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  1. #1
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    Question Control Panel Voltage

    I had my maintenance guy come in today and in conversation he mention something that I thought was worth looking into. He said a place was cited from OSHA for having high voltage at the at the operators finger tips, push buttons. I tried to find some documents relating to this but go lost in an ocean of OSHA jargon . I have to build some control panels in the near future and I was planing on using 110V push buttons and I want to make sure I am not in violation. I don't see why it would be but better safe then sorry as I know in some situation OSHA considers anything above 50V to be high voltage or not low voltage.

    Does anyone have any experience with this? Which OSHA regulation would cover this?

    Any help or knowledge is appreciated. Thanks in advance.

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    Ten years ago the national electric code,NEC, for home wiring said 50 volts or less is exempt from nec code. Thie means doorbell and furnace controls. But they stil lhave grouinding rules for tv and cable tv. I think also for phones. But the wirng and junctionws can be in the open.
    Bil lD.

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    Your maintenance guy is correct. You can be cited for having high voltage control circuits.

    You should probably start with OSHA 3075, Controlling Electrical Hazards. NFPA-70 will also cover some of the regulations that OSHA will deffer to.
    JR

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    In the UK if the panel needs a tool to gain access to the inside you can do what you want in side it. A tool could be a simple screwdriver. Else your TV set could not have any high voltages in it. Good practice though, says, secondary insulation should be applied to give the maintenance man protection against high voltages unlike TVs. This could be PVC tape applied by the maintenance man himself.
    I used to work in High power transmitters where DC up to 30 KV at 8 A was used. There was no possibility of gaining access while the kit was powered without taking off a panel with a tool.
    It is customary to have high (?) voltages at the operators fingertips in the UK, all our light switches run on 230V, The switches are rated for that voltage and are in a sealed enclosure.
    Frank
    Last edited by chuckey; 03-10-2014 at 12:46 PM. Reason: bit more added

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    Unless you have a real reason, it's best to just use 24VDC, it's what's expected in modern designs.
    If you use 110 VAC your LOTO and special tools requirements go up.
    Plus it's safer all the way around.

    I have been popped with 110 out in the field on old equipment, not a cool thing.

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    The only reason is convenience and simplicity. Everything in the box and down line is 110V.

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    I gotta agree with above, its almost definitely more a code requirement than anything else. Also worth adding, often 24v ac is just as viable a option as dc. Advantage is you can just use a little control transformer and ac rated relays.

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    Quote Originally Posted by sundewzer View Post
    The only reason is convenience and simplicity. Everything in the box and down line is 110V.
    Add a 110/24vac transformer and use contactors with 24vac coils. Problem solved.

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    Quote Originally Posted by jlevie View Post
    Add a 110/24vac transformer and use contactors with 24vac coils. Problem solved.
    I agree, and it is quite simple. My issue is everything is currently designed and accepted at 110V. I need to know if it legally required for me to change it. I can design to the 24V in the future but I don't have the man power to spare on a redesign, new drawings, new acceptance letters, ect. I have looked over the document recommended by JR but I can't find anything that say push buttons on controllers must be under 50V.

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    Quote Originally Posted by sundewzer View Post
    I agree, and it is quite simple. My issue is everything is currently designed and accepted at 110V. I need to know if it legally required for me to change it. I can design to the 24V in the future but I don't have the man power to spare on a redesign, new drawings, new acceptance letters, ect. I have looked over the document recommended by JR but I can't find anything that say push buttons on controllers must be under 50V.
    I don't want to sound crass, but . . .

    24VDC will make your machine far less apt to trigger a fine from OSHA - and when someone is able to bypass a safety contactor / guard door . . . and OSHA looks at your safety logic and gives you another fine . . . converting 24VDC circuitry to a suitable Category Safety System will require far less effort than trying to get a 110V safety system upgraded to a Category 1, 2 or 3 Safety rated system.

    We build dozens of large machine control systems a year employing 100's of pushbuttons, HMI's, PLCs, Drives, actuators, etc. Every single one is designed to CAT3 Safety Standards with redundant logic for all safety circuits. Putting anything new on a plant floor without these features is just asking to be sued out of existence the first time someone is injured on that machine.

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    Quote Originally Posted by sundewzer View Post
    I have looked over the document recommended by JR but I can't find anything that say push buttons on controllers must be under 50V.
    Another factor to consider is whether your customer has their own requirements for control circuit voltage regardless of NEC, NFPA, or OSHA. HP for example have their own specs for circuit design and wiring of equipment.

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    Different rules in different places.

    Lower voltage is safer thsn high.

    Also of note that if there are any voltages present when a panel is ooen you need 36 inches in front of it.

    No clarity on what voltage...coukd be 1 or 100 same rule applies.

    If "accepted as is" what does that mean?

    Purchasing agent accepted the bid or has engineering blessed it including safety?

    There are certian rules thst generally apply and for varying voltages for control panels there may be specific things that need to be done at some point.

    Maybe look at allen bradley web documents or other vendors to see if there is any standards they use to support their product.

    I would suggest locating actual osha documentation that requires you to change or that allows it as is and attach it to your design package.

    If you keep the high voltage I woukd assume interlocks and high voltage stickers ate in order at minimum

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    Quote Originally Posted by sundewzer View Post
    I agree, and it is quite simple. My issue is everything is currently designed and accepted at 110V. I need to know if it legally required for me to change it. I can design to the 24V in the future but I don't have the man power to spare on a redesign, new drawings, new acceptance letters, ect. I have looked over the document recommended by JR but I can't find anything that say push buttons on controllers must be under 50V.
    I can understand the cost of a redesign, but that would pale in comparison to the liability costs if your 110vac control system results in an injury.

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    Quote Originally Posted by Tony Quiring View Post
    If "accepted as is" what does that mean?

    Purchasing agent accepted the bid or has engineering blessed it including safety?
    We have sent all the documents for the system, including the control panel and the customer has signed them.

    I would suggest locating actual osha documentation that requires you to change or that allows it as is and attach it to your design package.
    I have been looking for this but have been unsuccessful in locating it. Any idea where I might be able to find it?

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    Quote Originally Posted by sundewzer View Post
    I have been looking for this but have been unsuccessful in locating it. Any idea where I might be able to find it?
    OSHA will defer to NFPA or ANSI on a lot of requirements. As Guru attested, everything must be redundant. There should also be provisions for lock-out, tag-out. You don't say what kind of a machine that you're building, but most machine stuff will come under ANSI B11 series. I have a hard time believing that you can't find some of the standards that will relate to this. Obviously, you didn't read 3075 yet or you wouldn't be asking
    29 CFR 1910.147 Control of hazardous energy - lockout/tagout
    29CFR 1910.333 Selection and use of electrical work practices
    NFPA 70, National Electrical code
    NFPA-70E Electrical standard for industrial machinery
    NFPA - 79 Electrical standard for industrial machinery - this covers the stops and E stops
    ANSI does allow some 120 VAC control voltages, but the secondarys must be isolated. Yours doesn't sound like it from your description
    ANSI/IEEE 518 also has requirements concerning electrical interference

    JR

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    JIC required that any control circuit leaving an enclosure could not be more than 120VAC. That which is inside a complete stand alone starter could be line voltage. One thing to keep in mind for using control voltages less than 120VAC is that 90 V is the minimum to provide reliable control using silver contacts. This has been shown through years of experience. The caveat is if you want to use low voltage for control, make sure the control is suitable for the application. Bi-furcated contacts, gold flashed contacts, wiping action and reed switches are some of the methods used to achieve high reliability at low voltage.

    Tom

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    Quote Originally Posted by JRIowa View Post
    OSHA will defer to NFPA or ANSI on a lot of requirements. As Guru attested, everything must be redundant. There should also be provisions for lock-out, tag-out. You don't say what kind of a machine that you're building, but most machine stuff will come under ANSI B11 series. I have a hard time believing that you can't find some of the standards that will relate to this. Obviously, you didn't read 3075 yet or you wouldn't be asking
    29 CFR 1910.147 Control of hazardous energy - lockout/tagout
    29CFR 1910.333 Selection and use of electrical work practices
    NFPA 70, National Electrical code
    NFPA-70E Electrical standard for industrial machinery
    NFPA - 79 Electrical standard for industrial machinery - this covers the stops and E stops
    ANSI does allow some 120 VAC control voltages, but the secondarys must be isolated. Yours doesn't sound like it from your description
    ANSI/IEEE 518 also has requirements concerning electrical interference

    JR
    I did read them
    29 CFR 1910.147 Control of hazardous energy - lockout/tagout
    Any equipment that can be turned on must be locked out

    29CFR 1910.333 Selection and use of electrical work practices
    anything over 50V had to be locked out

    NFPA 70, National Electrical code
    No specifics on control panels

    NFPA - 79 Electrical standard for industrial machinery - this covers the stops and E stops
    This one doesn't show up on in their list of digital products. But google found it and it has what I need!! It clearly states that controller circuits can not exceed 120V.

    JR you are my hero!!


    Knowing where to look is the hardest part...

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    Just remember, if you use 120 VAC, this has to be isolated from the rest of the circuit. There are different ways of doing that. NFPA and ANSI just say that it has to be done.

    CFR 1910 has not been changed in years. OSHA will deffer to "Accepted Industry Standards", which right now is the ANSI B11 series (metal working machines) and NFPA & NEC. Look through the ANSI stuff and you will more than likely find a standard to fit your machine. Robots and fully automated machinery are also covered. The final user of the machine is required to do a risk assessment.
    JR

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    Quote Originally Posted by JRIowa View Post
    Just remember, if you use 120 VAC, this has to be isolated from the rest of the circuit. There are different ways of doing that. NFPA and ANSI just say that it has to be done.

    CFR 1910 has not been changed in years. OSHA will deffer to "Accepted Industry Standards", which right now is the ANSI B11 series (metal working machines) and NFPA & NEC. Look through the ANSI stuff and you will more than likely find a standard to fit your machine. Robots and fully automated machinery are also covered. The final user of the machine is required to do a risk assessment.
    JR
    Can you elaborate on what you mean by 'isolated'. Do I have to have 2 different power sources? I apologize for my lack of understanding on control circuits. I will definitely look into ANSI B11, thanks.

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    This is quite interesting to me. 90% of the control podiums (operator podiums, away from the control panel) are 110 VAC.


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