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Author Topic: Mystery panel device  (Read 5044 times)

Jonathan Johnson

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Mystery panel device
« on: April 14, 2014, 01:04:11 am »

There is an old (now out of service) electrical panel in my barn, built in 1940 as a dairy barn. (The panel was disconnected long before I bought the place in 2012 so I don't know any history beyond what I can deduce.)

One of the devices in the panel is pictured below. It is wired in series with a cartridge fuse -- the fuse is missing, but based on the size it would have been a maximum 30A. This device was on one leg of a 240V circuit.

The first picture shows it with the removable cover on. The window in the cover is mica, with an aluminum ring. It indicates that it is rated for 10A at 550V, is made by General Electric, catalog number 256928. It is protected by a patent dated May 7, 1918.

The second picture shows it with the cover off and the circuit "closed." The third picture shows the circuit "open."

There are four basic components:
  • The incoming feed is a coil of wire, approx. 12 AWG, 3 turns wrapped around then connected to...
  • ...a post approx. 7/32" (6 mm) diameter and 1+5/8" (42mm) long;
  • a U-shaped clip that holds...
  • a springy "tongue" against the aforementioned post.

None of the components seem to be ferric. Or at least a magnet won't stick to them.

I suspect it is an early form of circuit breaker, or maybe a fast-opening fuse, though I don't quite understand how it works.
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Jonathan Johnson

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Re: Mystery panel device
« Reply #1 on: April 14, 2014, 01:07:49 am »

There is an old (now out of service) electrical panel in my barn, built in 1940 as a dairy barn.

P.S. -- I hope you'll forgive me for posting something here that has absolutely NOTHING to do with audio/visual stuff. But it appears to me that there are quite a few electricians in the group who've seen a lot of stuff, so maybe there will be someone who knows what this it.
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Mike Sokol

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Re: Mystery panel device
« Reply #2 on: April 14, 2014, 03:02:42 am »

P.S. -- I hope you'll forgive me for posting something here that has absolutely NOTHING to do with audio/visual stuff. But it appears to me that there are quite a few electricians in the group who've seen a lot of stuff, so maybe there will be someone who knows what this it.

I believe it's a slow-blow fuse for a motor starting circuit. I did a quick patent search and came up with this: http://www.google.st/patents/US1265576

Here's some of the patent text for "an electrical cut-out". I don't see the listed illustrations for this patent, but that should be findable as well. It could be that the post is held in place by lead-tin solder in the little latching piece and the wire wrapped around the post causes it to heat up and melt from prolonged overload. Hence an early motor starting "time delay" fuse. I think I've seen one of these on a dairy farm back in the 60's when I was a kid. 

===================================

In some cases, also, it may be desirable to allow the motor 30 to be subjected to excessive currents for limited periods (as at starting or under special conditions of use), if only it can be insured that no such current shall continue long enough to be injurious. Now it will be apparent that the cut-out of Fig. 1 will always require time for the member 1 to heat up. before the circuit will be opened, the length of time dependingon the currents; and by a'proper design of the heater 7 and the other parts it is possible to make the heating characteristics of the cut-out similar to those of the motor with which it is meant to be used,-with a proper margin of safety, and thus to insure that the cut-out will always act before any damage can be done, no matter how light or how heavy the overload on the motor, and at the same time it is ossible to allow operation of the motor to e continued for a reasonable time under any overload it can bear at all.

What I claim as new and desire to secure by Letters Patent of the United States, 1s:-

1. An electric cut-out comprising an insulating support having a socket, a pair of terminals associated with said support, a relatively rigid contact member in said socket and means detachably securing it therein accessible at one side of the support, said member being in electrical connection with one of said terminals, a spring contact member secured to said support and in electrical connection with the other of said terminals, fusible means holding said spring contact member flexed toward said rigid member and serving to keep said members in electrical connection with one another, and heater means for releasing said spring contact member electrically connected between said terminals.

2; In an electric cut-out, the combination of an insulatin base having screw shell and center termina s, a spring contact member mechanically secured and electrically connected to said screw shell at one end and extending upward through an opening in said base, another contact member detachably secured to said base, and heater means carried by said detachable contact member and electrically connected between the same and said center contact.

3. In an electric cut-out, the combination of a base comprising insulating parts, center contact means serving to secure said parts together, and a screw shell having a portion clamped between said parts, a spring contact member having one end clamped between said portion of said screw shell and one of said insulating parts, and another contact member secured to said base, and a heater coil connecting said latter contact with the center contact.

4. A fuse member for an electric cut-out consisting of a metal yoke with a metal bar secured across its opening by readily fusible metal.

5. A fuse member for an electric cut-out consisting of a U-shaped metal yoke and a metal bar secured against the ends of the U by readily fusilble solder.

In witness whereof, I have hereunto set my hand this 30th day of April, 1915.
« Last Edit: April 14, 2014, 03:17:13 am by Mike Sokol »
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Jonathan Johnson

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Re: Mystery panel device
« Reply #3 on: April 14, 2014, 10:35:52 am »

The page you linked has Portuguese text. Here it is in English:

http://www.google.com/patents/US1265576

Patent image:

http://patentimages.storage.googleapis.com/pages/US1265576-0.png

It makes sense. It appears that the device I have is actually "blown" -- based on Fig. 2 in the image, the clip ("A fuse member for an electric cut-out consisting of a U-shaped metal yoke and a metal bar secured against the ends of the U by readily fusible solder") should be two pieces soldered together. In the case of my device, the smaller part of the clip is missing; the clip has been reattached in such a way as to effectively defeat the purpose of the device.

With the spring pressure of part 2, it ensures that the device opens immediately as soon as the "fusible solder" melts. And by opening quickly, it breaks any arc that might occur due to inductance.

The patent document describes the device as having an Edison-base screw-in shell. My device sports a pair of bolt-on terminals, and mounts to a ceramic backing plate containing wire lugs.

Now, I wonder where a guy could get a supply of replacement fuse links for this?
« Last Edit: April 14, 2014, 10:43:44 am by Jonathan Johnson »
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TJ (Tom) Cornish

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Re: Mystery panel device
« Reply #4 on: April 14, 2014, 12:58:21 pm »

Now, I wonder where a guy could get a supply of replacement fuse links for this?
I know you're kidding, but this is the modern replacement:
http://www.automationdirect.com/adc/Shopping/Catalog/Motor_Controls/Contactors_-z-_Starters_-z-_Overloads/Manual_Starters_-z-_Protectors./MS25-2500
or
http://www.amazon.com/Magnetic-Starter-Control-electric-definite/dp/B006LAYMWU

These use a similar heating concept for motor overload, and the push-button types are designed so the motor will not automatically restart in the event of power loss.
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Stephen Swaffer

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Re: Mystery panel device
« Reply #5 on: April 14, 2014, 01:20:46 pm »

Not to be picky, but the feature preventing restart on power loss has more to do with the "3 wire" start concept than with the overload unit.  Many overload units are actually "overload relays", so they do not actually break motor current, rather they affect control circuit much like pushing the stop button does.

With electronic overloads, such as the one Tom linked to there are different styles-including some that function as both overload and short circuit protection.  If you install one, make sure you understand how it works and how it should be wired.  I have seen more than one overload unit installed by "qualified??" people that because of an improper install would not protect the motor even once it tripped-because the relay contacts were not wired into the control.   

You can still get NEMA style overloads that use fusible solder in a resettable device-but you won't find them in very many new installs mainly because the electronic ones are much more convenient to set-and adjust properly in the event of a motor replacement with a slightly different current draw.  (Not sure how many people really worry about setting them properly-though they should!)
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Steve Swaffer

TJ (Tom) Cornish

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Re: Mystery panel device
« Reply #6 on: April 14, 2014, 01:25:58 pm »

Not to be picky, but the feature preventing restart on power loss has more to do with the "3 wire" start concept than with the overload unit. 
Agreed - two different functions.
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Jonathan Johnson

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Re: Mystery panel device
« Reply #7 on: April 14, 2014, 03:36:19 pm »

Now, I wonder where a guy could get a supply of replacement fuse links for this?
I know you're kidding, but this is the modern replacement...

Not quite kidding. I'd never actually put this device back in service, but in the interest of having a complete museum piece, an intact fusible link would be a nice.

I guess I could make one; I'd need to sharpen up on my metalworking skills and find some sheet copper of the appropriate gauge. The only metalworking tools I have are tin snips, a hacksaw, a grinder, and an arc welder. I never learned to arc weld; hopefully I'll get it wired in soon so I can practice. But I digress; I know better than to use an arc welder for making a fusible link.
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Re: Mystery panel device
« Reply #7 on: April 14, 2014, 03:36:19 pm »


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