shock in electrical panel learned something new

It still might be a good idea to ask the service people to come out and look the interface over. And be sure to ask if their fuses are late-model current limiting fuses or not.

So, now you know better for next time! :)

If you wanted, stick a rubber plug in the holes or just tape over them, but now you know they're there, you'll remember to keep hands on the nonconductive parts, so I'd not worry about it.

In my experience that can lead to an expensive retrofit.

Welcome back to the living.

And I'm warned.

You were right the first time. He should plug or cover the holes. He's not the only one who will use the box, now or the next owner's family.

What are current limiting fuses. I looked at a couple webpages and it didn't say. I thought all fuses were current limiting.

"A current limiting fuse is a fuse that, when its current responsive element is melted by a current within the fuse’s specified current limiting range, abruptly introduces a high resistance to reduce current magnitude and duration, resulting in subsequent current interruption."

For ordinary distribution panel there's no point. The fuse will open and protect what it's there to protect.

They're useful for motor starters, etc., ...

I had read that and didn't understand it.

So there will still be some current to the motor starter. What's a motor starter? ;-)

IDK what service people those would be, since what he's dealing with appears to be customer eqpt, not the utility's side.

Typically a relay but it can be anything that gets a motor going and may have some protection built in. A lot depends on what kind of motor you are talking about and the application. Some 3p starters are pretty sophisticated electronic circuits that bring them up slowly.

So why would you want some current to be still going through it if there had been enough to blow the fuse? There must be a short circuit so even the small amount of current will be going through the short circuit and it won't be enough to close the relay.

The same question for a starter like this.

This might be more than you want to know about time delay fuses. A motor pulls several times the normal current load while it's starting. A time delay fuse lets that extra current go through for a short period of time before it blows. But it cuts the current completely when it does blow.

It's used residentially and commercially for starting "stopping, reversing and protecting electric motor" devices, supports and disconnects, etc. You could have a pool on the premesis. An upstairs whirlpool? And you have a lot of welding equipment in your garage? Plus a sauna? You just got a steam bath installed. The Mrs. has the kitchen expanded for the catering service. This may all call for a 60 amp breaker.

While not technically correct, I refer to it as a one shot inverter or speed control. In the AC line are some SCRs or Triacs and a control circuit to drive them. They ramp the speed of the motor up slow and when it gets near full speed a relay usually pulls in to put the full voltage to it. Most often used in motors of 50 HP and up. We had them on some

The definition is really awful.

Current-limiting fuses can be particularly useful on circuits that can have high available-fault-currents. The fuse melts _and clears_ in less than 1/4 cycle (before the fault current rises to its peak). The peak fault current that gets through the fuse will be significantly less than for a fuse that takes a cycle to clear. The fuse will, indeed, limit the peak current when compared to a slower fuse. Nice diagram on page 17

Why is that important?

IMHO there is seldom a reason to not use a current-limiting fuse on power circuits.

==================================== A motor starter is very likely to have motor overload protection. In the good old days this was overload "heaters" that caused the starter to open on an overload. The "heaters" are available in a large number of sizes to tailor the protection to the specific motor current. The overload system is also designed for motor protection. Fuses aren't designed for motor overload protection.

Motor starters now may have electronic adjustable motor current settings. ==================================== IMHO the fuse pull-out originally had insulating plugs in the holes over the brass screws. That is why the screws are recessed. Even an incompetent manufacturer would not make pullouts without insulating plugs.

On Sun, 16 Aug 2020 12:01:51 -0700 (PDT), trader_4 posted for all of us to digest...

Any disconnect I ever saw had some kind of protective panel over the line side. It might be old and have fallen out or disintegrated. I saw a piece of cardboard shoved in one once. I'm sure Greg & Clare have other stories to tell.

It's a contactor with some added stuff.

The safety panel is in place.

The fuse block holds two cylindrical fuses, looking something like fat AA batteries. The fuse block pulls completely out if you need to change fuses or cut power completely - you insert it rotated while power is out. The fuses are hidden on the back side of the fuse block when it is inserted. There is no obvious way to do Lockout/Tagout or ZeroEnergyState or whatever OSHA calls it lately.

The fuses are held in copper clamps. The clamps are secured to the fuse block with large brass screws from the front side; the holes are a good half inch across and a finger can slip in.

I suppose it is possible there are little plastic caps made to fit those holes.

Here's an image online. It looks like the upper screw holes are sealed, which is a good idea because his thumb is in a risky spot otherwise:

You can take the block with you, hide it, etc. That prevents anyone from putting the power back on and killing you. But it does still leave the hole in the panel open and energized where some dummy could kill themselves, so it's not totally safe.

You would hope so. Like Tekkie, I never saw a disconnect where any live parts were exposed in anyway.

It looks to me like they put a raised block across the upper part as a comfortable spot for your thumb. You can't tell what's going on with the bottom two holes, I'd be surprised if they are not covered/insulated.

Interesting, but I wonder what that really means.