split buss panel

[wire monk]

Is it a violation to install a 110volt breaker above the main in a split buss panel..The inspector said only double pole breakers can be installed in the top half of a split buss panel..We disagreed that if it does not exceed 6 means of disconnect it should not be a violation..You input please..

 

[LarryFine]

..You input please..

In my opinion, you are correct. We're not required to make an installation "non-compliant-proof." We're only responsible for the present installation.

What would he say if you had fewer than six 2-pole breakers up top? You must make the upper half of the panel unable to accept any more breakers?

 

[jumper]

Larry,

For us junior grades, could you explain "split-buss" panels.

Thanks.

 

[al hildenbrand]

. . . could you explain "split-buss" panels.

In the decades around the Code driven transition from 60 Amp minimum service size to 100 Amp, the split bus panel was a way to side step the quantum jump in cost of a single 100 Amp fuse pull out or circuit breaker as the single service disconnect.

The single panel enclosure had two separate bus systems in it. The service entrance conductors landed on lugs directly connected to the first bus system. This first bus system usually came with one service disconnect installed, commonly a 60 Amp, that disconnected the feeder to the second bus system. The second bus system was designed to hold the bulk of the branch circuits installed in the occupancy.

As noted, the first bus system could have up to six service disconnects (assuming there weren't others in the grouping just outside the panel), so this is where the larger loads, say the central AC, electric range, electric hot water heater, etc., were installed.

As a result of the split bus, no service disconnect needed to be larger than 60 Amp for a 125 Amp rated service center. There was a certain economy realized . . .

The service entrance conductors were sized for the load calculation at the time of installation, plus any "room to grow" the designer deigned to add.

 

[LarryFine]

For us junior grades, could you explain "split-buss" panels.

Absoloopy!

Picture a main-lug panel whose buses are cut into separate sections. The top half is 6 spaces tall, allowing for six 2-pole breakers, one (or two, for larger panels) of which feeds the bottom half (or third) of the buses, acting as a lighting main breaker.

The five largest loads would normally be supplied by the top section, which, along with the 'main' breaker(s), allow for deenergization (except the upper buses), which complies with the six-throws-of-the-hand exception to the main-breaker requirement.

 

[jumper]

In the decades around the Code driven transition from 60 Amp minimum service size to 100 Amp, the split bus panel was a way to side step the quantum jump in cost of a single 100 Amp fuse pull out or circuit breaker as the single service disconnect.

The single panel enclosure had two separate bus systems in it. The service entrance conductors landed on lugs directly connected to the first bus system. This first bus system usually came with one service disconnect installed, commonly a 60 Amp, that disconnected the feeder to the second bus system. The second bus system was designed to hold the bulk of the branch circuits installed in the occupancy.

As noted, the first bus system could have up to six service disconnects (assuming there weren't others in the grouping just outside the panel), so this is where the larger loads, say the central AC, electric range, electric hot water heater, etc., were installed.

The service entrance conductors were sized for the load calculation at the time of installation, plus any "room to grow" the designer deigned to add.

Thank you sir, Al if I may, I appreciate it.

 

[al hildenbrand]

Thank you sir, Al if I may, I appreciate it.

My pleasure.

 

[jumper]

Absoloopy!

Picture a main-lug panel whose buses are cut into separate sections. The top half is 6 spaces tall, allowing for six 2-pole breakers, one (or two, for larger panels) of which feeds the bottom half (or third) of the buses, acting as a lighting main breaker.

The five largest loads would normally be supplied by the top section, which, along with the 'main' breaker(s), allow for deenergization (except the upper buses), which complies with the six-throws-of-the-hand exception to the main-breaker requirement.

Thanks Larry, I am totally clueless with this old stuff. As always I am grateful for your knowledge. I still gotta a lot to learn

 

[ZinskI/E]

Thanks both to Larry and Al. I've worked on these panels throughout my career and never new the reasoning behind the oddball configuration.

Side note: take special care if ever installing a backup generator feeding a split-bus panel; incorrect connections can result in a dangerous situation!

 

[Pierre C Belarge]

The photo I tried to post did not work

 

[rt66electric]

zinsco had a convertable

zinsco had a convertable

I recently replaced a zinsco panel. It had a optional section on the buss bars that could be "snapped off" to use as a split buss panel or it could be left in place for a standard 100 amp buss.

I have also worked on a Square d panel the upper half had provisions for 3-phase buss and the lower section was 2-pole. Some of the center buss stabs were adjustable, able to be bolted to either phase.

 

[RICK NAPIER]

Here ar some pictures

 

[LarryFine]

Here ar some pictures

I know where you got those pix.

 

[lakee911]

:-?Why does it appear that those little jumper wires have breakers on BOTH sides? I would expect a breaker on one side and the bus on the other. Also, one side appears to be 2-1P and the other 2P. :-?

Jason

 

[Electrical Student]

WoW Those panels look like a hot mess. But as far as the breaker location in a panel i can put the double poles at the bottem if i had to, correct? I think they would draw more heat and may not be the best configuration but are code compliant.

 

[lectriclee]

split buss panel

I know, late to the party, again.

From my memory split buss breaker panels were limited in the mains section to 2 pole c/b's no less than 30 amperes. This would then require that a 2 pole 20 or 15 would have to be installed in the sub section(s). I am currently in the process of upgrading the panel in my father-in-law's house, which has a 200 amp. dual split buss panel.

Anyway my $00.02 worth.