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Old 07-02-2015, 06:11 AM   #1
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Surge/EMS install question

New RV is going to get a Progressive Industries EMS installed. It will be a hardwired unit. I had planned on putting it between the shore cord and its connection to the converter. For generator power we have to plug the shore cord into the generator outlet. My wife brought up a very good point. What happens if weíre on shore power and the EMS decide to shut us down due to low power or some other issue? I said we lose power and we would have to plug into the generator depending on how long the issue was going to last. She then asked if there was an automatic way to switch from shore to generator. Of course, a transfer switch. Which leads to this question. If the EMS is installed after the transfer switch, the switch wonít transfer to generator if the EMS shuts down due to a power sag or some other issue. Itís still going to see shore power and keep it on that side. The EMS will have to be installed on the shore power cord before the transfer switch. How likely is it that the generator will throw something that the EMS should have stopped? Is the risk of running the generator feed unprotected worth the convenience of having the transfer switch? I havenít figured out how much weíre going to be using the generator vs being plugged in.
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Old 07-02-2015, 06:56 AM   #2
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With the Gen running the transfer switch will always favor the Gen and not the shore power connection.
Mine is wire so Gen and shore power goes through the surge protector its up to you I never had a problem with the Gen causing a problem with coach electrical system.
This link will cover both types of surge protectors and wiring and much more.
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Old 07-02-2015, 10:28 AM   #3
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Quote:
Originally Posted by 007";2630195]With the Gen running the transfer switch will always favor the Gen and not the shore power connection.
Mine is wire so Gen and shore power goes through the surge protector its up to you I never had a problem with the Gen causing a problem with coach electrical system.
[B][URL="http://www.irv2.com/forums/f54/technical-info-links-28855.html
This link [/URL][/B]will cover both types of surge protectors and wiring and much more.
Mine is also wired after the transfer switch; so, shore power and generator power are covered. If there are problems that fry the transfer switch, that is a much cheaper and easier problem than causing severe electrical problems in the coach or inverter.
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Old 07-02-2015, 01:36 PM   #4
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Quote:
Originally Posted by 007";2630195]With the Gen running the transfer switch will always favor the Gen and not the shore power connection.
Mine is wire so Gen and shore power goes through the surge protector its up to you I never had a problem with the Gen causing a problem with coach electrical system.
[B][URL="http://www.irv2.com/forums/f54/technical-info-links-28855.html
This link [/URL][/B]will cover both types of surge protectors and wiring and much more.
Your saying that I can start the generator even if there is power on the shore cord and the transfer switch will automatically switch to the generator and not blow us or the utility company up? I'm not concerned about a total loss of power, just wondering what to do if the EMS shuts us off for a brown out or a pedestal issue. I really want to run them both through the EMS but I need a way to bypass the shore power if something goes wrong with it and have to resort to the generator.
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Old 07-02-2015, 03:38 PM   #5
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I don't know what gen you have but typically the gen does not need to go through an EMS as it has its own. My shore power goes directly to the PI. The PI then goes to the ATS, automatic transfer switch.
When the gen kicks on the ATS shifts to the generator. Shore power and the PI are out of the picture entirely. Shut the gen down and the ATS goes back to show power which is filtered through the PI.
If you hard wire you gen to an ATS you might be able to install an automatic generator start system. Depending on your generator and a couple of other things.
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Old 07-02-2015, 06:42 PM   #6
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I don't know what gen you have but typically the gen does not need to go through an EMS as it has its own. My shore power goes directly to the PI. The PI then goes to the ATS, automatic transfer switch.
When the gen kicks on the ATS shifts to the generator. Shore power and the PI are out of the picture entirely. Shut the gen down and the ATS goes back to show power which is filtered through the PI.
If you hard wire you gen to an ATS you might be able to install an automatic generator start system. Depending on your generator and a couple of other things.
We have an Onan 5500 generator, made in 2014, 5.5HGJAB-1038K

I was wondering about the generator output and could not find much of anything that said it could bypass an EMS.

What ATS do you recommend? I have been pricing out the ESCO units, some others I have read about had a lot of problems. ESCO seems to be a good brand, are there any others I should look at?
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Old 07-02-2015, 08:55 PM   #7
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I don't know enough about the different brands of ATS so I really can't recommend one over another. Hopefully someone with more experience will chime in.
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Old 07-03-2015, 02:24 PM   #8
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There are several styles of ATS (automatic transfer switches.)

The transfer switch has a set of relays that switch from one input source to another, and that is where a lot of the variability comes in:

Some transfer switches are normally in the shore power position, and they turn on the relay coils to switch over to the generator input. Others are normally in the generator position, and they turn on the relay coils to switch over to the shore power input. Then, some transfer switches use DC powered relays, while others use AC powered relays.

So, there are some different combinations:
  • DC powered relays, relays turn on to switch to generator power: this is the best arrangement in my mind. The relays are powered only when the generator is running, and being DC powered they don't make noise.
  • DC powered relays, relays turn on to switch to shore power: I don't like this as much, as the relays are powered on all the time that the shore power is present, which generates heat and wastes power. But at least the relays are DC and don't make noise.
  • AC powered relays, relays turn on to switch to generator power: This is almost as good as the first option, but with AC powered relays they can tend to hum. Fortunately, this would only be while the generator is running, which for most people is a minority of the time.
  • AC powered relays, relays turn on to switch to shore power: this is the least desirable in my mind, as the relays are on the whole time there is shore power (which is most of the time for most people) and because they are AC powered they can hum. This style of transfer switch has been known to hum most of the time, and there are many people who have found this to be objectionable.
Then there is the issue of priority: if both power sources are present, most will favor the generator, which will let you start the generator and run loads off of the generator even when shore power is present. I think this is the ideal arrangement, as I have used it in the past when only 15 amp power is available, and I want to run some heavy loads like air conditioning. With the generator having priority, it is not necessary to unplug the shore power before starting the generator.

Some transfer switches give priority to the shore power, so that if both sources are present the generator is disconnected and shore power is used. I don't favor that arrangement, because in the just mentioned scenario it would be necessary to unplug shore power every time the generator is started, which in my mind defeats the purpose of putting in an ATS. As a personal observation, I've noticed that many of the switches that give priority to shore power are also the ones with AC powered relays that are on (and humming) all the time that shore power is present, which is another reason I don't favor that style.

ESCO has a good reputation for transfer switches, but they make a variety of styles which cover several of the variations mentioned above. So even with a well known brand, you need to pay attention to which model you are looking at. I've heard of many people who are very happy with their higher-end ESCO switches, and just as many who are very annoyed by the humming from their lower-cost ESCO switch.

Quote:
Originally Posted by Crankshaft View Post
Which leads to this question. If the EMS is installed after the transfer switch, the switch wonít transfer to generator if the EMS shuts down due to a power sag or some other issue. Itís still going to see shore power and keep it on that side. The EMS will have to be installed on the shore power cord before the transfer switch. How likely is it that the generator will throw something that the EMS should have stopped? Is the risk of running the generator feed unprotected worth the convenience of having the transfer switch?
The EMS and the transfer switch are NOT mutually exclusive. Just make sure to get a transfer switch that gives priority to the generator. For example, I have my Progressive Industries EMS after the transfer switch, and the switch gives priority to the generator. If the EMS cuts off power because the shore voltage is too low, I can start the generator, the transfer switch switches, the EMS now sees the correct voltage from the generator, and allows the power to pass. When the generator stops, the EMS will again be seeing the shore power voltage, and if it is still low, it will once again disconnect power.

You ask how likely is it that the generator will cause a problem? Not real likely, but it does happen, and that's why I put my EMS after the transfer switch: it protects against faults from both shore power and the generator, and as a bonus it lets me use the display to monitor voltage and current even while on generator power. I like knowing whether I'm close to overloading the generator. (Some will say the generator is sized so that you can't overload it, but I have tripped the generator output breaker in the past, so that's obviously not true.)

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I don't know what gen you have but typically the gen does not need to go through an EMS as it has its own.
I beg to differ. Some of the inverter equipped models might have some electronics to control the output, and may be less susceptible to throwing out bad power. But looking up the model number of the OP's generator and checking the wiring diagrams, it shows the output of the generator going through a pair of circuit breakers and then straight out to the load terminals. There is no sort of output circuit protection that would be provided by an EMS. The generator is quite capable of putting out incorrect frequencies if the motor speed is off, and high/low voltages if there are transients or a problem with the voltage regulator.

Even inverter equipped generators are not immune from power problems. There is a current thread where it appears there is a broken neutral wire between the generator and the transfer switch, and it is causing low voltage (104) on one line, and high voltage (145) on the other line. That is enough to cause damage to equipment in a coach, damage which would be automatically prevented by having the EMS after the transfer switch.
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Old 07-03-2015, 02:46 PM   #9
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I have had the Lyght x-fer switch installed for several years with no issues....Like having the surge protector and the e-xfer switch separate--one fail wont kill the other. Guess the genset could be a source of bad power but am more concerned about shore power. Again, like the idea that genset will run thru ex-fer [genset has priority] in the unlikely event the surge protector fails. Also like the PI surge protector....
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Old 07-03-2015, 03:56 PM   #10
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Good write up Adam.
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Old 07-04-2015, 10:21 AM   #11
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Good write up Adam.

Excellent write up, thank you
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Old 07-04-2015, 02:30 PM   #12
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Excellent write up, thank you
You're welcome, I hope it helps.
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