I would tend to agree, but you should check the specs on the equipment being used to make the measurements. Typical resistance measurement involves passing an accurate, controlled current through the item being measured, then measuring the voltage drop across the item. With a 2 wire measurement, the same wires / probes being used to pass the current are also being used to measure the voltage, and your measurement will include any resistance in the measurement system. With a 4 wire measurement, the current and voltage measurement are separated, and the measurement does not include any lead or contact resistance. 

Blair

On Wed, 31 Aug 2016 14:17:54 +0000, Wayne Thayer - EXT <[log in to unmask]> wrote:

>4 wire shouldn't be necessary. Threshold should be around 1ohm or 0.5 ohm. This is determined by when the variable portion of the contact resistance is "close to or greater than" the resistance being measured. 4 wire can get you into the milliohms, which is nice if you are trying to find the location of a short.
>
>Wayne
>
>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of Craig Sullivan
>Sent: Wednesday, August 31, 2016 6:31 AM
>To: [log in to unmask]
>Subject: [TN] Bare board testing - low continuity threshold
>
>We have a customer that requires "DC resistance testing" of particular nets on a PCB to a 2 ohm threshold.
>
> 
>
>Understanding certain PCB flying probe manufacturers offer a "4-wire kelvin"
>testing option on their equipment, my question is: At what point do you require the 4-wire option to be used? Or in other words, what is considered "low ohm" as it pertains to PCB electrical testing?
>
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>Craig Sullivan
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