Square D heaters, sizing

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mefalk55

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:-?Hello all,
I took a look at the Square D overload chart and went cross eyed.
I have a 3/4 HP motor. Name plate 1.6 A at 440 V, 3 phase. Standard squirrel cage with internal thermal protection. The existing heaters are tripping 1 hour into operation of a room heater. The controller is mounted about 4 feet to the left at same level. The overload heater size is B2.65, square D contactor size 0. Oh, the service factor on nameplate is 1.0. Do I calculate at 170% due to internal thermal protection? Or should I calculate at 115% service factor? Does anyone have access to info. that could explain how to read the square D heater chart? I would appreciate any assistance.
 
mefalk55 said:
:-?Hello all,
I took a look at the Square D overload chart and went cross eyed.
I have a 3/4 HP motor. Name plate 1.6 A at 440 V, 3 phase. Standard squirrel cage with internal thermal protection. The existing heaters are tripping 1 hour into operation of a room heater. The controller is mounted about 4 feet to the left at same level. The overload heater size is B2.65, square D contactor size 0. Oh, the service factor on nameplate is 1.0. Do I calculate at 170% due to internal thermal protection? Or should I calculate at 115% service factor? Does anyone have access to info. that could explain how to read the square D heater chart? I would appreciate any assistance.
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From the sq d controllers I have worked on if you read the chart sq d has all ready added the % service factor in. So there is no reason to calculate any thing else into it. I have ran into situations where people have added to the heaters causing the heater to be so way over-sized the motor would fry before the heaters would take them out. The heaters may be doing their job and are trying to tell you that there is a problem with the motor. Put a amp meter on fan you could have bearings going out causing higher amp draw.
 
square D heaters

square D heaters

The Amperage is 1.5 amps per leg. No fluctuation , no noise and shaft free wheels for 30 seconds after de-energization. Motor bearings and fan shaft bearings are fine. I will hit it with an meg-ohm meter to check for leaks to ground or phase to phase on windings.
 
Square D Digest page 16-129.

1. Determine motor data
a. full load current rating
b. service factor

2. Motor and controller in same ambient temperature
a. All starters (except Class 8198)
1. For 1.15 to 1.25 service factor motors use 100% of motor FLC
2.For 1.0 service factor motors use 90% of motor FLC

3. Motor and controller in different ambient temperatures:
a. Multiply motor FLC by the multiplier in Table A.

4. Locate proper selection table from index pages 16-130 and 16-131.
a. The proper thermal unit number will be found adjacent, to the right of the range of full load current in which the motor FLC or resultant full load current resides.

Assuming you have a starter in its own enclosure, you should be using B2.40 thermal units. How hot is the room, is the unit heater blowing air on the starter? Are the mounting screws for the T.U. tightened correctly? Is it always the same T.U. tripping (look at the ratchet mechanism before your reset the starter)?
 
Heaters

Heaters

Your should require a heater almost 2.0 but I have found that when you are very close to the high end of the range (1.74-2.02 amps) you are better to go one higher. A B-3 will probably end your problem.
 
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