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3 wires enter from the top. My understanding is that this is single phase service. Why are all 3 black? Shouldn't one of them be white? Am I correct in stating that the other two wires are out of phase by 180 degrees and the potential difference between both should be around 240V?

I am confused as to why they aren't hooked up to the lugs directly at the top. Instead they hook it right to the breaker.

The breaker on the lower left goes to a subpanel which confuses me a bit. Are the two service entrance hots on the same bus? I assume that they are not.

I'm looking to have this service upgraded to 200 amps.

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The breaker feed method feeds every other finger in the panel. You can see that clearly in Jasen's answer.

I'm not sure why the wires were not attached to lugs. It is connected so the top left breaker is used as a single main breaker, but up until the 2020 edition of the NEC the code allowed a configuration where up to 6 breakers were allowed to disconnect power, tied handles counted as one. If the power had been connected to the lugs then only 4 throws would be present. Wired that way wouldn't have been illegal or particularly unusual.

What is illegal (but also not particularly uncommon) is the top left breaker is an ITE brand breaker, which isn't UL/CSA/ETL Listed or tested as safe for use in a GE panel. Would be better if it was fed by the main lugs. Unfortunately the only likely way to fix that is to de-energize the feeder wires by having the utility remove the meter.

Also Code requires backfed breakers used as mains need to be fastened in place, but I can't speak to how long that has been a requirement. Even if was wasn't required the illegal breaker certainly couldn't have been properly approved as installed. (The 2020 NEC has not been uniformly adopted, you may be able to re-configure as 6-disconnect, or if adopted your local authority may allow/prefer restoring your panel to this original configuration.)

When you upgrade everything you see will need to go, the running thread pipe is too small to for 200A wires, and it is likely the meter that feeds it and it's enclosure are rated for only 100 or 125A.

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  • Also concerned that the lug for the white neutral feeding the downstream panel is not properly installed and may not be able to handle the current as attached. The cat. no. for the proper Listed lug to fit the bar was probably listed on the label that has been punched on the inside of the enclosure, but now may be unreadable.
    – NoSparksPlease
    Dec 6, 2021 at 5:05
  • Traditional "Rule of Six" was banned a long time ago - that one involved multiple breakers that summed up to more than the service rating. What was banned in 2020 was multiple breakers that matched the service rating e.g. two 200A's for a 400A service.
    – Harper - Reinstate Monica
    Dec 6, 2021 at 5:59
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Wires

At #4 or larger wire (yours is #2 TW), you are allowed to use colored electrical tape to identify black wires as neutral (white or gray) or ground (green). Note that this has not been done, which is a Code violation, but a very common one.

100A is the correct breaker for #2 TW wire.

Bus arrangement

Service panel buses actually "zig-zag", like this.

So breaker rows 1 and 3 are on one phase (call it "black") and rows 2 and 4 are on the other phase (call it "red"). Here's a great 25m video on split-phase.

The reason they aren't hooking to the lugs is this is (apparently) a main service panel, and requires a main breaker. If power went to the lugs, then nothing would prevent the service from being loaded to 150A (100A sub + 30A dryer(?) + 20A DFCI on each phase).

This is a type of main breaker called a "Back-feed main breaker". It's a regular breaker supplied in reverse (they don't care, it's AC). Code requires back-fed breakers be bolted or strapped down, so it can't "rock out" like other breakers. If yours is able to "rock out", post a photo of the panel label - we may have an answer to that.

Many service panels are factory-assembled this way. However it's fine to field-assemble a panel like this, and then you end up with a superfluous set of main lugs. (or maybe, not so superfluous.)

Those main lugs

In the 1970s, breakers over 60A were prohibitively expensive. So the "Rule of Six" was written that said a "main breaker" could be several breakers, as long as there were no more than six hand throws. However this design was prone to being overloaded when new loads were added to the house, so it was outlawed as soon as >60A breakers became affordable. So you do need the 100A main breaker, and cannot do without it.

However, here's an interesting question. If the main breaker is 100A, why is a second 100A breaker needed for the subpanel? The answer is, "It's not". Since the main 100A breaker assures subpanel current can't exceed 100A (nominal), the second breaker really is redundant. So how could the subpanel feeder be connected without use of a breaker? The main lugs!

Essentially running the whole panel in back-feed.

That would free up 2 spaces here, which could be used for other things.

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    But since there are other breakers the second 100A breaker allows the second sub panel to be de-energized without turning off those other 30A + 20A breakers in this panel.
    – Matthew
    Dec 6, 2021 at 6:15
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    @Matthew Yes, there is that. It doesn't need to be a breaker for that purpose, but a 100A breaker is the cheapest 100A switch you'll find.
    – Harper - Reinstate Monica
    Dec 6, 2021 at 6:22
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above a certain size black is allowed for neutral, but I think it should still be marked.

The breaker is used instead of the lugs so that the breaker can act as the service disconnect

Behind the breakers the busses interleave, so the top breakers are on bus 1 and the next row on bus 2 etc.

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  • 6 AWG and smaller (higher numbers) must be white or gray. 4 AWG and larger (smaller numbers) can be all black, should be marked (tape, paint, etc), but MAY actually be marked with a white stripe that might not be visible due to the position of the wire (more likely just not correctly marked, it's not that uncommon to see.) Those are 2 AWG.
    – Ecnerwal
    Dec 6, 2021 at 1:46
  • @Ecnerwal Is it normal not to even mark the neutral?
    – Jeff T
    Dec 6, 2021 at 2:50

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