Proper melting alloy

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StitzieJ

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I am looking for a melting alloy thermal unit that will be used with a manual motor switch.

The motor's full load amperage is .4 amps (at .03" WG static pressure).

I need to use the type of motor starter that is single-pole, manual reset, NEMA 1, 1 HP Capacity at 115V/230V.

I believe the starter I should use is Square D 2510FG1, as it seems to meet all my specs, but the matching table that lists the appropriate thermal units by motor full load current (table 43) do not show for a motor with a full load of .4 amps (of course, it starts at .41 A, because life).

Does anybody know the melting alloy thermal unit I am going to need here? Preferably Square D, but if you know of a different fit, I'd be okay with that too.

Thanks in advance!
 
StitzieJ said:
I am looking for a melting alloy thermal unit that will be used with a manual motor switch.

The motor's full load amperage is .4 amps (at .03" WG static pressure).

I need to use the type of motor starter that is single-pole, manual reset, NEMA 1, 1 HP Capacity at 115V/230V.

I believe the starter I should use is Square D 2510FG1, as it seems to meet all my specs, but the matching table that lists the appropriate thermal units by motor full load current (table 43) do not show for a motor with a full load of .4 amps (of course, it starts at .41 A, because life).

Does anybody know the melting alloy thermal unit I am going to need here? Preferably Square D, but if you know of a different fit, I'd be okay with that too.

Thanks in advance!
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the difference between 0.4 and 0.41 is so small I would just go with it.
 
luckylerado said:
Is there a melting alloy thermal unit that is resetable? Those are one shot and done are they not?
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Yes, they are re-settable. Consists of a wheel with ratchet teeth and a spring loaded metal "plate". Wheel is held in place with solder. When the solder melts due to overload, the wheel rotates (due to the spring tension), releasing the "plate" and trips the contacts. When the solder cools, pushing the reset slides the spring loaded "plate" back onto the wheel, again holding it in place. But, why exactly, do you need a melting alloy. I'm pretty sure solid state O/L relays are available at that low of a setpoint. Maybe not. Melting alloy has a problem, in that if it trips too many times, the solder fails to hold the ratchet wheel and will not reset. The latching mechanism can also wear and fail to "catch" in the ratchet teeth. Pretty old techonolgy. Later thermals used the bi-metallic strip that flexes under heat and trips the latch. The main advantage of SS O/L's is that they are adjustable. No need to keep an inventory of heaters in stock. I think they're available for starters 00 on up.

http://www.schneider-electric.us/en...61526-motor-logic-solid-state-overload-relays
 
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petersonra said:
the difference between 0.4 and 0.41 is so small I would just go with it.
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Reason I am asking is because the specs say....

"furnish with thermal element at not more than 125% full load current of motor connected".

The chart I'm looking at already adjusts for that 125% when making a suggestion, at least I think it tells me that. I'm looking at the Square D Thermal Unit Charts, by the way.
 
StitzieJ said:
Reason I am asking is because the specs say....

"furnish with thermal element at not more than 125% full load current of motor connected".

The chart I'm looking at already adjusts for that 125% when making a suggestion, at least I think it tells me that. I'm looking at the Square D Thermal Unit Charts, by the way.
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You're correct. The 125% is figured into the Amp rating. I think "thermal element" is just their way of saying an overload that simulates the heating characteristics of motor loads. That's why thermal overloads were developed. Solid state do that as well. The .41 you mentioned is not an exact thing anyway. We had to test O/L relay back in the nuclear days and they had to be +- 10%. Most just barely made it.
 
meternerd said:
You're correct. The 125% is figured into the Amp rating. I think "thermal element" is just their way of saying an overload that simulates the heating characteristics of motor loads. That's why thermal overloads were developed. Solid state do that as well.
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Well, crap. That means the table I'm looking at starts product matches at .01 Amps higher than where I need it to be...

x(

looks like I'm calling Square D. Oh, joy
 
StitzieJ said:
Well, crap. That means the table I'm looking at starts product matches at .01 Amps higher than where I need it to be...

x(

looks like I'm calling Square D. Oh, joy
Click to expand...

Read the edit to my post...+- 10% if you're lucky.
 
So I can go with the one that is rated for .41-.45 amps then? I should clarify this is for an EPEC assignment, so I am not sure how strict they're gonna be here.
 
StitzieJ said:
So I can go with the one that is rated for .41-.45 amps then? I should clarify this is for an EPEC assignment, so I am not sure how strict they're gonna be here.
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In my opinion, you're still withing the 10%, so unless your motor is some exotic thing that needs extreme accuracy, you're good. But keep in mind, that any thermal device depends on ambient temperature, so if the environment could be fairly hot, the set-point could change. Also, if the motor current changes for some reason, you have no way to adjust the trip to allow continued use. I'd still check out the SS ones they list in the link. here it is again.

http://www.schneider-electric.us/en...61526-motor-logic-solid-state-overload-relays
 
meternerd said:
In my opinion, you're still withing the 10%, so unless your motor is some exotic thing that needs extreme accuracy, you're good. But keep in mind, that any thermal device depends on ambient temperature, so if the environment could be fairly hot, the set-point could change. Also, if the motor current changes for some reason, you have no way to adjust the trip to allow continued use. I'd still check out the SS ones they list in the link. here it is again.

http://www.schneider-electric.us/en...61526-motor-logic-solid-state-overload-relays
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It's a motor for an exhaust fan in Tampa, FL, according to the book.
 
StitzieJ said:
It's a motor for an exhaust fan in Tampa, FL, according to the book.
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Not to worry...unlikely it will draw full load even when starting. Any obstruction of the airway will drop current, not increase it. If it's lubed properly, you're golden. If you're concerned with the bureaucrats you'll be up all night. Motor overloading is pretty rare if the motor and load are sized right and maintenance is done properly. Just my nuclear Navy/nuclear power plant/water utility experience, though. My opinion is just that...my opinion.
 
StitzieJ said:
So I can go with the one that is rated for .41-.45 amps then? I should clarify this is for an EPEC assignment, so I am not sure how strict they're gonna be here.
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When I 'graded' EPEC I would expect that you would go beyond the EPEC literature and look at references like manufacturer's catalogs or on-line forums.

You need to determine if the .41A thermal unit will protect your .4A motor per the NEC. Different manufacturers have different ways of choosing thermal units. You need to know the one you are selling.
Look at a Schneider Electric Digest, like on page 16-135 in Digest 177. Now substitute your values for those in Example 1.
 
Looks like the "A49" that is good for .41 amps in your application is the smallest unit they make in that series. If it isn't small enough (I'd probably use it anyway as close as it is to what is needed) then you need to select a different controller that can accommodate the protection necessary.
 
kwired said:
Looks like the "A49" that is good for .41 amps in your application is the smallest unit they make in that series. If it isn't small enough (I'd probably use it anyway as close as it is to what is needed) then you need to select a different controller that can accommodate the protection necessary.
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No.
The OP needs to determine if the A49 thermal unit will protect your .4 motor and meet the requirements of the NEC article 430.

If you are choosing Square D overloads, follow their procedure. Do not use an Uglys book, do not use a Rockwell method. Likewise do not take what you know about Square D and try to select a GE device.
The overall concept is the same, but the individual steps is important.

By the way, there is a definitive answer and 'close enough' is not it. I will tell you it involves using the NEC 125% factor.
 
jim dungar said:
No.
The OP needs to determine if the A49 thermal unit will protect your .4 motor and meet the requirements of the NEC article 430.

If you are choosing Square D overloads, follow their procedure. Do not use an Uglys book, do not use a Rockwell method. Likewise do not take what you know about Square D and try to select a GE device.
The overall concept is the same, but the individual steps is important.

By the way, there is a definitive answer and 'close enough' is not it. I will tell you it involves using the NEC 125% factor.
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Okay, I couldn't find the power factor for the fan, but are you saying if it isn't listed it is most likely 125%? My specs say that the thermal unit melting current should be no more than 125% of the full load current. I know that means that so long as it melts at or under .5, that would satisfy it (.4 * 125% = .5). What makes this confusing is the Square D procedure lists the proper thermal units based on the full load amperage of the motor. Is there a more expanded version of this chart? I am looking at table 43 of the digest 177, like you mentioned. Trying to read the NEC book makes me want to bash my head into a wall.
 
jim dungar said:
No.
The OP needs to determine if the A49 thermal unit will protect your .4 motor and meet the requirements of the NEC article 430.

If you are choosing Square D overloads, follow their procedure. Do not use an Uglys book, do not use a Rockwell method. Likewise do not take what you know about Square D and try to select a GE device.
The overall concept is the same, but the individual steps is important.

By the way, there is a definitive answer and 'close enough' is not it. I will tell you it involves using the NEC 125% factor.
Click to expand...
My reply was assuming he was using the correct selection table for the application (sounds like it was sent with the controller - so the chances of it being correct table are pretty high, but can still be factors that may dictate using a different table). Using the correct table for the application will result in compliance with NEC requirements

If using the correct table for the application and the current value needed is not in the table, you basically need a different controller with a different possible current range for the overload elements available to it.

There are many tables in the Digest, you need to look at selection information at the beginning of that section to determine what table you need to use for your application. Same overload element has different amp ratings depending on conditions at the point of use.
 
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