shock in electrical panel learned something new

It is more about being fast-acting than it is about the current it allows while resisting.

This isn't the best picture in the world but might serve the purpose.

That does make sense. I'll see if I can get a photo.

There was one curious thing.

This is the same shed I posted about before, where I pulled the disconnect lever, and still had hot outlets, so I had to pull the fuse block also.

Well, this time I didn't bother pulling the lever, I just pulled the fuse block, knowing that cut all the power.

Only it didn't. One of the lights stayed on. I guess I really should figure out how this thing is wired.

You were doing well up to this point. The fuses are not long because of

Most of the motor contactors are designed to have a way of 'blowing out' the arc when the contacts open as opposed to some similar looking relays (contactors) that are designed for resistance only loads.

In the same type of motor starter, many contactors will have a transformer across 2 legs before the contactor that converts the 480 to

The large relay in a motor starter is called a contactor.

If you are referring to the "high resistance" in the fuse definition, the definition is incredibly bad. CL fuses do not any intentional resistance other than the resistance of the fusible elements (which may be silver). See the definition in my other post.

The defining characteristic of a current-limiting fuse is that it melts and clears in a shorter time than 'ordinary' fuses - less than 1/4 cycle when the fault current is high enough to cause the fuse to current limit.

If others are deciphering the picture, the fuses are not installed an go in the open space toward the middle. The fuses are long because they are for 480V.

"Motor starters" almost always have an "overload" unit that trips the starter off (by opening the control circuit that powers the coil). The overload is at the bottom of the black blob (contactor) at the bottom. This overload uses "heaters" - one in each phase. There is probably a table on the door label for selecting the size of the heaters using the motor current. The black disc toward the bottom of the door pushes a post on the overload to reset it.

Fuses/circuit breakers don't provide overload protection - they provide short circuit protection. g posted an example years ago where a circuit breaker at the source of a motor circuit could be twice the wire amp rating (and the wire rating is higher than the motor full-load current). (Fuses sometimes are used - i.e. a 6 1/4 amp fuse may be used on some small motors.)

You really don't want single fuses to blow in a 3 phase set.

Most of the pump panels I've seen had a "Hand-Off-Auto" switch under the disconnect switch handle. Others had it on the right side of the panel. They all had some sort of switch for the contactor though. Do you suppose this one's switch is on the left hand side of the panel? I can't see the picture well enough to tell where the little red wires are going.

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The red/green buttons are start/stop; the round plunger in the door is reset...had hundreds of these and just a few years earlier versions in power plants -- have about three of them salvaged from the scrap heap when a retrofit went on but haven't found anything large enough yet to use them for -- the versions a few years earlier did have to separate start/stop buttons towards the bottom on the case; not sure just when they went to the integrated ones like this.

The contactor just isn't wired to the buttons in this picture...

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Oh. Here's link to a bunch more pitchures...

IMHO that is saying the same thing (with more detail).

Motor contactors have to be rated for the locked-rotor current, which is about 6 x the run current. Circuit breakers have to be rated for the available-fault-current.

I have seen pictures of high rated circuit breaker contacts with arc-chutes and magnetic blowouts. I haven't see that on contactors, but you likely had some real big motors where you worked. [you picked a great time to retire.]

Seems a little surprising there are not even start/stop buttons on the door in the picture. The only motor control is the disconnect.

Wouldn't work so well to run 480 coil voltage outside the controller (switches and sensors would have to be rated 480), and it would have to be fused. in both legs.

Everything I remember was 120V control like you describe.

(Sorry if this is a duplicate)

Not clear what you have.

A "main and range" 60A service used to be common. There were 2 - 60A pullouts, both were service disconnects. One was for an optional range (or anything else), and the other pullout fed the plug fuses (the rest of the panel).

My mother had a 100A service with 4 pullouts - all service disconnects. One 60A pullout fed the plug fuses. The other 3 pullouts (30, 30, 60) fed whatever.

If you have multiple service disconnect pullouts, some of the loads may be fed from a pullout other than the one for the plug fuses. A 15A cartridge fuse could be in a 30A pullout, or could be in a 60A pullout using fuse reducers.

These are versions of a "split-bus" panel. Note that with multiple service disconnects the service fuses may total more than the service rating. The minimum required service size is determined by a "load calculation"

======================== If I had a pullout with exposed screws, I would make sure the screws were tight and cover them with epoxy, preferably black.

I retired about 7 years ago from a small plant that had about 40 acers under roof and had over 3000 people there at one time.

Dealt with many things. From small motors you could hold in one hand to some around 300 HP. Not sure how how the big compressor motors were as I dealt very little with them. They operated on 4160 volts. They had fuses that were about 6 inches across and 2 feet long. The fuse in the primary of the control circuit that dropped the 4160 to 120 volts was about 2 inches in diameter and almost a foot long. Rated for only 1 amp,but 6000 volts.

Some of the big contactors that I dealt with were rated around 300 amps at 480 3 phase had 480 volt coils but there was an interposing relay that was fed with 120 volts to run outside the cabinet.

Some of the big resistance heaters that had 300 amp fuses and 480 volts had 3 contactors in series. One would pull in and about 10 seconds later the other would pull in. This was a safety so that if one contactors contacts welded together, the one that pulled in first not under load should release. They were both wired to seperate thermocouple safety switches to if it got too hot they would release and not have a thermo meltdown. We made ployester out of raw materials, so it could be a really bad thing if it all melted or caught fire.

That is a newer one. Notice how the switch that disconnects the power is red for on and green for off. Some asshole about 20 years ago decided that the green should stand for safe to open the cabinet and the red was danger the power is on and it is not safe to enter the cabinet.

I am not sure, but believe that backwards red and green came from a foreign country as the first time I remember seeing that was some foreign made equipment. Confusing as hell when you have a room that is about 20 feet wide and 75 feet long and there is a mix of the old and new. I got to the point that I did not pay the colors any attention.

Can not remember is any of the disconnects were up for off and down for on.

You can download the picture and change the brightness and contrast and see better. I don't see wires going anywhere but to terminals on the contactor. Putting a switch on the side would be dumb.

Looks like a stock motor control center that is to be modified by the buyer - maybe that is why there are no switches.

Agreed. It makes handling it just a little tougher if for no other reason. Some college boy with a tie tried to think. That old saying "Common sense isn't" comes to mind.

It sometims makes sense to have the start/stop buttons on the side. Think of it this way. If you have to work inside the box with the power on such as to check the current the motor is drawing you have the power going to the switch on the door. The door is pulled closed by the tension on the wire and hits your bare hand or face. Big shock hazzard.

It still burns me up that some asshole decided that the Green ment the power is switched off and it is safe to go into the box. For many years the green ment that the power was switched on and red ment it was off. Maybe ok if all new in a building, but a big CF when an older building is added to and you have some of each.

Yea - "small plant" ("You picked a great time to retire" is a delayed response to another recent description of your place.)

I think I said before - it sounds like an interesting place. Sounds even more interesting.

My experience is limited to irrigation wells and pivots. I can't imagine working in a big manufacturing plant and such. It's bad enough when someone gets creative in my world. They'd change something just to get by without thinking it through. I always thought the red and green was to mimic stop lights. Green is go, safe: red is stop, danger. I'm the tender of 65 though, so there's an awful lot I haven't seen.,

At one time there were around 70 electricians/instrument people in the plant deviced into several shops of around 15 men each and responsiable for a small area of the plant. There were around 100 mechanics devided similar. As the company down sized there were around 20 electricians for the same ammount of different equipment, but just not as much in each area.

We did have some that would just move wires around and change things just to get by. Then there was some major construction going onfrom time to time. Interisting to have to go over a few hundred wires in a cabinet to find out why things do not work correct. One of the more interisting things to me was very simple. A small set of scales would trip out a ground fault. It would work fine on another receptical in the same room. After a few others had looked at it, I was called. I discovered that anything plugged into that receptical would trip the GFCI breaker. To make a long story short, after about an hour,I found in a breaker box of about 20 breakers and some GFCIs that some nuckle head had just picked out a neutral wire and ran it to the 'faulty' receptical. Then took a while to find the correct neutral for that circuit.

I enjoyed much of the work except in two areas. One was the waste treatment area of the plant we had. Jut did not like working around the crap and smell, but the equipment was simple. Another was greasy and nasty.If I could have just worked on what I wanted to,I probably would have stayed a few more years, but retired at 62 from there.

I worked in a small manufacturing plant. We had a fire, and sprinklers discharged, as well as using hoses.

After we got the plant on line, we had electrical faults pop up every so often for more than a year. Rip out the old, run new circuits, throw the old wire in the burn pit, the maintenance foreman put a kid through college selling old copper.