Switch for 3 phase motor

[Paul Alciatore]

I am not a licensed electrician, so correct me if I am wrong, but lockable disconnects are only required in a commercial/factory environment. In a home shop you still need a disconnect, but unplugging a power cord or a simple disconnect without a lock is OK, at least if it is at the machine or motor. Many home AC units are installed like this. Mine are. You may even be able to get away with it in some commercial/factory installations if the disconnect is right at the motor/machine.

+10

This is a HUGE area of mis-understandings.....

IF IT IS NOT LOCKABLE, IT AIN'T A DISCONNECT. and so it doesn't have to follow those rules..... but you DO need a LOCKABLE disconnect somewhere..... so you do not have to wire up the machine "hot", and so you can KNOW the machine will not be started up while you have your head and hands inside.

[macona]

I am not a licensed electrician, so correct me if I am wrong, but lockable disconnects are only required in a commercial/factory environment. In a home shop you still need a disconnect, but unplugging a power cord or a simple disconnect without a lock is OK, at least if it is at the machine or motor. Many home AC units are installed like this. Mine are. You may even be able to get away with it in some commercial/factory installations if the disconnect is right at the motor/machine.

I believe even in homes you are required to have disconnects. I see them for water heaters, hvac, hot tubs, etc.

[mike4]

Here in Australia we have to have a lockable switch located in sight of or next to the machine as even the plugin units can be reconnected by some well meaning person who cannot see that you are holding the hot lead in you hand while trying to reconnect it or what ever , with the obvious results.
Michael

[phil burman]

Domestic appliances plugged into wall sockets, no lockable disconnect. If you work on it you unplug it and while doing so make sure that little Johnny doesn't try to help with your electrical problem by plugging it back in again.

If the plug/socket is in the same room as the equipment I see no practical problem.

If the plug/socket is in another room where other people have access I would be somewhat more careful!!! How much more careful would depend on WHO had access. A rocky marriage and large life insurance might require that you cut the plug off before any intervention work.

Phil

[Black Forest]

"A rocky marriage and large life insurance might require that you cut the plug off before any intervention work."

No No! You get your spouse to hold the hot wire and YOU plug in the machine! uppps Darling. Sorry I disconnected the ground fault breaker. I'll go connect it right after I finish my coffee!

[J Tiers]

Domestic appliances plugged into wall sockets, no lockable disconnect. If you work on it you unplug it and while doing so make sure that little Johnny doesn't try to help with your electrical problem by plugging it back in again.

If the plug/socket is in the same room as the equipment I see no practical problem.

If the plug/socket is in another room where other people have access I would be somewhat more careful!!! How much more careful would depend on WHO had access. A rocky marriage and large life insurance might require that you cut the plug off before any intervention work.

Phil

Here in Australia we have to have a lockable switch located in sight of or next to the machine as even the plugin units can be reconnected by some well meaning person who cannot see that you are holding the hot lead in you hand while trying to reconnect it or what ever , with the obvious results.
Michael

I am not a licensed electrician, so correct me if I am wrong, but lockable disconnects are only required in a commercial/factory environment. In a home shop you still need a disconnect, but unplugging a power cord or a simple disconnect without a lock is OK, at least if it is at the machine or motor. Many home AC units are installed like this. Mine are. You may even be able to get away with it in some commercial/factory installations if the disconnect is right at the motor/machine.

Already covered........... the solution was developed LONG AGO. I am surprised it has not penetrated to OZ or (apparently) to other places as well. These plug covers are sold in the US by the same folks who sell the multi-lock OSHA compliant safety lockouts.... OSHA can be an abusive nuisance, but this is one area where the requirements are good.

Multi-lock means that several trades can lock out the disconnect (or equivalently, the plug cover) at once, the disconnect is not released until the last one removes their lock from the locking clip.

Obviously if the machine is unplugged, it is not powered and is safe to work on. The equivalent of a lockable disconnect is a lockable cover for the plug that prevents it being plugged-in.

[wmgeorge]

430-102. (b)
which says that a disconnecting means must be provided and shall be located in sight of the motor.
Doesn't matter what HVAC does, we are talking machine shop machinery, and safe practice
"Disconnecting" does not mean leaving a hot connection
Rich

Well I am (was now retired) a licensed electrician and a disconnect and motor control as pointed out by others are two different devices. A disconnect is required to remove all power from a circuit for both the controller and the motor. You can have it by the machine but a circuit breaker in a box remotely and out of sight of the motor can also be a disconnect if the breaker can be turned off and the box locked. It is in the Exceptions under (A) and (B) Controllers and Motor disconnects 430.102. In a lot of cases there can be two disconnects one for the controller and another at the motor for a work switch.

The plug and cord connections qualify as a disconnect and yes they can be locked. Small padlock inserted in the holes provided in the blades or they sell lockable covers for the plugs.

[jhe.1973]

I have a switch for a 3phase motor .5 kw. This switch puzzles me because on of the phases actually is passed through the switch directly to the motor. The switch has the other two phases connected and it allows me to stop the motor in the middle position and turn the switch either direction for CW or CCW turning of the motor. Does that seem correct that one phase is always going to the motor. There is no sound or buzz/hum coming from the motor when it is off but will something burn up in the motor if I use this switch?

Black Forest: Thanks for asking this. The responses have cleared up the same mystery for me.

One of my latest additions is a 2 head Barker mill and it has 2 factory installed switches as you describe. I didn't like the pass thru phase & bought drum switches that kill all the lines. I haven't has the time to replace the switches yet but I probably won't bother now that I understand the thinking for these switches.

While this topic of disconnects is up I'd like to ask the group, is it OK to use one disconnect for more than one machine? I'm a one man band w/shop so I only use one machine at a time.

It would seem to be alright seeing as how a locked breaker panel can qualify. But, I've been in trouble before 'cuz I used logic & common sense when trying to talk to code enforcers.

Thanks for any help.

[Rich Carlstedt]

Boy, talk about a thread gone haywire, quit killing the messenger guys !
Black Forrest wanted to know if it was safe to use a drum switch and have a live lead.
wmgeorge answered him professionally and accurately and it is appreciated.
My original response was that a means of disconnecting the power is normally used with drum switches .
I said nothing about plugging, nor do I care about contactors or fuses, nor plugs, or plugging
The point is you do not want a live winding in your motor when you work on equipment OR when you leave the shop, regardless of electrical codes, single phase experience, or other seemingly related issues !.
I have experienced fires in industry from grounded 3 phase motor windings (Yes, I know what a "Megger " is )
I would never have live fields in my shop.
Years ago, many machinery manufacturers used fuses on only two poles of a 3 pole circuit. they don't do that anymore. Guess why ?
I would not want anyone here on this thread to experience a shop fire and resultant loss or experience accidental electrocution .
Safety is never to be ignored
Rich

[macona]

Black Forest: Thanks for asking this. The responses have cleared up the same mystery for me.

One of my latest additions is a 2 head Barker mill and it has 2 factory installed switches as you describe. I didn't like the pass thru phase & bought drum switches that kill all the lines. I haven't has the time to replace the switches yet but I probably won't bother now that I understand the thinking for these switches.

While this topic of disconnects is up I'd like to ask the group, is it OK to use one disconnect for more than one machine? I'm a one man band w/shop so I only use one machine at a time.

It would seem to be alright seeing as how a locked breaker panel can qualify. But, I've been in trouble before 'cuz I used logic & common sense when trying to talk to code enforcers.

Thanks for any help.

Yes, you can use one disconnect but there is no point if you are plugging in the machine to the disconnect. No, you cant have all machines hard wired in to one disconnect.

No, a locking panel does not count. It is easily defeated. There are individual lockout clamps that go on the breakers themselves.