Circuit Breaker Test Rig

beaug45

Member
Location
Oklahoma
Occupation
Engineer
Several low voltage breaker panels at our facility have been contaminated with the oily substance that results from the plasticizer used in wire insulation, Schneider Bulletin 0110DB0301R05/11

The bulletin recommends that any breakers that have been contaminated be replaced but I have removed several and cleaned them and I suspect they are probably fine, but I would like to test them. I imagined using a 120/12V 750VA transformer feeding the breaker then eight (8) 2 ohm 100W resistors in parallel (0.25 ohm total resistance. This would allow 12V/0.25 ohm = 48A to flow through the breaker and cover my power requirements (12V x 48A = 576W) for the transformer (750 VA) and resistors (8 x 100W = 800W). The breakers are rated at 20A which means that they will trip in less than 2 min at 40A (I am hoping that 48A will help them trip faster).

just looking at the breaker panel I would need to replace at least 15 breakers ($1680 @ $112 each) and possibly more if there is contamination that is not immediately visible. I could purchase the items for the test rig described above for about $200.
  1. Does this test setup seem feasible? Did I miss anything?
  2. Does it seem worth it?
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
Will it be a UL standard you will be testing them to?

What if not abiding by the bulletin's recommendation results in an injury? Is saving less than $1500 worth that?
I'm sure that guy down the street could rig up something to make them trip for less than $200.
OP is suggesting that operating voltage has nothing to do with safe operation of the breaker, as long as it trips at 48 amps, or whatever. Correct?
 

beaug45

Member
Location
Oklahoma
Occupation
Engineer
I'm sure that guy down the street could rig up something to make them trip for less than $200.
OP is suggesting that operating voltage has nothing to do with safe operation of the breaker, as long as it trips at 48 amps, or whatever. Correct?
Yes that's correct. The breaker is meant to protect against overcurrent not over voltage. If the breaker was faulty due to the contamination and allowed a much higher current than its rating without tripping, then there would be a risk to equipment and/or personnel (if they were standing in front of the breaker wit the panel open when the fault current was flowing).

From my understanding of the bulletin, the concern is that the contaminated breakers would not trip at their ampere rating (20A in this case). Per NEMA Standard AB-1, a 20A breaker has an allowable trip time of 120 seconds @ 200% rating (40A). My thought was that if I could get them to trip in under 2 min @ 48A that I would be confident that they were functioning correctly.

These breakers are in a building that is no longer used and only feed light circuits.
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
So, as long as they trip safely in the time frame you suggest, you feel they will be good at whatever fault level is available at whatever voltage they are being used at?

If the building is no longer used, remove the power from it, otherwise it is still in use if someone needs to turn the lights on.
 

beaug45

Member
Location
Oklahoma
Occupation
Engineer
So, as long as they trip safely in the time frame you suggest, you feel they will be good at whatever fault level is available at whatever voltage they are being used at?
My thought was that if I injected a current level that would normally cause the breaker to trip (i.e. 200% rating) and it tripped in under 2 min, then it would be likely the breaker is functioning correctly. I do see your point, though, that I would only be able to confidently say that the breaker functions correctly for the current level that I tested.

If the building is no longer used, remove the power from it, otherwise it is still in use if someone needs to turn the lights on.
Fair enough.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Seems like a lot of effort AND RISK to try to save some cheap breakers. Remember, the primary PURPOSE of circuit breakers is to prevent FIRES.

Electrical testing companies use what is called a "Current Injection Test" on LARGE circuit breakers, which is a device that is essentially what you are describing; high current at low voltage. But nobody that I know will bother doing a current injection test a 20A breaker, it's not worth it.

The issue with breakers becoming contaminated with foreign materials is not so much about affecting the calibration of the trip sensors as it is about gumming up the mechanical workings of the breaker. If the trip sensor functions correctly and the trip mechanism fails to move, did it matter that the sensor was good when the facility burns down?
 

robertd

Member
Location
Maryland
Occupation
electrical contractor
Google turns up:
New $39.35, New surplus $29.20.

Ebay:
$11.99 each, 58 available new.

I've never done business with ether company. If it was me, I'd just give the numbers to my boss and let him decide how much he want's to send and be done with it.
 

robertd

Member
Location
Maryland
Occupation
electrical contractor
Google turns up:
New $39.35, New surplus $29.20.

Ebay:
$11.99 each, 58 available new.

I've never done business with ether company. If it was me, I'd just give the numbers to my boss and let him decide how much he want's to send and be done with it.
Well this is interesting, I just pasted in the URL for each item and the forum "software" added the photo and description from each web page.
 

paulengr

Senior Member
See NEMA AB4.

You cleaned it off the outside. No way to open them for inspection.

There are two trio mechanisms. The first is thermal. If you apply say 48 A with a timer it should trip in a certain amount of time. The second is magnetic. Testing this is a bit tricky but you need to know the trip range for magnetic trips. Pulse current just below and just at the trip setting and again you need a timer but it will be in milliseconds. The tricky part here is that the voltage drop plays a role so you often have to adjust the output to get the desired current. Again see NEMA AB4. It is written in English, not lawyerish, and it’s free to download.

This is actually how a high current circuit breaker tester works. Small Phenix sets can be found for a few thousand. Or you can rent them very cheaply. But you can replace the entire lighting panel and all breakers for a few hundred. I rent because for instance I can rent a 20 kA range tester for $1500 for a week. It costs $30k and I have to periodically send it out for service. Unless I’m doing over a dozen breaker testing jobs a year it’s not worth the money.
 

ramsy

Owner/Operator
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
Several low voltage breaker panels at our facility have been contaminated with the oily substance
Schneider Bulletin 0110DB0301R05/11
Thank you for posting that bulletin

In addition to Paul's $1500 test rig, the Mega Beast injects 40, 60, & 80A.

However, your Schneider bulletin prohibits AHJ acceptance of any cleaning method by citing manufacture instructions 'Not to attempt Repair', subject to enforcement per NFPA-70 110.3(B)

Another source, besides NEMA AB4, that illustrates the complexity of MCCB inspection & test methods. This inspection method with thermal imaging is interesting.
 

Attachments

Last edited:

paulengr

Senior Member
AB4 is very simple. All required tests are visual inspections. The optional test is time current tests that are function testing of the trip mechanisms. On larger breakers we also Megger them, use a micro ohm meter for contact testing, and grease the parts that are manufacturer recommended. Vacuum bottles get a vacuum test. SF6 has a pressure check. Where accessible contact wear is checked. On thermal trips 1-3 tests is plenty depending on design. On breakers with separate relays we have to test with reduced voltages.

However getting to OPs problem you don’t know if the plasticizer changed the integrity of the insulation or weakened it structurally. So this is exactly like water damage...unless you send it in for rebuild to a shop certified by the manufacturer on molded case breakers, and NOBODY is going to bother with 15 A breakers, you replace. Don’t clean, test, any of that. NEMA has a water damage standard that says this same thing. I’d just apply that standard to this situation. I could test them easily but I can’t make any guarantees about whether they will keep working.
 
Top