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  • Emergency Lighting Question

    Let's see who can figure this one out.

    A 6 Volt (nominal) emergency lighting unit is being used for this. It is rated for a maximum load of 90 lamp Watts and will handle that load for a little over 90 minutes.

    On the unit there are 2 lamp heads and each one has a 9 Watt rated sealed beam lamp in it.

    I wish to add two remote lamp heads and each will have a 25 Watt lamp. The first one will be at a distance of 22 feet from the unit. The second one will be 15 feet from the first. What gauge wire should I can use to keep the Voltage drop to under 5.0% as per code requirements? Please answer this as a two part question. Unit to remote A and remote A to remote B.

    For safety there is a 15 Amp fuse inside the unit for the attached lamp heads and at the terminals for remotes there's a second fuse of 20 Amps. To put this another way there are 2 fused circuits for loads.

    Please remember this is a 6 Volt system and thus a 5% Voltage drop is 0.3 Volts.

  • #2
    Re: Emergency Lighting Question

    Just use 0AWG and it won't be an issue...


    Unit to remote A and remote A to remote B.


    8AWG and 12AWG respectively...

    Comment


    • #3
      Re: Emergency Lighting Question

      The power drawn by both 25 watt lamps is 50 watts, therfore the current drawn by both lamps is about 8.5 amps. If you are going to run 2 separate wires from the battery to each lamp, you can use #16 wire. If you are going to run from the battery to lamp 1 and then on from there to lamp 2 then you will probably want to use #14. Any larger wire size will be overkill!! Lou

      Comment


      • #4
        Re: Emergency Lighting Question

        Each 25W bulb will draw 4.167 A
        For the first 22 feet the wire will need to support 2 bulbs or 8.333 A
        The allowable drop is 5% of 6V or 0.3 V as stated
        If you use 12 AWG lamp cord the voltage drop at 22 feet for a draw of 8.333 A will be 0.2975 V (just in spec at the first lamp) 10 AWG would be 0.1867V drop.

        For the second run of 15 feet you only need to support 4.167 A
        If you use 16 AWG lamp cord the voltage drop will be 0.2554

        Taken individually it would appear that you could use 12 AWG to the first lamp and then 16 AWG to the second but that would result in a 0.5529 V
        drop at the second light which is almost double spec.

        So if we use 10 AWG to the first lamp we have to now be less than 0.1133 V
        drop over the second run of 15 feet which would require AWG 12 lamp cord
        with a drop of 0.1013 leaving us with only 0.012 V to spare. So it would be safer to go with Newman's AWG 8 and 12 solution to give you a drop of 0.2188 V at the second lamp

        If you home run each lamp assume 22' to the close lamp and 22+15=37' to the second you could use AWG 14 (0.2363 VD) lamp cord for the 22' run and AWG 12 (0.2500 VD) lamp cord for the second run of 37'

        I would suggest home runs. As I think you will find that 8 AWG is rather pricey

        Comment


        • #5
          Re: Emergency Lighting Question

          Thanks to everyone so far.

          I'm going to try doing this with a wire run from the unit to each remote. Doing this I can use #12 wire for both. Because of fusing, I really can't safely use lighter than #12. Newman's idea of using #8 and then #12 would work too. It's most likely the way I'm going to do this. Wire cost really isn't that bad for short runs and especially in that I already have both here and ready. All of this will be pulled through 1/2 EMT and there will be a 2 gang size recessed boxes so there's loads of room for wires and wire nuts. The SS plates are pre-punched for 2 heads, but the holes (square) aren't that big so it really won't matter.

          Don't worry. I'm not doing this by myself. A licensed Master Electrician is working on this too. There's lots more going on than just this one installation. We were mostly trying to find out who on this forum can think straight.

          It's way past time for me to shut up and quit barking so much on this forum. Off to my dog house I run.
          Last edited by Woussko; 03-30-2007, 05:15 AM.

          Comment


          • #6
            Re: Emergency Lighting Question

            NEC Articles 210.19 (A)(1) FPN No. 4 and 215.2 (A)(3) FPN No. 2 relate to this voltage drop business.
            It is fairly clear by reading this that it is intended to regard general load wiring.
            I think you will find that an inquiry to the local AHJ [authority having jurisdiction] will reveal that they will not consider the load leads of the battery-operated emergency unit remote heads to fall under this rule.
            I have never seen anyone use ten gauge wire for remote heads, much less eight gauge.
            The purpose of emergency lighting is to allow egress after power disruption.
            I don't think you will even find this in Mike Holt's forum. http://forums.mikeholt.com/
            Licensed Philadelphia electrician
            Philadelphia emergency lighting certification

            Comment


            • #7
              Re: Emergency Lighting Question

              One thing to remember is that my remotes have 6 Volt 25 Watt rated lamps in them. Normally we would use 7-9 Watt lamps on a 6 Volt system. This is in a pretty large room. I think that I might recommend the use of 12 Watt Halogen sealed beam lamps. They put out lots of good light. I have to agree with Robert that it seems almost insane to run #8 AWG copper wires for such. I think we can run 4 wires to the unit and connect each remote head to it's own pair. Doing this #12 wire should be fine. Actually #14 would work (I ran some tests) but our local code demands no lighter than #12 on a low Voltage DC system. When I contacted the manufacture of the emergency lighting units and remotes, they said they have seen cases where #6 wire was needed and used. I can see such, but would simply move the equipment first. Anymore there's no need to hide it. They do make some pretty nice looking equipment. Gone are the big gray boxes and what looked like 1930-1940 vintage gray farm tractor headlights. Actually that's what they used back then. Another better choice would be to change this over to a 12 Volt system. There are 24 Volt DC emergency lights but such are way beyond our needs for this room. I'm waiting for LEDS to take over in this useage. I bet I'll see it soon. I have seen them being used more and more for some pretty wild lighting applications. I really like the new LED EXIT signs. Low power requirements and they do last a long time.
              Last edited by Woussko; 03-30-2007, 11:14 PM.

              Comment


              • #8
                Re: Emergency Lighting Question

                Woussko needs to remember that this is not the place to post adds for companies or products. Bad Woussko Bad
                Last edited by Woussko; 04-05-2007, 04:12 AM.

                Comment


                • #9
                  Re: Emergency Lighting Question

                  There's a local electrical lighting outfit here where I buy can ligthts. I remember they had some high intensity LED lighting on display. They were something like 3"x4" flood lights if I recall corectly.

                  Comment


                  • #10
                    Re: Emergency Lighting Question

                    I am with Wilber on this one, I did not want to get into it, but I knew about the code not getting into low voltage drop. #14 will be just fine for this job, but if some other code requires min. #12 then OK, but #8 wire for this is out of the question as far as I am concerned! Lou

                    Comment


                    • #11
                      Re: Emergency Lighting Question

                      Originally posted by QROKING View Post
                      I am with Wilber on this one, I did not want to get into it, but I knew about the code not getting into low voltage drop. #14 will be just fine for this job, but if some other code requires min. #12 then OK, but #8 wire for this is out of the question as far as I am concerned! Lou
                      Are you guys basing your calculations on a 6V system?
                      You need to re-check your math.

                      The OP requirement was 5% voltage drop.
                      Based on standard copper conductor, with 2 25W lamps in parallel the current draw is 8.33A. Using 14AWG @ 22FT results in a ~18% voltage drop, and ~12% using 12AWG.

                      Comment


                      • #12
                        Re: Emergency Lighting Question

                        Actually Newman is the only person so far to get this correct. The max under load Voltage drop would be at head "B" and that must not be more than 0.30 Volts less than supplied at the unit. When I checked this out using a Voltmeter, it was found that running from the unit to head A, I really would need to use #8 wire if I then ran over to head B from A. The run to B would require #12 or heavier. I seriously doubt the rest of you kept in mind that this is a 6 Volt system.

                        If I did run wires to head B from the unit, then I could get away with #12 for both. My reason for running heavy wire to head A and then lighter to head B was so at not to need 4 wires going to the unit powering them.

                        In the end, it was decided to use 2 smaller units each having 2 lamp heads on them and having no remotes. It was less trouble to simply run power (same circuit as the other unit) over to where the second emergency light needed to be installed.

                        Comment

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