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Blew a 300 amp fuse
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My former company made the power pedestals we connect to for shore power. We produced them under our own name as well as private labeling for 3 other companies. We literally bought tens of thousands of circuit breakers annualy and dealt directly with the manufacturers of those breakers. Every breaker manufacturer said they would handle 80% of the rating all day long, but beyond 80% of their rated loads there was no confidence they would not trip.
That’s what we were told and that is what has guided me. I have not looked at the UL standard for breakers so I don’t know if the reason that statement would be made was that the breaker certification test had zero tolerance for tripping beyond the rating or if there was an allowable range for tripping that went below the rating.
I don’t know how all transfer switches work so I won’t try to describe the mechanical aspects. I do know the inverters themselves have a delay upon power up. I do know when connecting to shore power there is a brief delay in the transfer switch. I do know when connected to shore power and with the generator started there is a delay. On my coaches the auto-start on low battery voltage or shore power interruption is a selectable feature and I never used either because I store the coach in my garage and did not want to risk generator operation in the garage. My point being those features are not a given.
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Another good reason to make sure that you shut down your major electrical loads, including AC units, prior to switching power sources is to minimize arcing between the switching contacts within your inverters.
Contacts that are “dirty” with arcing deposits will eventually prevent your inverter from working properly, most likely when you need it most……far from home…..in a dark and lonely area….
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Jon,
We’ve been down this path before on how much current a circuit rating can carry. They can carry 100% of their rating up to 104 degrees. I thought it was 125 degrees. So, it’s entirely possible for a pedestal to exceed 104 degrees and the breaker become derated. Here’s what I said before.
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I used to state the 80% rule like you do until someone called me on it. My basis for stating the 80% rule is that is what my power production team’s used as their criteria for circuit breaker replacement during our annual inspections. These were critical Air Force telecommunications facilities, so we would always err on the side of keeping the plant operational. After I was called on this I discovered I was more wrong than right.
Here’s what I discovered:
“To meet the requirements of Underwriters Laboratories Standard 489, molded case circuit breakers are designed, built, and calibrated for us on 60 Hz ac systems in 40°C (104°F) ambient temperature. When applied at ambient temperatures other than 104°F, the current-carrying capacity and/or trip charasteristics of the circuit breaker may vary.”
If you take for example Square D’s specification, http://ecatalog.squared.com/pubs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QO-QOB%20Circuit%20Breakers/0730CT9801R108.pdf you can see that a breaker is not suppose to trip until it reaches it’s stated current rating as long as it’s temperature doesn’t rise above 104 degrees F.
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In the case of Square D even at their highest rated temperature, 140°F, it appears capable of about 45A or 10% below it’s UL rating.
Yes, at 80% of a breaker’s rated load carrying capacity it shouldn’t trip nor should it trip at its rated capacity if its temperature is less than 105°F. When you have the greatest need for power is when it’s the hottest outside, so beware that you may only get 45A or so from the pedestal breaker.
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Isn’t that what I said? In the summer you cannot put your hand on a power pedestal after if has been in the sun. Your tolerance level may be around 115F.
But I don’t care what the trip point is on a UL certification test. I know from dealing with customers that their problems often stem from their failure to periodically retighten the connections. If they would just do that annually there problems would all but go away. Instead they do not and after a while the breakers trip at ever lower loads.
I have just gotten to the point where I have removed the front panel, retightened the connections to the 50 amp breaker and gone on with life rather than trying to get someone to fix the problem.
Nobody has an issue with power in the winter. Of course who wants to be going where it is cold anyway? Been there, done that, have the heavy coats to prove it.
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Just for grins I read the standard. All the standard breakers are required to do is carry 80% of the rated capacity for standard breakers in the smallest enclosure. I did not read the definition of the smallest enclosure.However breakers rated as 100% breakers had to carry 100% of the rated load.
Since you were dealing with Air Force facilities and public money you were undoubtedly dealing with 100% capacity breakers and not standard breakers which are used in temporary power outlets certified to UL 230 which covers the outlets we use.
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I just looked at another transfer switch and although its 3 relays are set-up a bit different, and more logical it still looks to have the same switching times as the other. This one has a relay dedicated to ach AC source and the output.
One thing you have to realize any time delays that are built in or user configurable have nothing to do with relay switch times. As an example, if you have commercial power applied and start the generator the transfer switch is going to monitor the generator power for 30 seconds (typical). During this monitoring period commercial power is still being provided to the coach. At the end of that 30 second time, the relay is going to switch from commercial to generator power. The switch time between one AC source and the other is solely determined by the switch time of the relays.
It doesn’t have to be this way, but the transfer switches I looked are that way. I’m guessing too many people complained about having to reset their clocks so they moved to near hitless switch over of power.
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We have about a one second delay on our coach accepting shore power. I can turn on the 50 amp breaker and in about a second hear the relay in the transfer box.
I was going to open up my box and take a picture but I loaded the bay with stuff going to Rick at the Lobster rally so when we are in Maine we can open it up and over spirits discuss the meaning of life and transfer switches.
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Yep, 1 to 3 second delay on commercial power seems right. Again, that has nothing to do with how much time there is between when generator power takes over from commercial power. It’s simply how fast do the relays change state. My guess is milliseconds. The switch from generator to commercial may be slightly longer if it has to sense generator voltage absense first. I don’t think so though. I’m pretty sure the relays are energized by generator power and when that power goes away they simply deenergize and accept the commercial power (assuming it has been on) that’s already past it’s 1-3 second delay circuit being triggered.
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My ears are tuned to the generator start which is a rumble, then the whirr as the radiator fan spins up to speed because its power is generator power. I can’t say I sense when the generator supplies power because I am aware of the other noises and their sequence. Whatever it is however works.
There will never be an instantaneous switch from shore to generator power even if the “generator start on shore power interrupt” is engaged because my generator start cycle has a time delay for the glow plugs. If it has not been run for a while the generator cranks a few turns also so whatever has dropped off when shore power was lost like Cruiseairs or the satellite receiver all have to be restarted. I would guess the generator start takes 15 to 30 seconds.
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Yours has glow plugs? Mine does not. I have not seen them on a newer diesel for some time….maybe a special Liberty order thing?
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Jon here’s a simple test you can do while enjoying the sweet sound of your generator starting. I think you’re going to be surprised.
Turn on commercial power.
Plug in 2 lamps with incandesent bulbs. One needs to be plugged into an outlet that is not serviced through the inverter/charger. The other plugged into an outlet serviced by an inverter. Turn them both on and make sure you can see them both from where you start your generator.
Start the generator without turning off commercial power.
After 15-30 seconds the generator will take the load. The non inverter light will likely have a very short flicker. If you have a Trace inverter you shouldn’t even see a flicker in thr inverter powered light. With any other inverter there may be a very short flicker, if there’s any noticable switch time.
Turn off the generator and see if you don’t get roughly the same results.
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Mark,
I’ll have to verify that. Maybe glow plugs is the wrong term, but I believe I have a reason for the 15 to 30 second start delay. The current engine is a Yanmar and all my others that I am thinking of had a Kubota.
Now you got me thinking.
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Jon,
For what it’s worth, our generator also had the Yanmar engine and it also had about the same start delay from the moment I hit the start button or the auto start sequence started. I always figured it was some sort of pre-start diagnostic routine that was part of the Liberty Watch Dog system.
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It must be a Liberty thing as mine starts up right away..no delay at all. Hit button and it cranks and starts.
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my 05 went through the heating cycle,my 08 starts immediately.
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