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Old 07-12-2013, 04:55 AM   #1
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Power Panel Issue (perhaps)


I own a unit in a condo complex. The complex was built in the mid-60s as a rental property, and then converted to condo. It's your typical garden-style. Each building has a central staircase, with four units stacked on one side of the stairway and four more stacked on the other side.

Each unit has its own 125 amp power panel (GE model TL612F). The panel has slots for 12 breakers. Originally, eight slots were used. During my renovation, I added four more circuits, and maxed out the box.

The panel is serviced by a 3-wire. One wire feeds the left half of the panel. Another wire feeds the right half of the panel.

The 3-wire connects to a main power panel in a utility room in the basement. The lashup is not straightforward, however. Each hot wire is connected to a split-bus, which is protected by a 100 amp breaker. The split-bus services two units (in this case, mine and the unit above me). Thus, if a main breaker is tripped, only half of the unit's circuits are affected. The downside is that if you trip a main breaker, you affect someone else's unit.

I've tripped main breakers twice now. The first time was an out-and-out short on a circuit protected by an original (old) breaker on one side of the panel. The second time is still being investigated, but was on a new circuit protected by a new breaker on the other side of the panel. In both instances, the breakers in the unit's power panel did not trip.

Can anyone suggest why my panel's breakers did not trip, but the one's in the basement did?

Thanks,

Richard

P.S. - Just prior to the second main breaker trip, I tried testing my new circuit by tapping into an existing GFCI protected circuit. When I powered up the GFCI protected circuit for the test, the GFCI tripped but not the breaker in the condo unit's power panel. I don't know if this helps or not, but thought I'd pass it along just in case ...

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Old 07-12-2013, 07:31 AM   #2
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Power Panel Issue (perhaps)


There is probably a lot of available fault-current present at the main switchgear. A downstream "short" can cause a much larger breaker to trip out, without tripping the branch circuit breaker.

The available fault current can be determined by complex calculations involving a lot of factors, some of which are (in no particular order):

Utility transformer size
Feeder cable size
Feeder cable composition
Feeder cable length
Utility capacity
Etc.

Tripping out a GFCI has nothing to do with overcurrent protection, and therefore is a moot point.

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Old 07-12-2013, 02:56 PM   #3
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Power Panel Issue (perhaps)


There is probably a lot of available fault-current present at the main switchgear. A downstream "short" can cause a much larger breaker to trip out, without tripping the branch circuit breaker.

Does this mean that there are problems that have developed over time such that anything will cause the main circuit breaker to trip? Could I test this out by simply taking a black and a white and touching one to the other? If I did that, should the breaker in my power panel trip, without tripping the main breaker?

Or, per your list, was this not configured correctly in the first place?

Should the condo association hire a master electrician to look into the matter?

Thanks,

Richard
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Old 07-12-2013, 06:41 PM   #4
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Power Panel Issue (perhaps)


You should not worry too much !
All is as would be expected for a system like yours,
running at close to maximum capacity.
It will cost a tidy sum to upgrade your system.
All is as would be expected.
There is no major problem.
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Old 07-13-2013, 01:18 AM   #5
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Quote:
Originally Posted by RichardZ View Post
.... Does this mean that there are problems that have developed over time such that anything will cause the main circuit breaker to trip?....
Most likely scenario is Pepco upgraded their distribution system within the past 50 years. Installed a larger transformer, or changed their system voltage to a higher value, etc.

This results in a higher available fault current value than what was originally designed/installed.

Quote:
Could I test this out by simply taking a black and a white and touching one to the other? If I did that, should the breaker in my power panel trip, without tripping the main breaker?
I would not recommend performing such a test.

Quote:
Or, per your list, was this not configured correctly in the first place?
See comment above. Probably was correct in the first place, but other factors have been altered since then.

Quote:
Should the condo association hire a master electrician to look into the matter?
At the very least. Better to hire a qualified electrical engineering firm for a proper evaluation since this involves complex calculations, etc.
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Old 07-13-2013, 01:42 AM   #6
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Power Panel Issue (perhaps)


Quote:
Originally Posted by RichardZ View Post
There is probably a lot of available fault-current present at the main switchgear. A downstream "short" can cause a much larger breaker to trip out, without tripping the branch circuit breaker.

Does this mean that there are problems that have developed over time such that anything will cause the main circuit breaker to trip? Could I test this out by simply taking a black and a white and touching one to the other? If I did that, should the breaker in my power panel trip, without tripping the main breaker?

Or, per your list, was this not configured correctly in the first place?

Should the condo association hire a master electrician to look into the matter?

Thanks,

Richard
The only way to test out the inside wiring to make sure it is still safe, is by having an electrican use a MegaOhm tester.
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Old 07-13-2013, 10:07 AM   #7
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Power Panel Issue (perhaps)


Unless the OP has a metallic conduit or wiring method the 3 wire feeder sounds wrong.
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Old 07-14-2013, 04:28 PM   #8
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Power Panel Issue (perhaps)


All,

I'm not sure where this leaves me ...

My experience is that if I overload a circuit, the main breaker in the basement trips, not the one in my panel. When this happens, I lose half my circuits, as does another unit. And, I need to call the condo management company to have someone unlock the utility room and reset the breaker. Which is especially not fun at 6:00 pm on a Saturday night when your neighbor is throwing a party.

In effect, my panel is worthless.

(And, I know, I know, I'm ranting a bit here.)

Ahem. On a more rational basis, is it you guys opinion that, short of having the condo association hire an electrical engineering firm, I (and my neighbors and the condo engineer) simply need to live with the situation?

Thanks,

Richard

Last edited by RichardZ; 07-14-2013 at 04:35 PM.
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Old 07-14-2013, 11:11 PM   #9
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Power Panel Issue (perhaps)


Richard,

As kbsparky pointed out, your suggestion to create a dead short by directly connecting the neutral to the hot is not a wise one and actually would be quite dangerous in my DIY opinion. I think you are losing perspective here and getting caught up in the challenge of trying to figure out why the main breaker is tripping in the locked closet before your individual breaker in your unit. Diagnosing a potential power issue in a multi-tenant, multi-building complex is well beyond the scope of this forum and your ability. DIY electrical work in multi-tenant buildings is off limits to only those that are licensed. There is simply nothing you can do as an owner of an individual unit to determine/diagnose if there is a potential problem.

Reach out to the condo management group, document your concerns with them and have them take it from there and see how they respond.

Respectfully,

Clyde
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Old 07-14-2013, 11:49 PM   #10
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Power Panel Issue (perhaps)


Before going thru the expense of all these tests, I would replace the breaker. It is possible the branch circuit breaker is simply bad.
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Old 07-15-2013, 02:35 AM   #11
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Quote:
Originally Posted by RichardZ View Post
All,

I'm not sure where this leaves me ...

My experience is that if I overload a circuit, the main breaker in the basement trips, not the one in my panel....

Intentionally shorting out a circuit is NOT the same as an overload.

Are you sure that a simple overload is tripping out the main breaker? If this is the case, your main breaker may be bad ....
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Old 07-16-2013, 02:50 PM   #12
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Power Panel Issue (perhaps)


KBSparky, I think I understand what you're saying, A short (crossing two wires) is different than trying to draw too much current through the circuit (e.g., when two daughters simultaneously try to use a hair dryer in their respective rooms, and Mom decides to start vacuuming at that point).

Even so, shouldn't a power panel circuit breaker trip in either case?!?

Richard
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Old 07-16-2013, 03:55 PM   #13
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Power Panel Issue (perhaps)


Quote:
Originally Posted by RichardZ
KBSparky, I think I understand what you're saying, A short (crossing two wires) is different than trying to draw too much current through the circuit (e.g., when two daughters simultaneously try to use a hair dryer in their respective rooms, and Mom decides to start vacuuming at that point).

Even so, shouldn't a power panel circuit breaker trip in either case?!?

Richard
Not if the rooms were wired on their own dedicated circuits. Hallways usually come off the Livingroom circuit if it is a short hallway.
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Old 07-16-2013, 06:27 PM   #14
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Tripping a breaker for your unit should not affect another unit. Something does not sound right.

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