Bldg lost power for 2 long seconds

[electricalist]

Went to a service call where an account breaker was tripping. It was a egc34020 square d.,480 v 3 ph 20amp breaker.
The name plate on the condenser says 24 amp wire 30 amp max fuse. I checked the amps on start up.( the breaker had been reset before I got there) 61 amps start up then 12 amps for 5 -10 min. So I'm calling about prices for a new breaker just in case,,when I hear a loud buzz and every I could see went off...there was a lot of rack mount equipment plus computers in there. All went off plus any light in eye sight. A kitchen worker said the kitchen did the same and the manager said all here stuff went off all for about 2 seconds and came back on.
What am I looking for? I've seen service drops that were old and the phases bounced off each other on windy days that did the same .
Thanks

 

[ptonsparky]

Start with the POCO. They can tellyou if a blink occurred. Squirrel, bird or whatever.

 

[meternerd]

Sounds like a recloser operation. Most are set for one or two "fast shots" where they open on a fault at a programmed current value, then reclose after only a short time. If the fault remains after the fast shots, they close again on a "slow shot" a couple of times at a higher current and hold for a longer period with a longer wait time between recloses. If the fault is not cleared in the programmed number of re-closes, they "lock out" and stay open until closed by the POCO. The idea is to try to burn a fault (such as a tree branch) clear or give a downstream device such as a fuse time to blow and clear the fault on the tap, rather than de-energizing the entire feeder.

 

[JRW 70]

Sounds like a recloser operation. Most are set for one or two "fast shots" where they open on a fault at a programmed current value, then reclose after only a short time. If the fault remains after the fast shots, they close again on a "slow shot" a couple of times at a higher current and hold for a longer period with a longer wait time between recloses. If the fault is not cleared in the programmed number of re-closes, they "lock out" and stay open until closed by the POCO. The idea is to try to burn a fault (such as a tree branch) clear or give a downstream device such as a fuse time to blow and clear the fault on the tap, rather than de-energizing the entire feeder.

This is what ran through my mind also, but that seems to
be really tight settings on the recloser or sub. breaker.
Probably only time could show if this was an event that
happened at the same time as something else. But a delay
with that long of a blackout sounds intentional.

 

[electricalist]

I called the poco any usually when I call they are very helpfull,but today not so much. The lady said the address didn't match the tenant name and more or less cut me off.
I was there to check on a ac that the breaker was smaller than the name plate. The unit has been working on the 20 amp breaker for 2 years. The 30 amp version of the egb type is at least 500.00 or more,so I pulled out the #12 wire and pulled in #10s .
Maybe that will help, before buying the breaker.

I don't like not knowing why the power " BLINKED."

 

[ActionDave]

I called the poco any usually when I call they are very helpfull,but today not so much. The lady said the address didn't match the tenant name and more or less cut me off.
I was there to check on a ac that the breaker was smaller than the name plate. The unit has been working on the 20 amp breaker for 2 years. The 30 amp version of the egb type is at least 500.00 or more,so I pulled out the #12 wire and pulled in #10s .
Maybe that will help, before buying the breaker.

I don't like not knowing why the power " BLINKED."

Maybe it's just me, but I'm thinking that if you did anything to that air conditioner so that it sucked all of the power out of the whole building then either you wouldn?t have gone home that night to ask about it or, you would be so omni powerful that you wouldn't need to ask at all.

 

[ptonsparky]

Maybe it's just me, but I'm thinking that if you did anything to that air conditioner so that it sucked all of the power out of the whole building then either you wouldn?t have gone home that night to ask about it or, you would be so omni powerful that you wouldn't need to ask at all.

Similar thought, although "Omni powerful" never entered in.

 

[Fulthrotl]

I called the poco any usually when I call they are very helpfull,but today not so much. The lady said the address didn't match the tenant name and more or less cut me off.
I was there to check on a ac that the breaker was smaller than the name plate. The unit has been working on the 20 amp breaker for 2 years. The 30 amp version of the egb type is at least 500.00 or more,so I pulled out the #12 wire and pulled in #10s .
Maybe that will help, before buying the breaker.

I don't like not knowing why the power " BLINKED."

well, a 20 amp branch circuit breaker isn't going to shut off
an entire building for two seconds. the inrush on start up is
appropriate in relationship to the running current, but it
depends on the sample rate of your meter, 100 ms or 1 ms
peak will have a huge difference. i'm assuming it's a 100 ms
sample rate.

so i'd say throwing a $500 breaker at it isn't gonna do much
other than annoy the customer if it happens again after
you put a breaker in.

short of putting a data logger on the service, there isn't much you
can do. my experience with poco's is that they don't venture
more information than they have to, to limit their liability.

 

[electricalist]

When the breaker tripped they called the ac guy first and they said it's supposed to have a 30 amp. The name plate says the same, that was my reasoning for pricing a new breaker.
The power just happened to blink while I was there.

 

[ptonsparky]

When the breaker tripped they called the ac guy first and they said it's supposed to have a 30 amp. The name plate says the same, that was my reasoning for pricing a new breaker.
The power just happened to blink while I was there.

Had the A/C unit been running for some time on the smaller breaker? Not that it matters much. The A/C guy gets to chase the problem if one is in the process of developing.

 

[kwired]

If AC had been running and you had a "blink" in the power supply, you will be trying to restart that compressor against high head pressure. If you have marginally sized breaker in the first place it has higher probability of tripping when trying to start in this condition. If it starts just fine after it had been idle a simple $10-20 timer on the control contactor to delay starting in such instances is an easy solution. They even make a "delay on break" timer that will not pass current for a set time after power interruption. This allows instant starting other then immediately after the unit had been running.

 

[cadpoint]

I agree with others in the various aspects of what went wrong.

The biggest part that was not mentioned is that is your area had a tropical depression
go through.

Your forgetting what you just experienced:

Forecast Discussion Posted Tuesday 6/16 at 9:40 am

***Tropical Storm Bill Will Soon Make Landfall***

Here are a few noteworthy concerns that I have at this time:

? Atmospheric precipitable water content > 99th percentile for June
? 3 to 5 inches of rain (locally 8 to 10)
? Sustained winds 25 to 35 mph late tonight/Wednesday, gusts to 50 mph
? Some uprooted trees due to the saturated soil
? Power outages and flash flooding
? Near-record rainfall amounts for the month of June
? Embedded mesocyclones and isolated/brief tornadoes

I came in late Thursday night!
I've noted various power poles leaning on to high level over passes.
But my day travel has been very limited to one area of the metro-plex.

The edge of DT Dallas is now flooding and expected to touch the bottom of various bridge structures.

 

[electricalist]

Had the A/C unit been running for some time on the smaller breaker? Not that it matters much. The A/C guy gets to chase the problem if one is in the process of developing.

Yes about 2 yrs. It was there when we got the account.
They called today and said it tripped again. Still I didn't believe the breaker was the culprit. I went and un landed the load side of the disconnect and checked the contactor L1 L2 L3 to ground and 2 and 3 were grounded. I opened the panel where the wiring harness was and found the 3 wires on the bottom had rubbed on the frame and had exposed copper.
I guess the ac would vibrate and some times short out. Just never knew when.

 

[gadfly56]

Yes about 2 yrs. It was there when we got the account.
They called today and said it tripped again. Still I didn't believe the breaker was the culprit. I went and un landed the load side of the disconnect and checked the contactor L1 L2 L3 to ground and 2 and 3 were grounded. I opened the panel where the wiring harness was and found the 3 wires on the bottom had rubbed on the frame and had exposed copper.
I guess the ac would vibrate and some times short out. Just never knew when.

Well, you figured it out, so for now you're a hero. Since the nameplate calls for 30amp and the HVAC guy agrees that it needs 30amp, I'd see if I could encourage the owner to upgrade. I'm sure he'll say "Well, it's been fine for 2 years aside from the vibration rubbing the wires." You're reply might be along the lines of "If you ever have a fire that's even remotely connected to the HVAC and the insurance company finds out there was an undersized breaker in the mix, what do you think will happen to your claim?" That $500 will seem cheap.

 

[GoldDigger]

I find it hard to think of a situation where an undersized breaker would cause a fire!
Undersized wiring, maybe, but there is a large safety factor in NEC calculations.

 

[gadfly56]

I find it hard to think of a situation where an undersized breaker would cause a fire!
Undersized wiring, maybe, but there is a large safety factor in NEC calculations.

I won't quibble with you on that. The issue is more about CYA and pro-forma adherence to the NEC. My dad, may he rest in peace, was a big football fan. His observation was "The number one rule in football is don't give the ball to the other team". Putting in the larger breaker is one way not to give the ball to the other team.

 

[ptonsparky]

I frequently use less than the Max allowed. If not using the max circuit break Is a code violation, cuff and stuff me now.

As the OP found, A/C techs are frequently overworked this time of the year and don't take the time they should.

 

[electricalist]

Well, you figured it out, so for now you're a hero. Since the nameplate calls for 30amp and the HVAC guy agrees that it needs 30amp, I'd see if I could encourage the owner to upgrade. I'm sure he'll say "Well, it's been fine for 2 years aside from the vibration rubbing the wires." You're reply might be along the lines of "If you ever have a fire that's even remotely connected to the HVAC and the insurance company finds out there was an undersized breaker in the mix, what do you think will happen to your claim?" That $500 will seem cheap.

I told the customer when 2 trades are involved you will pay us both when things like undersized breakers are installed.. I said it's probable that if the breaker was as the name plate said,the ac guy would have looked closer at the unit.
Personally I like things like that to be what they say they are. I hate when I hear,,, this is really like that cause the plumber knows an ac guy who use be a electrical maintenance man and he has seen it work,,so that's what it is.

 

[electricalist]

Actually I didn't figure it out. It figured me out. My first trip I had A and B phase showing to be grounded. Maintenance man said ac guy swears its the breaker and not the equipment so I figured it has to be a problem in the circuit so I pulled it out and replaced it with #10 . as I pulled it out I was looking for a bad spot but I was on a ladder on top of a freezer above the ceiling, at a j box. I figured I didn't see the problem. I checked my wires and no problem no worries. When I had to go back I realized my mistake.
I should have disconnected the line side at the disconnect. That would have saved a trip and new wire. I'm not the hero but the customer is happy, I tell them what I find and a solution and if I make a mistake I offer to pay for it personally out of my pocket.. They said its better to have the new wire from the panel to the unit especially since it had joints in 2 diff j boxes.
Action Dave does this mean I can never be omni powerful now.?

 

[ActionDave]

...... does this mean I can never be omni powerful now.?

I hope so. That's a burden no one should have to carry.