Hi All,

I'm looking for some additional info please, on the Kraus & Naimer key-operated cam switch, possible p/n: CH10 A221 *FT1 – according to a short feature article about it in the UK's Pilot magazine, sometime back in 2018/19 (see image attached).

This switch comes recommended by 'Siggi' – a senior Rotax engineer and private pilot, who according to the article fitted one to his gliding club's 91xiS powered tug aircraft.

I'm posting a request here as I suspect CH10 A221 *FT1 is not the full part number, due to a missing designator for a spring-loaded return function from start position, according to datasheets at krausnaimer . com. The fact Kraus & Naimer custom builds cam switches only gives further reason to suspect an incomplete part number.

I've already read some of the pros and cons of rotary (key) switches being used in place of separate switches for power to EMU, Lanes A/B and Primary/Aux Fuel Pumps, however I'm still interested to explore this particular option as it appears to come (so highly) recommended by a Rotax factory engineer.

Disclaimer (esp as this is my first post here): I've no affiliation or business interests with any of the above-mentioned commercial entities or persons.


Many thanks for any info!


10061_1_krausnaimer_CH10A221FT1.jpg (You do not have access to download this file.)
  • Re: Looking for Details - Kraus Naimer Key Operated Cam Switch

    by » 3 months ago

    Hi Hamish

    Try this: https://www.krausnaimer.com/ca_en



  • Re: Looking for Details - Kraus Naimer Key Operated Cam Switch

    by » 3 months ago

    That's a tough one.  Kraus & Naimer's website isn't exactly user-friendly, and the datasheet for the CH10 series switch doesn't have a part number build-up chart.  That's the thing about something like a cam switch: no two applications are identical so there are no standard configurations.  Everything they sell is probably built to suit a customer.

    There are a few things about the CH10 switch that concern me WRT using it in an aircraft:

      - In the datasheet, in the "Size of conductor" chart in the middle of page 2, it shows a minimum wire size for "flexible" wire of 0.75mm² (18 AWG).  Elsewhere in that chart, it shows a maximum size for "stranded" wire of 2x 4mm² (10 AWG).  Is "stranded" wire different than "flexible" wire?  If so, then what's the minimum size for stranded wire?

      - Under "General Information" at the bottom of page 3 it says, "Use copper wire only. Do not coat the wire end with tin."  The Mil-Spec wire we all use in our aircraft (MIL-W-22759/16) is a tin-coated wire.  Is there a material incompatibility issue with the switch terminal plating?

      - The terminals on this switch appear to be screw-down crush plates for bare wire (or worse, just a screw), which aren't really suitable for a high-vibration environment like an aircraft.  This switch is clearly intended for use in a stationary industrial application.

    If you want a cam switch, it looks like K&N make other models that accept ring terminals.  One of those might be a better choice, as they could be installed following normal aircraft wiring practices and would be insensitive to wire type or size.

    If you do make a custom order from K&N, I wouldn't mention the word "airplane," as they'll probably refuse.  Just make yourself a chart that correlates each item with a circuit number...

    EMU = Ckt 1  |  Lane A = Ckt 2  |  Lane B = Ckt 3  |  Pri Pump = Ckt 4  |  Aux Pump = Ckt 5  |  Start = Ckt 6

    ...then list the circuit contacts that you need to be closed at each switch position:

    Pos 1 = Off  |  Pos 2 = Ckt 1  |  Pos 3 = Ckts 1, 2 & 4  |  Pos 4 = Ckts 1, 3 & 5  |  Pos 5 = Ckts 1-5  |  Pos 6 = Ckts 1-6 (spring return to Pos 5)

    If they ask what you're doing, tell them you're wiring the lights and dust collector in your woodworking shop!

  • Re: Looking for Details - Kraus Naimer Key Operated Cam Switch

    by » 3 months ago

    Hi all

    I will pass on the concerns and see if we can find someone who can give us an answer.  

    Regarding K&N, they were sued years ago over the filters on an aircraft accident.  Needless to say if you did not get it with Rotax and under a Rotax part number you assume the responsibility.  The rubber actually will have the name Rotax on it.  It is not a Rotax problem it is a US legal system issue that allows open ended lawsuits for everything. Same thing with spark plugs and other bits on the engines.   Just my rant on that part. 


  • Re: Looking for Details - Kraus Naimer Key Operated Cam Switch

    by » 3 months ago

    Hi All,

    Many thanks for your thoughts and suggestions Eric and Rotax Wizard.

    To address Eric's points and concerns, re 'min/max wire size' and 'Do not coat the wire end with tin':

    I suspect both arise from suboptimal translation of the original German language (Austrian) catalogs. Google Translate provides a better translation of 'mehrdrähtig' than the 'stranded wire' appearing in the English catalog, which should probably read 'multi-wire'; at least that makes more sense to my mind. Whereas the translation of 'Feindrähtig' to 'Flexible wire' is more appropriate than Google Translates 'Finely wired':
    | English Catalog | German Catalog | Google Translate of German Catalog |
    | Solid wire | Eindrähtig | Single-wire |
    | Flexible wire | Feindrähtig | Finely wired |
    | Single-core or stranded wire | ein- bzw. mehrdrähtig | single or multi-wire |

    "Use copper wire only. Do not coat the wire end with tin." – I interpret as a warning against tinning the ends of stranded wire with solder prior to assembly.

    I also agree with Eric that ring terminal style switches (Kraus & Naimer's 'CHRxx' Type) would be better suited to aircraft use than the CHxx Type. But as you'll see below, a German company is offering solutions using the CH10 Type. Kraus & Naimer also offer rotary switches with spade terminal connections, which I'd also have no hesitation in using, when used with Tyco/TE PIDG spade terminals or similar quality.


    I made some progress on two fronts in the last couple of days, in reverse order:

    2. Reading the Rotax 912i installation manual from this site – in Figure 3.18: Wiring Powerside (optional) (Section 24-00-00 - page 36 / pdf page 82/200) I found reference to a key switch!

    Visting the supplier mentioned on that page – rs-flightsystems.com, it turns out they offer custom built Kraus & Naimer key switches in a number of their Rotax engine management products,
    from a simple key switch:
    to the latest incarnation of their 'Engine Panel v3':
    – that's way more belt-and-braces than I'd want, but interesting to see and think through some of the design philosophy (excessively cautious as it may be). The Installation/Operating Manual (available at that link) gives a good overview and I'll cogitate on the logic over the next few days. In the mean time feel free to share your own thoughts.

    Whichever solution, the rotary switch and the part number shown in the magazine article image I originally posted, are both either completely incorrect or no longer the most appropriate item.


    1. I finally located the Kraus & Naimer English Main Catalog – not on the US or UK sub-sites, but on the BE(lgian) site, here:
    https://www.krausnaimer.com/be_en/catalogs - Welcome to Europe 😁

    Here's the beginning of the relevant (online catalog) switch section detailing the part number build-up:

    From the catalogs link above, I also grabbed the following:
    Catalogue 120: CG-, CH-, CHR-Switches: 10 A – 25 A
    Catalogue 101: Optional Extras and Enclosures
    Switch wiring diagrams pocketbook

    And from the eSwitch page I grabbed the Form for customized switch (sample)


    Page 6 of Catalogue 120 also details the part number build-up shown in the Main Catalog, just much less clearly.


    Lastly, a thought regarding the EMU circuit of a DIY custom rotary switch build, after Eric posted a suggested switch-logic chart (thanks Eric!):

    EMU = Ckt 1  |  Lane A = Ckt 2  |  Lane B = Ckt 3  |  Pri Pump = Ckt 4  |  Aux Pump = Ckt 5  |  Start = Ckt 6
    Pos 1 = Off  |  Pos 2 = Ckt 1  |  Pos 3 = Ckts 1, 2 & 4  |  Pos 4 = Ckts 1, 3 & 5  |  Pos 5 = Ckts 1-5  |  Pos 6 = Ckts 1-6 (spring return to Pos 5)

    Can anyone see any benefit to the EMU utilising a circuit on this hypothetical rotary switch? Considering the EMU is ON from Pos 2 to Pos 6 – i.e. any time the rotary switch isn't OFF, as long as the Battery Master is ON, why should the EMU remain unpowered, except for maintenance perhaps?

    In Figure 3.19: Wiring HIC Switch and warning lamps of the Rotax Install Manual (Section 24-00-00 - page 37 / pdf page 83/200) the EMU is shown powered via a switched circuit breaker. Equally, a regular aircraft circuit breaker would suffice – and of course be pulled any time maintenance requires the EMU to be de-powered with main ship battery or back-up battery powered ON.


    Thanks for any further thoughts,


    PS As far litigation issues and not telling manufacturers their industrial products are being used in an aviation environment; that is one aspect of the otherwise enviable freedoms of the US Experimental Aviation scene – as far as I can tell – that hasn't made its mark this side of the pond. Surprising perhaps, but long may it continue.

    Thank you said by: RotaxOwner Admin

  • Re: Looking for Details - Kraus Naimer Key Operated Cam Switch

    by » 3 months ago

    Excellent update, Hamish.  It looks like you're on the way to a workable solution.  I hope you'll report on what you finally decide, and if you do buy a cam switch, let us know which one, how you wire it, and how it works for you.

    Thank you said by: Hamish Mead

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