Using ohmmeter to determine when to replace wiring

[Paul Elliott]

Originally Posted by dave948

if you not willing to invest $10,000 or so in test equipment your never going to accurately be able to test your wiring.

Perhaps, but all you need is a $20 digital voltmeter and your normal working loads to adequately test most boat wiring. Spend $200 more and get a DC clamp-on ammeter, and then you've got it pretty much covered. You won't be able to solve every conceivable problem, but you will be able to find and fix the vast majority.

Of course you have to know what you're doing, but the fundamentals are pretty easy.

And no. I wouldn't use resistance measurement as my primary troubleshooting technique. Turn on the loads and measure the voltage at the load and at the battery. Measure voltage drop across connectors and terminals. Consider your ground wiring as just another part of the circuit -- many times ground problems go un-diagnosed since we think of "ground" as something special.

[Wotname]

+1 Paul E.

Originally Posted by dave948

Finally a subject I can say I know what I'm talking about, I've made a living at it for the last 30 years.
1st if you not willing to invest $10,000 or so in test equipment your never going to accurately be able to test your wiring. One of the key pieces of equipment you will need is an ultra low ohm meter, one that places a 10 amp load on the circuit will work well. This is a $6000 meter that needs to be plugged in and uses a four wire system to calculate the resistive loss of the leads....l.

I guess prices change

Not sure what part of the world you are in but here in Oz, one can get a 4 wire lo-ohm 10A, portable meter including calibration certificate for $1,500. Good for 100 micro-ohms. I priced one only last week for work.

Add a 600 or 1,000V megger and a middle of the road Fluke MM, say $1,000 and you are good to go around $2,500.

Nevertheless, I reckon the OP can sort out most wiring issues with a chinese MM for less than $100 if he uses his noggin.

YMMV.

[bill good]

For interest only, the black wires on my boat turned to copper dust. Put it down to the die in the plastic insulation. Neg & pos both were switched. All black wires replaced.

[esarratt]

Originally Posted by dave948

Copper wire has no moving parts, left alone it will out last you and your boat. Green and black copper wire conducts just as well as bright shinny wire, that's why it's used as a wiring method, unlike aluminum, copper salts conduct very well.
Most problems are going to come from switches, fuses, terminations and just plain bad installations. Physical damage can also be an issue.
The majority of problems come from years of equipment upgrades with no regard to upgrading the 10 year old system your hooking into. Boat builders don't give you much in the way of head space when it comes to your electrical system.
Upgrade your system as needed to support new loads but very rarely do properly fused wires fail. Keep your terminations tight and clean but the wire in between will be the last thing to fail.

Nice. Thanks.

[esarratt]

Originally Posted by Wotname

Nevertheless, I reckon the OP can sort out most wiring issues with a chinese MM for less than $100 if he uses his noggin.

YMMV.

Yep. Been using an el cheapo Radio Shack one for years.

[Paul Elliott]

Originally Posted by dave948

Green and black copper wire conducts just as well as bright shinny wire, that's why it's used as a wiring method, unlike aluminum, copper salts conduct very well.

What??? Cupric Oxide and other oxides of copper are poor conductors. They have about 10x or 100x the resistance of copper. A little bit of oxidation on the surface of a wire won't have much effect, but heavy oxidation will kill a connection.

Have you ever had a crimped connector pull off a wire that has been in a salt-air environment? I've seen wires that have turned to powder from oxidation. These corroded contacts can be a fire hazard, if they work at all.

Tinned wire isn't required by the electrical codes, but it sure holds up better than untinned copper to the forces of oxidation.

[Cadence]

Originally Posted by Paul Elliott

Perhaps, but all you need is a $20 digital voltmeter and your normal working loads to adequately test most boat wiring. Spend $200 more and get a DC clamp-on ammeter, and then you've got it pretty much covered. You won't be able to solve every conceivable problem, but you will be able to find and fix the vast majority.

Of course you have to know what you're doing, but the fundamentals are pretty easy.

And no. I wouldn't use resistance measurement as my primary troubleshooting technique. Turn on the loads and measure the voltage at the load and at the battery. Measure voltage drop across connectors and terminals. Consider your ground wiring as just another part of the circuit -- many times ground problems go un-diagnosed since we think of "ground" as something special.

Paul makes some great points. A $20 meter is all you need with a little bit
of knowledge. Also checking the ground is as important as the supple, what goes in has to come out to be simplistic.

Are you having problems? Speaking about rewiring seem extreme.