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Topic Title: 125A 220VDC 4POLE CHANGEOVER SWITCH
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Created On: 01 March 2014 04:10 PM
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 01 March 2014 04:10 PM
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ptracey63

Posts: 5
Joined: 05 July 2012

Gents,
I am planning to install a manual 125A 220V DC 4 pole changeover switch.The aim is to enable switching from a battery set to UPS in normal operation(mode 1) to battery set to a Load Bank(mode2). I have found several suitable switches that switch AC circuits at 125A however, I am not sure of the AC type switch would be ideal for switching 220VDC.
I would be most grateful if anyone could advise of suitable model please.

Thanks
PTracey
 01 March 2014 08:47 PM
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JonathanHill

Posts: 225
Joined: 09 September 2002

Your suspicions are correct. You cannot assume any dc switching capability unless confirmed by the manufacturer. With dc, there is no zero-point crossing as in ac circuits, so inappropriate switching devices will develop an arc if switching dc, which will continue until some component self-destructs - potentially very hazardous to life, limb and equipment. Some switching devices may be rated for operation at 240V ac, but only around 24 - 30V dc (and only if the manufacturer says so!).

For higher voltages such as yours, you need a device with a large separation between contacts, and it'll probably incorporate a magnet blow out feature to cause an effective increase in the length of the arc path to aid extinction. In a previous life working with dc systems we frequently used contactors developed for electric vehicles (Albright is a manufacturer's name that comes to mind) . However, from a quick Google search, it seems like the usual suspects (ABB, Schneider et al) all have offerings. Suggest you follow this route.

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Jonno
 02 March 2014 04:57 AM
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ToniSM

Posts: 26
Joined: 21 November 2006

If I remember right the ABB, Schneider are a legacy of an original BHI design. As Mr. Hill has said they have blowout coils to draw the arc.
I will say now they weren't quick extinguishing the arc. The bigger ones opened with a hell of a bang.

Please be careful with them, I got burnt by a 220C DC breaker opening under load.

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Could there be a better way?

In theory yes, but in practice?
 02 March 2014 05:49 PM
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ptracey63

Posts: 5
Joined: 05 July 2012

Gents,
Many Thanks for your feedback it is much appreciated, the present battery set to UPS cabling configuration isprotected by a 125A circuit breaker which has a lock off facility and my intention was to install the 125A 220 VDC 4 pole between the said circuit breaker and UPS.I had considered writing an instruction that would prevent any major arc at the changeover switch.The steps would be as follows;
1. Isolate and lock off the main 125A breaker at battery end 2. Isolate and lock off on battery load input at UPS.3. Operate Changeover Switch from battery set to UPS( On 1) battery set to Load Bank (On 2) this process should prevent the heavy DC arcing? Many Thanks P Tracey
 11 March 2014 04:27 PM
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iie63674

Posts: 80
Joined: 17 May 2006

A procedure won't prevent anything unless you can ensure that it is followed. Could you interlock the switch with a contactor to remove the load current?
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