I love electrical - service and panel questions

[live4ever]

I'm planning on slowly rewiring the house. The plan starts with a panel upgrade to give me extra spaces and flexibility as I rewire.

I wanted my panel upgrade done by a pro, so I called in several electricians. As usual, they all said very different things, each discovered different problems, and came to completely different conclusions about what work was needed.

So I'm looking to learn a bit more about my service entrance/main/subpanel, or at least check my understanding. Here's the story:

Facts:
- Aerial service drop comes to the back of the house and drops down to an outdoor main panel, which has a 100A breaker. However, the three service wires are #2 copper.
- From the main panel, there is approximately 80' of 1-1/2" aluminum conduit running through the house carrying the 2/0 to the meter and subpanel, located in the garage.
- The subpanel has 10 circuits.
- Lastly, and perhaps most importantly, it appears the system is not grounded properly. I do not see any bare copper in the main panel outdoors, and no evidence of thicker bare copper in the subpanel in the garage. I have had an outlet tester read grounded on the 3 prong outlets in the house, and it's possible the system is grounded to water/gas pipes somewhere, but there is no evidence of that around the water or gas pipe entrances.

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My understanding
(not necessarily what I have been told by electricians - their thoughts varied widely)

My understanding is that due to the size of the conduit between main breaker panel (outdoors) and the meter, 125A is the largest total amperage I can have, which would be accomplished by swapping the 100A breaker for a 125A (assuming the 125A breaker is allowed by the specs of the outdoor box). I could feasibly upgrade to 200A by replacing the conduit to 2" Sch80 PVC since the wires are 2/0. Is this all correct?

My other understanding is that it is OK to use a 200A rated panel as the new subpanel even though it would have a 100A (or potentially 125A) main breaker in front of it.

Regarding the grounding, I know that code calls for 2 grounding rods. Where should they be located? Does it matter if they connect to the main box outdoors or to the subpanel? Could there be one grounding rod in each location?

Thanks in advance for your help. If I can get some corroboration on some of what I've been told so far or what I understand at least I'll know who to go with.

[TDKPE]

live4ever said:

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Facts:
- Aerial service drop comes to the back of the house and drops down to an outdoor main panel, which has a 100A breaker. However, the three service wires are #2 copper.
- From the main panel, there is approximately 80' of 1-1/2" aluminum conduit running through the house carrying the 2/0 to the meter and subpanel, located in the garage.

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What conductors are you referring to here? The overhead service conductors that are (presumably) owned by the utility, or the conductors connected to those and running down to your panel? The meter is not right at the bottom of the service drop from the utility? And are they 2/0, or #2 (huge difference)?

live4ever said:

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- The subpanel has 10 circuits.
- Lastly, and perhaps most importantly, it appears the system is not grounded properly. I do not see any bare copper in the main panel outdoors, and no evidence of thicker bare copper in the subpanel in the garage. I have had an outlet tester read grounded on the 3 prong outlets in the house, and it's possible the system is grounded to water/gas pipes somewhere, but there is no evidence of that around the water or gas pipe entrances.

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It's possible that's it's not grounded, if it's old enough, but that's kind of surprising. There should be grounding electrodes at the first disconnect, wherever that is. Metal cold water pipe, and a secondary electrode system is the norm, like ground rods (among other types).

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live4ever said:

---

My understanding
(not necessarily what I have been told by electricians - their thoughts varied widely)

My understanding is that due to the size of the conduit between main breaker panel (outdoors) and the meter, 125A is the largest total amperage I can have, which would be accomplished by swapping the 100A breaker for a 125A (assuming the 125A breaker is allowed by the specs of the outdoor box). I could feasibly upgrade to 200A by replacing the conduit to 2" Sch80 PVC since the wires are 2/0. Is this all correct?

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The conduit size is dictated by the conductor number and size. The ampacity of the conductors is dictated by their material and insulation rating per NEC Table 310.15(B)(16). BUT, for service entrance conductors that supply the entire dwelling unit, a different table is used [NEC 310.15(B)(7)], which allows higher current on the same size conductors. 2/0 copper is good up to a 200A service, while #2 copper is only good to 125A as service entrance or feeder conductors supplying the entire dwelling unit.

live4ever said:

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My other understanding is that it is OK to use a 200A rated panel as the new subpanel even though it would have a 100A (or potentially 125A) main breaker in front of it.

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Yes, the main breaker serves as a disconnect only at that point, if the upstream breaker is lower rated. The conductors can be sized to the upstream breaker. But if it's a subpanel that doesn't serve the entire dwelling unit, you have to size the conductors using the well-known ampacity table 310.16 (recently changed to 310.15(B)(16)).

live4ever said:

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Regarding the grounding, I know that code calls for 2 grounding rods. Where should they be located? Does it matter if they connect to the main box outdoors or to the subpanel? Could there be one grounding rod in each location?

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Grounding electrodes are supposed to be at the service equipment, or the first disconnect (same thing, AFAIK). A single ground rod is adequate IF it has a resistance to ground of less than 25 ohms, which isn't easy to test, so normally two are driven with no testing required. Outbuildings are also required to have a grounding electrode system, so you could have more than one such system. Doesn't matter if there's a 3- or 4-conductor feeder to the outbuilding (3-conductor is grandfathered, but no longer permitted for new work).

I'm doing this from memory, so I may be a little off on something, but not drastically. I wouldn't think.

[live4ever]

TDKPE said:

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What conductors are you referring to here? The overhead service conductors that are (presumably) owned by the utility, or the conductors connected to those and running down to your panel? The meter is not right at the bottom of the service drop from the utility? And are they 2/0, or #2 (huge difference)?

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I'm referring to the conductors in the first (outdoor) breaker box, so this is after the presumed splice with the utility company. These conductors travel down the side of the house and into the 100A breaker box. I didn't realize 2/0 and #2 are different - this is 2 AWG, so that answers the 200A thing. We're limited at 125A. We've also eliminated one of the electricians.

TDKPE said:

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Grounding electrodes are supposed to be at the service equipment, or the first disconnect (same thing, AFAIK). A single ground rod is adequate IF it has a resistance to ground of less than 25 ohms, which isn't easy to test, so normally two are driven with no testing required. Outbuildings are also required to have a grounding electrode system, so you could have more than one such system. Doesn't matter if there's a 3- or 4-conductor feeder to the outbuilding (3-conductor is grandfathered, but no longer permitted for new work).

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Ok, so from what you're saying, the 2 grounding rods should be located at the back of the house (first disconnect, aka my 100A breaker box). The copper would simply travel from those two rods to that outdoor breaker box. Back in the garage, the water and gas pipes (which enter in the garage in the front of the house) could be bonded by attaching to the subpanel, correct?

If the system were already grounded, I should be seeing thick copper in either the 100A single breaker box (first disconnect) or in the subpanel in the garage...which I don't. The system was last inspected in 1975, and the house is 1938. Could I look for the copper from a ground rod in the meter box?

Thanks for your help, Tom, much appreciated as always.

[Bob10]

I don't quite want to address all the things you mentioned as I believe most don't mean a thing if you change to a larger panel. If you plan to do that here is what I would do again without much knowledge of what is in front of you. I would install the grounds now to water supply and bond across water heater and one ground rod next to the main and sub panel. I am trying to suggest everything that can be done without touching anything that might be live. I would call the power company to schedule a disconnect in the morning remove the old box and supply conduit after disconnect replace with new box and weatherhead 2/0 in pipe hanging 3 to 4' out the weatherhead. I am assuming old conduit to garage would be pulled into new box and connected to properly sized and marked breakers along with ground to panel. Call inspector already have power co scheduled to return late that afternoon to reconnect after inspection. They might call you out on the sub panel as it should have a 4 wire feed and separate neutral and ground bars in it which can be checked now. That sub might require pulling a neutral or ground all things you can find out before starting

[Estrogen Hostage]

How big is your house? Is the problem that you are running out of space?

[Bob10]

Could just be dealing with making things code the kitchen alone could be 7 or more spaces by itself.