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#22610 - 02/25/03 07:21 PM AC motor control swtiches and DC.
Sandro Offline
Member

Registered: 12/30/01
Posts: 449
Loc: Stoney Creek, ON, Canada
Just thought I would re-toss this question out to any new members or lurkers in the forum. Since virtually all the manual motor control toggle switches (30 amp 2 pole) that I have come across are NOT rated for DC, does anybody know of a manufacturer that does have an AC/DC rated switch? What would happen if one used an AC switch to power a DC motor? The mechanical guys on the job say the switch should handle it. I emailed Leviton and all they said was 'our switches are not rated for DC'.

Any thoughts?

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#22611 - 02/25/03 07:39 PM Re: AC motor control swtiches and DC.
frenchelectrican Offline

Member

Registered: 02/06/03
Posts: 938
Loc: Wi/ Paris France { France for ...
can you please describe the dc motor and what voltage it will be and howmany horsepower it will be ???

you have to remeber the ac switch is not rated for dc appactions due the current flowage the dc go one way all the time and it will burn the concats on ac switches .

there are few manufactuers can make switch for dc appaction genrally is drum siwitch or mangatic contaters one of the two common appcation but please let us know what is the size and voltage on the motour you are working on


merci marc
_________________________
Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)


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#22612 - 02/26/03 04:28 AM Re: AC motor control swtiches and DC.
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
I wouldn't use an AC-only switch on DC. The arc associated with breaking a DC circuit is more difficult to extinguish due to the lack of the zero voltage point found an AC circuits.
DC contacts are heavier and have a wider air gap to help extinguish the arc.

Have you tried Allen-Bradley?

[This message has been edited by Redsy (edited 02-26-2003).]

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#22613 - 02/26/03 08:41 AM Re: AC motor control swtiches and DC.
SvenNYC Offline
Member

Registered: 08/19/02
Posts: 1685
Loc: New York City
If you're looking for an AC/DC switch that looks like a standard toggle walls switch I think Eagle Electric/Cooper still makes one.

It's catalog #777 for a single-pole tungsten filament lamp load rated switch (on-off) - 10A 125V "T"; 5A 250V

then there's also #784 and #787 which is 10A 125V; 5A 250V.

Are these the switches that used to go CLICK CLACK when you would turn them on and off? I have these installed at home (they're old though). Mine are Leviton.

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#22614 - 02/26/03 02:13 PM Re: AC motor control swtiches and DC.
Sandro Offline
Member

Registered: 12/30/01
Posts: 449
Loc: Stoney Creek, ON, Canada
Thanks for your comments so far.

The motors in question are 90VDC. There are a total of 12 motors each running a single conveyor belt, varying from 1/2hp to 1hp each motor.

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#22615 - 02/26/03 02:44 PM Re: AC motor control swtiches and DC.
CDN_ELECTRICIAN Offline
Member

Registered: 01/22/03
Posts: 75
Loc: Concord,Ontario,Canada
Some manufacturers have both ratings for disconnects.

One that comes to mind is a Square D class 2510/2511 or 2512 (these are Canadian product numbers and should be the same)

Something to keep in mind though is the rule relating to using a Manual Starter as a "Disconnection Means".
Both the NEC and CSA standards have specific rules about the use of Manual Starters as Disconnects.

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#22616 - 02/26/03 07:32 PM Re: AC motor control swtiches and DC.
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
Sven hit the nail on the head.

"AC-only" wiring-device switches can be slow opening because they rely on the zero-crossing of 60Hz current to extinguish the arc. DC doesn’t do this, so faster, "clunkier" switches are needed to work. Using an AC-only switch on a DC load runs the risk of not being able to extinguish the arc across the switch contact when opening.

"XOP" disconnect switches typically have a DC rating.

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#22617 - 02/26/03 07:33 PM Re: AC motor control swtiches and DC.
frenchelectrican Offline

Member

Registered: 02/06/03
Posts: 938
Loc: Wi/ Paris France { France for ...
ok the other question is the motoer is perment mangent or shunt wound type ( it can indefify by numbers of connetion at motor ) if straght pm motoer it will have only 2 wires but wound or shunt motours will have anywhere from 4 to 8 wires there and it will make a diffrence how it can be termatited to the disconnet switch

merci marc
_________________________
Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)


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#22618 - 02/26/03 07:55 PM Re: AC motor control swtiches and DC.
NJwirenut Offline
Member

Registered: 09/15/01
Posts: 816
Loc: Bergen County, NJ
If these 90 VDC motors are being controlled by solid state variable speed drives of some type, then I would NOT advise connecting a switch (DC rated or not) in series with the motor winding, unless specifically suggested by the drive manufacturer.

In an inductive circuit (like a motor armature), opening the switch with any current flowing will generate a HUGE voltage spike that can easily damage SCRs or transistors in the drive's power converter stage.

If you need a safety disconnect switch, put it in the AC supply circuit to the drive, not the DC armature circuit.

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#22619 - 02/26/03 08:45 PM Re: AC motor control swtiches and DC.
SvenNYC Offline
Member

Registered: 08/19/02
Posts: 1685
Loc: New York City
Bjarney,

I wasn't the one who said don't use the AC switch on DC. The credit must go to "frenchelectrician" and "Redsy." I just suggested a product out of a catalogue.

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