Gallery, Projects and General > How do I??

High Voltage Switches

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Darren:
I'm looking to make up an electrical control panel that will involve a couple of reversing switches.

Need to swap over two poles backwards and forwards.

I have one switch, but need another....but for 440-600V


Something like an intermediate lighting switch (that's a good tip for lower 240V use btw... :thumbup: )
Or a DPDT switch

Trouble is I'm having a job finding any rated at the higher voltages, any ideas ??

Current is not particularly high, it's just the voltage rating.

Bluechip:
Darren,

Had to do a similar thing years ago for a 400V 2/3 hp dc motor. Could not get suitably rated switches or relays either.

Had to do it with contactors. These are usually 440 VAC, or so. Fortunately had two going begging, they are NOT cheap.
The contacts had no rating for DC, but motor only took about 1.5A, so, what the hell eh?.

Diag attached. I think. Done from memory. You need to be sure that there is an effective interlock to prevent any chance of both contactors being energised at same time .. otherwise ' Phuttt ....  who's turned the soddin' lights out ? etc. '





Check diag. if you use it. Think it's OK, .... have been wrong before tho'. ::) ::)

Dave.

Edit  All my drawings slope to right, to let spare electrons drain away  :D

Darren:
Thanks Dave,

I can see how that works, might have to resort to such a thing if I can't find a suitable switch.

You wouldn't credit how hard they are to find. It seems these days everyone uses contactors and remote switching = complicated.... :doh:

What's wrong with a simple switch with the proper ratings.... :scratch:

Darren:
I found this, that might do it

http://uk.rs-online.com/web/search/searchBrowseAction.html?method=getProduct&R=2225936

Weston Bye:
Darren,
Switches for directly controlling voltages that high are seldom used, save for mains power disconnecting.  The issue involves arcing as the contacts open.  Most high voltage switching makes use of snap-action contacts to very quickly open and close the contacts to momomize arcing.  This makes the switch operating mechanisms necessarily cumbersome and require high operating forces.  Also, for safety reasons, the structure of the switch needs to provide physical isolation for insulation to keep the voltage or arcs from reaching the operator's fingers.

For these reasons most control panels operator stations use pilot-duty devices for pushbuttons, pilot lights and switches.  That is, lower voltages are used at the operator station to control relays, motor starters and contactors to switch higher voltages elsewhere in the control panel.

One notable exception is the drum switch typically used at the motor of a Bridgeport or other machine tool.  If you absolutely need to directly switch the high voltage, I would recommend this last option.

I have dealt with these issues for the last 35 years, 18 of them as a self-employed controls system contractor.

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