What is hermetic refrigerant motor-compressor?
What is a hermetic refrigerant motor-compressor? It’s a combination consisting of a compressor and motor enclosed in the same housing. These have no external shaft or shaft seals, and the motor operates in the refrigerant.
What is the minimum ampere rating of the disconnect required for a hermetic refrigerant motor-compressor with a branch circuit selection of 30a?
Disconnecting means For a hermetic refrigerant motor-compressor, the ampere rating must be at least 115 percent of the nameplate rated-load current or branch-circuit selection current, whichever is greater [440.12(A)(1)].
What is the allowable rating for branch overload protection if fuse is used for a hermetic motor-compressor with a rated-load current of 37a?
Fuses sized for branch circuit protection only must not exceed 175% of the hermetic motor-compressor rated-load current or branch circuit selection current (whichever is larger).
What is a hermetic compressor used for?
It is used in domestic refrigerators to prevent leakages of refrigerant. It is used to supply air at constant low volume in high pressure applications such as in industrial operation.
How does a hermetic compressor work?
A compressor is said to be hermetically sealed compressor, when the compressor and motor operate on the same shaft and both are enclosed in a common casing. These types of compressors eliminate the use of crank shaft seal, which is necessary in open type compressors in order to prevent leakage of refrigerant.
What is hermetically sealed compressor?
A hermetic or sealed compressor is one in which both compressor and motor are confined in a single outer welded steel shell. The motor and compressor are directly coupled on the same shaft, with the motor inside the refrigeration circuit.
What’s the minimum percentage of the nameplate rated FLC that the disconnect means for a refrigerant motor compressor needs to be?
115 percent
The FLC ratings on the nameplate or the nameplate branch circuit selection current of the compressor and condenser motor, whichever is greater, must be used at 115 percent to size the disconnecting means.
What is slugging in a compressor?
Liquid slugging is the phenomenon of liquid entering the cylinder of a reciprocating compressor, a common cause of failure. Under normal conditions, the intake and output of a compressor cylinder is entirely vapor or gas, when a liquid accumulates at the suction port liquid slugging can occur.
What is slugging in refrigeration system?
Essentially, slugging is the result of trying to compress liquid refrigerant and/or oil, in the cylinders. Slugging indicates extreme floodback in air-cooled compressors and severe flooded start on refrigerant-cooled compressors.
How do you calculate maximum overcurrent protection?
Maximum Overcurrent Protection (MOP) In short, the basic MOP is calculated by multiplying the rated current of the largest motor times 2.25, and adding in all other loads of 1.0 amp or more that could be in operation at the same time.
What is hermetic and semi hermetic compressor?
Both “hermetic” and “semi-hermetic” refer to the airtight seals used to protect components. The goal is to isolate the main compressor and engine in a safe environment. This prevents the infiltration of dust and other contaminants that interfere with the operation and can make liquid slugging or flooding more likely.
How are hermetic compressors cooled?
Cooling of hermetic refrigeration motors is important to the efficiency and life of the compressor. In the past, two methods which have been used generally to cool hermetic motors are oil recirculation and refrigerant gas circulation, usually augmented by some type of centrifugal pump and/or fan within the unit.
What are the types of hermetic compressor?
Types of Hermetic Compressors One of the most popular types of the hermetically sealed compressors are the reciprocating compressors. They were the first to be used as the hermetically sealed compressors are still being used widely. These days the vane type of rotary compressor has become more popular.
What is a hermetic system?
What is the allowable rating for branch overload protection?
The maximum allowable rating for this device is 60A. The calculated 61A shall not be exceeded, so it must be sized down to 60A. This concludes the series on single motor calculations and the Code.
What causes refrigerant slugging?
Slugging can result in broken valves, broken head gaskets, broken connecting rods, and other major compressor damage. Refrigerant-cooled semi-hermetic compressors will often draw liquid from the suction line through hot motor windings in the motor barrel, which will assist in vaporizing any liquid.
What is the difference between slugging and flooding?
What is the difference between flooding and slugging? Flooding is a little liquid refrigerant reaching the compressor; slugging is a lot of liquid refrigerant reaching the compressor all at once.
What is compressor slugging?
Slugging is a short-term return of a mass of liquid, consisting of refrigerant or oil, or as a mixture of both. The slug enters the cylinders of the compressor instead of super-heated vapor. Slugging almost always occurs on startup, but a very rapid change in system operating conditions can also cause slugging.