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Go Back   SailNet Community > General Interest Forums > Gear & Maintenance
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  #1  
Old 06-13-2005
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A/C Light switches

can anyone tell me why I can''t use a A/C light switch for a D/C circuit?
Got a wash-down pump (12V/20A) that I want to put a switch for in a potentially wet spot, so I''m looking at those exterior water-proof boxes and covers designed for house light switches...
I''d appreciate any input or leads for a 12V/30A light switch that''ll fit.
Thanks,
Oz
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Old 06-13-2005
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A/C Light switches

You''ve answered your own question.

Most AC switches are rated to either 10 or 15 amps. (Domestic lightswitches). A switch is a switch is a switch in terms of Ac or DC...but the amperage is the important part. Put too much amperage across a switch and either it will overheat form the metal contacts not being adequate or it will sometimes "bridge" so that when you turn the switch off, the thing starts to growl and glow blue and get hot while the item at the other end of the switch still tries to work.

So if you have a 30amp cirucuit, you need a 30 amp switch!

I''m guessing by the name that you are based in Australia. A company called Radio Parts tends to have the peculiar and heavy duty stuff that Dick Smith and the like do not. And there is always Whitworths marine...
As a suggestion, though, tr cruising around the Clipsal website first and see if anything pops up. If you find something note the number, then you can just get Middendorpe electrics to order it for you if they do not have it in stock.


Sasha
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Old 06-13-2005
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A/C Light switches

There IS a difference between switching AC & DC. Use only DC Rated switches on DC circuits, and only Inductive Rated Switches on Motor Circuits.

You need a 20 Amp Minimum 12V DC Inductive Rated (as opposed to Resistive) Switch c/w W.P “Boot”.

In AC circuits voltage and current vary in a sinusoidal pattern. The 60-Hz rate of voltage and current means they both cross the zero reference 120 times a second. Therefore, there is only a remote chance of closing or opening a switch when the voltage and current are at their maximum.

There is a different situation with DC circuits, however. The voltage and current in a DC circuit generally do not vary. They are always at their rated levels. Compared to AC circuits with the same voltage and current, DC circuits handle 1.414 times the power.

Sasha_V Is totally WRONG when he states that “...a switch is a switch is a switch in terms of AC or DC...”
And, in North America, domestic AC light switches are typically rated 15A or 20A @ 120VAC (not 10 or 15A).

HTH,
Gord May
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A/C Light switches

So are you saying that it''s in the construction of the switch that causes a problem? And what happens?
I was looking at the 20A switch (assuming that a switch was a switch), should I be dividing the 120V by ten to get them on par? That could explain where I was wrong in thinking that something that was rated at 2400W is actually 24W??
Attempting to jump through the ABYC and Jabsco hoops,
Oz "I just ran 40'' of 6 gauge"
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Old 06-15-2005
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A/C Light switches

Answered myself there again...
The problem that I''m having is that the words "FOR A/C USE ONLY" are stamped onto the switch.
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