On Sat, 25 Jan 2014 00:35:34 -0800, DaveC wrote:

Looking to provide switching for 1-phase, 220 AC, 1/2 hp motor that doesn't
include use of a contactor. I appreciate the need for precise current limit
(LRA) that a branch breaker can't provide.

So, I choose to not have a contactor but instead, this, which provides the
power-fail protection:

http://www.amazon.com/Woodstock-D4160-110-Volt-Paddle-
Switch/dp/B005W17HYY/ref=pd_sim_hi_1/191-4569239-2528519

This has a relay (rated 1/2 hp) that drops out on power fail, and has
external connections for additional e-stop mushroom switch. But no provision
for motor protection.

Would 2 precisely-matched (ie, to the 1/4 amp), slow-blow HRC fuses be
sufficient to protect this motor?

Thanks.

You have three options.

1 - Fuse block for 2 fuses. Slo-blow type.

2 - Overload Line heaters with control cicuit to kill the relay if either
one of the overloads trip.

To size the heaters or slo-blows you need a MAX AMP rating if possible, if
not then size it for the RLA or FLA times the service factor. Typically SF
1.15 If the motor is rated at 115/230 Volt 7.2/4.1 FLA and you are using
230 then use the 4.1 Amp times 1.15 or whatever the SF is. Size and buy the
heaters for the closest amp range above the amp rating of the motor. Fuses,
same thing, fuse at the rating or the next step above.

With the heaters you can reset them after they trip. (once you determine
the cause of the overamping.)

If your belt is too tight the motor can over amp. If your actual voltage is
200 not 220/230 get a buck n boost transformer. 200 is way to low, and with
cause motor failures, high energy costs and loss of HP.

By all means buy an amp clamp to verify operation especially after changing
belts. Many people over tighten their belts.

The third option, get a linecontactor, 2 pole with contacts on each pole,
and get the line contactor with an overload 2 pole heater block attached
directly to the line contactor. They are not that expensive and the control
circuit can also be routed through your switch.

Fuse blocks can be deadly as one might blow, but not the other, same with
single wire protection. With one line hot motors can go to ground on the
unprotected line and zap you into the next world ready or not.

This is not a place to take shortcuts.

The circuit breaker should be rated at least 20 % over the normal load on a
dedicated circuit. Do not fuse at LRA's I have seen motors get crisp at
half that rating, that is pretty much the same as no protection at all.

Next time post to an electrical Where you will find professionals in that
trade. I snipped the other NG's outside of woodworking.