to skin this cat I came across the Fluke 12B service manual @ http://assets.fluke.com/manuals/12b187xxsmeng0000.pdf In page 4.10 we can see what they use for their Low Z input protection one 1.1Kohm PTC resistor in series with a bunch of 470 ohms, 3W resistors. So it looks like this Low Z input is somewhere around 2k5ish ohms. It looks to me this configuration will dissipate a hell of power if something goes wrong with the PTC resistor. Is this thing even fused according to the schematics? Cheerio

[jeroen79]

You will have to decide on a combination of measures:
-dissipate the power up to a point
-then increase the impedance (ptc)
-finally open the circuit if that still is not enough ((poly)fuse)

And set a clear maximum voltage rating that the user should respect.

[Kalvin]

Alternative approach: You can also measure the current through the resistor, and use Ohm's law to calculate the voltage. Place a fuse in series with the resistor which will protect the resistor and your multimeter.

[jeroen79]

How about using something like a low power mains rated lamp?
It can dissipate the power and if it burns out the circuit will open.

[facosta]

Thanks all for your answers. All your ideas will solve the problem. I was thinking more on a short of fixture small enough to sit nicely directly on the multi meter jacks when needed, so it cannot be too bulky. By the end of the day and analogue meter, been inherently a much low input impedance device, will do the trick but it will be trash in the toolbox in no time at all.