Breaker adventures..

[RonHebbard]

200 amp service entrance, 4/0 Al feed to the meter and the box. PECO loops a #6 Al from the pole to the SE head. I call it "the fuse."

@JD Think of it as eliminating the additional weight of accumulating ice build-up during freezing rain and drizzle seasons.
Toodleoo!
Ron Hebbard.

 

[RonHebbard]

Do you think the SCRs distort the sine wave of the input enough to make a significant difference? I know they do the output, and I know they can affect the feed, but I thought it was a relatively small amount, and very dependent on a lot of feeder side conditions - like how much wire between load and transformer and so on. Someone else can espouse on harmonics, triplen harmonics, and harmonic mitigating transformers - which I always ask for but are always way to expensive according to the engineer. I suspect asking for feeds for dimmers that would support a nearly fully loaded rack helped, considering dimmers in a dimmer per circuit system are probably not loaded to 50% on average.

I worked on a renovation (the black box at the University of New Mexico if anyone is familiar) and powers that be made the decision to not upgrades - all 2.4kw (e the feeder for the dimmers - 225 amps IIRC. We put in two 96 dimmer KW - CD80 - and I had asked for 600 amps. It would have required a major upgrade of the service and finding real estate for a new transformer, so not an unreasonable fiat. So facility reopens and the LD wanted to test it so he hung all he has and ran 1-192 @ FULL. Again, 25+ years ago, but IIRC 350 amps if balanced. Popped around 40 minutes. Conclusion was the stress test was far more than a reasonable load in normal use, so OK. I never heard if it presented a problem and I can only guess now, in the age of LEDs and green, its more than enough.

@BillConnerFASTC I've read and re-read your post many times and can't for the life of me comprehend what you meant when you typed "not an unreasonable fiat". Please elaborate, educate and elucidate. @GreyWyvern , can you help me out here?
Toodleoo!
Ron Hebbard.

 

[BillConnerFASTC]

Despite my recommendation to provide a new larger feed, the powers that be said no.

Let me google the definition of fiat for you: http://bfy.tw/GPF7

If your time is short, here it is:
a formal authorization or proposition; a decree.
an arbitrary order.

So substitute "It would have required a major upgrade of the service and finding real estate for a new transformer, so not an unreasonable formal authorization or proposition."

 

[JD]

Do you think the SCRs distort the sine wave of the input enough to make a significant difference? I know they do the output, and I know they can affect the feed, but I thought it was a relatively small amount, and very dependent on a lot of feeder side conditions - like how much wire between load and transformer and so on. Someone else can espouse on harmonics, triplen harmonics, and harmonic mitigating transformers - which I always ask for but are always way to expensive according to the engineer.

Since dimmers are a series circuit ( Line > breaker > SSR > choke > load > Neutral ) I would expect any current irregularity found on the output to be found on the input side as well.
I hope when they tripped that 600 amp breaker under full load they replaced it after the trip! Despite being enclosed, arc-flash damage would still occur on the contacts inside the breaker.

 

[BillConnerFASTC]

Wouldn't that be one big a$$ line> 100s of breakers, SCRs, Chokes, and loads >one bigger a$$ neutral, and that all of those chopped waves on the outputs sort of ameliorate the irregularities one the feeder. I could be wrong but I don't think a scope on the feed will look anywhere as near torn up as the output of an individual dimmer.

 

[JD]

Wouldn't that be one big a$$ line> 100s of breakers, SCRs, Chokes, and loads >one bigger a$$ neutral, and that all of those chopped waves on the outputs sort of ameliorate the irregularities one the feeder. I could be wrong but I don't think a scope on the feed will look anywhere as near torn up as the output of an individual dimmer.

Scope wouldn't show it as a scope would only look at the voltage. The irregularity would be in the current not the voltage. Now, if you put a few windings around the leg of the feeder and looked at the induced voltage caused by the current, you would see the exact same noise being produced on the input side as you would on the output side.

 

[Malabaristo]

Scope wouldn't show it as a scope would only look at the voltage. The irregularity would be in the current not the voltage. Now, if you put a few windings around the leg of the feeder and looked at the induced voltage caused by the current, you would see the exact same noise being produced on the input side as you would on the output side.

Congratulations! You've just invented the oscilloscope current probe!



While we're on the topic, it's generally a bad idea to connect a regular scope probe directly to line-voltage (unless your scope has fully isolated inputs). Use one of these instead.

Also, you're both right: the input isn't nearly as bad as the output, but it's still pretty ugly when that much load is dimmed at once.

 

[BillConnerFASTC]

Scope wouldn't show it as a scope would only look at the voltage. The irregularity would be in the current not the voltage. Now, if you put a few windings around the leg of the feeder and looked at the induced voltage caused by the current, you would see the exact same noise being produced on the input side as you would on the output side.

Oscillicscopes won't see the wave form and distortions in the sine wave?

 

[JD]

Oscillicscopes won't see the wave form and distortions in the sine wave?

Some on the voltage. But the primary is a low enough impedance and a high enough gauge that the real story would be when you look at the current. That's when you would see the true firestorm of havoc. Try it some time. I did.