Installing generator inlet box/wiring

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Old 08-15-09, 07:35 AM
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Installing generator inlet box/wiring

Currently I have a 20 amp generator (5 KW running) and while I plan on upgrading in the future, I would like to hardwire once. Whether I go to a 30 or 50 amp generator, could I use the same wiring for all of them?

Would I be able to wire for a 50 amp, and still use the 20 amp generator? Looked at a few ways to go about this and I will be using the Interlock kit which is basically a moveable piece of aluminum which will only uncover the GEN breaker when the main is turned off, to avoid any backfeed to the transformer.

This setup IMO is overpriced but still allows for anyone to use the generator to avoid backfeeding the transformer which in the longrun is the safest way.

I will need to move my 3 top right breakers down using piggy-back breakers and leave the top 2 open for the generator breaker to feed both sides of the panel.

How would I do this for a 50 AMP inlet box on a 20 AMP generator?

Worst case, I can run 3 sets of wires for a 20, 30, & 50 amp from the panel to the inlet box, leaving the unused wires hidden for when I ever upgrade generators.

Like I said, I just want to be able to dig between the walls once and have the wiring there in case I ever upgrade generators. I know a 5 KW won't run the house but it's will be easier than unplugging the fridge's and running extension cords.

Another thing, with nothing else connected, can a 5 KW gen start a well pump or is this dependent on what pump I have?
 
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Old 08-15-09, 08:36 AM
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I would probably run a 3/4 or 1" PVC conduit and pull #10 conductors. You could use the #10 with the 20 amp inlet and the over sized conduit would allow for larger conductors to be pulled in later.

Does your panel allow the use of tandem breakers? Can you post the brand and model number?
 
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Old 08-15-09, 08:45 AM
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The 5 kw generator MAY be able to start the well pump, you won't know until you try.

As for the rest, as long as the generator has a circuit breaker mounted on it that is sized for the particular generator's output you can use whatever size circuit breaker at the panel as you desire. If you only want to do it once then install a 60 ampere circuit breaker and run number 6 THHN copper conductors to a fifty ampere inlet box using flexible conduit. You only need a number 10 for the equipment ground.

For the interconnecting cable from the generator to the inlet box use the appropriately sized conductors for the generator and use a 50 ampere connector at the house end to mate to the 50 ampere inlet. You could use a 6-4 cable initially and just install the appropriate plug for whatever generator and change just this plug as you upgrade the generator.
 
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Old 08-15-09, 09:43 AM
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So using a 20 amp plug at the generator and a 50 at the house, I could accomplish this with the same cord? That would be great but I wasn't sure if the larger wire would attach to the 20 amp plug.

Here's a pic of the panel.

Slot 6/8/& 10 would need a piggyback opening up 2 & 4



 
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Old 08-15-09, 09:49 AM
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Actually the double-pole on 12/14 would need to slide down one leaving 6 singles above it using piggypacks open up 3 slots since the switch requires 3 open slots on the top right.

One dummy in #6 and two for the gen on 2&4.

Looks like it will work.
 
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Old 08-15-09, 10:22 AM
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You still nedd to determine if you can even use tandems in your panel. Even if you can I would use a standard single pole wherever I could to avoid the tandems or leaving a blank filler.
 
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Old 08-15-09, 11:56 AM
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How do I determine if I can use them, size? The empty slot is used to allow for movement of the lockout plate...there will be no hole there just a cover over the opening.
 
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Old 08-15-09, 01:19 PM
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If you can use doubled-up circuit breakers in that panel most likely they would only fit the last five positions on either side. The label on the door should specify if doubled-up breakers can be used although it won't use the term "doubled-up" but may have a part number.

Are you absolutely sure that panel has a Interlock kit available? Usually they fit panels where the main circuit breaker is parallel in action to all the other circuit breakers.

As for the generator-to-inlet cable...you might indeed find it difficult to locate a plug 20 ampere plug that would fit on a 6-4 cable. In that case the easiest would be to make a short "pigtail" with a 10-4 cable with a 20 ampere plug on one end and a 50 ampere connector on the other.
 
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Old 08-15-09, 07:28 PM
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They do have one avail for my panel which is why I need #6 open to allow for the lock to slide down when the main is thrown.

With the main off, I can then slide the lock down to allow movement of the gen breaker...the piece that blocks the gen breaker from moving is moved down over the dummy slot.

My original plan was to take a 20' 20A gen cord and remove the inlet end and replace with a 50A end. Or take a 50A cord and replace the gen plug with a 20A connector.

I don't know what wires are in a 50A circuit so please pardon my lack of knowledge there.

Don't want to do this to risk any problems so whatever works safely is my only option.

I like the Interlock kits but they are very $$$ for what you get, makes me want to search elsewhere.

For $150 they should include the inlet box and up to 2 piggyback breakers. A piece of aluminum and a few screws doesn't justify it so any other options out there I would surely entertain. Not to slam Interlock but just pricey IMO.

I do want to install some watt meters and have looked at these....



How accurate are these and do they just loop over the hot for each feed to each side?
 
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Old 08-15-09, 09:18 PM
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I'll agree that the price of the Interlock kits seems outrageous for what it entails, I guess that's the price for having a UL approval. There are other options but they either cost more (a 200 ampere transfer switch is about $360.) or limit you to what circuits you are able to energize from the generator. By rights you really need to pull a permit and have this inspected by your local electrical authority and they almost certainly will require that whatever means you utilize be UL approved.

If you're serious about eventually upgrading to a 12 kW generator then you should decide if you want that generator to be a portable or fixed model. If you want a fixed generator then there is no need to have a 50 ampere cord set, you would simply use a flexible liquidtight conduit with THHN/THWN conductors from the genset to the circuit breaker panel. In the interim you could install the smaller power inlet and utilize the smaller portable cable to the portable generator. By running the required size conductors to the power inlet box that will eventually be required with the larger generator you can avoid having to do that part of the job a second time.

However, if you want the larger generator to still be portable then I would simply go with everything from the circuit breaker panel to the generator with number 6 conductors and utilize a 50 ampere power inlet. Make up the short "pigtail" to convert the 20 ampere receptacle on the smaller generator to the fifty ampere genset-to-power inlet cable and save a couple of dollars in the long run.


Those meters are most likely ammeters, not wattmeters although they may be calibrated in watts. They will likely have an error of +/- 5%, plenty good enough.
 
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Old 08-16-09, 05:23 AM
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So the 50A wireset is the same # of wires just larger gauge correct and of course a different pigtail?
 
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Old 08-16-09, 07:17 AM
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I've seen some CH panel tandem breakers for older panels that are listed "for replacement only" that cost like 3 times what an average tandem cost.

I think they do this to discourage their use.

Also, I know Cutler Hammer makes a cover that has a generator interlock already installed for the BR panels so, they may make one for the CH panels.
 
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Old 08-16-09, 08:52 AM
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Originally Posted by i6pwr View Post
So the 50A wireset is the same # of wires just larger gauge correct and of course a different pigtail?
Correct. You will always need four conductors, two "hot", one neutral and one equipment ground. For fifty amperes you need #6 for the hots and neutral with a #10 for the equipment ground. The larger wire works fine for lower amperage but you cannot substitute smaller wire for larger amperage.
 
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