Results 21 to 36 of 36
07-27-2009, 08:06 PM #21
This is all taking place in my garage addition,just want to make sure Im doing things the right way the first time,if it was just single phase I wouldnt have a problem,but using the rotary phase converter and the 3 phase motors just has me messed up.
But thanks to you guys I think I have it sorted out now!
Thanks everyone for all of your input I really do appreciate it!!!!
07-27-2009, 09:50 PM #22
"Can I use a 3 POLE 100 AMP 240V DISCONNECT SWITCH and just change the fuses to whatever I need,or say it was a 660V disconnect could I still run 220V into it and use 220 fuses or am I way out of line here?"
Monarch supplied 600 volt 30 amp fusible disconnects on one of its models when ordered for 460 volts. When ordered for 230 volts a 300 volt 60 amp fusible disconnect was supplied.
If the disconnect is 600 volts, then it may be used on any voltage from 600 down. Just substitute the correct amp rating fuse.
If the disconnect is 300 volts, then, similarly, it may be used on any voltage from 300 down. Again, just substitute the correct amp rating fuse.
You may use any of the poles, at your option, but it is probably best to use A, B and C, left to right, and omit B if it is single-phase.
Lately, I have been wiring my VFDs for three-phase input even if it is used on single-phase.
What I do is wire from the load side of the fusible disconnect to the VFD with 12-4 (or whatever).
The line side of the disconnect has a 12-3 (or whatever) cordset and a single-phase plug. The middle terminal of the line side is not connected, and there is no fuse in the middle position.
In the future, all I have to do to change to three-phase line power is change the cordset and install the middle fuse. No other changes to the machine are required.
07-28-2009, 07:35 AM #23
Might be a dumb question here and truly showing my ignorance and inexperience but why can't the machin on and off button be the means of disconnect??? I have a home shop in my garage with a table saw(3hp motor single phase), mill(3hp 3phase), lathe(1.5 hp 3ph) and a few other 3hp machines. These all have stop and start buttons or levers.
Please educate me here as to why or if I would need this fuse lockout component on these machines to be safe.
07-28-2009, 09:40 AM #24
Catch 22: I question why you would use a 3 phase breaker @ $100.00 each + enclosure instead of using a 3 pole disconnect @ $50.00 including enclosure. Also each machine must have a disconnect in close proximity to the machine. This diconnect must have the ability to be locked out. The correct NEC way to do this would be:
Circuit breaker at the main supply panel for a single phase circuit to supply power to the phase converter.
3 phase power from the converter outlet to a 3 phase circuit breaker mounted in an enclosure. This protects the wire after the breaker. If a rotary converter is used then also run a 3 phase line from the converter outlet to the idler motor.
3 phase power from the 3 phase breaker - run a circuit to the machine locations and make connections to this circuit in paralell to each machine. You must cut the wire and use wire nuts for this.
Run the machine circuit wires in conduit to each machine and place a 3 pole disconnect at each machine location.
From the disconnect use flex or liquid -tite conduit to each machine.
Use fuses rated at 1.97 times the FLA rating of the motor.
Hope this helps.
07-28-2009, 09:55 AM #25
Imported, the disconnect code was put in place so that machines could be locked out for service or repair. The disconnect provides a positive way that the stored energy (in this case electricity) can be isolated away form the machine by means of the power on / power off lever, and the lever can be made inoperable by means of a safety padlock. Each mechanic or operator places their lock and tag with their name on the disconnect and the machine is then locked out until the last lock is removed. This is the lock -out / tag out procedure that keeps people from being hurt while working on machines. I will note though that a machine that has a twist-lock plug can be considered isolated from stored electrical energy if the plug is capped with a locking cover that will accept a lock-out padlock. Osha requires that all stored energy by removed from a machine and that lock/ tag out procedures must isolate all stored energy from the machine. This could mean electrical, pnuematic, hydraulic, mechanical or other forms of stored energy with potential to do harm to persons if released.
07-28-2009, 07:33 PM #26
Your environment is a simple home shop with one employee...you! Forget about all the 'lockout-tag-out' baloney...that's for the factory floor with multiple millwrights and electricians.
Anyway you can turn the machine OFF to change a blade or replace a drive belt in a one man garage/shop is just ducky. This means unplugging the thing or flipping the circuit breaker OR, just doing the fix without turning it ON!
Just remember that each machine needs some form of electrical protection just for itself. This can be a motor that has a built in thermal overload or a manual starter that has overloads (heaters), or a little enclosure that has fuses.
The breaker in the box might protect the circuit (wire) with a 20 amp breaker but your 7 amp saw needs protection closer to that 7 amp rating...way under the 20 amp breaker. Hence the individual protection at each machine.
I have a Hitachi 10 hp drive on a 40 amp circuit for my lathe. The lathe motor would be in flames before that breaker tripped, but the drive has a feature that I program to the load of the motor, so that's my individual protection for that lathe motor.
Fusing and circuit protection is a very big bag of worms, especially when you add NEC stuff and OSHA lockout stuff. For a home shop, follow the basics of wire size and ampacity and you can't go wrong.
07-29-2009, 04:35 AM #27
Great info. and I feel a little smarter now. I always make it a habit to unplug my machines when i'm down working them so it seems that would be just as good I guess.
I will get some overload heaters as I don't have those on my RPC panel. It also sounds like I need to get some for each machine as well.
What is the difference between an overload relay and an overload heater???? This RPC schematic that I have shows both of these in it.
07-29-2009, 07:16 AM #28
The overload relay is the actual tripping device. This plastic relay 'holds' the heaters themselves. The three heaters are in series with the motor leads and are sized for the motor current.
You purchase three heaters of the appropriate current range for the motor and screw them into the overload relay. If the motor works too hard and pulls lots of current, the heaters 'heat up' and this heat trips a thermal relay positioned nearby in the overload block. This opens a contact and drops the mag out!
07-29-2009, 08:28 AM #29
Sounds easy. Thanks for the info. and I will add these to my American Rotary panel. I'm hoping there is enough room in there. I guess this might be something I could hook up to the actual machine maybe since some threads I've read have mentioned that machines have heaters already on them.
02-13-2010, 03:52 PM #30
Not sure if I should start a new thread or try and revive this older one. Since my question seems to fit this thread, I'll ask it here.
I understand the need for a disconnect switch at the machine. However, the disconnect switches are usually referred to as "fused disconnects". It seems to me that the breaker at the panel provides protection for the wiring to the machine, and the motor starter provides motor protection and so additional circuit protection in the form of fuses in the local machine disconnect switch is redundant and not needed.
That's my question, are fuses in the disconnect switch really needed? Of course my question is based on economics as I already have a couple of unfused disconnect switches.
02-13-2010, 05:40 PM #31
What does a fuse in a safety disconnect box look like when it blows?
02-13-2010, 07:41 PM #32
A standard single phase panel can be be just fine.
Tie the power "Lines" in as usual, The breakers feed two lines to each machine.
Connect the generated leg from the RPC together with all the "third legs to the machines" within the panel box. Just one big "U" lug all taped up.
If the breakers are sized somewhere near right for the wire size, you will be protected
If you really want to protect the motors, Use motor starters with heaters at each machine.
A search of the web for RPC wiring will provide a picture and description of the scheme.
I can't recall which page at the moment.
02-14-2010, 03:38 AM #33
02-14-2010, 07:35 AM #34
02-15-2010, 10:58 PM #35
"Fusing and circuit protection is a very big bag of worms, especially when you add NEC stuff and OSHA lockout stuff."
Lockout/tagout kits are available for most manufacturer's panelboards.
One kit per breaker.
You only need these for machine feeders, and then only when there is no other means of lockout/tagout, such as a safety switch.
For 2 HP and under, a cordset and receptacle is acceptable for a disconnect.
I'll admit to using this method on my 3 HP Delta Unisaw, which is the extra-cost 24 volt control version.
02-16-2010, 08:05 AM #36
"Might be a dumb question here and truly showing my ignorance and inexperience but why can't the machin on and off button be the means of disconnect?"
A classic chicken before the egg situation.
You have to have line power to the "three-wire control station" in order to START or to STOP such a machine.
Therefore, such a machine must have power at all times, and that is NOT safe.
So, what these machines require is a disconnecting means.
The easiest is a fusible safety switch, for machines rated 2 HP and above.
The easiest is a receptacle and flexible cordset, for machines rated 2 HP and below.
Lockout/tagout devices are available for cordsets.
All safety switches have a provision for lockout/tagout.
Panelboard-mounted breakers often have a provision for lockout/tagout, available as an accessory item from the manufacturer.
In a simple home shop situation, where there are no employees and probably no possibility of a surprise safety inspection, a main feeder breaker to your shop with lockout/takout on that single breaker is probably good enough as all shop power may be removed at a single location, and then made tamper-proof for the duration of the repair actions.