# Solved: How to check a power cord with a multimeter?



## LoveGoldens (Sep 23, 2008)

I want to know the proper procedure for using a multimeter to check my 50Amp 'Shore-Power cord.' I want to determine if its wiring (inside its rubberized sheathing) has any defects, which might show up as resistance, etc.

When I was much younger, I used to know what to check for and how to use a multimeter to do it, but I've long since forgotten.

It's 25' long and has a male connector on one end, and a female connector on the other.

I vaguely remember setting the multimeter on the "Ohms" setting, but I'm no longer certain of that. Hopefully, you can explain just what it is that I'm trying to measure, which would tell me if the cord is still good, or faulty.

Will someone be so kind as to provide a thorough, and easy-to-follow "step-by-step" procedure which I can follow?


----------



## etaf (Oct 2, 2003)

do any of these help at all
http://www.ladyada.net/learn/multimeter/continuity.html
http://www.electronics-radio.com/articles/test-methods/meters/multimeter-resistance-measurement.php
http://www.doctronics.co.uk/meter.htm
http://www.wikihow.com/Use-a-Multimeter


----------



## K7M (Feb 27, 2000)

When you say a 50 amp shore power cord, I assume it is for an RV????? You should have continuity on each of the four connectors. On the male plug, the round pin is ground, the flat blade on either side are "hots", and the center blade is the neutral. The other end, I assume is a twist lock. The "tab" on the side of the connector is ground, The curved blades with the little "l" in them are the hots, and the last curved blade is the neutral. You should have continuity (.5 ohms or less, this will depend on the accuracy of your meter) between the Neutral to neutral, ground to ground, and one of the hots to hot and the other hot to the remaining hot. I hop I explained it correctly for you to understand.


----------



## paisanol69 (Sep 7, 2005)

> How to check a power cord with a multimeter?
> I want to know the proper procedure for using a multimeter to check my 50Amp 'Shore-Power cord.' I want to determine if its wiring (inside its rubberized sheathing) has any defects, which might show up as resistance, etc.


since your screen name is" old salt ", and your asking how to check a shore power cord rated at 50 amps, I'm sure you are concerned about a ship to shore electrical hookup?

Be advised, that with a good multi-meter, you will be able to check the integrity of the power cable's inner conductors between themselves.

HOWEVER, this does not provide a complete safety check, since any one of those conductors might/could be exposed to the outside environment ( ie- the ground, or other physical devices, including a person walking along, who happens to contact the cable at just the wrong time) and this WILL NOT show up when you do a continuity check on the conductors.

should your power cable happen to have cracked insulation, that is difficult to see with the naked eye, and say it's laying in a walkway area, that could be covered in water during a rain storm, what you check now with a meter will not show this fault.

There is a piece of equipment that will show cable insulation faults, quite easily, and it;s called a megger.

It is not a common household tool, so if it were me, and I had concerns about that ship to shore cable, I would contact a local electrical company (marine specialty) and have them come out and test it for you. I don't know how long your cable is, but I think it might be less expensive to have the test performed, rather than replacing the cable. The test is simple, and should only take a very short time ( less than 1 min, once the megger is hooked to the cable), and the megger test will show/provide an absolute result, for any damage to the cable, including potential future failure caused by aging material.

Good Luck!!
Let us know how it turns out!


----------



## LoveGoldens (Sep 23, 2008)

Thank you, everyone, for your kind and helpful replies! I've read them all, and I also visited each of the links provided, and read them. However, they didn't provide a definitive (simple) answer to the following:

At this point, I want to ammend my original question(s).

1. When and why should I perform a test for RESISTANCE rather than checking for continuity? Note: I'm referring to an electrical cable (_not under a load_), not a PCB, nor anything that has resistors, transistors, capacitors, etc.

In other words, what is or what are the distinctly different purposes of each kind of test?

2. What will checking for RESISTANCE tell me that checking for continuity won't tell me? I know how to check for continuity.

Each of you has brought many good points to my attention, and I really appreciate your replies!

Thank you.


----------



## K7M (Feb 27, 2000)

I always check for resistance because the screws holding the wires to the connectors can loosen up and heat. When this happens you will get a high resistance reading, even when cold. This will cause more heat, low voltage to your devices, and possibly fire, especially when under load.


----------



## LoveGoldens (Sep 23, 2008)

Thank you for answering so quickly.

To see if I understand these two kinds of tests proplerly, let me ask you if I'm correct in the following questions:

If I check the cable for continuity, and the multimeter shows that current is getting from the plug on one end of the cable to the corresponding plug on the other end of the cable, that there may still be a problem caused by resistance of some sort?

In other words, if the cable (_since it is comprised of many wires wound together internally_) has been damaged physically, or has areas of corrosion within the wiring caused by water condensation over time, or has _loose screws (as you mentioned_), would performing a check for resistance help to identify one of those possible issues, whereas merely checking for continuity would NOT identify any one or more of those issues?

I'm sorry to keep asking what sounds like the same question. I just want to be certain.


----------



## K7M (Feb 27, 2000)

That is correct. You could have a high resistance on one conductor, and that would be a problem. Depending on the way you check for continuity, you can show continuity and have a high resistance, say 10 to 15 ohms, and that is about the resistance of the heating element in your electric water heater.


----------



## paisanol69 (Sep 7, 2005)

how long is the cable you want to check?

when you put your multimeter on ohms, for the continuity/resistance check, short or touch the two probe leads together, and read the resistance that is displayed on the meter.( be sure not to touch either of the conductive part of the probe leads, with your fingers, while doing this) If the meter is digital, you may read a small resistance, say .2 ohms or so. then go ahead and check your cable for the resistance of each conductor. By measuring the inherent resistance of your meter leads first, you will eliminate any false reading.

Be advised, the a resistance/continuity check will verify the individual conductors health, and checking each conductor against the others in the cable will verify if there is a potential short between the conductors, However,these tests WILL NOT ensure that the cable is completely safe to use.

Depending on the age/condition of the cable, you may well have a break in the outer cable insulation, that might also extend to one of the inner conductors, and be very hard to see.

If you decide not to megger the cable, another way to determine if the entire cable is safe, would be to immerse the entire cable in a tub of water, being sure that the two ends of the cable are not covered, or gotten wet, and then conduct the same tests ( resistance/continuity) as above. Any potential cable damage would then become obvious.

I don't know how practical this would be, since I am unaware of how bulky your cable is.

Good Luck!


----------



## K7M (Feb 27, 2000)

Paisanol69, being that it is rated for 50 amps it would most likely be a #6 gauge wire, and four conductors in the sheath.. He stated that it is 25' long. From experience with RVs I find that most problems are with the screw connections loosening up at the plugs, and causing heat and melting the conductors and the plugs themselves. He mentioned that it was rubber, but I have only seen vinyl cords, not saying that his is not rubber, as this could be something that was fabricated.


----------



## LoveGoldens (Sep 23, 2008)

K7M, I believe you've answered my questions. Here's the answer that I think fits my question the best:

You wrote:
_"That is correct. You could have a high resistance on one conductor, and that would be a problem. Depending on the way you check for continuity, you can show continuity and have a high resistance, say 10 to 15 ohms, and that is about the resistance of the heating element in your electric water heater."_

And, yes... the 50Amp cord is vinyl-coated (yellow). It's about 3/4" to 1" in diameter X 25' long. I live on a boat, and cords of this type are seen commonly around marinas.

*I believe this topic has been answered. Thanks to everyone for the help you've offered to me.*

Take care.


----------



## etaf (Oct 2, 2003)

> I believe this topic has been answered.


 if you wish to close the thread - you can mark as solved

*You can mark your own threads solved using the







button at the top of the page of the thread in the upper left corner.*


----------

