Criteria acceptance for Control Cables Continuity Test

[Julinios]

Dear all:
For firefighting panel circuits our contractor is measuring 4 ohms for some cables.
Most of the cables have less than 1 ohm.
We are looking a norm to see the criteria acceptance.
Please advise if you have seen a similar issue.
Regards

 

[zappedagain]

Unfortunately there can be a lot of variation in what is acceptable. You'll hae to refer to a design standard for the panels. Typically when I see something like this it is an improper crimp terminal, with insulation stuck inside the crimp. Or it could be a wire with corrupted insulation that is rotting away slowly.

Z

 

[ScottyUK]

How big is the deviation from the calculated value for the cables? Is it a measurement problem, or a cable which is installed properly but just longer than the others?

 

[Julinios]

The Nationoal Electrical Code 2011 Chap 9 Table 8 Conductor Properties: 16 AWG, not stranding, copper and coated: 16.7 ohm/Km. The cable run is 60 m then we have 1.002 ohm but our measure is 4.1 ohms, the instrument calibration is ok, we are looking a "criteria acceptance" for "continuity check" to reject this circuits.
Thanks

 

[zappedagain]

How are you checking your 60m cable? Two hooked together for a loop so you can measure at one end? Could be a problem with your test connection. Can you confirm the high reading with a different return path/wire?

Are there other wires in the tray with the wires that are giving 4 ohm readings? Crosstalk may be corrupting your measurement. Maybe you could try an AC impedance measurement. Or a brute force test with a power supply and a current meter (1V/1A = 1 ohm, 1V/0.25A = 4 ohm). That may overcome any crosstalk, but may give a false positive if your panel circuits aren't as strong.

Have you tried other testers?

1.5 ohms seems like a very generous specification. Unfortunately you are failing that badly.

Z