ECN Forum
Posted By: wewire2 Split buss panelboards - 11/06/10 03:19 AM
Just a little warning about split buss panelboards. Some of you may not have run into these. These are panels where the top half and the bottom half of the busses are separate and fed independently. A lot of times the voltage will be checked at the feeder lugs at the top and if it is a split bus the bottom half could unknowingly be live and present a shock hazard. I've run across two of these in the last few months. The second one had the line lugs at the bottom, right behind the neutral buss. It also explained why they had such a substantial shield over the neutral buss. Also, there was no labeling to indicate it was a split bus panel.
Posted By: Tesla Re: Split buss panelboards - 11/06/10 03:57 AM
That's the style of 50 years ago. High amperage circuit breakers really went at a premium so the engineers came up with the 6 circuit rule and the split bus.

If top fed, the largest loads would be ganged there -- a five double-pole maximum -- with the sixth position leading off to the daughter bus directly below.

The daughter bus could have far more breakers -- overwhelmingly 15A single poles.

--------

One must be on the look-out for bottom fed split bus panels. Obviously, the scheme is turned upside-down.

--------

Beyond that, the panel designs from the 1950s are truly scary.

Very tight quarters for our field conductors.

Lots of live exposed bussing -- typically two straight copper rails. This layout makes 240V circuits or running 14-3 very odd. To get to the other phase one must cross over to the other side of the breaker array! It also means that you don't have a chance in hell of working a two-pole handle tie!

When the budget permits these panels need to be retired.

In the mean time work on them cold and meg them before power-up.
Posted By: renosteinke Re: Split buss panelboards - 11/06/10 04:50 PM
Not to let the air out of a 'blame the lazy, greedy manufacturers' theory, but the split-buss panel is the only legit way to get single pole breakers in a three-phase panel with a delta feed.

Absent a split-buss, you need to feed a separate panel to have single-pole circuits.

Code requirement? Not directly. If you look to the fine print in the lables on the panels, you will see this restriction where they discuss the feeds for which the panel is approved. It's therefore a 'listing and labeling' requirement.
Posted By: ghost307 Re: Split buss panelboards - 11/06/10 05:01 PM
I use these quite a bit when I have a number of outdoor site lighting circuits and don't want the hassle of the usual multipole lighting contactor. I run my normal circuits from the upper bus, my lighting circuits from the lower bus, and feed the lower bus via a contactor inside the panelboard.
It sure neatens up the installation IMHO.
Posted By: Tesla Re: Split buss panelboards - 11/12/10 03:43 AM
Reno...

I've seen central-tapped neutrals on delta 240 all over my area.

The inspectors have permitted single pole breakers all over the 240 3-phase panel -- as long as they skip the stinger phase -- it being well marked.

Just what are you proposing ?

Mother, daughter 3-phase/ 1-phase boards ?
Posted By: renosteinke Re: Split buss panelboards - 11/12/10 02:16 PM
Tesla, that's exactly what I believe the 'fine print' would require: that a two-pole breaker feed a separate panel.

Don't infer that I am 'proposing' anything, though. I'm not sure I agree with the restriction on the listing / labeling. After all, ours is a 'skilled' trade, and making things ever more 'idiot proof' only inflates the egos of the untrained ... who only think they know what they're doing.
Posted By: gfretwell Re: Split buss panelboards - 11/12/10 06:29 PM
I have seen single phase loads in red leg panels. Like Tesla says, you just have to be careful to stay off the red leg and to only load the real transformers when you have delta vee.
A lot of 240v load across the missing transformer will make you some strange phase balancing. That can get tricky when a 3 phase machine has single phase loads.
Posted By: sparky Re: Split buss panelboards - 11/30/10 12:31 PM
On theother hand, i gotta job from a home inspector who claimed the 'panel had no main breaker'

and hey, who am i to dis him?

~S~
Posted By: renosteinke Re: Split buss panelboards - 11/30/10 02:12 PM
HI's ... you gotta love 'em. Now I understand why they put 'keep out' stickers on panels laugh

"Just be careful and don't use the stinger" certainly works, and I've seen this more times than I can count. Yet, speaking academically, doing so is a violation of the listing and labeling - at least, if you read the fine print on the sticker inside the door.
Posted By: tdhorne Re: Split buss panelboards - 12/01/10 12:45 AM
Not all of those that I have seen have single phase loads prohibited by the listing and labeling, although perhaps they should have been so restricted. I have never seen one were there was a three phase buss arrangement and a single phase buss arrangement in the same cabinet. Do such panels actually exist. I would love to see a picture of one.
Posted By: renosteinke Re: Split buss panelboards - 12/01/10 05:20 AM
Yes, the split bus panel - three phase above, single below- does exist. One of my customers has one in his restaurant.

You need to look a wee bit closer at the lables. They don't simply say 'no single phase circuits.' Rather, they describe the distribution systems for which the panel is approved; for the 'delta' distribution systems they'll say they're approved as power panels only, or not approved as lighting panels.

In other words, the panel neglects to include the 240/120 delta as one of the approved applications.

I'll see if I can find such a lable and post a pic. Heck, even when younger I needed a magnifyer to read the blessed things!
Posted By: wewire2 Re: Split buss panelboards - 12/01/10 06:41 AM
That's interesting Reno. I've seen single phase loads in
probably every Delta panel I've been in. I guess I'm guilty of not reading the ol fine print and I sure do miss my good eyesight!! I'm thinking that the labeling is a liability related move by the manufacturer since someone could inadvertently overvolt equipment with the stinger. What other reason do you see for a single phase restriction? I don't get it.
Posted By: renosteinke Re: Split buss panelboards - 12/01/10 02:04 PM
I couldn't agree more ... as soon as they make something 'idiot proof,' they come out with a better idiot.

Ironically, I only noticed this fine print myself when a service call brought me to an industrial rental space that had some electrical problems- including some 208V receptacles. Gee, I wonder how that might have happened laugh

The gent there was so confident that 'electrric work wasn't rocket science' and that 'electricians charge too damn much' that -naturally- he couldn't bother to learn anything before trying to do it .... let alone read the fine print on the panel.

IMO, if you know enought about the trade to even understand tha lable, you already know enough to identify and avoid the high leg. The lable isn't the most absurd that I've seen, but it's on the list!

Still, in this day of third party inspections and hungry lawyers, it's only a matter of time before this little detail hits the inspection seminar circuit.

As I see it, that leaves us with two code-compliant ways to address 240/120 delta systems: 'sister' a single phase panel (fed from the three phase panel), or use a split buss panel.
Posted By: HotLine1 Re: Split buss panelboards - 12/02/10 03:44 AM
Reno:
In the split buss, delta panel, was the top (3 phase) section barriered from the neutral buss?? I personally have not seen a split buss panel in many years.

I recall coming upon a attempt at 120 volts, from a 3 phase 240 delta, 3 wire, by a rocket scientist using the ground for a neutral, as this was 'power panel' only!



Posted By: renosteinke Re: Split buss panelboards - 12/02/10 01:50 PM
If you see a panel without a neutral buss, you can be sure it was intended as a 'power only' panel. Remember that in the days before the 2008 NEC, there was a distinction between panel types, with the 'lighting and appliance' panel being defined as having a large number of neutral-served circuits, and then went on to limit the number of circuits allowed.

In 2008, that distinction -and limit- went away.

In a split buss panel, there is a split between the two halves - but you might not be able to see it without removing the breakers. Typically, all of the busses are separate, with the single phase part fed from a breaker in the three phase part.

Though I need to be careful as to what I claim is 'typical.' I haven't seen that many split-buss panels- and all of them were old enough that the 'neutral buss' was a plate at the top, where you had to wrap each wire around a screw.

There is no barrier separating the sections, and wires commonly pass through the 'other' part of the panel.
Posted By: HotLine1 Re: Split buss panelboards - 12/02/10 02:18 PM
Thanks Reno.

Yes, I remember the old screw/wrap neutral blocks. Now, that's an old panel.

Reaching into memories, the split buss had a cb in the 'power' section that fed the GP section via factory conductors to lugs on the lower buss. The ones I remember were FPE Stab-Loc. No 'Main' OCP, and utilized the six switch rule, until some hack made modifications.

Posted By: EV607797 Re: Split buss panelboards - 12/02/10 04:07 PM
New Jersey (in my day) was full of split-bus panels, mostly FPE and Murray, 60 amp "lighting" main for the sub section.

The DC metro area also had them quite frequently, especially in total-electric homes since 200A main breaker panels were still fairly expensive back in the 80's.

I remember some of the larger ones even having two sub-sections, thus limiting the mains section to only four disconnects. We would often find all single-pole circuits in one sub-section and heating/AC loads in the other, leaving the dryer, range, water heater, etc. breakers as
mains.

No matter the location, hack jobs almost always resulted in single-pole breakers ending up in the mains section or <gasp> some Harry Homeowner managing to cram twin breakers in those spaces. Ah yes, those were the days.....
© ECN Electrical Forums