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A common anecdote, and one that is not without substantiation, is that some home insurers refuse to insure houses with fuses in their electrical system.

While this is substantiated in the typical case, where the presence of fuses for circuit protection is a sign of an electrical system that is generally obsolete and/or has a significant risk of overfusing and/or fuse bypassing, there are cases where circuit breakers are not readily applicable to the circuit protection need at hand. This is true where extensive DC systems are present, circuit protection devices of unusual ampacities are needed such as for a power meter potential tap or for overload protection of motors, or if power is stepped up to 480V onsite for a long feeder run to an outbuilding.

In these cases, modern fusible hardware, such as fuse holders/blocks and fusible safety switches, that has rejection features engineered into it to prevent bypassing or gross overfusing, represents an effective and NEC-compliant alternative to circuit breakers that either don't exist (there are no UL489 breakers with a fixed 100mA overcurrent trip, and probably never will be) or are cost prohibitive to install (such as large DC or 480V straight rated breakers). This hardware is made by reputable manufacturers and widely distributed, accepts UL-listed rejection-type ferrule/cartridge or blade fuses that can be obtained through most suppliers of electrical equipment, and is fully rated and listed for service in the applications in question.

How can someone who is planning an electrical installation where engineering constraints may put fuses back on the table as a circuit protection means avoid finding themselves in a situation where insurers are refusing insurance coverage over a safe and Code-legal installation? Is the aforementioned anecdote truly an overgeneralization of the situation?

  • I think this is an overgeneralization of the situation. Just looking at your first two links - both are "preferred" with quite a few limits, not just fuses. One of them only says "fuse box" - implication is that fuses in specific code-appropriate locations would not be a problem. The other uses "fuses" in a more general sense, though to my mind the implication is that they are referring to fuses in a general electrical panel mode, not fuses within any equipment (e.g., I have plenty of computer equipment with factory-supplied fuses inside - I can't imagine that simply having such... – manassehkatz Jan 9 at 5:12
  • equipment on premises would invalidate the policy). In these 2 policies are they going a bit overboard on restrictions - absolutely positively YES. But that is the nature of a "preferred" policy. My house wouldn't qualify because of fuses, but would probably fail in a few other ways too - but I have no problem getting "regular" insurance. – manassehkatz Jan 9 at 5:17
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I think this is an over generalized thought. Since you mentioned 480, many industrial equipment sets using variable frequency drives require class j fuses for protection, their are still some AC units that state max fuse size (most have changed to max fuse or hvacr breaker in the last few years) in these cases it would violate the listing to use a breaker. I have updated quite a few homes in my area from fused to breakers because of insurance requirements but there are still companies that will insure homes with fuses or even FPE stablock panels, where fuses would be safer if properly sized in my opinion. I think the bigger problem is on fused system k&t or cloth wrapped wire was used and some of that insulation is failing being the root cause of the problem.

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I think the key to it is they want to see modern circuit protection on everything. They don't want to insure cases where the only circuit protection is obsolete.

So if you have fuses, but the fused thing is behind a competent circuit breaker, that is all they will care about. For instance:

  • the 100ma fuse protected device is behind a 20A breaker and fully encased in metal EMT, so even if it has a sparky-bangy moment, it won't be able to expend more than 4800W trying to burn through the junction box metal.

  • The 30A on 480V fuse is in the shadow of a 60A on 240V modern breaker, and is basically there for statutory reasons, as it would only activate in an edge condition where it exceeded 30A without the supply breaker exceeding 60A. That would require the intersection of several highly improbable events which would share no common cause.

  • In my own house, a legacy fuse box is fed by a 120V/20A "QO" breaker. Nothing on it anymore but lights, so that is adequate.

  • Low voltage DC systems remain a mystery to me. Firstly, an obligatory disclosure: DC above about 40 volts is not to be trifled with, it has extremely, nay, phantasmagorically hostile arcing behavior because there is no zero-crossing to snuff the arc, and equipment made for AC is derated often 10:1 for DC voltages. That said, it occurs to me that breakers cannot discern voltage or frequency. I cannot see why a common-as-dirt mains panelboard like a QO130M200PC couldn't be used to distribute 12/24 VDC.

  • In fact, Square-D QO breakers are rated for 5kAIC@48VDCmax, so your line of thinking with that QO panel works...up to a point. (A typical 12V SLA can crank out 1kA of fault current, so you could only connect about...six batteries to that QO130M200PC before you exceeded the interrupting rating of the breakers if you were trying to use it as a DC battery combiner.) – ThreePhaseEel Jan 9 at 23:34
  • However, things start getting ghastly as you add more and more batteries -- breakers capable of handling DC faults upwards of 22kA are precious, and become nonexistent past 42kA, while a hardware-store RK5 cartridge fuse is rated for 20kAIC@125VDC, and better fuses such as the Cooper LPx-RK familes of RK1 fuses can handle 100kA faults when used in DC systems. – ThreePhaseEel Jan 9 at 23:42
  • @ThreePhaseEel I also would not consider it abnormal to have fuses near the battery box, simply to protect the run from battery box to panelboard... irrespective of the main breaker.. . So everyone can win. – Harper Jan 10 at 0:15
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I think the key is finding a company that is willing to work with you.

You need an agent to whom you can explain the situation, explain that you are sure this installation is in line with all their policy's rules, you just can't check a box that says "no fuses" on the application. If you can provide a written explanation for review by an underwriter, it's likely that they'll agree that this specific use of fuses does not violate the policy's rules prohibiting fuses and you'll get the coverage.

If the insurance company's agent is an app on your phone and an offshore call center, you probably won't be able to work out coverage with that company, and you might wind up paying more premium, but it might be worth it to be with a better company if you ever need to make a claim.

Show them this video:

https://www.youtube.com/watch?v=3dckmSgp1nw

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