Current Injection testing for new MCC

[BK32]

Hi All,

I am currently involved in a new switchboard build project. We are currently having a new MCC manufactured for installation on a ship. The switchboard is to be integrated into a 440V system.

The new switchboard is to be fitted with MCCBs fitted within integral overcurrent protection. My question is whether or not we should be getting the switchboard builder to perform primary injection tests on the MCCBs, or whether this would have been done by the MCCB manufacturer and therefore does not need to be done again?

Any assistance would be greatly appreciated.

 

[davidbeach]

The acceptance testing should be done after the board is installed on the ship. Anything before that won't uncover shipping/installation damage.

 

[DTR2011]

NETA specifications cover what tests should be performed and acceptance criteria.

 

[BK32]

Thanks for your replies so far.

Has anyone ever received advice from the circuit breaker manufacturer that the performance of current injection testing post installation would void the warranty? I have been told by some colleagues of mine that this has been the case in the past.

 

[davidbeach]

That seems surprising. While it's been a decade plus since I was involved in that type of work, the primary injection testing was always done post installation. I'd tend to write any vendor who objected to post installation testing out of my specifications.

 

[FreddyNurk]

I've never heard of it either. I've definitely seen difficulty in supplying enough current for LV systems that it can make primary injection impractical, but don't know that I've ever heard that it voids the warranty.

Having the circuit breaker vendor insist on their technicians carrying out the test at your cost, however...

 

[davidbeach]

Ultimately it's at the owner's cost no matter who does it, unless the installing contractor leaves it on the table at bid time. As an Owner, the only time I'd consider it money well spent is post-installation. Product line type testing and post assembly, pre-shipping testing should simply be part of the catalog price of the breaker/gear.

 

[FreddyNurk]

You're right, davidbeach, I should have expanded that statement a little bit more. I used to work for an Owner that had their own breaker test kit and experienced technicians. During discussions with the OEM for breaker replacement kits they kept insisting that they had to send their own techs to carry out the testing, at the Owner's cost, after originally supplying quotes for supply of equipment only.

You're also correct, the owner eventually foots the bill, and everything else should just be part of breaker price.

The only reason I could think of not to carry out full testing on installation is such that its impossible to access the required equipment in order to carry out primary injection testing, such as a front only cubicle where the CTs and busbar aren't easily accessible in-situ. I'd also expect such an installation to be quite painful to maintain should any issues arise.

 

[BK32]

FreddyNurk,

You mention that the only reason you would not conduct it post installation is if there was no access to the equipment in order to carry out the testing. These devices are largely installed in withdrawable units. They are all MCCBs with integral overcurrent protection and are not connected to a seperate overcurrent relay with a trip signal to open the MCCB. Therefore, there are no CTs.

One quick point of clarification, if the breaker unit is tested at factory prior to delivery to switchboard builder, what is the rationale behind testing again post installation? I can only think that the trip mechanism within the MCCB is damaged during transport to site or installation. But what is the likelihood of this occurring on an MCCB?

 

[FreddyNurk]

There's probably some semantics in the descriptions, but to me, primary injection is connecting directly onto the busbar or breaker terminals to test it. It obviously provides a more complete test, as in the case of separate protection relays and CTs, the entire protection chain is being tested, whereas for secondary injection, the instrumentation is bypassed.

With regards to MCCBs with integral protection units, I've seen short circuit curve tests not being able to be carried out as the test kit can't provide enough current to reach the trip setpoint. Most times I've seen the manufacturer's secondary test kit specific to that protection unit being used. In this case there is less of a benefit for additional testing onsite but there is still possibility for transport damage and so on to be picked up.

Its also quite useful if there is any connected equipment that is monitoring breaker status, or extra trip coils are fitted to the units, then the onsite testing can also verify that the connections external to the MCCB are correct, something that can't be done in the factory. There is also the distinct likelihood that the protection settings will either not be defined at the time of manufacture, or that the settings will change onsite. Where I used to work, the policy was that if the protection settings change, a retest is required, although that was a utility perspective. Carrying all this out at commissioning stage ensures it all gets covered.

 

[dpmac]

I would doubt primary injection testing of any MCCB is ever carried out at the factory unless it is a design or qualification test.
I suppose it is possible they could do it if requested. But I doubt it.

We have found many breakers that have been successfully "Factory Tested" only to fail primary injection testing post installation.
Miswired CT's, wrong CT's, defective CT's, loose primary path connections, etc. It happens.

I am starting to get concerned with new insulated case breakers not being robust enough for primary injection testing.
The contact structures, although high tech, are not as rugged as they used to be and may suffer permanent damage during some tests.
With some MFG breakers just the act of racking, cranking, removing, testing, re-installing scares the crap out of me.
I really don't want something to break while I'm testing it.

I once recommended a customer request a quantity of spare breakers in lieu of primary injection testing.
They were better off.