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Discussion Starter · #1 ·
Hi. I am buying a new 10,000 watt portable generator with the intent to plug it into a transfer switch to my main panel. I plan on bringing an electrician in but have a couple of questions in the meantime. I have a main panel that is 200 amps and a subpanel in my garage but the main panel has the circuits that I want to use with the transfer panel. The new generator has a 120/240V, 50A – (NEMA 14-50R) outlet. It also has a 30A NEMA L14-30R outlet but I believe it's the 50A outlet I need to use to connect to the outdoor outlet for the transfer switch once it is installed. My question is whether there will be any issues tying in the transfer switch into the main panel given that there are only 2 slots left. I have an acquaintance who is a contractor and he was going off about potential issues I may have and that I may need to upgrade my panel. Anyway, see attached photo of my main panel. Slots 28 and 30 are available. Slots 16 and 18 go out to my subpanel which does have a number of open slots. I only know the basics about how a transfer switch ties into the main panel. I don't know any more than that so I am looking for an assessment and any advice anyone has. Thanks!
 

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Discussion Starter · #8 ·
I would either use a MA24 GenerLink or move down breakers to make space below the main breaker and install a Square-D interlock (check to see which one is appropriate for your panel).
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Thanks for the reply. I will need to digest this more but so far it seems like there are no red flags which is what I was concerned with.
That load center doesn't accept tandem breakers. Spec sheet indicates maximum number of tandem breakers is zero. It has 30 slots and 30 circuits:
 

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Discussion Starter · #10 ·
OK I have learned alot already. I found a photo of what it would look like although this photo is if the main was on the bottom. Mine is on top. It seems like the electrician would move all of the breakers on the right side down two slots so that the two available slots would be on top. The breakers for the generator would fill those two slots and the interlock switch would switch between those breakers and the main. I am sure this is straightforward for everyone on this forum, but new to me. If there are any gotcha's or anything I am missing, let me know. Thanks for your help.
 

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Discussion Starter · #22 ·
Thanks for your response as well as responses by everyone else. It is clear to me that I should move the top 2 breakers on the right side down to the bottom. I have been reading alot about interlock vs transfer switch and it does seem like interlock is the way to go. Most of the circuits I want to run are on the main panel but I am adding central air which is being wired to the subpanel due to the lack of slots on the main panel. Another reason why the interlock sounds like the way to go. I was concerned with overloading the generator but it sounds like I need to manage this by managing the load, flipping off some circuits and worst case the breaker on the generator will trip if overpowered. I am planning on buying a Firman tri-fuel generator with the following specs:

OUTPUT
Running Watts8000(Gas) 7250(LPG) 5500(NG)
Starting Watts10000(Gas) 9050(LPG) 6900(NG)

I plan to hook it up to my natural gas line that is going to my gas grille. The supported wattage is alot less than gasoline so I will need to be more careful when running with natural gas. Maybe I will run gasoline during the day when usage is higher and natural gas at night. If anyone has any comments, let me know.
 

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Discussion Starter · #27 ·
what is the btu rating on that gen set?
make sure the line is large enough for the gen set.
that is the cc's on the engine?
i like 1 inch on NG feed to medium gens.
then size down to 1/2 couplers and use 3/4 id hose.
Yes, I have been reading about the issues with gas pressure and line size. Attached are the specs for the generator and a picture of my gas line. I have no idea what the gas specs mean. Firman told me they require a 1/2" gas line to regulate the gas pressure. In the photo of my gas line, I have a clamp controlling my shutoff. The shutoff says 1/2", but then it seems to get reduced. I couldn't see any labeling on the hose to my grille. The gas line comes out of the house about 10 feet away and the gas coming into the house is about 30 feet away if that matters. Any advice would be appreciated.
 

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Discussion Starter · #31 ·
most gens need 150k btu min.
a gas grill needs 30-80k btu depending on how large the grill is.
3/4 would be the bare min.
so on the 1/2 line what is the total feet from the T from the larger line and the size on the larger line
and how many 90 deg fittings? each 90deg fitting is a minus 5 feet from the size chart.
Thanks for your reply. I attached two photos of my indoor gas line. The photo that is titled 3/4 to 1/2 inch (the one with the red water shutoff), you can see where I think it goes from 3/4" (could be 1") to 1/2". From the tee moving to the right is what the next photo shows. The 1/2" inch gas line from the previous photo continues on in this photo where the red hook on the left is. The distance from the 3/4" to 1/2" fitting to the red hook is about 3 feet. As you can see, there is an elbow that runs to the tee on the right. That is about 2 feet. From there, it's about 12 feet outside to an elbow and another foot to the shutoff valve that I showed you in my last post. I attached the shutoff valve photo again. What I am going to try to do is attach a 1/2 gas hose from my generator to the quick connect on the shutoff valve but I am not sure if the pressure is reduced there and won't give me enough pressure. Firman told me that a 1/2" hose should be used to regulate the pressure to the generator. Any thoughts and advice would be appreciated.
 

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Discussion Starter · #35 ·
This site has alot of good info on pipe sizing.

My suggestion is to draw a pipe map with lengths and diameters For us to see And for your own experience. Your system looks to be 3/4 and 1/2 in those pictures. I can almost guarantee that you don’t have enough volume tapping into your existing system. A home run from the meter would be the best move.

Your generators 439cc engine is approximately 14-15hp. A safe rule of thumb is 10,000btu per HP, so 150,000 btu of supply volume will guarantee proper fuel Quantity. In all likely hood you’ll need far less supply during normal operation with the generator mildly loaded but that leaves zero reserve for when other NG appliances are operating. Inadequate supply can cause the generator to bog and send voltages and frequency tumbling. It’s not worth damaging your devices and appliances.
Well I had alot of fun after Thanksgiving dinner lol! Thank you so much for the information and the link to the generator pipe size page. Incredibly helpful! Attached is the pipe layout for my house as well as the calculations I came up with. I am pretty sure I have 1" and 1/2" pipes. I measured the circumference of each and used a pipe size chart I found and it looks like those are the pipe sizes. I don't believe I have any 3/4" pipes. In addition to the 2 notes in the diagram, there were several BTU numbers on my gas boiler so I included 2 of them. Note that the boiler is 30 years old. Here are some comments on my calculations. I realize this is new to me and I may be way off on my assumptions:
  • I used the 14.5 horsepower number you provided and the 145 CFH full load number that was derived from the horsepower. One thing I wondered about was that the generator specs have the generator running natural gas at 69% of the wattage compared to gasoline. I was wondering why that is and whether the CFH full load number with natural gas is also 69% which would be around 100 CFH.
  • The only thing off of legs I, J, K and L is the gas grill. If it is not used during an outage, that seems to give me 73 CFH which seems to get me close to the 100 CFH number but pretty far away from 145 CFH.
  • If I was to tap off of Leg G, that should give me 180 CFH (286 - 106) which would get me to both numbers but where does that leave the gas stove when that needs to be used? The 55,000 BTUs is if all 4 burners + oven are used at 100%, but at 2 burners + oven that would be fine if we are trying to get through a power outage. Seems like that would fit within the available CFH.
It seems like tapping off of Leg G (before the gas stove) is the way to go. It's certainly doable because it should be fairly easy to tap in there and run a line to the outside wall. It would be close to where I was planning on locating the generator as well. Of course, that would require a plumber and extra expense. I'd love to be able to run it off of the existing 1/2" line but that may not work if 73 CFH is not enough. Let me know your thoughts on all this. If anyone else wants to chime in, please do.

Finally, what did you mean in your last post by "A home run from the meter would be the best move. ". Thanks again!
 

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Discussion Starter · #38 ·
Nicely done. The pipe map really clears things up. I agree tapping off of G should be satisfactory. The 1” x 1/2” x1” tee can be replaced with a 1”x1”x1” and keep 1” all the way to the end necking down to the right sized quick disconnect.

”home run” meaning a dedicated pipe from the meter right to the generators location. If your existing trunk line was 3/4 this would have been absolutely necessary.

The only limiting factor to your system is the gas meter itself. Most are rated for 250cfh. A buddy of mine that works for the gas company tells me that there is more wiggle room to that number as long as the distribution lines in the street are under pressure. Essentially if you have a pressure regulator before your meter.

“home run” meaning a dedicated pipe from at the meter to the generators location. Since your trunk line is 1” you should be ok. If the trunk line was 3/4 tapping off of it would not have been sufficient.
Thanks for the explanation around the home run pipe. It is a possibility but would mean I would need to locate the generator further to the front of my house which is not preferable. I'll probably go with tapping in at the end of the 1" pipe as discussed. Do you think there is any chance the existing 1/2" connection would work? Firman said they require a 1/2 inch hose to regulate the pressure so there seems to be an expectation for a 1/2" connection.
 
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