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My home has a 200amp meter box with 6 double breakers beneath the meter under a flap - 4 breakers are 60amp (stove heater, AC, unknown) - there are also 2 100amp breakers going to load centers inside - I believe the previous owner must have added a 2nd panel since they are different makes. the original box 200amp has neutral and ground connected to same bus and a green screw that appears to bond the bus to ground. the 2nd panel is 125amp. It also has neutral and grounds on the same bus but there is no green bonding screw - should there be a green screw since this is not a sub panel but appears to be a second (parallel panel) added to increase circuits. Everything seems to be working - I'm asking because we want to do solar grid tie and company says they will need an available space in the meter box and wiring looks odd. It got me looking at the set up and alos questioning??

  • Parallel main panels? Are you sure? That's a new one for me. Does you meter box have a disconnect switch? – longneck Jun 20 '16 at 16:55
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    If the 125 amp panel is directly fed from the meter base the neutral and ground can be bonded. If there is a breaker that can turn off the 125A panel with the 6 in the base it is a sub and the ground and neutral must stay Isolated. That was the call an inspector made for me with just 2 service disconnects in my meter base. – Ed Beal Jun 20 '16 at 18:19
  • Are the 200A "original box" and the 125A "second panel" the two indoor load centers, or are they in addition to the two indoor load centers and their 100A feeders? – ThreePhaseEel Jun 20 '16 at 22:20
  • Sorry for the delay responding - I had trouble logging in- The outside meter box is apparently called a combo. The six 220v double breakers are outside and directly under the meter - apparently these breakers would all be disconnects?. Four of the breakers are 60amp (stove, heater,AC, unknown) The remaining two breakers (@ 100 amp) feed the two inside boxes (panels). A copper ground cable is connected from the ground bar to a copper ground rod in the ground under the combo meter box. – Jose Jun 22 '16 at 3:41
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If the second panel is fed by the first (power is fed to the second panel through a breaker in the first), and the service neutral is bonded at the first panel. Then the ground and neutral should be separate in the second panel, and separate grounding and neutral conductors should be run between the two panels.

  • Thanks Tester - The 2nd panel(125Amp)is fed by a 100 Amp breaker located outside under the meter.. – Jose Jun 22 '16 at 11:48
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Neutral and ground should be bonded only in your main service panel. Sounds like, in your case, that's the one attached to your meter. Secondary panels should have separate neutral and ground bus bars. Bonding ground and neutral elsewhere in your home will not appear to affect functionality, but is a safety hazard.

The reason it's a safety hazard is that you're creating multiple paths through your electrical system for current that should go entirely over neutral conductors. In this case, your ground conductors (between panels) are probably routinely carrying current. Ground conductors should only carry significant current during a fault.

This is a relatively easy fix - just add a bus bar to your second panel so you have separate neutral and ground buses. But the fact that it wasn't done this way originally likely means your wiring was done by someone not entirely clueful, and it might be good to have an expert review the whole system.

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    @Shimon Rura Adding a ground bus would be easier since the existing buss is currently setup as a neutral buss. – Kris Jun 20 '16 at 21:15
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    @Tester101 There's more than one reason why it's dangerous, but it's not that useful to list them all. A big reason relates to lost connections. Lose a neutral and current is returning on the potentially smaller ground. Lose both neutral and ground, and now your ground floats with your neutral, energizing every switchplate screw. – Harper Jun 21 '16 at 0:49
  • @Harper I agree. I'm just asking for an explanation on one of the dangers listed, as I can't understand how it would work. Although I don't think a dropped conductor was a major motivator in the development of this code, otherwise I'd think that they'd require the ground to be sized the same as the neutral. The separation is mostly to avoid current on the grounding conductors, enclosures, and other grounded items. – Tester101 Jun 21 '16 at 1:36
  • Thanks for the pointers Tester101 and Harper. I've edited and hope it addresses your concerns. But what exactly do you mean that if you lose ground and neutral then your ground floats with neutral? – Shimon Rura Jun 22 '16 at 2:41
  • Shimon - Thanks - The outside box (under the meter) holding the six breakers has a ground bar with a grounding rod the rod and bare wires and neutrals (white wires) for the six circuits are all bonded/connected at this ground bar. So it appears that meter location would be the 1st disconnect location? and that would make the inside panels actually sub panels requiring separation of neutrals and grounds. Is that correct? thanks. – Jose Jun 22 '16 at 12:15

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