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Black Forest
01-14-2014, 02:32 PM
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?

wmgeorge
01-14-2014, 03:40 PM
Yes, it will work. Is it safe? Only if the person servicing it turns off the main power breaker or fuse box that kills all three legs. I am assuming the motor is internally protected in some way because otherwise you have no overload or overcurrent protection, especially on the leg that is "hot" all the time. Except for the 3 Phase branch circuit or motor circuit breaker.
To reverse a 3 phase motor only need to swap any 2 phase leads around, and your rotary switch does that.

Switching only 2 of 3 legs is popular on HVAC applications. Or only one of 2 hot legs for single phase 230 volt compressors.

RWO
01-14-2014, 03:45 PM
It's permitted now to control a motor as you see it. Having one phase always connected does no harm. It's just a cheap way to make a motor control. This is common on HVAC condensing units that run on 230V-single phase and 3-phase. They commonly have a single pole or 2-pole contactor. The sole advantage is that a ground fault on the passed thru phase will trip the overcurrent protection whether the motor is running or not. I don't know when UL and NEMA decided it was OK to do this. I'm sure there are some regulations on how the practice is applied.

RWO

Rich Carlstedt
01-14-2014, 04:02 PM
Switch is meant to reverse the motor, AFTER, a motor contactor turns power on/off

macona
01-14-2014, 04:58 PM
It also makes things cheaper when using a solid state control like a soft start. No need to switch three phases when killing two is just as good.

macona
01-14-2014, 04:59 PM
Switch is meant to reverse the motor, AFTER, a motor contactor turns power on/off

No, you can plug reverse, thats one of the huge benefits of three phase.

Rich Carlstedt
01-14-2014, 07:06 PM
No, you can plug reverse, thats one of the huge benefits of three phase.
True, but that doesn't mean you leave a machine with a 240 Volt hot motor lead!
Illegal to do so.

rich

wmgeorge
01-14-2014, 07:33 PM
True, but that doesn't mean you leave a machine with a 240 Volt hot motor lead!
Illegal to do so.
rich

Quote me a section of the NEC. Its done a lot on HVAC equipment.

J Tiers
01-14-2014, 08:45 PM
Sheesh.....

We got safety nannies everywhere! Misinformed ones....

You do NOT HAVE TO BREAK ALL HOT WIRES to control a motor. Not even under EC rules, and B-F is in Germany, where they are under EC rules, NOT UL.

Now, under UL/NEC rules, you DO have to have some sort of "disconnect" which DOES totally disconnect all power wires and allows work to be done on the machine. This can be a switch of a specified type (lockable) OR a plug and socket.... I assume the EC rules have a similar requirement.

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.

But a standard switch cannot be a disconnect, since it isn't lockable. So do not try to force a "switch" to work like a disconnect, there is no need.

Under EC rules, the symbol for the "on" and "off" cannot be the "I" and "O" unless all power wires are disconnected by the switch. But for regular switches all that is required is that they turn the item on and off...

What B-F has sounds like a standard "drum switch" of the type used for on/off/ reverse on single phase and 3 phase equipment.

jlevie
01-14-2014, 09:30 PM
Three phase is a four wire circuit. What you have sounds like a fwd-off-rev switch for a DC motor. It will reverse a three phase motor if one hot leg is wired through, but that leaves the motor hot when off. I know of no code that allows that.

As to posts stating otherwise. 220 single phase in the US, is 120-0-120 and requires a 2 pole switch or contactor with a through wired neutral. Reversing the two hot legs will not reverse the motor. To do that the start windings have to be reversed.

lakeside53
01-14-2014, 09:46 PM
Three phase is EITHER 3 or 4 wire circuits...

The switch is a typical fwd-off-rev drum switch.

The confusion is motor control with machine isolation - they do not have to be the same.

Jerry's post #9 spells out the code/issues.

Rich Carlstedt
01-14-2014, 11:26 PM
Quote me a section of the NEC. Its done a lot on HVAC equipment.

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

macona
01-14-2014, 11:43 PM
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

A service disconnect and an operator switch are two different things. What happens inside a machine is separate from the service to the machine.

J Tiers
01-15-2014, 12:21 AM
A service disconnect and an operator switch are two different things. What happens inside a machine is separate from the service to the 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.

rdfeil
01-15-2014, 12:29 AM
Rich I am going to stir this one time only...

You are both right and wrong. As stated by J Tiers and Lakeside, A disconecting "DEVICE", either a switch, plug and socket or other approved device, is REQUIRED as a DISCONECTING MEANS. The switch BF has is a CONTROLING device and therefore does NOT have to disconect all 3 phases to "Control" the motor or machine. The NEC and the EI and CSA all have very specific rules about electrical equipment and the way it is installed. A disconect is not nessisarily a control device nor is a control device nessisarily a disconecting device. An example refering to J Tiers post... If you unplug your machine and lock a cover over the plug you have met the requirement for a disconecting means. Npw would you consider pluging and unpluging your lathe every time you needed to start or stop it, of course not, you would use the "Control" switch. Anyway Rant off, the important thing is to be AWARE of your equipment and be safe.

Paul Alciatore
01-15-2014, 02:15 AM
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
01-15-2014, 03:00 AM
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
01-15-2014, 03:31 AM
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
01-15-2014, 04:25 AM
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
01-15-2014, 05:56 AM
"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
01-15-2014, 08:24 AM
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
01-15-2014, 09:03 AM
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
01-15-2014, 12:23 PM
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
01-15-2014, 03:40 PM
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
01-15-2014, 04:45 PM
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.