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I have an old house (1955) with two overhead wires going from the house to the detached garage (15') where they connect to an old fuse box (picture) old fuse box

My first question: how does this work? Two wires at the top come from the house, hot and neutral, I presume. Two wires at the bottom power several lights and an outlet in the garage. No ground wire. Those are 30amp fuses. Why do the hot and neutral wires each appear to have a fuse? That's not how breakers work, is it?

My second question: how can I replace this with something safer with breakers rather than fuses? Thanks!

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    Fuses are just as safe as 'regular' breakers, you should opt for a differential breaker that will protect you against live-earth, neutral-earth issues. So if you accidentally touch the live and a piece of metal you're not going to be electrocuted. Also, if you're in north america, I suggest you to pull a new 3 wire feed (L1+L2+N) so you can install 230V appliances and also add a separate grounding for the garage. – DDS Feb 7 '18 at 14:38
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    Have you measured the voltage? Usually 240v will have 2 fuses where 120v is normally fused on the hot leg. I have seen garages / out buildings with only 240, Are the lights 120v? – Ed Beal Feb 7 '18 at 14:50
  • @DDS USA now requires ground to be carried -- so 4-wire unless OP only wants 120V. Also there is nothing wrong with putting overload protection on neutral, but it must be common-trip with the hots. Not doing so is simply "economical". – Harper Feb 7 '18 at 17:21
  • I measured the voltage today. 120 on black, white is neutral. As far as I can tell, the two wires come in directly from the main service panel off a 100 amp breaker. If so, overload protection is obviously necessary for the garage. I would prefer breakers. – Hooky Feb 7 '18 at 22:18
  • Does anyone have any ideas as to what I could use to replace the old fuse box. I would like to have breakers and just 2 or 4 circuits for the garage lights and a few small tools. The main lugs and sub panels I see for sale don't seem designed to work with a 2-wire system. I also would want to ground the thing on the spot--I've already driven in a rod. – Hooky Feb 7 '18 at 22:22
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That thing is more of a shutoff switch -- the fuses just happen to be "a thing" they often put in shutoff switches. A shutoff switch is required in an outbuilding, and so for that reason, I would retain the switch even if you changed the wire. It looks like a fine switch to me.

GFCI and done

This uses GFCI to provide electrical safety on the existing setup.

The simplest way to provision the power you want is to install a junction box, wire the cable out of the shutoff switch so its first stop is this junction box (which may already exist) -- and install a $20 GFCI+receptacle combo device. Voila.

GFCIs only protect stuff downstream of them, so it's best to put the GFCI protection in the house, either as a breaker in the main panel, or a GFCI device (+receptacle or deadface) enroute.

Subpanel

With this option, you must trench a separate ground wire back to the house.

You cannot drive a ground rod and call it done, for reasons often discussed here. Given that 90% of the cost is in the trenching, you almost might as well just run new and proper /3+ground cable of the ampacity you desire.

A subpanel is almost a lost cause because with only 20A (12AWG) or 30A (10AWG) capacity at 120V, you won't be able to support more than 2 circuits and no more than 2400/3600W. You cannot support 120V and 240V loads using this method.

I would retain the shutoff switch because there's nothing wrong with it. But if you use a "main breaker" type subpanel, that "main breaker" satisfies the code requirement for a shutoff switch.

Keep in mind when you run a common subpanel off 120V only, every other row in the subpanel is dead, so you'll use the spaces at twice the expected rate. Yet another reason to get an ample sized subpanel.

DO NOT consider installing a generator interlock panel on the hopes of backfeeding the house using this cable. Ask us how to do that if you want it. You'll still have to trench something though.

New main cable

In this case you trench and run a 12/3 or larger + ground cable. Rearrange the shutoff switch so the switch interrupts the two hot wires, and the neutral bypasses it. From there you either

  • run it as a multi-wire branch circuit, splitting each hot into two circuits along with the shared neutral and ground, breakering it for 20A.
  • run it into a subpanel as above, but using both hot wires and separating ground from neutral. You still need a local grounding rod.

Transformer; new main service.

No ground wire retrofit needed, but it requires a transformer. It will allow you to exceed 3600W in the garage.

In this scenario, you come directly out of the legacy shutoff switch straight into a transformer's 240V primary. The transformer 120V/240V secondary goes to a new sub^H^H^H main panel. Since it is a main panel off a transformer-isolated service, it must have a local grounding rod and must bond neutral to it. Running a ground back to the main building would be unhelpful.

Back in the house, you punch these two wires down to a 240V breaker of correct size to protect both the wire and the transformer.

  • Thanks Harper! A lot to chew on there. I've asked an electrician to come by later this week to have a look at my situation. I'm warming to the idea of installing some new wire from the main. I take it that it is no longer legal to run overhead wire? – Hooky Feb 8 '18 at 2:40
  • I for one love to preserve legacy wire; it's cheaper. Overhead wire is legal, go for it. There's a section in Code that talks about it, but it's specialized enough that you won't find much in the DIY world about it. If your existing overhead has a steel messenger wire supporting the two conductors, that's your ground wire. I have an installation where the steel messenger is the neutral, but it's for street lighting and it never touches the ground. – Harper Feb 8 '18 at 3:32
  • @Harper, are you saying the fuses themselves act as a shutoff switch or there is a mechanical switch that is not shown in the picture? In your first scenario (GFCI and done) it's not a proble that the neutral wire is on it's own fuse? If we short the hot wire to a metal frame that has been grounded and the current is sent back thru this neutral wire to the service entrance won't it blow the neutral fuse rather than the hot fuse and leave the equipment energized? I'm probably missing something basic here. – Stanwood Feb 8 '18 at 4:38
  • I am saying there is actually a switch there with its handle cropped out of shot. And the point of the device is to be a switch. The switch is required, the fuses are not and probably just came with the switch. Your concern about neutral is fair but no worse than a wire break: like aircrashes, other failures must stack to cause a problem. It wouldn't bother me if OP replaced the neutral fuse with a slug or larger fuse. In a perfect world neutral is fused but common trip with the hots. – Harper Feb 8 '18 at 8:11
  • Yes, there is a switch: photo link. @Harper, I'm still a little unclear as to where my overload protection for the garage is, as with the GFCI solution. Those two little wires come over directly from a 100 amp breaker at the main service panel. And those 30amp fuses, if they are acting as fuses, seem unsafe. – Hooky Feb 8 '18 at 13:36

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