# DPDT rating combined?

https://www.utvinc.com/switches/utv-inc-back-lit-dual-blue-dpdt-on-off-on-vertical-turn-signal-switch/

I want to use a few of the switches in the link above. They are double pole double throw and rated at 20 amps. I want to know if that is 20 amps on one side or 20 amps combined.

I want to run 12V electric fan override by flipping the switch to lets just say the up position.

I am thinking if they are 20 amps on one side I can wire both poles separately, run that wiring into two 25amp fuses and then combine the wiring at a 40 amp relay to send 40 amps continuous to the fan.

Unless they are 20amps combined then my plan will not work and I will be overloading the switch.

If I use two of the DPDT poles can I increase my maximum current rating? OK I was thinking of it backwards. Above is how I am going to wire the switch using it as a ground interrupt. Thank you for all the help.

• Question is confusing though. You mention using a relay... so why does the switch need to carry that much current.... ? Perhaps you need to draw up a schematic. Commented Mar 13, 2017 at 15:34
• Typically relays amperage rating is the business end, not the coil end. The coil will probably take <<1A. Commented Mar 13, 2017 at 15:35

Ratings like that are usually per contact.

However, that doesn't mean you can combine two 20 A contacts in parallel to get a 40 A switch. You can not count on mechanical contacts to share current equally. You especially can't count on them to open and close, including all the bounces, at the same time.

Imagine what happens when two switches in parallel open, particularly with a inductive load. One will inevitably open first. Since the other is still closed, the voltage will be low, no arc will form, and that switch will open even with a very small air gap. Now 100 µs later, the other switch starts to open. At this point all the current is going thru it. It will arc when the contacts first separate, but will continue to arc much longer than intended due to the high current.

Most of the wear on mechanical switches is when they open. Closing also causes some stress. Paralleling multiple switches isn't guaranteed to reduce these stresses on any one switch.

If you want to switch 25 A, use a 25 A switch. Or, control a relay or transistor with a smaller switch, with the relay or transistor rated for the full current.

Well.. here is the point....

Each contact is rated at 20A, however that does NOT mean you should tie them in parallel to get 40A.

Here is the reasoning.

Most of the AMPERAGE value of a switch has to do with life of the switch due to arcing at the contacts as the switch makes or breaks circuit.

However, unless it's your day to win the lottery, no dual pole switch EVER makes or breaks contact on both poles at exactly the same time. When closing, whichever contact makes it home first does the switching, the other just adds reinforcement later. Similarly, when opening, the contact that breaks last does all the switching.

As such, for a brief period one side will be carrying, and worse SWITCHING, the full current. When switching it actually reverts to a single pole switch.

So in effect, though capable of transferring 40A when closed, you can still only switch 20A.

HOWEVER: Your question is confusing. You mention a relay, but seem to be under the impression you need to send the entire load current through the switch. Relay current ratings are for the business end. The coil current is << Relay Rating Current. If for some reason your relay coil current actually IS 40A, which I seriously doubt, buy a better relay.

• <a href="s398.photobucket.com/user/cerial0411/media/…" target="_blank"><img src="i398.photobucket.com/albums/pp70/cerial0411/…" border="0" alt=" photo switch_zpslioylivj.jpg"/></a> I was thinking of this backward. I need to use the switch as a ground not to carry current. Above is a very rough layout on how I want to wire it. I am only using the one pole to run the fan/relay in the up and give ground to the auto thermo switch (that goes to the relay) in the down position. The other pole will run a second relay/thermo switch/fan. Commented Mar 13, 2017 at 18:58
• That link does not work, but yes, if the circuits are independent 20A circuits you can use both sides of the switch as you describe. Commented Mar 13, 2017 at 19:05
• Commented Mar 13, 2017 at 19:05
• @Cerial..just edit your question and click on the icon that looks like a mountain in the editor to add images. Commented Mar 13, 2017 at 19:06
• Found the answer with your guys help I just needed to draw it out. Thanks for the help Commented Mar 13, 2017 at 19:08

Typically, switch contact ratings are for each contact (pole).

EDIT: ...but, as others have pointed out, it doesn't necessarily mean wiring the poles in parallel is a sound solution.

• This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review Commented Mar 13, 2017 at 15:10
• @laptop2d, doesn't it? From what I can tell, the only question is if the 20A rating is for both contacts or each. Commented Mar 13, 2017 at 15:13
• It customary to either fully explain the question or just leave a comment, maybe put a little more information than just a one sentence answer which SE considers low quality. Like explain how or why the ratings can be combined. Thanks Commented Mar 13, 2017 at 15:20