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Home built in the 50's has a fuse box that's currently being used as a subpanel in the garage. The garage is attached to the house by the means of a 8 foot wide enclosed breezeway/mudroom. My problem is I would like to add some grounded outlets and the fuse box has no place for ground wires. If I understand correctly I don't want to attach ground wires to same place as the neutrals. correct? There are only 3 wires coming into the fuse box -2 hots and 1 neutral. the come in above the ceiling in the breezeway into the garage from the main panel in basement.

  1. can i leave the grounds unattached in fusebox or can i not do this?

My longer term plan is to install a load center with breakers but that leads to my next question.

  1. Can I just pull a ground wire from subpanel to main or do i need to replace all the wires from the main to the subpanel? Any help is appreciated. thank you!!
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    Does the fuse box electrically isolate the neutral bar from the metal box? Also any chance you know the make of the box? – Harper Aug 8 '18 at 21:00
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The NEC now allows a single ground wire to be pulled, since you would be putting in this single ground your neutrals would need to be isolated from ground. A simple isolated buss would do the trick for the neutrals and use the grounded buss for the grounds.

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Neutral and ground must be separate in a subpanel

Neutral and ground never touch, except at the equipotential bonding point in the main panel. That is a special feature with a special purpose.

The first thing you must ascertain is whether the neutral is bonded to the subpanel (fuse panel) chassis. This may have been done for the purpose of equipotential bonding. It may be separable, or may not. Sometimes the neutral bus is isolated and you can remove a screw or jumper. Otherwise you will need to obtain an accessory neutral bus that is isolated and move all the neutrals to it.

If you need a ground bus too, you may be able to get away with just clumping all grounds into a wirenut or daisy chain of wirenuts, at least for as long as it'll take to change out that fuse box. Don't use stab connectors, they are not allowed for grounds.

No ground is an island

See what I say in this answer about the danger of islanding grounds.

So don't attach grounds from a receptacle circuit to this subpanel and then stop. It is essential that the ground path go all the way back to the equipotential bond at the main panel.

Never, never, never bootleg ground

Tying ground to neutral is always a bad idea. Even if a bad old compromise exists in Code.

If the (over-tasked) neutral wire fails between the panel and the bootleg point, it energizes at line voltage everything that's supposed to be grounded. That is what makes NEMA 10 so dangerous, and it has killed. A wire simply failing should never create danger! Wires fail all the time, just look at all the "a whole bunch of outlets went out at once" questions we get.

And bootlegging ground breaks one of your essential protections: GFCI. If you bootleg ground past the GFCI -- and a device there suffers hot-ground leakage -- the GFCI has no idea and is unable to provide protection. Current is returning on ground (bad!) but the GFCI thinks it's returning on neutral like normal.

Retrofitting grounds

Your building is attached so you do not need a separate ground rod.

You can do as you propose: run just a ground wire from the main panel to the fuse box. The wire must be big enough for the circuit (same size wire is safe, but smaller wires are allowed for some sizes) and it can follow any viable route back to the panel or anywhere else that is grounded and whose ground path is big enough - including the house's grounding electrode system.

I'm not sure a retrofit ground would be legal at the time of subpanel replacement, but it's legal now since you still have the fuse box. Later when you upgrade to a subpanel, it should be grandfathered.

Once you establish solid ground in the fuse box, you may then retrofit ground to any circuit fed off that fuse box.

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Well, depending on local code, you may be grandfathered into this setup: You would connect the subpanel as you would a main panel, by connecting the grounds and neutrals to the same terminal bar.

If you have easy access to the conduit between the main panel and the subpanel, it may be smarter to go ahead and run the ground wire.

  • So to be clear, in the existing fusebox I could connect the grounds and neutrals in in the same terminal bar? The existing subpanel/fusebox (glass fuses) is powered from the main which is grounded btw. Also, there is no conduit for the feed from main to subpanel currently. It appears to be running above the breezway ceiling to the garage subpanel. Thank you very much for you reply! – Neophyte Aug 8 '18 at 16:52
  • This entirely depends on what your local code says. The 2017 National Electric Code does allow you to use the grounded conductor (neutral) for equipment grounding when there is no equipment ground, no continuous metallic paths between the structures, and no ground fault protection installed upstream of the panel. Check out NEC 250.32 (B)(1) exception 1. Your local code may say you can't though. – N R Aug 8 '18 at 16:57
  • If there was conduit from the main to the sub this would be a grounding method and no wire would be needed. – Ed Beal Aug 8 '18 at 19:30
  • Only if it's metallic conduit and actually continuous... – N R Aug 8 '18 at 20:32

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