Saw a setup today where there is a 200 amp disconnect in the meter panel
and a 150 amp in the main panel in the house.
Is there anything wrong with 2 separate disconnects? The house panel is treated as the service panel with bonded ground and neutral. The service is wired for 200 amps. No issue there.
Thanks,
Tim
Tim, it sounds like the disconnect at the meter is the service disconnect and the house should be wired as a remote distribution panel (isolated neutral, etc.).
Did they install 4 wire cable from the 200amp disc to the 150amp panel, they should be separate GC and isolated neutrals
No. Three wires from the meter. Panel has own GC.
Tim
Once you are past the first service disconnect the feeder should be 4 wires. The grounding would be at the service disconnnect.
It was acceptable under prior NEC editions to have a 3 wire feeder to a detached structure if there were no metallic paths between buildings like a phone or water line.
Are you dealing with an attached structure or detached?
i think I am reading the OP’s question wrong. Are you saying their is a service disconnect outside and another service disconnect inside…because if this is the case and the panel inside is not being fed from the panel outside then we have a grouping issue. Please be more specific…Is the exterior panel feeding the interior panel…lets start with that question and go from there.
Disconnect #1 is in the meter panel on the pole 150 feet from the house.
Disconnect #2 inside the house. There is 3 conductor 4/0 al running underground from meter to house panel.
While I have you, Paul, just out theoretical curiosity, why is it important for the sub panel (any sub panel) to have separate ground and neutral? I’ve been studying this for 6 months and haven’t actually heard a reason.
Thanks,
Tim
Is the second disconnect actually a main breaker in the house panel?
The most important reason for seperation is to remove the case to neutral connection which causes current that returns to the source via the grounded “Neutral” conductor which could put the return current on all metal parts since we all know the neutral carries current. Among some other reasons this in my opinion is the most dangerous of events. This means that potentially equipment grounding conductors that in many cases are bonding ( as the NEC now says it also does ) to metal enclosures and so on that has no need to impose currents onto and doing a case to neutral connection where you are not supposed to increase this situation. There are other reasons as well but this is the major of the ball of wax. Now, heaven forbid the conduit is the equipment grounding conductor and we have a poor connection, well now you have a point that is not a low impedance path and you impose current onto it and more problems happen.
Hope this was helpful.
Tim,
This exact question has been asked many times here on this MB.
A SUB-PANEL, or REMOTE DISTRIBUTION PANEL, is merely an extension of the main service panel (SERVICE ENTRY). Since the neutrals are bonded to the grounding wires in the MAIN SERVICE PANEL, the grounding wires (bare) and the neutral wires (white) should never be connected in any manner beyond the main panel. However, the grounding wires should be bonded to the sub-panel.
And “objectionable current” may flow on metal parts (grounding wire or metal conduit) when the grounded neutral conductor (white wire) is bonded to the metal case of a panel-board that is not part of service equipment (such as a sub-panel). Occasionally, the wires may come in contact with each other in their jacket causing a short circuit in the grounding/grounded system.
If a neutral wire became disconnected (and, it does happen), the return path for electric current could be along a ground wire. While that itself may not always be a hazard, if that ground wire also became disconnected somewhere, parts of the ground system could be energized. That is NEVER supposed to happen.
The neutral wire is essentially a “low-risk” return path for the electric current in that branch of the system. All of the neutral wires have the same electrical potential…zero. At least, no potential compared to ground. There is, of course, 120 volts of potential difference between a neutral wire and any hot wire in the average residential system.
If one were to touch the metal part of a live neutral wire one should not receive a shock. (Don’t try it!) By tying the neutral to ground at one point (in the main panel), half of the conductors (in a typical 120 volt circuit) have no dangerous electrical potential. Of course, as always, the hot wires are still dangerous.
Thanks Paul and David.
Cheers,
Tim
If you come between a disconnected neutral and a grounded object it is quite possible to receive a shock. You would be the circuit conductor at that point.