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post #1 of 7 (permalink) Old 02-18-2017, 09:13 AM Thread Starter
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Home backup generator questions

I am hoping that y'all can help me sort out a few things regarding the selection and use of a backup generator for my house.

First, the basics:
I'm got a power inlet box mounted on an exterior wall, which is wired to my panel with 8/3. Its a Reliance model, rated for 30A. The breaker that this is connected to is a 30A double breaker, and it has a mechanical interlock on it that prevents it from being energized at the same time as the main breaker for the entire panel.
The gen set will be run outside and away from doors / windows, obviously.
The intended use of the gen set will be only during outages, and periodic running to keep things operational. It will only be connected to the house during these times, otherwise it will sit in the garage disconnected, fuel stabilized and waiting for action.

Now on to the main question at hand:
I've done lots of reading and research across various sites, but cannot seem to find a definitive answer to one particular question. If I select a gen set that has an L14-30 receptacle, and use that connection to feed my panel, will I have issues with the GFCI breakers in my panel and/or the GFCI breaker on the gen set itself? Seems like most portable gen sets are neutral bonded, and 50% of the internet says this will cause issues and 50% says it won't. (1) Is there a definitive answer?

Second question, regarding THD. (2) Will my TVs, furnace controllers etc., live with THD above 5% or am I just asking for trouble >5%?

Final question, (3) any recommendations for a portable gen set that yields 8000/8500 running watts via an L14-30 and has THD <5% and wont' break the bank?

Thanks for your help
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post #2 of 7 (permalink) Old 02-18-2017, 01:27 PM
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As to the issue of bonded neutrals or not, it is my understanding that any portable generator used as a backup and wired into your house panel should not have a bonded neutral. Most Major manufacturers such as Generac & Champion have instructions on how to unbond the neutral. It is generally just a matter of disconnecting the neutral bond wire from a lug to the ground terminal. If you intend to use the same generator as a portable you need to reconnect the neutral bond or risk getting shocked.

I recently purchased and connected a Champion 7000/9000 watt generator purchased from Costco and it runs my whole house including my 220v well pump with no issues. I am also building a vented generator shed to house my generator against the weather making it essentially a permanent installation. The Generator I purchased has a THD of <5% which is better than most Gensets on the market but I think most major brands of generators of that size should be fine.
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post #3 of 7 (permalink) Old 02-18-2017, 08:48 PM Thread Starter
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I am considering this generator;

http://www.troybilt.com/wcsstore/Tro...8_OpManual.pdf

Nowhere in the manual did I find anything about unbonding the neutral.

The l14-30 is not GFCI protected. If I leave it as-is and connect it to my house, will I have problems with the gfci breakers in my panel? Will I have safety issues at the generator and/or in the house (shock hazard)?
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post #4 of 7 (permalink) Old 02-18-2017, 10:01 PM
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Interesting question. My understanding is that per the NEC, your entrance panel can only be grounded at one location, usually the service entrance via driven ground rod, etc. When you connect your genset to the entrance panel via "power inlet box," 2P30A breaker, and the mechanical lockout has the main breaker "off," you are not adding an additional ground. UNLESS you have provided a separate ground and attached it to the lug provided on the chasis of the genset, in which case you have provided two grounds and are in violation of the NEC. (I actually found a neighbor doing that). The confusion seems to arise from the use of "switched neutral transfer switch" and the possible need to separate the neutral and ground at the generator. The OP seems to have a purely mechanical transfer switch, lockout, etc. so that shouldn't be an issue. I've attached a link which describes the connection. Portable Generators and Your Home's Electrical Ground | Norwall PowerSystems Blog Here's another link that shows the L14-30 plug: http://www.generatorsforhomeuse.us/w...ds/l14-30r.png GFI breakers shouldn't be an issue unless there is one. GFI's are essentially "comparator circuits" in that they look at the current flowing out and back on the proper paths, if an imbalance is detected, e.g. current is not returning on the neutral it trips out the breaker. The current imbalance is 5mA, you might get a tingle, but shouldn't be life threatening. I would not disconnect the ground at the genset in your application. THD I'll leave for folks concerned with it. The 30A breaker you're feeding your house with is about 6500W. Hopefully one of the more senior members will weigh in on this for further clarification.
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post #5 of 7 (permalink) Old 02-18-2017, 11:30 PM Thread Starter
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Thank you for the excellent answer!!

Regarding the 30A breaker only being good for ~6500 watts, moving up to a 40A is a simple fix, and the 8/3 wire would handle that load. However, if the generator's breaker is 30A, would increasing the size of the feed breaker in the panel make any difference?
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post #6 of 7 (permalink) Old 05-19-2017, 05:34 PM
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Quote:
Originally Posted by TX3001 View Post
Thank you for the excellent answer!!

Regarding the 30A breaker only being good for ~6500 watts, moving up to a 40A is a simple fix, and the 8/3 wire would handle that load. However, if the generator's breaker is 30A, would increasing the size of the feed breaker in the panel make any difference?
I saw this thread come up in the pingbacks on Norwall's blog. Since I wrote that post, I thought I'd respond.

First, the lockout breaker you are using is a two-pole connection. It does not switch the ground or the neutral wires. The portable generator's frame should not be bonded to the neutral. Only one bonding point is allowed and that permanent connection is already made in your home's panel. Most manufacturers provide instructions for bonding or not bonding so check your manual.

Regardless of your lockout breaker size, you are limited by the outlet capacity and size of the breaker on the generator. If you're connecting the inlet box with a cord to the 30-amp receptacle on the generator, the generator receptacle breaker will trip if the current exceeds 30 amperes. Further, if you bought the cord for a 30-amp receptacle, more than likely it is only rated at 30-amps.

There is a problem going to a 40-amp breaker however and maybe it's not quite so obvious. The inlet box is rated at 30 amperes and the wires are rated for 50 amps (assuming 75 C insulation). Suppose you up the lockout breaker to 50 amperes. Later you sell the house. The next owner sees the 50 ampere breaker and assumes (wrongly) that the entire connection is good for 50 amps and they rig a cord to connect a 50 amp generator outlet to the inlet. The connection now poses a definite risk of fire because the inlet box was only rated at 30 amperes.

So no. Don't change the lockout breaker size to anything greater than 30 amps.

This is also why you never use a smaller gauge wire on a circuit just because you're only powering a light socket. If you have a 20-amp circuit, don't think to get by with #14 to connect a light socket. The next guy may come along and plug a 2200 watt heater into that socket and the wires are only rated for 1800 watts (15 amps).

A generator rated at 8000 running watts will supply a continuous 33 amps at 240 volts. Don't worry about those 3 amps. The 30-amp outlet and breaker on the generator won't allow you to exceed the 30 amps anyway.

Remember. Turn off the power when you make changes to your electrical system. If you don't feel confident or don't understand what you are doing, call an electrician.

Best regards,

MJ
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post #7 of 7 (permalink) Old 05-31-2017, 05:54 AM
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