-------------------------------------------------------- Sorry Charlie, only the best get to be StarKist.
The motor and overload are in series and see exactly the same current.
BTW, at least 95% of all 3 phase motors are protected by an overload relay that is art of the magnetic motor starter used to control the motor.
Lew
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???????
Lew
Sorry Charlie, you're in the wrong ocean.
But NOT the same temperature. If it were a matter of current, motors wouldn't have Klixons.
Irrelevant. All fractional-horse motors are protected with Klixons, or similar.
>
Reduced airflow, perhaps???????
An overload relay and thermal protection are two different things - and this is a single phase motor
So much to be said for almost anything made 40 years ago in the US. You could take them apart and fix them. The trend is toward lowest cost and minimum amount of materials. Not so fixable. I tried to fix a motor start on a Sears washing machine not long ago. Not only was that not possible but the part was over $60 (not retail), on a used washer worth $80 used, not a good plan.
Seems like the right plan. I thought the switch was no longer available.
Sears parts departments used to be quite good, and relatively cheap. I believe much of that has gone by the wayside.
The switch assembly. Switch, box, cord, and plug and cover.
I am sure some where there is a replacement switch, that will fit in the box.
Not necessarily true either. I didn't look in detail at theat switch's specifications, but I believe it had current-sensing heaters in it matched to the motor size, similar to what a magnetic starter with overload protection uses.
Which will PREDICT temperature based on load, but cannot take into consideration reduced air flow and other factors.
Like most of what used to be good about sears
It has nothing whatever really to do with predicting the motor temperature, per se, it's simply overcurrent motor protection (as opposed to overcurrent _circuit_ protection that is the function of the breaker/fuse). Sizing is based on FLA and motor rating of how long is allowed before protection kicks in.
The devices have colloquially been called "heaters" at least in the US (I don't know about the frozen north jargon :) ) as they're just thermal links. Some are resettable bimetal strips (the builtin motor variety for example) whereas typical magnetic starter heaters are fusible links.
On 4/15/2014 9:22 AM, dpb wrote: ...
That is, yes, the motor ratings are generally based on what the internal insulation and all will stand as temperature overloads but that is protected against by the current draw and manufacturers' ratings with the presumption of proper installation, cooling, maintenance including removal/prevention of dust buildup, etc., etc, etc., ... so that by limiting the current draw within the expected time the internal temperatures will not reach danger levels.
I've used the 'motor rated' switches that look like a typical wall light switch for an old 3/4 HP table saw. These have the red/black body and are reasonably cheap. They don't last forever though (I've eaten up 2 over the years with light use)
-Bruce
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