# Help with rotary switch configuration **URL:** \ **Category:** Factual Questions\ **Created:** [July 5, 2017, 11:03pm UTC](https://boards.straightdope.com/t/help-with-rotary-switch-configuration/790570 "2017-07-05T23:03:06Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [July 5, 2017, 11:03pm UTC](https://boards.straightdope.com/t/help-with-rotary-switch-configuration/790570/1 "2017-07-05T23:03:06Z")
I need to spec a rotary switch to read voltages from 4 sources. I am measuring a total of (6), 6vdc batteries hooked in series for a total of 36 vdc. I want to sequence a panel mount DC volt meter like this: Bank 1 (batteries 1 and 2 = 12 vdc) Bank 2 (batteries 3 and 4 = 12 vdc) Bank 3 (batteries 5 and 6 = 12 vdc) Overall (batteries 1 through 6 = 36 vdc). I know I need a 4 position wafer switch but am not sure how to spec the poles. Everything is non shorting when switched away from the meter. Do I need 4 wafers, or 2 wafers with 2 circuits each, or what? Dennis ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 5, 2017, 11:12pm UTC](https://boards.straightdope.com/t/help-with-rotary-switch-configuration/790570/2 "2017-07-05T23:12:12Z")
You need a double-pole, 4-throw switch. How it is arranged isn’t important. Something like this: > **[R20407RN02Q | Digi-Key Electronics](https://www.digikey.com/en/products/detail/c-k/R20407RN02Q/2043283)** > > Order today, ships today. R20407RN02Q – Rotary Switch 4 Position DP4T, Adjacent Contact 5A (AC), 500mA (DC) 125 VAC Through Hole from C&K. Pricing and Availability on millions of electronic components from Digi-Key Electronics. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 5, 2017, 11:35pm UTC](https://boards.straightdope.com/t/help-with-rotary-switch-configuration/790570/3 "2017-07-05T23:35:24Z")
> [@beowulff](#): > > You need a double-pole, 4-throw switch. How it is arranged isn’t important. > > Something like this: > > [R20407RN02Q C&K | Switches | DigiKey](https://www.digikey.com/product-detail/en/c-k/R20407RN02Q/CKN10134-ND/2043283) Good find. Just wanted to add… This switch is probably fine for this application if it is for a non-critical / hobby project. But I wouldn’t use it for a commercial or hi-rel application. Reason being… if the voltage signals are going to a voltmeter, then the signals are considered a “low-level/low-current,” and thus gold contacts should be used in the rotary switch. This switch has silver contacts; silver contacts can cause problems for low level/low current signals. (Note the “Q” at the end of the part number.) I would use the “B” version of this switch if you can find it. Or another DP4T switch with gold contacts. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [July 6, 2017, 12:48am UTC](https://boards.straightdope.com/t/help-with-rotary-switch-configuration/790570/4 "2017-07-06T00:48:50Z")
Thanks, guys, I figured DP4T would do it, but wasn’t sure how to specify that in the 14 selectable fields for ordered those switches! I looked for a gold plated contact but didn’t see any of them in stock. Dennis ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [July 6, 2017, 2:07am UTC](https://boards.straightdope.com/t/help-with-rotary-switch-configuration/790570/5 "2017-07-06T02:07:09Z")
I wouldn’t be too concerned about silver contacts. Rotary switches are inherently self-cleaning, due to their wiping motion, and even if they get a bit tarnished, the input impedance of your DMM is essentially infinite (20MΩ or better), so a little contact resistance isn’t going to matter. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [July 6, 2017, 8:19am UTC](https://boards.straightdope.com/t/help-with-rotary-switch-configuration/790570/6 "2017-07-06T08:19:09Z")
I don’t disagree. But the OP didn’t state the application. If it’s a commercial, military, or “high reliability” application, then gold-plated contacts must be used for all low-level signal paths, and silver (or silver alloy) contacts must be used for power circuits. If it’s not commercial or military then I wouldn’t worry about it. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [July 6, 2017, 7:20pm UTC](https://boards.straightdope.com/t/help-with-rotary-switch-configuration/790570/7 "2017-07-06T19:20:39Z")
It’s for a very critical application. My vintage golf cart. I did find a gold plated contact version in stock so what the heck, I bought it. Damn it’s small, only a half inch OD, gonna need my magnifiers to solder to it. I ordered a terminal block to make it easier and a shaft seal because of the possibility of moisture. Dennis