60's-vintage motor overload heaters

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Original on the left, purchased replacement on the right.

Questioning whether these are equivalent for an old General Electric motor starter overload (CR106).

Seems like slightly different approaches to get a bimetalic bend effect when a specified current flows through each of these. One requires a resistance wire to heat the metal, whereas the newer one incorporates the resistance in the metal? Is that what?s happening?

Does the element do the physical ?tripping? of the OL, or do these do nothing more than generate heat which heats up the separate mechanism that opens N.C. contacts?

Thanks.

Reply to
DaveC
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All they do is generate heat. The part that is heated is in the block those things go in. That is where the actuall tripping goes on. It trips a small switch and if you look at the block they go in you will see the screw terminals for the actual switch. If you could turn them so they are outside the block, nothing would actually be heated and the switch would never trip.

If you look at the bottom of them, near the screw holes you will see a set of letters and numbers. That tells the rating of the heater (a chart will show the current range the overloads will trip at).

I think you will find that you have 2 that are of greatly different current ranges. The one with the wire is a much smaller current rating than the large flat one.

Reply to
Ralph Mowery

You are correct! (c;

With the wire: 5.46A; without: 19.8A.

So they are compatible (will work in the same OL)?

Thanks.

Reply to
DaveC

The main overload block is made to take a wide range of the heaters. It has been a while ( I retired about 4 years ago) but I think there were atleast 2 to 5 sizes of the GE overload blocks. The heaters from one size will not fit the other sizes. Each block will hold a lot of different size heaters.

The way they are most often uses is that you have the motor starter (relay) mounted vertically and the heater block is attached just under it. The heater goes from the bottom contacts of the starter through the heater and then out to the motor (load). You install the heater to match the current of the load.

The heater heats up something in that block that trips a switch in the block. That switch is in series with the motor starter coil and the stop/start switches and only carries the small current that activates the coil. Most often the motor will be 480 volts 3 phase and the voltage for the coil and switch will be 120 volts.

While the numbers I am giving out are made up as I don't want to look them up, you may have a size 1 starter rated from 1/2 amp to 30 amps, a size 2 rated from 20 to 50 amps, and so on. You install the heaters in that range to match the load.

Reply to
Ralph Mowery

Measure the resistances!

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John Larkin         Highland Technology, Inc 
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John Larkin

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