Is this the correct setup to hookup generator?

av8rAugust 8, 2012

I am planning on hooking my 5500 watt generator up to my house. I have a 200 amp main breaker ge panel in our utility room. Hd sells an interlock kit for it. I'm going to install a 30 amp two pole breaker for the backfeed from the generator. I am going to run about 50 ft of 10/3 romex w/ground from an inlet box with watt meters in our garage between the inlet box and main panel and then use a pre-made 10/3 twist lock male to female extension cord made to go between the gen and inlet box. Is this the correct way to do this? Is the breaker on the generator acceptable for over current protection on the 10/3 from generator and the 10/3 romex in wall between inlet box and panel or should I purchase inlet box with a built in 30 amp breaker. The 30 amp plug on the gen is not gfci protected. I plan on turning off all non essential breakers in main panel and monitoring load with watt meters. Thanks in advance for any help.

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The key to this setup is the "interlock kit" or transfer panel. It must be designed such that the 200A main must be disconnected whenever your backfeed is in operation. Any arrangement that allows both to be physically connected at the same time is illegal and potentially fatal. I don't see any evidence that you're doing this correctly.

The 30A backfeed breaker would protect the 10/3 cable supplying it. It doesn't matter which end of the circuit it is on.

    Bookmark   August 9, 2012 at 9:12AM
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And if you forget to turn off enough breakers beofre connecting the generator the 30 amp breaker will open just about instantly, and you can damage the generator.

If you want to back up an entire panel you need a generator large enough to power the entire panel.

    Bookmark   August 9, 2012 at 9:45AM
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The 30 amp breaker will be installed on the top right corner of the panel and the interlock will prevent the main and the 30 amp from being on at the same time. I understand the importance of turning off the breakers and not overloading the generator. The watt meters are going to allow me to monitor the load on both legs. The other option would be to install a reliance 6 circuit all in one transfer panel beside main panel. It is equipped with watt meters and has 4-15amp breakers and 2-20 amp breakers and each breaker is its own transfer switch for the individual circuits. Would this be better? Also, just so I understand, what if the backfeed 30 amp were a 60 amp breaker? Would the remaining 30 amp breaker that is onboard the generator be adequate to protect the #10 wires or does the backfeed breaker have to be 30 amp?

    Bookmark   August 9, 2012 at 12:34PM
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In your scenario, it would be better to have the meters at the panel rather than in the garage 50' away. Just an opinion.

If you can get everything you need into a Reliance-type unit, then I think that is a better (perhaps safer) way to go. That way, you are only driving the circuits you want to drive when you want to drive them.

    Bookmark   August 9, 2012 at 3:45PM
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Electronic controls (like the ones in the generator) have a really nasty habit of failing before a breaker can even move.

Especially if a large fault current occurs suddenly.

Having watt maters is not going to do any good.

You need ammeters, and even then need to stay well below the continuous rating of the generator.

Do NOT believe the 'peak power' garbage.

It is better described as 'fantasy power' in the imagination of the seller of the generator.

Heating elements and induction motors pull significant surges when power is first applied.

Use a smaller panel and ONLY load it based on the generator, not the circuit breakers.

    Bookmark   August 9, 2012 at 4:26PM
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Ron Natalie

Why wouldn't a wattmeter work? Absent a little PF confusion, the amps and he watts are directly related. The cheasy little kill-a-watts in fact read voltage/amperage/watts/PF. The bigger TED units are in fact current sensors only anyhow. The assume you're going to tell it what the voltage is.

    Bookmark   August 9, 2012 at 5:11PM
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"Why wouldn't a wattmeter work? Absent a little PF confusion, the amps and he watts are directly related."

Generators are loaded by V-A. not watts.

    Bookmark   August 9, 2012 at 5:53PM
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Yes, I will definitely put them next to the panel. I'm confused on the Watt meters though. They are sold by reliance to monitor the load. Each watt meter has 2 parts. The watt meter itself and then there is a donut type pickup and connecting the 2 pieces is about 12 inches of copper wire. You pass each of the hot legs through one of the donut looking pickups. It seems to work the same as my amp meter? It's not the same? When i have experimented with them at a friends house on his house and hooked up loads, it seems to indicate the same as the amp meter. I think we had a frige and a few lights. If memory serves it was right at 5 amps on amp meter and the watt meter was just under 700 watts. It seemed like a good inexpensive way to get an idea of the load. Also, with regards to the max rating on the portable gens, if it says 5500 max continuous is a safe rule of them for continuous loads about 80% of that number? Actually, More like 80% of half that number per leg? Thanks very much for the input.

    Bookmark   August 9, 2012 at 7:13PM
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Ron Natalie

Brick, did you even bother to read what I wrote?

WATTS = V-A as long as the PF is 1.
The Killawatt tells you all of the information.
THe TED really only gives you V-A as it doesn't measure Watts at all (just current and assumes a nominal line voltage for it's reports.

    Bookmark   August 10, 2012 at 8:42AM
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It displays current continuously with a good update rate?

ALL you need is the current display with an update rate of around twice per second.

The Killawatt is NOT a measurement grade instrument that is worth risking the value of a generator on.

Even a clamp on ammeter would be far better.
At least it will have calibration traceability.

The problem is that the power factor is NOT 1.0 for anything but an electric water heater or electric heat.

The 'fantasy' ratings of 'peak power' or 'surge capacity' is to be avoided completely.
While it might allow for a heating element to start (where some voltage droop is not damaging beyond overloading the generator) it will produce voltage droop and non-sinusoidal waveforms (harmonics) that can easily damage an induction motor trying to start up.

    Bookmark   August 10, 2012 at 10:59AM
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Ron Natalie

I give up, you are incapable of listening.

I never said PF was 1. I said the two popular things out there sold as wattmeters did exactly what you told him he needed: Measure current.

The Killawatt displays Volts, Ampere, Watts, and PF.
The TED units don't measure Watts or VA or PF at all. They're purely current measuring devices.

While they may not update fast enough for surges, they certainly update enough to make rough load calculations.
You obviously have to allow some headroom for surges and the optimistic view of the generator manufacturer on the device ratings.

    Bookmark   August 10, 2012 at 1:06PM
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AV: I'm familiar with those little meters. They are actually ammeters scaled to watts (assuming 120v on each leg). For the rough things you would be doing (balancing each leg) they would be sufficient.

Personal opinion, running at 80% load continuously does not give you any 'headroom' for startup loads (fridge, freezer, blowers) that you may have. You're also putting more strain on the unit. For me, %50 is more like it. If you Google search around I think you can find discussions about loads. I don't think there are standards for the definition of 'surge capacity' given by these portable generator manufacturers. I would like to think that is is X amount of power for T amount of time before damage is done, but they don't tell you T.

R: there is a model of TED that I have that measures voltage (on both legs) as well as current. Hence it can give PF. FYI. Not really important to this.

    Bookmark   August 10, 2012 at 3:53PM
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Weed.....thanks for answering the question.

    Bookmark   August 10, 2012 at 9:11PM
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