Recently had the electrical panel upgraded and relocated. The electrician showed me the main wires coming from the street (in to the meter) and indicated they were 1/0 aluminum. The breaker panel had a 125 A main breaker, and he put in a 150 A main breaker on the new panel (the new panel is a 200 A panel). He replaced the wires from the meter to the panel with new copper (forget the gauge). From what I've seen around here on DIY.SE, though, 1/0 Al is sufficient for only 125 A, not 150. Should I be worried?

I'm in the Houston, Texas metro area.

We never tripped the 125 A breaker, but did add a 50 A 240 V receptacle for EV charging. No EV yet, and its breaker is off, so we're not drawing any more current than we used to. I'm not really worried about an immediate problem, only once we get the EV.

  • Is this an overhead or an underground service? – ThreePhaseEel Oct 11 '16 at 23:36
  • @ThreePhaseEel underground. The transformer box thingy is in our backyard neighbor's yard somewhere, I'd guess maybe 200 feet of wire at the most – mmathis Oct 11 '16 at 23:58

It depends on when the work was done, and which version of the code was being followed. In the 2011 code and before, there was Table 310.15(B)(7). This table listed the service and feeder conductor size for 120/240 volts, 3-Wire, Single-Phase Dwelling Services. The table listed 1/0 AL to be used for 125 ampere services.

The 2014 version of the code omitted this table, because folks were simply using the values, and not applying correction and/or adjustment factors properly. The 2014 version allowed you to size the conductors to 83% of the service rating, which usually worked out to about the same as the old table.

Looking at your 150 ampere service as an example (Excluding any temperature or other adjustments).

150 ampere x 0.83 = 124.5

Table 310.15(B)(16) says that 1 AWG copper is good for 130 amperes at 75C. So if no adjustments were needed, 1 AWG would be allowed as service conductors for a 120/240 volts, 3-Wire, single-phase dwelling service.


Main wires coming from the street are engineered to provide adequate power by the utility company. They do not have to follow the same wire sizing gauge as specified in the NEC because the NEC does not govern utility companies.

The recommendations provided on this site are generally taken from NEC tables which does apply to work performed on most residential and commercial spaces in the United States.

Assuming that your locality approved your panel upgrade per all required permits and contacts and the utility company was notified and involved to remove power, it should be fine. However, if you have concerns about the utility company's involvement/approval in the upgrade process, you should contact the utility company.

  • Good point. He did not state whether the electrician obtained a permit and had the new service inspected. – Mister Tea Oct 11 '16 at 22:03
  • No permit was required, since the meter wasn't being changed (we're out in the county, no other permitting jurisdiction yet). Utility did a quick check before reconnecting the service, but not sure how thorough it was, as it was 11pm. The new panel is on the opposite side of the garage wall as the meter, so he may not have realized the bigger main breaker – mmathis Oct 12 '16 at 0:02
  • @mmathis I would recommend checking the electrical meter to see how many amperes it is rated for. It is possible that it is rated to carry more than 125 amperes, however my guess is that it may also need to have been upgraded if your main panel increased to 150 amperes. In which case, you have the potential to pull more current than the utility company planned for your home. – statueuphemism Oct 12 '16 at 14:21

Depends on the setup. If the power company furnished the service to the meter pan, it does not fall under the NEC. The meter pan should have a minimum #1 copper wire to the main breaker. If so, then you're all good.

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