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Another sub-panel question


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I have a question regarding a sub-panel that I was hoping to get help with. At today's inspection there was a main panel and a sub-panel installed in this home. The sub-panel is installed directly next to the main panel and connected together with a 1 1/2" piece of metal conduit.

Removing the sub-panel cover, the first thing that struck me was the lack of neutral wires. There are 9 circuits and only 3 neutral wires.

All of the wires for the circuits along the left hand side of the panel and two on the right hand side run through the 1 1/2" conduit, into the main panel, where they pick up neutral wires and out through the main panel.

So basically what's happening is that power to these circuits is being supplied by the sub-panel and returning to the neutral bar in the main panel. I've never seen a panel wired this way. Is this allowed? Hopefully my explanation makes sense. Thanks for your help.

Tony

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The handful of circuits that do have all terminations in that panel are wrong. There are GCs and EGCs on the right bus that should be isolated, and without a better picture I can't tell if the GC on the left bus is connected to anything at all-I don't see a bonding screw, and there is no ground. That's enough to call a sparky on alone. Let him figure out what to do with the rest.

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The handful of circuits that do have all terminations in that panel are wrong. There are GCs and EGCs on the right bus that should be isolated, and without a better picture I can't tell if the GC on the left bus is connected to anything at all-I don't see a bonding screw, and there is no ground. That's enough to call a sparky on alone. Let him figure out what to do with the rest.

That's correct there is no bond screw, but there is a bar that extends across the top of the panel (just under the feeder lugs) that connects the neutral bars together. It's coated in black plastic and difficult to see in the picture.

As far as the ground, this is the land of conduit. The 1 1/2" metal conduit bonds the two panels together. The main panel is grounded and bonded.

So if I'm understanding you correctly, the circuit has to terminate where it started from. In this case it originate from the sub-panel and it needs to terminate in the sub-panel. Is that correct? Thanks again, btw.

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That's correct there is no bond screw, but there is a bar that extends across the top of the panel (just under the feeder lugs) that connects the neutral bars together. It's coated in black plastic and difficult to see in the picture.

So the GCs are all connected, and they are isolated from the enclosure. That's good. But there are two EGCs on the right bus that aren't supposed to be there. An accessory ground bus needs to be installed in the sub and the EGCs moved there. Get one big enough for the EGCs for all the circuits in that enclosure.

So if I'm understanding you correctly, the circuit has to terminate where it started from. In this case it originate from the sub-panel and it needs to terminate in the sub-panel.

That's my understanding.

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Yeah, that makes sense.

Portable generators are typically 5000 watts or less. The best way to connect a portable generator to a home is via a transfer switch. Basically a subpanel with a few circuts moved over to be powered by the generator sometimes but from the main panel most of the time. As a result, the wiring of those circuits is a bit odd.

What you got there is the makings of a transfer switch.

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Yeah, that makes sense.

Portable generators are typically 5000 watts or less. The best way to connect a portable generator to a home is via a transfer switch. Basically a subpanel with a few circuts moved over to be powered by the generator sometimes but from the main panel most of the time. As a result, the wiring of those circuits is a bit odd.

What you got there is the makings of a transfer switch.

Thanks Bruce. That does make sense now that you pointed that out. The wiring is unconventional, but I guess my question would be, does it need to be repaired?

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Yeah, that makes sense.

Portable generators are typically 5000 watts or less. The best way to connect a portable generator to a home is via a transfer switch. Basically a subpanel with a few circuts moved over to be powered by the generator sometimes but from the main panel most of the time. As a result, the wiring of those circuits is a bit odd.

What you got there is the makings of a transfer switch.

Thanks Bruce. That does make sense now that you pointed that out. The wiring is unconventional, but I guess my question would be, does it need to be repaired?

Yes, I believe it needs repair.

The subpanel has a neutral bus, and that is where the branch circuit neutrals should be terminated. Then they should leave the subpanel through separate cable clamps or conduit and go off to wherever, but never back to the main.

Amateur workmanship, maybe done without a permit, possible hidden faults. An electrician also can check that grounding is correct and adequate.

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. . . Thanks Bruce. That does make sense now that you pointed that out. The wiring is unconventional, but I guess my question would be, does it need to be repaired?

Yes. The split up circuit wires will cause inductive heating of the nipple.

Both the inductive heating and the reactive/resistive voltage drops that result from separating the two conductors would be insignificant. Even the currents of an electric stick welder would produce only small amounts of inductive heating, unless you form the conductor into a coil to compound the effect.

Industrial induction coils, such as inverter or motor/generator powered billet heaters used for the manufacture of high pressure forged steel pipe fittings, typically have current magnitudes in the order of several thousand amps. Conductors used for such purposes are water cooled.

Marc

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. . . Thanks Bruce. That does make sense now that you pointed that out. The wiring is unconventional, but I guess my question would be, does it need to be repaired?

Yes. The split up circuit wires will cause inductive heating of the nipple.

Both the inductive heating and the reactive/resistive voltage drops that result from separating the two conductors would be insignificant. Even the currents of an electric stick welder would produce only small amounts of inductive heating, unless you form the conductor into a coil to compound the effect.

Industrial induction coils, such as inverter or motor/generator powered billet heaters used for the manufacture of high pressure forged steel pipe fittings, typically have current magnitudes in the order of several thousand amps. Conductors used for such purposes are water cooled.

Marc

Ok, then, I'll just cite 300.3(B):

Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

The exceptions don't apply to this installation. They include an exception for parallel conductors, an exception for equipment grounding conductors and bonding conductors in certain existing installations, and an exception for certain kinds of non-magnetic sheathed cables.

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