Breaker Contact Resistance by Type

[adamwilson]

Which of these contact resistance (in micro-ohms) readings are passing?

A: 3200A Masterpact Breaker: A - 1252, B - 1300, C - 1171
B: 400A Eaton Molded Case Breaker: A - 850, B - 772, C - 813
C: 1200A VCP-W Breaker: A - 150, B - 151, C - 145
D: 15KV GE OCB Breaker: A - 175, B - 300, C - 425

What do you guys think? everyting seems high to me

[Kalbi_Rob]

Which of these contact resistance (in micro-ohms) readings are passing?

A: 3200A Masterpact Breaker: A - 1252, B - 1300, C - 1171
B: 400A Eaton Molded Case Breaker: A - 850, B - 772, C - 813
C: 1200A VCP-W Breaker: A - 150, B - 151, C - 145
D: 15KV GE OCB Breaker: A - 175, B - 300, C - 425

What do you guys think? everyting seems high to me

Per NETA, there cannot be 50% difference between readings, thus you take the lowest reading and multiply by 1.5, and the highest reading cannot exceed that value.

D is failing since 175*1.5=262.5, and both b and c are higher than 262.5

As a general look, A, C and D look abnormally high with regards to expected readings, but in spec per NETA.

[SecondGen]

Per NETA, there cannot be 50% difference between readings, thus you take the lowest reading and multiply by 1.5, and the highest reading cannot exceed that value.

D is failing since 175*1.5=262.5, and both b and c are higher than 262.5

As a general look, A, C and D look abnormally high with regards to expected readings, but in spec per NETA.

Agree that D looks pretty bad and the others are really high. Just knowing from experience that those specific breakers are way out of normal range, except maybe the molded case. I'd probably write up A and C as well in the real world.

Question could probably use some language that specifies NETA. If I wasn't going off NETA, all would probably fail by my standards, except the molded case, making my answer B.

[bob152637485]

Per NETA, there cannot be 50% difference between readings, thus you take the lowest reading and multiply by 1.5, and the highest reading cannot exceed that value.

D is failing since 175*1.5=262.5, and both b and c are higher than 262.5

As a general look, A, C and D look abnormally high with regards to expected readings, but in spec per NETA.

Thank you for the informative reply, I feel like I have come across this type of questions before, and now I know what to look for.

[TestingProToBe]

Which of these contact resistance (in micro-ohms) readings are passing?

A: 3200A Masterpact Breaker: A - 1252, B - 1300, C - 1171
B: 400A Eaton Molded Case Breaker: A - 850, B - 772, C - 813
C: 1200A VCP-W Breaker: A - 150, B - 151, C - 145
D: 15KV GE OCB Breaker: A - 175, B - 300, C - 425

What do you guys think? everyting seems high to me

I would have to agree with you. All of these results do seem high. However if I were testing these breakers and I knew they all had some years of service on them then I would probably only be concerned with the masterpact, should never be that high, and the 15kv breaker. I find medium voltage breakers usually have pretty great ductor readings, then again I test more low voltage breakers. And as far as the molded case goes- I’d try exercising the breaker a few times, see if it gets better and if it doesn’t just keep an eye on it. No need to junk it just yet.

[LarryJ]

Per NETA, there cannot be 50% difference between readings, thus you take the lowest reading and multiply by 1.5, and the highest reading cannot exceed that value.

D is failing since 175*1.5=262.5, and both b and c are higher than 262.5

As a general look, A, C and D look abnormally high with regards to expected readings, but in spec per NETA.

Where can I find this in the NETA Handbook

[rofo42]

Where can I find this in the NETA Handbook

Page 72 of the 2019 MTS

[LarryJ]

Page 72 of the 2019 MTS

[BruceG400]

Which of these contact resistance (in micro-ohms) readings are passing?

A: 3200A Masterpact Breaker: A - 1252, B - 1300, C - 1171
B: 400A Eaton Molded Case Breaker: A - 850, B - 772, C - 813
C: 1200A VCP-W Breaker: A - 150, B - 151, C - 145
D: 15KV GE OCB Breaker: A - 175, B - 300, C - 425

What do you guys think? everyting seems high to me


I would say C
It is within the 150% acceptable range.

A is very high for a 3200 amp breaker. B may be OK (but C is better), D is not within 150%.

The 400 amp breaker is 1/3 the size of the 1200 amp breaker, but the resistances are 5 times the amount. If the 400 amp breaker was closer to 450 per phase, I would say that would be passing for the 400 amp breaker.