"Ignoramus9394" wrote in message
...
On Thu, 28 Jul 2005 05:24:57 -0400, Wild Bill
wrote:
Yep, Carl is right about the protection considerations.

The overload protection devices aren't just to protect against the motor
developing a short to ground, they react to protect the motor from being
overloaded by a jam or machine malfunction/breakage, stalled or any other
condition that causes the current to rise to a point where the motor
would
be damaged/destroyed by the resulting heat in the windings.
The OLP's heaters are selected from a chart of currents for the specific
motor being used.
Some OLPs have adjustable trip settings so that heaters don't need to be
selected.
Each type of OLP will cause all 3 phases to be opened/interrupted.

Hm, I am confused. I agree with you on the need for overload
protection. I will install something, for sure.

What I am curious about is, can I simply use motor rated fuses on both
incoming 240V legs? That should provide all necessary protections for
the idler.

I do not mind installing an overload relay, as such, except that it is
a cost issue. Fuses are cheaper. (unless I can find something at that
junkyard). Realistically speaking, the idler is not going to bind. If
contacts to capacitors break, yes, I could have a stall issue, which
would be addressed by properly sized fuses.

A relay is more exciting and possibly a little more convenient (it is
resettable, I do not need to buy new fuses when a fuse burns out), but
in reality will provide about same protection.

Am I mistaken?

The OLPs are also available as a separate device, but are commonly
integrated into the overall starter/contactor box.

Yes, I saw some on ebay last night...

The best setup for an RPC would be a magnetic starter/OLP rated for the
size
of the RPC motor, and a separate (specifically sized) starter/OLP for
each
machine motor that's powered from the RPC.

Agreed.

Choosing not to use a second, separate OLP for the (usually) smaller
machine
motor will not offer any protection for the machine motor.

Agreed also.

i


I

Fuses can be expensive and overload heater type contactors are even more
expensive. If you use this RPC and tool fed by it, are used only when you
are "in attendance", you wont need any fuses, your 60 amp breaker will trip
before you burn anything up. If the 3 phase tool motor stalls for any
reason, just hit the kill button on the RPC.

Jerry