The clearing time of protective devices plays in important role in the magnitude of incident energy during an arc flash. The longer a device takes to operate, the greater the incident energy.

This week's question:

Do you have any protective devices that you are uncertain if they will operate correctly? (or operate at all)

• Yes
• No
• We'll find out when we have a fault

And of course, stories are always welcome and encouraged!

One place in the area I work, was built in 1958 and is running on the original gear.. There is some evidence of failures over the years, but there is more sign of a lack of maintenance... Guess that is what happens when a farmer (no offense) is in charge of running an aging gas plant/field.. He takes everything like it comes out of his pocket and wants to spend as little as possible on maintenance or upgrades..

When I was mentioning some changes that were going to need to be implemented, he said "We have a way around the electrical changes... We don't get inspections done." Needless to say, I trust NOTHING on that site to be de-energized unless it is me doing the work and can inspect it myself..

It is highly equipment dependent. For instance fuses are extremely reliable even with no maintenance. Circuit breakers have a lot of problems in general but newer designs are slowly eliminating them. One of the most interesting aspects though is the numerical data that Richard Brown collated showing that some equipment seems to be just about the same level of reliability irrespective of maintenance while other equipment suffers pretty poorly.

Ultimately although the progression has been towards more and more reliable and relatively maintenance free designs, we might look towards equipment with known/controlled failures or equipment which is inherently measurable. IE, even if it isn't more reliable if we can measure and predict failures ahead of time or control them in such a way that they are relatively harmless, that's even better than higher reliability. An example is "safety contactors" that have 2 sets of contact tips so that even if a set of contacts fails to open or close, we can still do so safely and better yet, detect the failure.

Our sytems is over 100 ysr old and may have been rehabilitated once once so it is possible there are protective devices that are 50 ysr old. Since we do not like fuse, we have devices thay are slow to operate.

Fuse are definitely reliable, but switches mechanisms are not.

In the past year, I was discussing assessment issues with a hospital's new risk manager and the facility electricians. It came out, by accident, that the facility had at least one M-T-M substation where the Tie switch had not been functional for at least the past five and maybe up to ten years. It failed so long ago no one could recall the exact specifics.

We test our main incoming and critical protective devices on a 3 year cycle. Each cycle we find a few devices that are not working. I would have a hard time saying I am "certain" any particular device will trip.

How do you test your devices? How do you determine that they are not working? What type of failures do you see?

We hire a maintenance testing firm to clean, inspect and test our incoming main circuit breakers, and fused disconnect switches. They perform meggar tests, Ductor tests, functionality tests, sometimes Doble test and trip tests on our electronic circuit breakers. If we get a questionable test, then we investigate.
As an example the ductor test shows the contact resistance. If the contact resistance is much higher then 3 years ago, we will agressively clean all appropriate parts and retest. If we cannot get to an acceptable value then we look at replacing the device.
There are quite a few preventative maintenance standards you can research, NETA has a good standard and IEEE publishes 70b which is a maintenance standard. I also always try to start with the manufacturers reccomendation ( if you still have the original documentation)
Our industry is the stone aggregates industry and we are very dusty, dirty, and exposed to weather extremes. Our failures are normally insulation breakdowns ( which we find via meggar or Doble testing) or contact resistance being high causing heat build-up.
Infra-red testing is another way to find these type of issues. We infra-red scan our switchgear and MCC each year to identify potential problems before they become issues that will cause failures. No downtime required for the infra-red scan.
Obviously, this testing requires downtime and a budget to pay for the outside contractor. Our company values the uptime and reliability that this testing provides and we have determined that the 3 year interval catches most of the problems. If you work in a different industry that has different demands a shorter interval may be warrented. I used to work in the paper industry and we tried to do this work annually since uptime was so critical.

I had a client that had an M-T-M bus arrangement, while I was making preparations to perform an arc flash assessment I noticed the the Bus Tie was closed along with the two main breakers. In this facility the bus has to be deloaded in order to close the bus tie. The bus tie had a mechanical and electrical interlock. When I inquired as to how long this situation existed the Maintenance Manager told me he did not know and he was there for over 25 years. The company made arrangements for the buses to be de energized and had the manufacturer come in to correct the problem. Also he could not remember when the last time any of the breakers in the switchgear were tested. They are now on a schedule to be tested on a regular basis with the manufacturer.

Specified clearing time is pertinent to equipment fault withstand rating, equipment series ratings and of course all selective coordination. If the mechanisms do not operate within specified clearing times, coordination and withstand ratings do not exist. At that point the problems transcend "calculated arc flash exposure" concerns.

I believe that within manufacturer specified maintenance procedures, that protective devices WILL RELIABLY clear on time. This has been an emphasis of clearign device manufacturers since the dawning of power distribution. If this were not the case we would be reading about horrific accidents for the same past 100 years. A slow breaker is a bomb.

I have heard that Federal Pacific Electric is no longer making circuit breakers or switch gear. The story I heard was their UL labeling capability was pulled when it was discovered their testing methods were incorrect. I understand their transformers are still being made and they are a quality product.

Almost the real story.
You are correct the FPE is no longer making breakers or switchgear, but then neither is ITE or Westinghouse.
Many people seem to judge all FPE products with the stories they have heard about residential load center performance.
Federal Pacific ran into problems with UL (back in the 80's) concerning one of their small 'residential' molded case breakers, something like a 2-pole 60A 240V.

The FPE residential 120V & 220V breakers JBD is referring to was called Pushmatic... they were notoriously known not to trip under OL conditions and if they did trip, wouldn't reset. Good idea but junk. I replaced many FPE panels in the 70's as a young electrician apprentice.

ITE is still being made but was bought out by Siemens.

Wrong. The FPE line was called Stab-loc

Yes, you are right... it's ITE that made Pushmatic & Bulldog, not FPE.