400 amp 277/480 main breaker tripping
- Thread starter burbsele
- Start date
- Status
- Location
- Massachusetts
Not that unusual, does the 400 amp breaker have Ground fault settings?
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
The short circuit current did not only flow through the 20 amp branch circuit breaker. It also flowed through the branch circuit panel?s main breaker (if there is one), through the feeder breaker upstream of the branch circuit panel, through the main breaker of the upstream panel, and through any and all other breakers that lie between the service point and the fault point. Why would you suppose that any one of them would trip before any other one? They all saw a current level much higher than their normal current ratings. The 400 amp main breaker saw a current much higher than 400 amps, so why should it not trip?
If you want to force the upstream breakers to delay their tripping, so as to give the breaker closest to the fault a chance to trip first, thus limiting the power outage to a small portion of the distribution system, then you need to have a ?selective coordination? calculation performed. Then you will probably need to replace some of the breakers, bases on the results of that calculation.
Welcome to the forum.
If you want to force the upstream breakers to delay their tripping, so as to give the breaker closest to the fault a chance to trip first, thus limiting the power outage to a small portion of the distribution system, then you need to have a ?selective coordination? calculation performed. Then you will probably need to replace some of the breakers, bases on the results of that calculation.
Welcome to the forum.
No ground fault settings on the 400 amp breaker.
What is a selective coordination calculation.
GBShade684
Member
- Location
- Kirkwood, MO USA
Below is a link to some detailed information on selective coordination.
http://spd.cooperbussmann.com/Documents/SPD_Sec5.pdf
http://spd.cooperbussmann.com/Documents/SPD_Sec5.pdf
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
That's a fairly long document. But you can get the essential concept from just reading page 4 of 53.
Thanks I'll check it out.
- Location
- Massachusetts
The thing to keep in mind is that the 20 amp branch circuit breaker does nothing to limit the current during a short circuit.
For the the time it takes for the breaker to sense the fault and open the contacts the current will be as high as the impedance of the conductors allows.
So for a few cycles you may have 100s of amps going through the circuit.
For the the time it takes for the breaker to sense the fault and open the contacts the current will be as high as the impedance of the conductors allows.
So for a few cycles you may have 100s of amps going through the circuit.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
But the unexplainable tripping of the main device for the store isn't?
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
Somehow, that's the concept that a lot of people fail to grasp unfortunately, especially bean counters who are focussed on immediate bottom line costs for a project.
I once did a down time / lost revenue study for the Costco corporate data center during an evaluation of a project to upgrade the power conditioners thay had on all of the cash registers to being a small UPS just capable of finishing whatever transaction was already started when the power failed. The premise was that when power failed, there were potentially 36 (the average number of register lanes in use at a store on a weekend) individual transactions being performed at cash registers at any given moment. When power failed they all became invalid, so putting in a UPS at each register allowed them to finish at least these transactions (there was no emergency power system, so each store had to be cleared in 10 minutes anyway, this just allowed the transactions in process to finish). At an average of $87 in GP per transaction (their data), it amounted to a lost GP on transactions of over $10,000 per year on average at each location (some better, some much worse) with an investment of less than $18K per store. Never flew, too expensive. About 5 years later the data center mgr for Costco that had commissioned me to do that study told me that he compared my projections against actual calculated losses and said that they had lost over $8 million in GP over that time due to power failures that reqired cancellation of transactions in process, whereas the investment, had they done it, was a little under $3 million. Short sighted.
kwired
Electron manager
- Location
- NE Nebraska
Does the 400 amp breaker have magnetic trip adjustment?
The less distance along with the larger the conductor is between the fault and the power source, the more likely this is to happen.
IOW if you are in the space right next to where the 400 amp feeder breaker is located, and the transformer supplying this is just right outside that area, your fault will have a higher current than it likely would if the same setup but the fault is in a space on the far end of the mall.
The less distance along with the larger the conductor is between the fault and the power source, the more likely this is to happen.
IOW if you are in the space right next to where the 400 amp feeder breaker is located, and the transformer supplying this is just right outside that area, your fault will have a higher current than it likely would if the same setup but the fault is in a space on the far end of the mall.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Preventing the trip may not be feasible for small 'stand alone' installations, however being able to explain why something happened is a different matter.
I have been involved in situations where 2 electricians, 3 company representative, and 2 engineer/consultants were brought in to begin the finger pointing and assign responsibility associated with compensation for an event. It would have been nice to have an "I told you so" report in the project file.
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- Location
- Massachusetts
What we commonly run into is that the construction of a new building comes out of one budget while upkeep and service comes out of another budget.
So the people in charge of construction costs are entirely focused on that with little if any thought to what the upkeep and service costs will be.
One possible reason is that there are overlapping areas when you compare the trip curves of both breakers. Most likely you'll find this area on the graphs at current levels of substantially more than 400A.
But I guess there is some small chance that the larger breaker tripped prematurely because it is defective.
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brian john
Senior Member
- Location
- Leesburg, VA
A properly installed electric system is expensive as well, but sure is safer. Shutting down a mall at peak season is expensive. Someone falling down the stairs in the 8-10 seconds it takes the generator to start is expensive beyond belief. It is all expensive, determine where your dollars are best spent.
What kind of money are we talking about ?
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
I always laugh when they talk about an engineered study should be done for the settings on that small of breaker, most of those type have no actual setting, just minimum and maximum. How is your engineer going to set that? Or require where the setting should be? Turn it just a smidge past halfway? turn it 3/4 of a turn? I can see an engineered study on a breaker that has definete settings such as multipliers or time delays.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
The tripping was explained, they created a short circuit, and the magnetic trip setting on the 400 amp breaker is lower than the 20 amp breaker, happens all of the time.
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