I am in the process of procureing all the three phase electrical supplies for my new shop. The fused three phase disconnects are amazingly expensive while breakers of the same amperage cost a lot less. What is the difference?
Thanks,
Mike
please excuse my spelling.
Replies
The markets are different.
3-phase disconnects: much, much lower volume. Customer base much less price-sensitive. Result; much higher prices; Economics 101.
Mike,
Check out http://www.automationdirect.com. These are the best prices I have found on this type of stuff. Great service too.
Steve
There are many not so oblivious differences. On the technical side fuses and breakers have different trip characteristics. Some machine nameplates specify what to use and that then comes under code, and may have a safety / insurance implication or if it is going to be inspected. Also original and replacement fuses can be unbelievably expensive. Modern fusing can be very complex and proper selection is a headache. They do provide somewhat better protection but for a woodworking machine unless there are CNC controls or electronic speed controllers breakers should be fine. If in doubt call the manufacturer.
Good luck, KDM, retired electrician.
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Check HD for 3 phase disconnects. I was really surprised to find that they stock them. My neighbor needed both a single phase (2 pole) and three phase (3 pole), fused disconnect. There wasn't a very big difference between the two pole and three pole. We were building a 3 phase rotary converter for three phase for his bridgeport mill and lathe.
I agree with KDM. It all depends on the application. The most common breakers have pretty generic current trip ratings and are of the time delay type. This delay feature allows time for a short duration surge to dissipate, like you see when a motor is starting, before they trip. Fuses, on the other hand, can be installed that are slow blow time delay, fast blow, instantanious, and a number of other configurations to more closely fit the application at hand. They offer alot of versatility in matching more precise protection to the load but can also add to the materials cost.
In most cases breakers are fine and will give you less headaches down the road than fused disconnects (breakers can be reset; fuses have to be replaced and can also, over time, get loose in their clips. If your not certain what will best suit your needs, it would be probably a good idea to consult a qualified electrician before buying the materials.
Are the breakers in an enclosure? I suspect that the main difference you are seeing is that the fused disconnect is already in a can. Add a lockable enclosure (w/ability to lock out the circuit) to the breaker and I think the prices are going to come together some.
PS1
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