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Old 04-25-2012, 06:43 AM   #46
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Central Air Condenser Disconnect


why can't we all just get along ok signing off enjoy guys...
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Old 04-25-2012, 08:19 AM   #47
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Hello All,

I'm a DIY'er for most things except things that I want perfectly done and I know my limits. My brother is a licensed Master electrician but has really only dealt with Commercial last several years - his company are commercial electricians who setup new building contruction etc..
Anyway, my wife and I are getting Central Air from our tax money this year. That project starts in two weeks. My brother is going to tie everything together for me (electrical) but I had to do the research and buy everything. The HVAC installer said I need a 30A 2P GFI breaker to a 30A disconnect on the side of my house. I have the breaker specific to my panel, 10-2 wire and PVC conduit, etc.

Question:
I did purchase a 30A fusible pull-out disconnect box and 2x 30A NOS type H fuses. Will this work? The condenser is a new Trane XB13 and I can't find any documentation stating it needs fusible over non-fusible.

Thanks,
~S
Use a simple disconnect, not a fuse or breaker.

Each fuse or common breaker (thermal) introduces a voltage drop since they use resistance to generate the heat to blow or trip. This wastes power and lowers voltage to the AC, thus it's performance however slightly.

Actually, buried in the NEC there is a limit on how many current limiting devices can be in some circuits just for this reason.

gerry
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Old 04-25-2012, 09:50 AM   #48
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~snicker*chortle~

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Old 04-25-2012, 03:40 PM   #49
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Removed text not needed for reply....
So your reply was ???
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Old 04-25-2012, 05:21 PM   #50
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So your reply was ???
"The only reason heater overloads are installed on large equipment is if the temperature goes below 32 deg". You asked.
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Old 04-26-2012, 02:53 PM   #51
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"The only reason heater overloads are installed on large equipment is if the temperature goes below 32 deg". You asked.
The three "opposed-question-mark" shaped devices in series with each phase going to the motor are called overload heaters. Each "heater" element is a low-resistance strip of metal intended to heat up as the motor draws current. If the temperature of any of these heater elements reaches a critical point (equivalent to a moderate overloading of the motor), a normally-closed switch contact (not shown in the diagram) will spring open. This normally-closed contact is usually connected in series with the relay coil, so that when it opens the relay will automatically de-energize, thereby shutting off power to the motor. We will see more of this overload protection wiring in the next chapter. Overload heaters are intended to provide overcurrent protection for large electric motors, unlike circuit breakers and fuses which serve the primary purpose of providing overcurrent protection for power conductors.

Overload heater function is often misunderstood. They are not fuses; that is, it is not their function to burn open and directly break the circuit as a fuse is designed to do. Rather, overload heaters are designed to thermally mimic the heating characteristic of the particular electric motor to be protected. All motors have thermal characteristics, including the amount of heat energy generated by resistive dissipation (I2R), the thermal transfer characteristics of heat "conducted" to the cooling medium through the metal frame of the motor, the physical mass and specific heat of the materials constituting the motor, etc. These characteristics are mimicked by the overload heater on a miniature scale: when the motor heats up toward its critical temperature, so will the heater toward its critical temperature, ideally at the same rate and approach curve. Thus, the overload contact, in sensing heater temperature with a thermo-mechanical mechanism, will sense an analogue of the real motor. If the overload contact trips due to excessive heater temperature, it will be an indication that the real motor has reached its critical temperature (or, would have done so in a short while). After tripping, the heaters are supposed to cool down at the same rate and approach curve as the real motor, so that they indicate an accurate proportion of the motor's thermal condition, and will not allow power to be re-applied until the motor is truly ready for start-up again.

Never heard the 32 deg factor. I see them all the time even when there is no way in h*11 that the space would ever reach 32 deg.

Just sayin
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Old 04-26-2012, 04:59 PM   #52
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Come on New You can't tell I was being a wise guy ? Your slipping.
Wow I thought you knew me better than that. 32 degrees has nothing to do with equipment heaters. Heaters are as described in your post and are sized by charts by each manufacture and equipment requirements.

Last edited by COLDIRON; 04-26-2012 at 05:26 PM. Reason: Changed text
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Old 04-26-2012, 06:38 PM   #53
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Originally Posted by newtech View Post
The three "opposed-question-mark" shaped devices in series with each phase going to the motor are called overload heaters. Each "heater" element is a low-resistance strip of metal intended to heat up as the motor draws current. If the temperature of any of these heater elements reaches a critical point (equivalent to a moderate overloading of the motor), a normally-closed switch contact (not shown in the diagram) will spring open. This normally-closed contact is usually connected in series with the relay coil, so that when it opens the relay will automatically de-energize, thereby shutting off power to the motor. We will see more of this overload protection wiring in the next chapter. Overload heaters are intended to provide overcurrent protection for large electric motors, unlike circuit breakers and fuses which serve the primary purpose of providing overcurrent protection for power conductors.

Overload heater function is often misunderstood. They are not fuses; that is, it is not their function to burn open and directly break the circuit as a fuse is designed to do. Rather, overload heaters are designed to thermally mimic the heating characteristic of the particular electric motor to be protected. All motors have thermal characteristics, including the amount of heat energy generated by resistive dissipation (I2R), the thermal transfer characteristics of heat "conducted" to the cooling medium through the metal frame of the motor, the physical mass and specific heat of the materials constituting the motor, etc. These characteristics are mimicked by the overload heater on a miniature scale: when the motor heats up toward its critical temperature, so will the heater toward its critical temperature, ideally at the same rate and approach curve. Thus, the overload contact, in sensing heater temperature with a thermo-mechanical mechanism, will sense an analogue of the real motor. If the overload contact trips due to excessive heater temperature, it will be an indication that the real motor has reached its critical temperature (or, would have done so in a short while). After tripping, the heaters are supposed to cool down at the same rate and approach curve as the real motor, so that they indicate an accurate proportion of the motor's thermal condition, and will not allow power to be re-applied until the motor is truly ready for start-up again.

Never heard the 32 deg factor. I see them all the time even when there is no way in h*11 that the space would ever reach 32 deg.

Just sayin
cut and paste?
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Old 04-26-2012, 08:09 PM   #54
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cut and paste?
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Old 04-27-2012, 03:44 AM   #55
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Come on New You can't tell I was being a wise guy ? Your slipping.
Wow I thought you knew me better than that. 32 degrees has nothing to do with equipment heaters. Heaters are as described in your post and are sized by charts by each manufacture and equipment requirements.

Sorry, had one toooo many ginger ales when I posted it
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