Why do X-ray machines require large guage copper wire and cannot use aluminum.

Asked December 2, 2013, 6:50 PM EST

X-ray machines commonly take line power (i.e. 240 volt single phase), rectify it to DC {this involves clipping of the tops of the classic sine wave and feeding it into a capacitor bank}, Taking this DC power through an inverter to a high frequency AC signal that is feed into a modern small high efficiency transformer to a high voltage (125 killovolts) feed to the x ray tube itself. A typical X-ray has a momentary draw of 150 amps at 240 volts but for a few milliseconds during rectification the draw will be several hundred amps and 0 amps for most of the cycle { most of the cycle will be below the voltage stored in the capacitor bank} . Manufacturers specify all wire to be copper: they claim aluminum reacts to the harmonics and produces interference or chatter that disturbs the electronics in the system. Aside from resistance differences what properties of aluminum create chatter. Aluminum has about twice the thermoelectric effects of other metals but what is the problem as a conductor. The other mystery is why can the utilty company use a small guage aluminum wire to the meter then according to manufacturer's specifications a giant wire (i.e. 2/0 copper) up to the box by the machine where suddenly it's OK to use a wire guage 4 sizes smaller for 12 feet from the box (power disconnect) to the machine. Their explaination is induction but it defies common sense to use a very small wire for the first 10% of the total run and for the last 10% and a giant wire in between. All manufacturers require this so what is the science behind it?

Monmouth County New Jersey

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