I need a line from our fuse box to a external fusible disconnect for a 220v AC condenser. It's an older fused box with only one 15/20a 110v spot open. Next choice to take off from is an unused 60a pull out fuse block(since we converted the stove to gas). Next choice to pull from is after the main box disconnect. My first thought was to put smaller fuses in the old oven circuit block but the 60a pullout uses the wider diameter fuses. What size/type wire do I need to supply from the 60a pullout to the exterior disconnect that will be fused at 20 amps? TY

  • Welcome! There's a bunch of information there and maybe more than one question (the "what wire size and type do I need?" but also the implied "where should I attach the wire to the existing system?"). If you could attach a few photos of your fuse boxes, blocks, and disconnects that'll help us better understand what you're working with. The wire is the most visible and satisfying part to buy, but because it's both expensive and non-returnable, it should be bought last after all the other parts are chosen or even installed.
    – Greg Hill
    Apr 25 at 22:57
  • 1
    Wire for 60 amps will be expensive, about 4 gauge. Would see if you can find a 30 amp fuse and go with 10 gauge wire. Might even be adapters for small size fuses.
    – crip659
    Apr 25 at 23:15
  • Is this a "fuse box" with actual, single blow, screw-in fuses, or is this a breaker box where there's a little toggle lever to flip back-and-forth if a circuit overloads?
    – FreeMan
    Apr 26 at 12:10

2 Answers 2


What has you confused is not realizing overcurrent protection must protect the wires. So you can use 60A wire (due to a technicality, 55A wire) off a 60A fused disconnect and carry that to another fused disconnect rated less.

The cheapest 60A rated wire is 2-2-4 aluminum, if it will fit on the terminals in question. (Actually 4-4-6 would suffice, but it is barely cheaper). If you are forced to use copper, then 6/2 w/ground.

Take that to your 20A fused disconnect.

Would there ever be cause to park a vehicle near where the heat pump will be located? Because many home sellers are finding they get better offers when an EV charging outlet is ready to go.

Also, remember Code requires a 120V outlet quite near the A/C unit. That is for the A/C maintainer to use, for vacuum pumps and the like. If you need to support a 120V device, then you need to run 4-wire to the subpanel (e.g. 2-2-2-4 or 4-4-4-6).

Now if you need that receptacle, or if you want an EV outlet or an RV outlet or anything else really, then change that fused disconnect to a small subpanel, like 8 spaces. A 20A 240V breaker provides the fused disconnect, 15A/120V breaker provides a 120V receptacle, then a 40A breaker for EV charging or really whatever you want.

No one has ever complained on this forum "my house has too many breaker spaces available, what ever will I do?" Spaces are cheap.


If you had a 60 amp breaker, you'd need to run wire that would handle 60 amps. You have a 60 amp fuse block that can use a variety of fuses so you only need to run the wire for your fuse size. You can get 60 to 30 amp reducers (see picture below) and install your 20 amp fuses in the reducers and plug them into your 60 amp block. Then run your 12 AWG cu wire to your disconnect. I'm pretty sure you won't need a fused disconnect there because you'll be fused at 20 amps in the main panel. Do check the name plate for your condenser for minimum fusing.

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