Using ohmmeter to determine when to replace wiring

[Wotname]

Originally Posted by MYTraveler

The problem is that increased resistance resulting from corrosion will be much more noticeable when as current increases. Voltmeter readings are usually taken without current flowing, so would not be a reliable indicator.

Not in my world
Voltmeter reading at the device or in the circuit must be taken with current flowing otherwise they are almost meaningless.

There is merit in taking voltage reading with and without current but this is getting away from the simple question asked by the OP.

[Colin A]

Originally Posted by HopCar

I wonder if you couldn't us an IR thermometer to quickly check if a wire was overloaded or spot a bad connection?

Yes they are pretty useful for this We use them sometimes when checking high current connections. It's amazing how hot a loose connections on a bowthruster can get.

[esarratt]

Thank you all for the information.

I think I am going to replace all the wiring in the boat now because of its age (30+ years). That comment about "new technology" was right on.

I had already bought some fuse boxes for the final runs and bus bars to split the pos/neg. BSS sure does help make things nice an neat.

I rewired the front end of an old Opel GT when I was 16 so this shouldn't be too bad.

My friend's comments had given me pause about replacing everything; originally I was just going to do the battery wires and the wiring for the key and gauges, but now the whole boat is on the list (slowly, slowly).

And I do appreciate the information about voltage drops and other methods to determine wiring problems. I'll file that information away in the recesses of my mind for future issues.

Thanks again!

[Cadence]

Originally Posted by esarratt

I got into a discussion with a friend about boat wiring.

Is it feasible to use a wires resistance, with an ohmmeter, to determine if a particular run of wire needs to be replaced?

He suggested that because some runs of wire were very long it would be difficult to get an accurate ohmmeter reading and instead to use amps?

Your thoughts? AND, does anyone ever actually use this to determine if wire needs to be replaced?

What is your "barometer" to know when it is time to upgrade your wiring? Time?

Thanks!

Look for a voltage drop from one end to the other. I'd look a connections long before wire. I would look at the wire for insulation failure long before resistance in the wire itself. JMHO

[MYTraveler]

Originally Posted by Wotname

Not in my world
Voltmeter reading at the device or in the circuit must be taken with current flowing otherwise they are almost meaningless.

There is merit in taking voltage reading with and without current but this is getting away from the simple question asked by the OP.

Sounds like you do it right. In my experience, few do.

[Cheechako]

I agree, use voltage drop. Problems are usually in the end terminations not the wire. Although once the wire is too corded, it's hard to fix the termination!

[CarinaPDX]

1) The shortcoming of the tests discussed is that they don't/can't test the insulation, other than for shorts. Plastic loses its flexibility with age and can degrade and become brittle. Other than being difficult to bend into new positions it is not likely to be a problem for anything built in the last half century, but my point is that nothing replaces a close visual inspection.

2) When FLIR first started they were developing IR cameras for airborne military use; the time required to actually sell something to the government was painful, so they looked for other applications to keep them going. One was to look at new (powered up) circuit boards with IR and identify hot spots which indicated high risk of failure. That was back in the 80's. So there is a long history of using IR for locating problems.

Today FLIR offers the FLIR One (FLIR ONE Personal Thermal Imager | FLIR Systems), which is an IR camera which attaches to an iOS device (and soon Android). Another option is the Seek Thermal camera (Seek Thermal Camera Android) which works on Android devices. Both cost $250. The Seek device is (or at least was) higher resolution (I am having trouble finding the FLIR spec, so I guess they don't want that comparison). My brother recently used a Seek thermal camera to find the myriad leaks in his house; it is very impressive, and I'm sure it would locate any resistive contacts on a boat as well.

Greg

[Bulawayo]

Originally Posted by smac999

wire condition can be tested with a megger. but that mostly tests the jacket condition.


otherwise you'd have test voltage with a load.

A megger tests the insulation resistance - and nothing else.

[F51]

The OP would be well advised to seek competent professional help rather than relying on internet advice. His questions show that he is not an expert in this area. In the first 22 replies the conflicting, contradictory information presented could only further confuse a novice. This is a subject not well understood by laymen. Unfortunately too many of them are ignorant of that fact. Electrical problems can be deadly. Cut thru the confusion and talk to a pro!

[Cadence]

Originally Posted by Bulawayo

A megger tests the insulation resistance - and nothing else.

Yep! And everyone knows what a megger is and were to find one. I'm not questioning the principal just the availability of one. Tesla would be proud.

[Wotname]

Originally Posted by MYTraveler

....... In my experience, few do.

You are probably right.

I tend to forget how many people don't understand basic electrical theory or more importantly, how to apply and use basic principles.

Thanks for the reminder

[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.

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.

[model 10]

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. 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.

That is all well and good but but those "green and black" wires are more brittle and will crack. Insulation failure is common in old wires too.

[Cheechako]

The problem is you have to attach an end to those green and black coated wires. poor conduction thru that cuprous oxide coating.
That might be one argument in favor of those that like to solder as well as crimp on end terminals...

[model 10]

Originally Posted by Cheechako

The problem is you have to attach an end to those green and black coated wires. poor conduction thru that cuprous oxide coating.
That might be one argument in favor of those that like to solder as well as crimp on end terminals...

I guess you are saying, maybe solder before they turn black or green.