PDP/Switch Board Age

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fraymond

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I have several 1968 vintage 800A/460VAC power distribution panels that I was considering replacing these PDP's based mainly on age and an incident where the knives did not disengage when turning one of the disconnects off. Luckily this was discovered after locking out and trying to start the machine. My question is does age contribute to failure i.e.corrosion over time? Some of the disconnects feed air handling units, machines, etc. Thoughts please...
 
Has it been well maintained? I would guess not if switch blades have suck in the closed position.
Another question can you get spares?


I’ve had boards far older than the 60’s that had been well maintained and perfectly serviceable.


Get a switchgear refurbishment company in and ask them.
 
Tony S said:
Has it been well maintained? I would guess not if switch blades have suck in the closed position.
Another question can you get spares?


I’ve had boards far older than the 60’s that had been well maintained and perfectly serviceable.


Get a switchgear refurbishment company in and ask them.
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That being said, it's also entirely possible that if, in the 50 years since that PDP was installed, someone has upgraded the service and/or increased the available fault current, that old panel may no longer have the proper ratings to be used now anyway. That vintage is right on the cusp of not having any kind of withstand rating (now called SCCR) commensurate with modern power distribution. In my experience, systems installed up to and through WWII did not, but things installed in the 70s began to have higher ratings. In between, so the 50s and 60s, it was hit and miss. Lots of older equipment designs were still being sold and installed. I started out in the late 70s at a steel mill, we had to go in and retrofit a lot of our 50s and 60s vintage boards even back then because we could not show the fault bracing and breaker kAIC ratings on them.

I generally find now that anything 40 years old or older cannot be re-connected if taken out of service, they can only be left in service if "grandfathered".
 
Fault bracing is the mechanical strength given to the bus bars in the distribution board and how much mechanical force they can hold up against during a major fault event. When a fault occurs, ALL of the Available Fault Current in the entire circuit will attempt to flow into that fault. So if for example when the equipment was built in 1968, the available fault coming from the utility transformer was 25,000A, the bracing of the bus bars, and the "Interrupting Capacity" of the breakers may have been only 25,000A and it would have been fine. But if someone installed a new larger transformer, or the utility added capacity up stream so the primary fault current increased, then that transformer may now have 35,000A or 40,000A of available fault current, but your 1968 gear is only designed for 25,000A (or also possible, it has NO design listing per modern standards). If that is the case, a fault on the system may cause the bus bars to come together and "fail with extreme prejudice", aka explode.

Here's a great treatise on this from our host, Mike Holt.
https://www.youtube.com/watch?v=EfepqZMKKck
 
Jraef said:
I generally find now that anything 40 years old or older cannot be re-connected if taken out of service, they can only be left in service if "grandfathered".
Click to expand...

I wouldn’t consider grandfathering any switchgear unless it met the required standard for fault clearance. Due to that I suggested getting a switchgear refurbishment company in. Neither you nor I know what the general condition of the switchgear or its prospective fault current.


OK I’m a tightwad, I hate to see money squandered on unnecessary improvement/replacement when they are not needed.
 
Tony S said:
I wouldn’t consider grandfathering any switchgear unless it met the required standard for fault clearance. Due to that I suggested getting a switchgear refurbishment company in. Neither you nor I know what the general condition of the switchgear or its prospective fault current.


OK I’m a tightwad, I hate to see money squandered on unnecessary improvement/replacement when they are not needed.
Click to expand...

No argument on what should be done. I mainly wanted to emphasize that what people do is often not what should be done, and the grandfathering issue is often used as an excuse to not change anything, when in fact it SHOULD HAVE been changed when the conditions changed.
 
Age does contribute, of course. Maintenance and brand do as well. I'd say conditions do so more so than anything else.

You may want to write into your maintenance procedures, if not already there, to double-check for stuck or failed disconnects.

"knives did not disengage when turning one of the disconnects off. Luckily this was discovered after locking out and trying to start the machine."

I have seen where it wasn't discovered until after. That man spent six months getting most of his eyesight back after the arc flash. I personally have had a disco break on me and it threw the corroded/welded together lug and live phase within a fraction of an inch of the deadfront.

Don't leave it to luck next time. Have procedure in place to check and deal with these kinds of failures, which can happen at any time, with any gear.
 
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