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Old 09-20-2007
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electrical insulation test

hi everybody,
can anyone here advice me of how to carry out the wiring insulation test?
thanks
rgds

jxing62
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Old 09-20-2007
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On What???

Do you just want to test the insulation of the wire on the boat? Insulation on motor windings? There are numerous ways to test insulation. Can you be more specific?

There is a device called a Megger. It produces high current and voltage that will blow a hole in a wire where the insulation is bad. You cannot use this method in an explosive atmosphere. It can also break down good insulation if you don't know what your doing.

Let me know what your want to do and I will try to help.

Fair Winds

Cap'n Dave
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Old 09-20-2007
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Quote:
Originally Posted by jxing62 View Post
hi everybody,
can anyone here advice me of how to carry out the wiring insulation test?
thanks
rgds

jxing62

kind of difficult to figure out what test you mean - test for electrical properties?, resistance to solvents?, elasticity test?, heat resistance?
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Old 09-21-2007
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thanks for replies .
i am trying to have this boat tested for its wiring insulation condition see if any replacement needed. Not the motor windings.

rgds
jxing62
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Old 09-21-2007
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You asked for it

Basically, you're applying a voltage (specifically a highly regulated, stabilized DC voltage) across a dielectric, measuring the amount of current flowing through that dielectric and then calculating (using Ohm's Law) a resistance measurement. Let's clarify our use of the term "current." We're talking about leakage current. The resistance measurement is in megohms. You use this resistance measurement to evaluate insulation integrity.
Current flow through a dielectric may seem somewhat contradictory, but remember, no electrical insulation is perfect. So, some current will flow.

it's a good idea to have a basic familiarity with the item you're testing. Basically, you should know what is supposed to be insulated from what. The equipment you're testing will determine how you hook up your meghommeter.
After you make your connections, apply the test voltage for one minute. (This is a standard industry parameter that allows you to make relatively accurate comparisons of readings from past tests done by other technicians.)
During this interval, the resistance reading should drop or remain relatively steady. Larger insulation systems will show a steady decrease; smaller systems will remain steady because the capacitive and absorption currents drop to zero faster than on larger systems. After one minute, you should read and record the resistance value.
When performing insulation resistance testing, you must maintain consistency. Why? Because electrical insulation will exhibit dynamic behavior during the course of your test - whether the dielectric is "good" or "bad." To evaluate a number of test results on the same piece of equipment, you have to conduct the test the same way and under the relatively same environmental parameters - each and every time.
Your resistance measurement readings will also change with time. This is because electrical insulation materials exhibit capacitance and will charge during the course of the test. This can be somewhat frustrating to a novice. However, it becomes a useful tool to a seasoned technician.
As you gain more skills, you'll become familiar with this behavior and be able to make maximum use of it in evaluating your test results. This is one factor that generates the continued popularity of analog testers.
What affects insulation resistance readings? Insulation resistance is temperature-sensitive. When temperature increases, insulation resistance decreases, and vice versa. A common rule of thumb is insulation resistance changes by a factor of two for each 10???C change. So, to compare new readings with previous ones, you'll have to correct your readings to some base temperature. For example, suppose you measured 100 megohms with an insulation temperature of 30???C. A corrected measurement at 20???C would be 200 megohms (100 megohms times two).
Also, "acceptable" values of insulation resistance depend upon the equipment you're testing. Historically, many field electricians use the somewhat arbitrary standard of 1 megohm per kV. The interNational Electrical Testing Association (NETA) specification Maintenance Testing Specifications for Electrical Power Distribution Equipment and Systems provides much more realistic and useful values.
Remember, compare your test readings with others taken on similar equipment. Then, investigate any values below the NETS standard minimums or sudden departures from previous values.

Remember you will need you will need a meter that reads megaohms.
Fair Winds
Cap'n Dave
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Old 09-21-2007
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While Dave gave you a wonderful technological definition...another simple way is to take any wires you can get a hold of and bend them as much as possible (like around a finger) if the insulation cracks, it's no good and will require re-wiring.
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Old 09-21-2007
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Smile Ahoy USCGRET1990

Isn't that what I said. See what happens when you ask an engineer about something?
There are a couple of other test I could of given but these require a highly technical understanding of electrical properties. The Smoke Test comes to mind. You bypass all fuses and then load up a circuit until the smoke comes out. You then make note of the smoke location, repair the area and put the smoke back in.

NOTICE this test should only be performed by a highly trained and experienced person.

Fair Winds

Cap'n Dave
I sail therefore I ARRRRRRRRRRRR!!!!
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