Single Pole, Molded Case Breaker Testing <600v

[buddy91082]

This is a follow up to the thread below:

thread238-444329

Would you normally perform primary injection testing on single pole, 15A/20A molded case breakers rated at 120v or 277v? (what you would see in a typical 100A/225A commercial panelboard that serves plug loads or lighting)? If not, what tests would normally be performed? NEAT ATS isn't clear about this or at my reading of it isn't. Same with NFPA 70B.

Don't want to have to spend too much money if these test are not helpful on these breaker ratings.

Thanks.

 

[thermionic1]

I know of two industries that perform this kind of testing on these types of breaker, Refineries & Telcom - there are probably others. I suppose both have their reasons for doing it. In my experience, we had about a 20% failure rate at a refinery, with over 200 breakers tested. This inevitably ends up in a urination match with the OEM. "We use NETA specs", ...."We don't recognize NETA specs"

If these are only 15/20A breakers, much smaller test equipment can be used, rather than the high current test sets used on power circuit breakers that can generate ~100kA. I know of one test set (Programma ODEN), that allows the user to preset the current, which reduces the negative effect of preheating the trip unit. Other test sets require hunting and pecking for find the 300% & or Inst current level. A preheated trip unit will operate quicker than the TCC states.

If you do choose to perform the testing, do it before the breakers are installed and the cables are landed. You could also have the breakers sent to the testing shop for the work to be performed there, in order to save on costs.

I know many utilities that slap a breaker in a AC or DC panelboard and nothing more.

If you choose not to have high current testing performed, it doesn't hurt to test the panel & breakers with a megger - quick and cheap. NETA specifies a contact resistance test (Ductor). Most OEM's don't recognize this, rather they rely on an AC mV drop test. The AC test can be conveniently performed during primary injection (mV drop @ rated current). My experience doing ductor tests on small breakers is that every time a bad result is obtained, operate the breaker and maybe it will get better the next time

 

[che12345]

Dear Mr buddy91082

Q1. ......... Would you normally perform primary injection testing on single pole, 15A/20A molded case breakers rated at 120v or 277v? .....Don't want to have to spend too much money if these test are not helpful on these breaker ratings........
A1. 15A/20A molded case breakers rated at 120v or 277v ...serves plug loads or lighting are considered as [non essential loads]. These are likely to be MCBs. These CBs are of [very low cost] items. It [does not make economical sense] to perform the thermal and magnetic tripping curve tests. The time taken and the testing fee would be [much higher] than the component cost.

FYI: 1) the thermal "cold" , "hot" and magnetic tripping tests take a very long time to cover from say 2X to 10X of the current rating. Both the "cold" and the "hot" tripping time is [not a single-spot value] but a wide band, with very large tolerances e.g. +- 20%.
1.1) for "cold" tests, the CB would have to be cool-down to the [ambient temperature], before the next test. A "hot" test would have to pre-heat the bi-metal.
1.2) the ambient temperature at the lab/site may differ from the published data by the manufacture.
2) A (Programma now Westinghouse ODEN) would be [too heavy] and it operates only on 380-400V.
2.1) Many manufacturers in the market have much smaller/lighter test sets (e.g 400A) which are portable and operates on 230V.
3) contact resistance test (Ductor) if with [low current] may [not] give the correct value. With "four-terminal method" with [current pumped up to the rated current] would give a consistent value. Note: "exercise" the breaker a few times before performing the test.
3.1) the contact resistance value may not be available from the product catalogue. An alternative way is by calculation, based on the published contact heat-loss in watt (W). A breaker with contact resistance which is higher by 10% than the average of the similar type and rating could? be faulty.
4) a mV drop @ rated current is equivalent to the four-terminal method, see above 3).

Che Kuan Yau (Singapore)

 

[oldfieldguy]

This has been a subject of much discussion. Documents concerning overcurrent protective devices (MCCB's in many systems) are supposed to be 'maintained' and many people expect this requires testing.

A search for manufacturer recommendations on periodic maintenance testing is an exercise in futility. One soon gets the idea that the manufacturers do not expect these things to be tested after installation.

Quite often then activity of accessing an MCCB to test it requires it being removed from service. The Act of removing the breaker for testing and returning it into service offers a great chance for mistakes and damage to equipment, and if the breaker must be removed from live equipment, it presents a great hazard.

Injection testing can actually test the fact that the trip unit functions on current input, but due to variables presented by test methods and equipment, accurate and repeatable results can be hard to attain. Still, you do come away with the information that if you put a lot of current through the device, it will trip.

As for contact condition, checking millivolt drop across a pole at rated current is doable, whereas many smaller breakers are not suitable for testing with most DLRO equipment without some innovative and time-consuming work to configure test leads.

My employer has finally decided that 'testing' is not part of the maintenance stream for MCCB's. I push our technicians to exercise the breakers - open and close manually, and to use the external 'Trip' button present on many modern breakers, in that this usually operated the trip link of the breaker whereas the on-off handle does not.



old field guy

 

[buddy91082]

So if I have a 3 pole, 100A, 480v molded case breaker, what is the procedure for testing? Do I need to remove the molded case enclosure to the breaker to perform a primary injection test and remove any shunt trips and then re-torque the breakers back into position? I have a manufacturer stating the if we perform primary injection test on breakers that are already installed within a newly installed switchboard that has not been energized yet, it will void warranty.

 

[jraef]

15A/20A molded case breakers rated at 120v or 277v ...serves plug loads or lighting are considered as [non essential loads]. These are likely to be MCBs. ...

Not here in North America. MCBs are an IEC terminology, over hear they are not used (outside of industrial control panels) in panelboards (what you would call Distribution Boards). His mention of 120V and 277V means the OP is in North America, likely the USA, so they would be MCCBs.

I do agree with the rest of your statement though, it's generally considered a waste of money to test 1 pole small breakers because the cost to test them exceeds the cost of replacing them, even as a prophylactic action taken upon suspicion of possible malfunction.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[che12345]

Dear Mr buddy91082

Q1. So if I have a 3 pole, 100A, 480v molded case breaker, what is the procedure for testing? Do I need to remove the molded case enclosure to the breaker to perform a primary injection test and remove any shunt trips and then re-torque the breakers back into position?
A1.1. It is [not] necessary to remove the breaker from the enclosure for the test. Therefore no re-torque is required.
Caution: Make sure that the board incoming is "dead" before opening the door! Fine, if it a newly installed switchboard that has not been energized yet.
A1.2. Attention: As it is a new CB, do whatever tests you wish but do [not] open the breaker cover. Do [not] tamper with the (sticker seal) usually stuck on the side "sealing" the CB cover and the body, after installation of the shunt trip release by the agent/suppler/manufacturer.
FYI: Shunt trip release usually comes with external leads, which can be tested by [voltage] injection to ensure that the [minimum] "pick-up voltage" is in compliance with the STD.
Caution: All shunt trip release coils are designed for "short" time rating! Most modern CB are designed with an (internal) NO micro-switch in series with the coil. It closes when the CB is switched on/close and opens when the CB is tripped/off/open; to prevent the coil being over-heated when inadvertently left energized for prolong time.

Q2. I have a manufacturer stating the if we perform primary injection test on breakers that are already installed within a newly installed switchboard that has not been energized yet, it will void warranty.
A2. I am of the opinion that it is irrelevant whether it had been already stalled or not, even after used. The warranty date commence from the date of receipt of the goods.
Reminder: Do whatever tests you wish, but do [not] open the CB cover. Do [not] tamper with the sticker seal.

Che Kuan Yau (Singapore)

 

[waross]

To test a 3 pole 100 Amp breaker in place, connect a load of about 50 or 75 Amps and do an AC mili-Volt test across each pole.
Use the Amps and the miliVolts to calculate the watts loss.
Use your judgement or compare with other breakers.
Consider the Watts loss times the number of breakers in the panel.
Do you think that it may be too much heat in the panel?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[che12345]

Dear Messrs waross ,buddy91082

W1. To test a 3 pole 100 Amp breaker in place, connect a load of about 50 or 75 Amps and do an AC mili-Volt test across each pole.
C1. If you are using a say 500A "commercial" primary injection test set that is available in the market, you [do not] need a 100A heavy adjustable resistor + a heavy load bank to "load" the CB. Connect the out-put of the test set across the CB. The output voltage from the test set is dependent on the capacity, it is not more than one volt. Depending on the out-put
current selected, the resolution can be as fine as 1A.

W2. Consider the Watts loss times the number of breakers in the panel.
C2. For watt loss in W, take into consideration that
a) [not all] the installed CBs are [in use] where some may be spare, and
b) [not all] the CBs which are [in use] are loaded to the rated [full-load] (at the same time) for 24h duration.

W3. Do you think that it may be too much heat in the panel?
C3. Reference: See IEC61439-x for guidance.

Che Kuan Yau (Singapore)

 

[waross]

If the Watts loss of a single breaker times the number of breakers or spaces in a panel is too much, then the breaker is faulty.
It will be producing more than its share of losses.
Even if it is the only breaker installed in the panel, the losses times the number of spaces must be acceptable.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[che12345]

Dear Messrs waross ,buddy91082

W1. To test a 3 pole 100 Amp breaker in place, connect a load of about 50 or 75 Amps and do an AC mili-Volt test across each pole.
C1. In the above statement, it is not explicit on how the injection current connection on a 3-pole CB. I would like to state that:
a) injection may be carried out with (single-phase supply) on a 3-pole CB [with all three poles shall be connected in series], e.g. test set T1 connected to CB terminal 1, short CB terminal 2to4 and 3to5 , test set T2 connected to CB terminal 6.
Note: 1. [All three poles shall be heated up with the same current value] i.e. in series during the test. Usually it doesn't matter on the direction of the current flow and which pole's heating element that had activated the (common trip bar).
2. do [not] inject the current "one pole at a time" respectively.
b) injection may be made with 3-phase supply.
Reference: IEC 60947-2, ANSI C37.50 etc.

W2. If the Watts loss of a single breaker times the number of breakers or spaces in a panel is too much, then the breaker is faulty.
It will be producing more than its share of losses.
Even if it is the only breaker installed in the panel, the losses times the number of spaces must be acceptable.
C2. If [only a single] CB watt loss (W) is excessive, replace that particular faulty CB. Do [not] based on the (only single) faulty CB watt loss (W) times the number of spaces (spares?) for the [total heat loss] calculation.
Reference: See IEC61439-x for guidance.

Che Kuan Yau (Singapore)

 

[TestMonkey]

Yes it is cheaper to replace than test. But the circuit breakers that are found not to trip would be my concern. Having tested thousands of these small circuit breakers it is interesting on the number that just simply fail to trip (thermal or magnetic). In my experience, the failures seem to come in batches, so testing a nominal percentage in an given panelboard may find a bad "batch" of breakers. Most of the failures I encountered were failures to trip. Nuisance tripping can be easy to find, but a complete failure to trip could cause damage to equipment or cabling. I have no real answer to the OPs question; the end user should determine the risks to connected loads.

Basic NETA test would include: instantaneous, long time delay, contact resistance, and insulation resistance.

TestMonkey