Wire running from neutral bus to the neutral bus

[Mike Lamb]

A wire is running from the neutral bus on the far left panel to the neutral bus on the middle panel. These are all main panels in a multi-unit building. All the panels were bonded together with metal conduit. Is this okay?

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[Marc]

Absolutely not. It creates a parallel path for neutral currents between the two panels. That small, it's a fire hazard.

Marc

[Mike Lamb]

Why do you think someone would do this?

[Jim Katen]

I have no idea why someone would do that or what purpose it might serve. However, I doubt that it's going to cause any harm. The neutral bars on all three panels should be connected through the grounding electrode system and through their multitude of conduits, as you observed.

That said, it's not a good thing. It's undoubtedly carrying some unintended current and that's not desirable.

[Marc]

I have no idea why someone would do that or what purpose it might serve. However, I doubt that it's going to cause any harm. The neutral bars on all three panels should be connected through the grounding electrode system and through their multitude of conduits, as you observed.

That said, it's not a good thing. It's undoubtedly carrying some unintended current and that's not desirable.

If the arrangement here is that the panels each have main disconnects, wouldn't the electrode grounding system still be bonded at only one location?

The concern is that little jumper between neutral buses is parallel to the much larger neutral conductors upstream of the panels. Break that neutral path and that little wire takes over, at least until it melts.

Marc

[hausdok]

Where's the main disconnect?

If it's at a big see-saw disconnect somewhere else inside or outside the building, aren't those grounded (neutral) conductors and buses each supposed to be floating - without any bonding screws or straps installed; and the equipment-grounding (ground) conductors and ground buses all supposed to be bonded to their respective enclosures?

[Mike Lamb]

Where's the main disconnect?

Each had a main disconnect at the panel.

[Marc]

Where's the main disconnect?

Each had a main disconnect at the panel.

If there is no single main disconnect for the entire service then the electrode grounding conductor should run to the gutter and bond to the neutral conductor within it and nowhere else. Each panel should receive from the gutter an equipment grounding conductor. This EGC should bond the enclosure and EGC bus of the respective panel.

I think.

Marc

[Jim Katen]

Where's the main disconnect?

Each had a main disconnect at the panel.

If there is no single main disconnect for the entire service then the electrode grounding conductor should run to the gutter and bond to the neutral conductor within it and nowhere else. Each panel should receive from the gutter an equipment grounding conductor. This EGC should bond the enclosure and EGC bus of the respective panel.

I think.

Marc

Almost, but if you're suggesting separating the neutral and the EGC in each panel then, no, that would be incorrect.

The NEC give three choices when there are multiple service panels: 250.64(D) 1, 2, or 3.

1: You run a common GEC and run taps from it to each panel. The taps have to be connected to the common GEC with exothermic welding, listed grounding and bonding connectors, or a 1/4" x 2" bus bar that's fastened in place and accessible.

2: You can run a separated GEC from each panel to the GES.

3: You can run a GEC from the GES to the neutral service conductor in some enclosure on the supply side of the disconnects (such as the gutter you were suggesting). However in that case, you don't run any grounding wires to the panels.