Electronic Molded Case CB Test Data ?

[mike01]

I received a test report for an molded case CB with electronic trip unit, in the comments it reads "Megger Load Side Only. Contact Resistance Does Not Meet NETA Spec." But did not list and deficiencies and at the bottom of the report was checked "Acceptable"

So I went digging to see if I could determine what the pole resistance reading should be reached out to the manufacturer all their literature says test per NETA standards.

Went looking for NETA testing procedures with no luck any suggestions on where I can locate some information related to this test would be appreciated. Thanks.

[SecondGen]

I received a test report for an molded case CB with electronic trip unit, in the comments it reads "Megger Load Side Only. Contact Resistance Does Not Meet NETA Spec." But did not list and deficiencies and at the bottom of the report was checked "Acceptable"

So I went digging to see if I could determine what the pole resistance reading should be reached out to the manufacturer all their literature says test per NETA standards.

Went looking for NETA testing procedures with no luck any suggestions on where I can locate some information related to this test would be appreciated. Thanks.

Unfortunately this happens a lot, many companies fail to provide quality, concise reports. You most likely have an issue with the contacts but the tech just forgot to change the dropdown at the bottom of the sheet. What were the values?

Its not uncommon to megger load side only, that indicates the breaker was open at the time of megger and all that was included was the load side from the open contacts to the lugs and whatever else may be connected on that end. This is usually done when the breaker is installed in the switchboard and there is a short on the line side or something else connected that cant take the voltage.

You should typically megger test a MCB closed, each phase to ground and then each phase to the other phases. Next, test the breaker in the open position, line to load. For a molded case, there isn't usually really a ground since the case is plastic, so in that instance its good to test from phase to the breaker operating handle as it has been documented in the past that these can become energized with poor insulation resistance. Test voltage is usually 1000V for 600V rated breakers.

[mike01]

Thanks for the information appreciated, the manufacturer did provide this I found interesting as well "wax on the breaker contacts put on for shipping purposes that would also affect the readings."

The circuit breaker is installed in a panelboard [main breaker / currently not-energized] there are insulation resistance table as you indicated with insulation resistance from "Pole to Pole", Pole to Frame" and "Line to Load" all readings are exactly the same in every cell of the table (2,000 Mohm) corrected to 20 degree C with a multiplier of 1.056. is it odd that every value is exactly 2,000 or is this just where meters top out at? The pole resistance readings is checked in Micro-Ohms with Pole 1=388, Pole 2=638 and Pole 3=399. I am not sure what the "pole resistance" method was / where the connections were made.

The phase to handle instead of ground is also interesting something I never thought of. I was not there when the testing was done so have no idea the procedure used or how it was done. I assume they removed the breaker and "bench tested" it does not appear to have been done that way, also it appears no injection testing was done that whole section of the form is blank. THANKS AGAIN.

[SecondGen]

Thanks for the information appreciated, the manufacturer did provide this I found interesting as well "wax on the breaker contacts put on for shipping purposes that would also affect the readings."

The circuit breaker is installed in a panelboard [main breaker / currently not-energized] there are insulation resistance table as you indicated with insulation resistance from "Pole to Pole", Pole to Frame" and "Line to Load" all readings are exactly the same in every cell of the table (2,000 Mohm) corrected to 20 degree C with a multiplier of 1.056. is it odd that every value is exactly 2,000 or is this just where meters top out at? The pole resistance readings is checked in Micro-Ohms with Pole 1=388, Pole 2=638 and Pole 3=399. I am not sure what the "pole resistance" method was / where the connections were made.

The phase to handle instead of ground is also interesting something I never thought of. I was not there when the testing was done so have no idea the procedure used or how it was done. I assume they removed the breaker and "bench tested" it does not appear to have been done that way, also it appears no injection testing was done that whole section of the form is blank. THANKS AGAIN.

Its possible the manufacturing wax caused higher readings, this would normally be burned off during primary-injection testing, was this performed first? Also, what was the test current for pole resistance? Most likely 10A but the manufacturer may recommend higher.

Minimum value on 600V rated equipment for insulation resistance would be 100 Megohm. If all the numbers are 2,000 then this is most likely the max scale for this instrument.

B-phase pole resistance is a bit high. You could try primary injecting and operating the breaker a bunch of times to correct it. 388 x 1.5 = 582 <- This would be your highest allowable reading based on your lowest number. So its not that off, but is out of tolerance.

[mike01]

It does not appear any primary injection testing was completed, I will reach out to the testing company to verify. T

I noticed you used a 1.5x multiplier using the lowest pole resistance reading is this a standard way of comparing these? I assume this is from a NETA standard document. If I was looking for more information like this to become more familiar with the different test, the actual procedures and results verification / interpretation is there a one source document for example the 2021 ATS manual or any other of the NETA documents on their website you may recommend just so I can become more familiar with the industry test methods and results.

One final question the report did not indicate the test current for each pole resistance test. is there a minimum or maximum reading that would be out of normal or are numbers typically acceptable as long as they are in the tolerance of each other. for example if the pole to pole were within 1.x but the lowest one was say 100 or as high as 600 does the starting point matter is there a range the lowest / highest number one should be in between?

thanks again.

[SecondGen]

It does not appear any primary injection testing was completed, I will reach out to the testing company to verify. T

I noticed you used a 1.5x multiplier using the lowest pole resistance reading is this a standard way of comparing these? I assume this is from a NETA standard document. If I was looking for more information like this to become more familiar with the different test, the actual procedures and results verification / interpretation is there a one source document for example the 2021 ATS manual or any other of the NETA documents on their website you may recommend just so I can become more familiar with the industry test methods and results.

One final question the report did not indicate the test current for each pole resistance test. is there a minimum or maximum reading that would be out of normal or are numbers typically acceptable as long as they are in the tolerance of each other. for example if the pole to pole were within 1.x but the lowest one was say 100 or as high as 600 does the starting point matter is there a range the lowest / highest number one should be in between?

thanks again.

Pole resistance should be within 50% of lowest value between phases per NETA. So you basically just take the lowest number and multiply times 1.5 to get your max allowable.

In the real world if you are a little off its not that big of a deal but per the standards its out of tolerance. You will need to obtain NETA ATS and MTS standards to get all of this information. They are expensive but your testing company may offer free copies to their repeat customers, you will need to ask.

Its not typical to document the test current for pole resistance but the standard is 10A. NETA doesn't have a recommendation but some manufacturers specify 100A. The higher the test current, the more accurate the reading.

[SecondGen]

Pole resistance should be within 50% of lowest value between phases per NETA. So you basically just take the lowest number and multiply times 1.5 to get your max allowable.

In the real world if you are a little off its not that big of a deal but per the standards its out of tolerance. You will need to obtain NETA ATS and MTS standards to get all of this information. They are expensive but your testing company may offer free copies to their repeat customers, you will need to ask.

Its not typical to document the test current for pole resistance but the standard is 10A. NETA doesn't have a recommendation but some manufacturers specify 100A. The higher the test current, the more accurate the reading.

Here is a good testguy thread on 10A vs 100A contact resistance tests to help explain more: https://testguy.net/threads/6372-Con...ts-10A-VS-100A

[Kalbi_Rob]

It does not appear any primary injection testing was completed, I will reach out to the testing company to verify. T

I noticed you used a 1.5x multiplier using the lowest pole resistance reading is this a standard way of comparing these? I assume this is from a NETA standard document. If I was looking for more information like this to become more familiar with the different test, the actual procedures and results verification / interpretation is there a one source document for example the 2021 ATS manual or any other of the NETA documents on their website you may recommend just so I can become more familiar with the industry test methods and results.

One final question the report did not indicate the test current for each pole resistance test. is there a minimum or maximum reading that would be out of normal or are numbers typically acceptable as long as they are in the tolerance of each other. for example if the pole to pole were within 1.x but the lowest one was say 100 or as high as 600 does the starting point matter is there a range the lowest / highest number one should be in between?

thanks again.

Another reference beyond NETA ATS/MTS is the NEMA AB4, which is the National Electrical Manufacturer's Association standard for testing breakers.

Depending on the manufacturer warranty and accessibility of the breaker, it is possible to open the breaker and take a light abrasive to the contacts to remove the wax and improve contact resistance. Unfortunately, alot of molded case breakers can have warranty seals that require the manufacturer's approval to cut if continued warranty is needed. If you have permission, any NETA company technician should be able to perform this easily.