When Replacing A Breaker Panel, Would You Do this?

[Evan]

@Bobby G:

A total of 100 amps load on each line of the service is what a 100 amp panel can support... If your circuits are working at capacity then you would only be able to have a total of 100 amps being powered off each buss inside the panel...

You can have MORE breakers in total theoretical load than the main breaker is rated for but if you exceed the main breaker rating it will trip if the actual loads on all the circuits being powered by the panel exceeds 100 amps on either line...

This is why load balancing is important, you want to evenly divide the load to both lines in your panel to ensure you don't experience nuisance tripping of the main circuit breaker...

~~ Evan

[clare]

42 circuit 100 amp panels are available. That's 630 amps with all slots filled with 15 amp breakers.

[DerbyDad03]

That works, but it appears to assume that you are the only one concerned with the directory. *You* know that each room has multiple circuits because your wired the house (or so it seems). I labeled the panel not just for me, but also for anyone who might need to work around the panel even when I'm not around.

The reason I have a breaker that says "First Floor, except..." is because there is one circuit that spans all rooms on the first floor. It is one of the few original circuits in the house and happens to also be part of an Edison circuit that includes part of the basement. Instead of trying to split up the Edison circuit, I made sure that any new outlets added to the 1st floor and basement were placed on new circuits. I don't necessarily like the fact that these 2 circuits span most of 2 floors, but I'm not into a complete rewiring.

[Robert Green]

< A total of 100 amps load on each line of the service is what a 100 amp panel can support... If your circuits are working at capacity then you would only be able to have a total of 100 amps being powered off each buss inside the panel...>

I added about 5 20A circuits to my panel with "dual skinny" breakers which brings the panel to the maximum it's rated for (100A) but they are never used simultaneously and they, in fact, replace the older 15A circuits still wired to the kitchen. I've tracked the maximum usage via the meter and the house never draws much more than 60A, even with all the big loads going at once. The question is - will it pass inspection or does the inpector have a cutoff-point where he won't approve a panel whose individual breakers (face value, not load) to some percent of the total rating of the panel?

That makes sense - what I am trying to determine is whether there's a point at which an inspector will say "that's too many 20A breakers for this panel" even *if* they are all powering very small loads.

[gfretwell]

The inspector will be asking for a load calculation if there is any question. You base the service size and panel rating to the connected load, not the number of breakers. Load calculations are part of the permit process on new construction or additions in most places. That usually includes a permit for HVAC or some energy hungry equipment like an electrically heated spa or instant hot water.

[Evan]

Well in certain commercial situations load balancing is VERY important, you can throw all kids of things out of whack with unbalanced loads...

They make a "super neutral" cable which is used with a 3-pole breaker where there are 3 current carrying conductors of #12 paired up with a #8 neutral conductor... It is used in making up power for cubicle systems... It is like a 2-pole "Edison" circuit on steroids...

~~ Evan

[Robert Green]

Thanks. I had assumed there was some recognition that electric heat and the A/C would rarely (if ever) be used at the same time. Good to know.

-- Bobby G.

[Robert Green]

That's interesting. I was told that on two-wire 240VAC circuits, the neutral could always be one gauge under the size of the other two conductors. Does adding a third wire change the dynamics that much?

-- Bobby G.

[Robert Green]

Ah, gotcha. I'm forever using oversized metal boxes just because in this house, every box seemed to be overstuffed and I use X-10 gear, which takes up more space than the average switch.

Fortunately, after I ripped out the two basement ceilings (installed to cover previous termite damage, In My Humble and Slightly Paranoid Opinion) it became just as easy to install new junction boxes and receptacles. Early on, I broke one wire very short in a wall switch box that ended in excavation and replastering/repainting. That might me very careful about overstuffing boxes.

Thanks for the explanation.

-- Bobby G.

[Robert Green]

It's hard to tell what's happened to a house's electrical system by the time it's over 50 years old. Fortunately, I live in one of the first true "developments" - cookie cutter houses built for office workers flocking to DC for WWII work. There's always someone around who knew what the original system looked like and the 88 year old guy who has been here since the war he says these were 60A total panels with screw-in (4/15A) glass non-safety fuses. I know there were fuses before I got here because I found the color-coded safety types AND a safety-type that was a breaker, not a fuse. That led me to believe they were alway having breaker tripping problems so I was happy to replace two old 15A breakers with newer duals. Not only did I gain a slot, I got new breakers with a known history.

-- Bobby G.

[gfretwell]

They call that non-coincidental loads. If the strip heaters and the A/C compressor are electrically interlocked, you only have to size for the largest one. If your heat pump is wired to allow both, you need to size for both.

[gfretwell]

Super Neutral cable is used where you have reactive loads, particularly switching power supplies where the current may lag the voltage. It can set up triplin harmonics in 3 phase line to neutral loads where the neutral load may exceed the individual phase load in some situations. It is not a common problem but when it happens it will burn up the neutral.

[gfretwell]

I grew up in an Allen and Rocks tract house in south east DC. It was built in 1954 and had breakers. That was fairly unusual.

[Evan]

Yes, harmonics on the line from electronic equipment can generate non-linear loads which are very tricky to balance...

There are two types of these cables, neutral per phase and over-sized neutral... When you get into type MC cable there are a lot of interesting purpose driven varieties of cable, like heavy gauge feeder cable used for supplying main power to breaker panels, as well as "home run" cable which have as many as 12 #12 conductors to allow for grouping multiple home runs in one cable as opposed to each circuit having its own cable...

~~ Evan

[bud--]

I finally saw the AskTOH episode. In the limited time I saw it I thought the wiring looked pretty normal.

Almost nothing was labeled.

As I wrote previously, I don't think simply using wire size is a good idea. The original panel would give clues whether #12 should be on a 15A breaker, and some 240V circuits may have a breaker larger than the wire size.

The violation the electrician cited was 2 wires on a breaker. It is not a violation when the breakers are listed for 2 wires. The breakers were SquareD, and they are listed for 2 wires on 15/20/30A breakers. It was not a code violation. As with all the other electricians on TOH, not my favorite tradesman.

One of the stated reasons to go from 100 to 200A was no room for expansion. It may (or may not) have been possible to add tandem breakers. It certainly was possible to add an adjacent subpanel.

The owner talked about expanding. Would be interesting what the service calculation is after the expansion (whether it is near or over 100A).

One of the things the electrician did was put an expansion fitting in the PVC riser above the meter can. One of the dumber ideas I have seen.

[bud--]

Take a different example. A cement block building has a pull box on the outside back wall. A PVC conduit comes out the side and runs horizontally into the side of another pull box. The conduit is constrained at both ends and is relatively long. The conduit can expand and contract significantly more than the cement block wall, which can cause problems. An expansion fitting is a good idea.

There are 2 factors, constrained at both ends and relatively long length. The service riser is somewhere near 10 ft. More important, it is not constrained at the top. The electrician made a point that the pipe straps allowed expansion. I don't see a problem. And did the electrician install the expansion fitting so it was not bottomed-out?

=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Your post, and a lot of other old ones, just showed up at the news source my isp uses. It has not showed up yet at aioe. Must be a space- time warp.

-- bud--