Are 240V. fused dis-connects safe and legal? (North America System)

The fuses are redundant to the breaker in your case. The same concern about someone not removing the disconnect could be said of a non-fused type. The whole point of a local disconnect is so that you can visually verify that power is disconnected. There's no need for the fuses in your case, but theres no harm there.

Breakers wear out, too btw.

John

| My air-conditioner compressor stopped working the other day. It's a | 240 V. 20 Amp Circuit with a (20 amp - dual pole) fused disconnect | outdoors at the unit and a dual=pole ganged 20 Amp circuit breaker | further upstream at the service entrance. | | The AC tech found one of the 20 Amp fuses at the disconnect had | weakened and (after 7 years) had just opened up due to the inrush | current on the first attempt at operation for the season. | | This got me to thinking. If someone less-experienced had opened up | the AC Compressor unit without removing the local disconnect, they | could have gotten a nasty shock (or worse) from the good fuse on the | other leg if they were grounded. (This is in the USA). | | So I conclude that circuit breakers are safer than fuses (because the | poles are ganged). But wouldn't it be safer to have a pull out | disconnect at the compressor without the fuses, relying on the service | panel circuit breakers for overcurrent protection? Anyone know what | the code says on this?

The idea here being that without a fuse to blow to confuse the situation, the A/C would run instead, and it would be obvious to pull the disconnect. But what if the thermostat is off? Now it's not running. So you still have a way to earn the Darwin award. Always pull the disconnect.

| I remember as a kid, all my dad's apartment buildings had dual-pole | fused disconnects for the 240 V. loads. I wonder if these were safe?

Should be fine.

This is one reason why they say trained people should work on electrical equipment. There are far fewer mishaps that way. Electricity can seem like a sneaky sneaky beast some times. For one thing you can't see it. LOTS of people have gotten surprise shocks from equipment they thought/figured/assumed was "dead".

Breakers may be "safer" if lay persons are poking around into electrics. Fortunately 120V usually just 'hurts' and only occasionally kills people or burns down their buildings as a result.

The Code, here, calls for a disconnect near to the equipment and visible from the equipment. Or, failing that, a padlockable disconnect. There are many places where an electrical worker would get in serious trouble if found working on equipment without opening the disconnect or taking even greater measures (lock out - tag out).

Older residential installations used disconnects that allowed access to one fuse at a time. Newer installations have "pull out disconnects" Pull the handle and you pull both fuses.

If the person is less experienced then they should not be "playing with electricity" though a lot of people do.

Fuses are usually installed to protect the motor not the wiring. The circuit breaker in the panel protects the wiring to the disconnect. My last house had a pull out disconnect. Mostly because it was cheap. A lot depends on the load and the contractor if you get a fused disconnect. My new a/c is fed with a 50 amp breaker, the unit draws 16 amps, the disconnect has 20 amp time delay fuses per the manufactures requirements.

And 277V _really_ hurts (recalling the exposed voltage that was present on the "open door" button for over 2 weeks in an elevator in a college dorm I once lived in).

Was that their fitness incentive program?

|> | Breakers may be "safer" if lay persons are poking around into electrics. |> | Fortunately 120V usually just 'hurts' and only occasionally kills people | or |> | burns down their buildings as a result. |>

|> And 277V _really_ hurts (recalling the exposed voltage that was present on |> the "open door" button for over 2 weeks in an elevator in a college dorm |> I once lived in). |>

| | Was that their fitness incentive program?

More like lowest bidder maintenance contract.

It is terribly unlikely that there was 277 volt AC being used for control power in an elevator. Older elevators use 600 volts DC. Newer ones may use 480/277 for traction power but not for controls.

-- Tom Horne

I believe it is required by the NEC to have a disconnect by the offset/outdoors AC Unit., be it a fuse or disconnect box., I've seen those fused pull box setups around here and they are legal and safe,(though just the disconnect is fine with the overcurrent protection at the panel) This way you don't have to fiddle around inside looking for and turning the breaker at the inside panel off. It assures you (the ac service tech) have control of the Supply Line on the Spot. =AEoy

The meter read about 277 volts between the base behind where the plastic button used to be, and the panel frame.