Page 1 of 2 12 LastLast
Results 1 to 10 of 18

Thread: class II supply

  1. #1
    Join Date
    Jul 2013
    Location
    Renton, WA
    Posts
    648

    class II supply

    Own home - Low voltage lighting,, using GE RR relays. After 45 years the class II 24 Vac transformer finally failed, internally shorted.

    45 years ago power electronics just about did not exist, now one can get a 85V-265Vac to 24 Vdc converter for $10 !
    Can set current limit to less than 1/2 amp on the unit to comply with class II, etc.

    Question is: Is the use of one of these NEC compliant? It is UL listed.
    I tend to interpret NEC to my own advantage (or ignore it altogether in some cases), but wondering how others would interpret this use. Standard cord plug-in, 24V output on external screw terminals.

  2. #2
    Join Date
    Oct 2007
    Location
    New Jersey
    Posts
    4,435
    Quote Originally Posted by junkhound View Post
    Own home - Low voltage lighting,, using GE RR relays. After 45 years the class II 24 Vac transformer finally failed, internally shorted.

    45 years ago power electronics just about did not exist, now one can get a 85V-265Vac to 24 Vdc converter for $10 !
    Can set current limit to less than 1/2 amp on the unit to comply with class II, etc.

    Question is: Is the use of one of these NEC compliant? It is UL listed.
    I tend to interpret NEC to my own advantage (or ignore it altogether in some cases), but wondering how others would interpret this use. Standard cord plug-in, 24V output on external screw terminals.
    If I understand you correctly, it sounds like you can set the power supply to operate outside the Class 2 limits. In that case I'd say it's not compliant because someone could change your setting. If I misunderstand what you mean, apologies.

  3. #3
    Join Date
    Aug 2004
    Location
    Northern illinois
    Posts
    15,508
    It is not a class 2 power supply unless it says it is.
    Bob

  4. #4
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,184
    170503-1139 EDT

    junkhound:

    I was under the impression that you operated more than one RR coil simultaneously. One RR coil has a resistance in the range of 50 ohms. Two ir more will be less than 25 ohms. Or approaching 1 A. I don't know the AC impedance of single coil.

    On my GE transformers I never load them with more than 500 ohms. Thus, if a switch gets stuck neither the transformer or relay coil will be burned out.

    Over a 50 year period I have had several switches get stuck closed, but no coils or transformers have failed.

    I much prefer the reliability of a simple transformer to a solid state power supply.

    .

  5. #5
    Join Date
    Jul 2013
    Location
    Renton, WA
    Posts
    648
    You have a good memory for old posts Gar!

    Yes, I operate up to 52 coils in parallel, one shot capacitor discharge sets the RR relays. Have about a total of 250,000 uF of Al electrolytics distributed at various places along the dc (35Vdc) line, rectified from the transformer to about 35 Vdc. Also need it to be dc for the extensive simple diode logic used for circuit control.

    At first suspected a capacitor or diode shorted which loaded the transformer, but nothing amiss except the transformer itself failed. Diode good, cap(s) good.

    Have done 'failure analysis' on class II xfmrs in the past, failure is usually that the windings were not potted sufficiently, and a shorted turn resulted from years of vibration due to 60 Hz magnetostriction.

    I'm assuming any AHJ inspector would say no, so will leave instructions for grandkids if any of them ever live here to throw a class II xfmr on the wall if they ever need AHJ inspection. Maybe make a sticker that says 'approved for ClassII use?

  6. #6
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,184
    170503-1615 EDT

    junkhound:

    You have about 5000 ufd per coil if all 52 relays are operated at once. I believe about 500 ufd is enough. T = 500 * 50 = 25 mS. At 5000 we have 1/4 second.

    I don't know how long one typically closes a switch to an RR relay.

    Have you had any switch failures actuating 52 relays at once?

    Also how much does line voltage drop when 52 relays are turned on at once?

    Depending upon how much discharge occurs you could have some large peak current loading on the GE transformer for recharge.

    If you added additional resistance in the charging circuit, then you could reduce peak load current on the transformer. With time limiting on discharge time to possibly 16 mS that would further limit the peak energy requirement per actuation of one or more relays at one time.

    .

  7. #7
    Join Date
    Jul 2013
    Location
    Renton, WA
    Posts
    648
    Only switch failures I've had are the copper leaf in GE switches becoming oxidized, bit of scotchbrite fixes that.

    Very seldom fire off all 52 at once, 4 or 5 at once a few times a week. The switches on anything more than 10 at once are 20A momentary dc rated toggle switches, not the GE type rocker switches.

    I figure the 24 Vdc supplies are electronically current limited, so no overcurrent concern.


    Ya know, I've never bothered to hook a scope up to a relay in the house to watch the current waveform, maybe should do that one of these days

  8. #8
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,184
    170504-1637 EDT

    junkhound:

    It appears that you and I are the only ones with RRs in our homes. iwire seems to work with RRs in what I suppose are commercial applications.

    I would think that many more electricians would get involved with RR relays because of their potential capabilities.

    I am amazed that you have had no significant problem simultaneously switching 10 RRs at a time with GE switches. This is roughly 5 A with a wimpy switch.

    At what current limiting level would you set a regulated DC supply? I would guess at 0.5 = I^2 * 50 or about 0.1 A as a high value. This would be about 5 V across a coil.

    .

  9. #9
    Join Date
    Oct 2007
    Location
    New Jersey
    Posts
    4,435
    Quote Originally Posted by gar View Post
    170504-1637 EDT

    junkhound:

    It appears that you and I are the only ones with RRs in our homes. iwire seems to work with RRs in what I suppose are commercial applications.

    I would think that many more electricians would get involved with RR relays because of their potential capabilities.

    I am amazed that you have had no significant problem simultaneously switching 10 RRs at a time with GE switches. This is roughly 5 A with a wimpy switch.

    At what current limiting level would you set a regulated DC supply? I would guess at 0.5 = I^2 * 50 or about 0.1 A as a high value. This would be about 5 V across a coil.

    .
    The relays are good for up to 20 amps resistive. Or are you talking about the 2XX series switches themselves? They are listed for up to 3 amps.

  10. #10
    Join Date
    Apr 2008
    Location
    Ann Arbor, Michigan
    Posts
    6,184
    170504-1915 EDT

    gadfly56:

    Yes I am referring to the control switch, RS2xx or whatever its part number might be, that switches the low voltage to the RR relay coil.

    In an RR specification I found there was mention of need for a 50 mS pulse. Using 50 ohms and 500 ufd I get a time constant of 25 mS, and I believe from memory this is sufficient to operate a relay. I need to run some controlled tests.

    I think it would be very rare for me to call a relay a switch. I would probably call it a relay contact, or relay output.

    In my opinion the price for GE RR relays is very high for what is there and what manufacturing costs should be. Even worse for the control switches. From a cost standpoint these components can not be justified. Only when function is considered can there be any justification.

    I believe the relay output contacts are rated 30 A resistive, and 20 A tungsten.

    .
    Last edited by gar; 05-04-17 at 07:43 PM.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •