I am stumped! Need some help.

Discussion in 'Landscape Lighting' started by Lite4, Nov 26, 2009.

  1. Lite4

    Lite4 LawnSite Gold Member
    Messages: 3,170

    OK, here is my situation. I have 2 Unique H-force 1838 transformers that are blowing their primary fuses every night. I installed them in July and they were working flawlessly until Haloween, then mysteriously they both started to randomly blow primary fuses. Here is the info I have on these:

    Both transformers are equipped with 16 amp fuses.
    Primary voltage readings:
    Transformer 1 - 12.87 amps
    Transformer 2 - 13.6 amps

    All of the secondary amperages are ranging between 3.3 amps up to 13.2 amps on the individual runs and I have not had any issue with any of the secondary fuses blowing at all. So, I am not recording any shorts in the secondary side at all. All the amperage is as it should be.

    Both of these units are wired directly into the panel, and we had maybe thought we had a problem with inrush current because the length of wire between the panel and transformer was about 5'- So we added new 20 amp heating and air conditioning rated breakers and replaced the 5' wire with a 50' roll of romex between the panel and the transformer. Still blowing fuses.

    After talking to Unique about this they decided to send me two new transformers thinking there may have been an internal issue with the wiring around the primary fusing. Replaced those last week and added full panel surge protection to elimate the possibility of spikes and surges, but after 4 days I had a primary blow again. All the amp reading on the primary and secondaries are still normal- no detectable shorts.

    When we replace the fuse the units will run all night and go off at dawn with the photocell, but come the next evening they don't come on because the fuse is blown. Sometimes it will go two evenings before it blows.

    The units have the 16 amp slow blow glass fuses that come with them. We were even substituting 20 amp fuses and they were getting fryed also. I have never run into any problems like this where all the amp readings and loads on the primary and secondary sides were well within range and still have some gremlin killing my fuses.

    I will also add that these two transformers are completely isolated from each other. Each transformer is at a different entryway and on its on panel (power supply)

    Any advice here would be greatly appreciated. Thanks guys
    Last edited: Nov 26, 2009
  2. JimLewis

    JimLewis LawnSite Fanatic
    Messages: 6,855

    Well, Tim. You know a boat load more about lighting than I do. So I probably can't be giving you advice. But here are just a few thoughts. (I'm interested to see where this goes anyway);

    When I have issues that don't make any sense I just try to begin isolating things. That is, removing parts of the system. If the part I removed leads to stability, then there's a problem with that part.

    So first thing I'd try is to run just one of the transformers by itself. Leave the other one off. It doesn't make any sense why 2 on at the same time should be a problem. But I'd just do that as a test. Who knows?

    Next, I'd try to use another power source. That is, get a 20w or more extension cord and plug them into a power outlet somewhere around the house, rather then hard-wiring them. I'd be sure the outlet I wired them into wasn't on a circuit that was being used - or instruct the homeowners to keep whatever else is on that circuit "off" during my test.

    I'd keep thinking of things like this in an effort to try to isolate something that leads me closer to the culprit. So like if the extension cord trick worked then I'd suspect something was still wrong with my hard wiring.

    The other thing I wonder about is if you are overloading the circuit. I don't know much about electrical, outside of low-voltage. But I do have an electrician we use as a sub-contractor from time to time. I know he's told me that with a 20a curcuit you really got to keep the load under like 16 amps. So I wonder with a 16 amp circuit maybe the limit is more like 12. The problem with that theory is you said you replaced them with 20a fuses and are still having the problem. So then I am baffled again.

    I don't know. I just thought I'd share a few of my thoughts. I am anxious to hear with this problem is, though.
    Last edited: Nov 27, 2009
  3. JimLewis

    JimLewis LawnSite Fanatic
    Messages: 6,855

    I was just reading up online to see what the max. rating for a 20a and 16a circuit was. The info. I found just on a quick cursory search said that the general rule of thumb is no more than 80% of the breaker (fuse) for a constant load for 3 or more hours. So if you have a 16a breaker, then following this rule, your max on each circuit would be only 12.8 amps. 16 x .80 = 12.8. So that would explain the occasional tripping of the fuse.

    Still baffled about why it would trip a 20a fuse, though. Unless the wiring from the transformer to the panel isn't sufficient for 20a.

    p.s. they call this the "derating factor". On a continuous load (e.g. constant, more than 3 hours) you have to account for this "derating factor" of 80% max.
  4. JimLewis

    JimLewis LawnSite Fanatic
    Messages: 6,855

    What gauge wire is the Romex?

    Is the Romex going through a conduit at any point? If so, what size conduit and does each run of Romex go through it's own conduit or are they sharing the same conduit.
  5. INTEGRA Bespoke Lighting

    INTEGRA Bespoke Lighting LawnSite Platinum Member
    Messages: 4,102

    Baffling and no doubt frustrating. It might take some time but a process of elimination is probably best. Start with running both trans unloaded. Then load one up. Then load the second and not the first. Etc etc. Move through all the components this way until the issue is found.

    I hope the site is close to home.

    Let us know what you discover.
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  6. Lite4

    Lite4 LawnSite Gold Member
    Messages: 3,170

    Thanks guys,

    These transformers are in different locations (2 different entryways about a 1/2 mile away from each other on their own dedicated power source. The problem with running the transformers unloaded is that their are a few people in the community that absolutely freak out and threaten to sue and demand refund if the lights are not on, so the only unloaded test I can do is a short one during the day.
    If I am not mistaken the whole purpose of derating is to only load a transformer to 80% of it's capacity since the other 20% will be figuired in wire resistance.

    The next trick I am going to try is to perhaps buy 4 transformers and try to split the loads down even more. I can't think of anything else to try, even though I am below the rated amp ratings of the 1838 watt transformers.

    Just looking for something I may have missed.
  7. RLI Electric

    RLI Electric LawnSite Senior Member
    Messages: 381

    Frustrating for sure, I have had defective cable with a high resistant short circuit in it. Interior wiring (mc cable) and it was tough to find out. Only shorted when under load. Time for some detective work. Try taking the loads off and simply have 1 fixture wired to the secondary on each. Run that if it holds, continue the troubleshooting. Place one xfmr back on and run that if it trips go to your hub or distribution point and isolate one leg at a time. If you can, see if you can use a resistance meter and look out at the legs (with the fixtures) disconnected and see if there is a resistance. If it is happening on both, sounds as if it can be a cable issue or better would be if you have a couple of faulty fixtures or lamps. Time consuming and frustrating but at this point necessary. If you have a friend that works for a phone company as an install or repair guy, have them throw on the meter they use to check lines. They can look for high resistance shorts from leg to leg and leg to ground and they can also "stress" the line which can bring the trouble out if it is hiding. Just a thought.
  8. RLI Electric

    RLI Electric LawnSite Senior Member
    Messages: 381

    One more thought, check you line side power. If it is "browned out" meaning down this would raise your amperage and throw you over if you are at the limit.
  9. RLI Electric

    RLI Electric LawnSite Senior Member
    Messages: 381

    One more thought and I will stop. Any other issues in the house? They may have a loose neutral and the power company can help with that. If the neutral is loose your A and B phase voltages can spike and cause all sorts of troubles. Bad things happen when a neutral is compomised.
  10. Lite4

    Lite4 LawnSite Gold Member
    Messages: 3,170

    Thanks Bobby,
    I have metered everything on the primary and secondary and all of my amp loads are dead on where they are supposed to be. I was hoping to find a reading on my secondary side that would indicate a short so I could isolate it and repair it boom, problem solved. However, this is not the case. Furthermore, in the H-force all of the secondaries are individually fused for their different loads, so even if I did have a random short in my secondary runs it should show up by blowing a secondary fuse which would leave only that run dark and not kill the primary fuse and all of the power.
    From my assesment and that of two electricians on my crew we are scratching our head. We have isolated the secondary side with individual, inline secondary fusing which is not blowing any fuses, and we have added full panel surge protection, a new HACer rated breaker and a 50' spool of romex between the panel and the tranx for inrush, and yet they still keep blowing.......? What am I missing here?

    Just seems odd that they would work great for 3 months and then both of them start going at the same time within a couple of days of each other. Oh, we thought the local energy company may have kicked up the voltage in the area to compensate for the increased winter loads but the primary at the panels are 122 and 123 volts respectively.

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