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30 Amp Inlet Box backfeeding to a dual pole 30 amp panel with a Square D- Kit

30 Amp Inlet Box backfeeding to a dual pole 30 amp panel with a Square D- Kit

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  #1  
Old 12-31-12, 08:34 PM
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Cool 30 Amp Inlet Box back feeding to a dual pole 30 amp panel with a Square D- Kit

I had a qualified electrician install a 30 Amp Reliance Inlet Box outside about 10 feet from my panel. The electrician relocated the 2nd and 4th Breaker and added a dual 30 amp breaker at the box. In order to turn on the power to the inlet box, I must shut off the main breaker and lift up the kit and so on. Nice inexpensive way to keep all the circuits in the house live. In addition I have gone to the extent of changing all the bulbs in the home to CFL's. I have checked all the amp ratings on the refrigerator, freezer, garage door openers, washer, dryer, oven, microwaves, computers, televisions and 4 circulator pumps. Designed a spreadsheet for constant amps and maximum amps and calculated everything. The constant amps to basically run the whole house at once at constant amps is about 43.5 amps. The maximum is 55.07. I even went to each circuit while everything was running and checked the amp/wattage for everything. Amazingly the CFL bulbs really do help. I even tested the whole house running circulator pumps, hot water, washer and dryer, opening and closing garage doors for a few minutes, had all the computers and televisions on in addition to lights on in about 10 different rooms (total wattage about 400 CFL) or about 2,000 + normal watts and the generator did not flinch or even surge.

Now my questions:

1) I have a Briggs and Stratton 5500/8250 surge storm responder. It states in the manual - This receptacle powers 120/240 volt AC, 60 Hz, single phase loads up to 5,500 watts at 22.9 amps for 240 volts or two independent 120 volt loads at 22.9 amps each. The outlet is protected by a two pole rocker switch circuit breaker. The AC Load Current at 120 Volts is 45.8 amps. The diagram shows 2 hot leads (X Hot and Y Hot) at 120 V on both sides. Neutral and Ground.

So it seems like the generator output at 120 is really 45.8 amps (unless I am missing something). My panel with only the required circuits are all single circuits of 110/120 and not 240. Only the air conditioning, well pump (irrigation only) have city water and air handlers are dual 110/120 circuits.

So now here is the real question: My generator cord is capable of handling 7500 watts maximum (25 foot) 4 prong NEMA. If the generator is putting out this type of amps/wattage and the cord is plugged into a 30 AMP 4 prong inlet Box (Reliance Box), am I getting the full 45.8 amps (many different circuits) or am I maxed out at 30 Amps or really 22.9 amps.? The amp ratings max is the refrigerator at 6.5 surge, freezer 5 surge (constant) 2 amps. The garage door openers are 5 amps @ surge and that only lasts a few seconds at most. The circulator pumps (are 1/2 amp to 1.75 amps max). So there are no appliances or areas that have huge amp requirements that are necessary (like a well pump 9.5 amps), the central vac (9 amps) and A/C Units drawing close to 15 amps.

I am assuming the 30 amp Inlet Box is only at 240 while at 120 I am doubling the amps? Not sure. Appreciate your help.
 

Last edited by Catanzaro; 12-31-12 at 09:47 PM.
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  #2  
Old 01-01-13, 12:22 AM
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Yes....you have roughly 45.8 amps of 120 volt AC power.
You have 22.9 amps per phase which means each hot leg will be carrying 22.9 amps.
The neutral is shared between the two hot legs.
Your loads in your panel are split on those two phases.

When you run a smaller generator like that on a house.....you must practice load shedding.
You listed a whole lot of devices.
No matter what your computations show you......you can't run them all.
You must prioritize your needs.
You can do laundry.....but you can't run the washer and dryer at the same time.
Garage door opener.....not a necessity.
Refrigerator and freezer......you're pushing it.
Four circulator pumps You need natural gas or propane. Same for dryer and cooking
Window air......maybe a small one. Central air......no way.
240 v irrigation pump......if absolutely necessary.....will probably be the only thing on at that time. Maybe some other small loads.

When you run your house on a generator......there is give and take.
You'll get to know what loads you can run at what times.
 
  #3  
Old 01-01-13, 01:56 AM
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I'm going to disagree somewhat with PJ. First of all, you do NOT have "two phases" on your electrical system but instead have a three wire-dual voltage system. You can thank Thomas Edison for that.

Think of three wires in a row like this: I I I Between either of the end wires and the center wire you have 120 volts. Between the two end wires you have 240 volts. Because the center wire is intentionally connected to the earth it also means that between either of the end wires and the earth you will have 120 volts. informally the end wires are known as "hot" wires and the center wire is known as the "neutral" wire.

Now here is the fun part, if you connect a 250 watt incandescent light bulb between an end wire and the center wire a current of approximately 2 amperes will flow from one wire, through the lamp and then through the other wire.

source
^ ^ ^
I-O-I I

(I signifies main wires. O signifies lamp bulb. - signifies wires between lamp and main wires.)

The same is true if you use the other end wire with the center wire. However, if you have TWO lamps, one wired from the left end and the other wired from the right end the circuit changes and there will be NO CURRENT on the center wire.

source
^ ^ ^
I-O-I-O-I

The current will still be about 2 amperes but now the voltage is 240 instead of 120 and therefore the wattage is doubled but the amperage stays the same. This is expressed via Ohm's law which states that the voltage is equal to the current multiplied by the resistance of the circuit. Ohm's law can be expressed in three different ways to find the unknown term as long as the other two terms are known.

I know, fascinating stuff but how does it relate? Here's how. By using the three wire system the utility can service your home with two different voltages and save the cost of a fourth wire. Higher voltages result in significantly lower voltage drop, power that is wasted as heat and requires the use of larger wires. Higher voltages are used with higher power loads such as electric water heaters, electric kitchen ranges, electric space heating, electric clothes dryers and such. The lower voltage is used for lighting and cord/plug connected appliances. To properly "balance" the various loads the electrician wires them to either the two end wires (for 240 volt appliances) or between one of the end wires and the center wire, alternating the end wire for different circuits. (No residential electrical system is ever perfectly balance due to the fact that the loads are always changing depending on the various circuits in place.) The end result is that the 120 volts loads often end up as variations in straight 120 volt loads and combinations of series 120 volt loads connected across the 240 volt service.

I hope I haven't lost anyone.

Your generator, just like your utility, serves you with a three wire-dual voltage supply. Unlike your utility the capacity of the generator is rather limited so you MUST properly connect the various loads to fully utilize this capacity. fortunately the existing wiring should be a fairly close approximation of a balanced load if the electrical engineer and the electrician did a good job of anticipating the loads. Bottom line is that IF all your 120 volt loads were concentrated on one end wire and the center wire the generator would be severely imbalanced and the maximum capacity limited to only one-half of its rating. But by distributing the 120 volt loads between the two end wires you end up with the generator "seeing" not several 120 volt loads but a few 240 volt loads (ever changing as various things are turned on and off) and can better supply the entire load.

While PJ is absolutely correct that you cannot run everything in your house at the same time on the generator you may indeed be able to run several of the smaller loads at the same time or even one or two of the larger loads with minimal usage of the smaller loads at the same time. If your clothes dryer is an electric (rather than gas) model it WILL take almost the entire output of your generator all by itself. The same is true if you try to bake a turkey in an electric oven. But you might be able to use a single surface burner on an electric range along with a few lights without problems. If your air handler has electric heating elements you are probably out of luck but if it is a fan-coil unit connected to a gas-fired boiler you should have no problem.

Generators are generally for emergency use when there is no utility power available due to some action of nature. Such outages are usually not all that long so a modicum of what I call "urban camping" can usually get you through the emergency. Not having laundry facilities for a few days is usually not a serious problem and if the outage lasts more than a few days you can usually get to a laundromat that is operating. Not having heat IS a major problem during the heating season and in some areas not having air conditioning could be life threatening under really adverse conditions. You may not like it but cooking via a hotplate, barbecue and microwave oven can keep you well fed and the refrigerator doesn't normally take a lot of power.
 
  #4  
Old 01-01-13, 02:24 AM
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Haven't you ever heard of two phase power
 
  #5  
Old 01-01-13, 02:57 AM
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Most assuredly I have! I worked in two different generating stations that had 2400 volt two-phase and I currently volunteer in a historical museum (one of those generation stations) that STILL has 2400 volt two-phase power.

BUT, the 240/120 volt power supplied to residences is NOT "two-phase" power but single phase power with a three-wire dual voltage system.

Nitpicking? Probably.
 
  #6  
Old 01-01-13, 03:08 AM
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You keep me on my toes.
 
  #7  
Old 01-01-13, 03:16 AM
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All is good.

The best to you and all in the new year!
 
  #8  
Old 01-01-13, 06:06 AM
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More Clarification

Happy New Year to everyone:

I do appreciate all the quick responses but maybe I missed something:

Is my 30 Amp Inlet Box a max of 30 Amps? Or is it more? Please see original question(s)

With regards to all the appliances, everything in the home is energy efficient. Everything runs on gas. There are no electric appliances besides the microwave and toaster oven. I had a test run and listened very carefully to the generator for strange sounds, etc. I had the following running in this sequence (daughter helped me with the use of cell phones, etc)

1) Turned on the laundry room lights, kitchen lights, family room lights, study lights, master bedroom # 1, # 2, # 3, #4, Bathroom # 1, # 2 & # 3 lights.
2) Turned on the computers and printers, etc.
3) Turned on the heat for the whole house, this kicked on ciruclator pump # 1, # 2, # 3 (generator noise constant) no surge.
4) Turned on washing machine (started a load) and waited 1 minute before the gas clothes dryer was turned on.
5) Then I turned on the gas oven, 4 burners to boil hot water in 4 pots (This lasted like 25 minutes) before shutting off.
6) Turned on all the Televisions (5 of them) as the cable power was reset already.

At this point the generator was still constant with no surges. I sat drinking coffee and slowly opened and closed each garage door one at a time for a few minutes and sometimes closing and opening both within a few seconds of each other. The only items that were not turned on but possibly kicked on (compressors) were the refrigerator and freezer.

I ran the whole house ont the generator for a total of 3 hours and everything worked fine through the 30 AMP Inlet Box.

So am I getting a maximum 30 AMPS on the Inlet Box or more? The generator is clearly telling me 45.8 amps at 120.What about the power running through the Box to the Fuse Box? That is my concern. I do not want to be overloading the generator. BTW, the generator breaker (30 AMP) no extension cords at 120 plugs never tripped.

Under normal circumstances the garage doors may be opened and closed 1X per day. I would only use the Washing Machine only and then the Gas Dryer. Not use any appliance like Coffee Pots or Microwaves unless everything else for the most part was shut off and there is no need for AC or Well Pump. Have city water and we can sweat a little if we lose power in the summer.

Thank you.
 

Last edited by Catanzaro; 01-01-13 at 07:05 AM.
  #9  
Old 01-01-13, 07:57 AM
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As long as the wiring between the inlet and panel is rated the same or greater than the generator breaker you should be fine. Your generator running output is less than 23 amps. Surge rating are to allow motors to start and only last part of a second or so.
 
  #10  
Old 01-01-13, 08:08 AM
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Sorry for being so wordy in my previous response.

Your power from the generator twist-lok receptacle, through the interconnect cable, inlet connector wiring and 30 ampere two-pole circuit breaker is rated for a continuous current of 30 amperes PER POLE. Three of the poles (wire connections) are current-carrying with the fourth pole being an equipment grounding connection. This means that the each of the three active wires (does not include the equipment ground) can safely carry 30 amperes but your generator can only supply a maximum of 22.9 amperes per pole. End result is that you are completely safe in regard to maximum amperage and/or power through this wiring arrangement.

I will now attempt to explain why the voltage, either 120 or 240 is an irrelevant term in this discussion. As I explained earlier you have a three wire-dual voltage system. Your generator will output the 22.9 amperes on EACH of the two "hot" wires at 120 volts returning to the neutral wire. Add those together and you would get the 45.8 amperes BUT only if each hot wire were returning current on the neutral wire. If the loads on each hot wire is equal there is NO current on the neutral wire and you instead have a 240 volt circuit of...22.9 amperes.

Your home electrical is divided between the two hot wires and ONLY the "unbalanced current" (from not having the exact same load on each hot wire) returns to the source (generator or utility) on the neutral wire. Because each hot wire from the generator is limited by design to only 22.9 amperes this is the MAXIMUM current that can ever return on the neutral wire.

A somewhat better means of calculation is to (for the moment) ignore volts and amperes and instead figure load by watts and/or kilowatts. Your generator can provide 5500 watts (5.5 kilowatts) continuously. We will ignore the surge rating for now. As long as the total load of your house is "balanced" between the two hot wire you can use up to 5500 watts of load in your house. If you have a 1,000 watt microwave oven on one hot wire and a 1,000 watt toaster on the other hot wire you have a total of 2,000 watts of load on the generator and can safely add another 3,500 watts of load.

HOWEVER, if both of these appliances are on the same hot wire then you while you still have the same 2,000 watts of load you can only add another 749 watts to the same hot wire before you reach the maximum load on the generator. Now 2,749 watts is only half of the generator's rating of 5,500 so why is this the max? It is because you MUST balance as much as possible the load between the two hot wires. In this example it is the same as you were skiing on one ski rather than two. Much easier skiing on two skis because you are balanced.

So let's look at this question of the power inlet from this angle of watts and volts rather than just amperes. At 120 volts ONLY your 30 ampere inlet is limited to 3,600 watts (more than your generator can put out on one hot wire plus the neutral) but at 240 volts the 30 ampere inlet has a maximum capacity 7,200 watts BECAUSE the load is balanced between TWO hot wires.

You have a fairly low electrical load in your home and I think you could live quite comfortably with a loss of utility power with this generator.

(I guess I was pretty wordy in this response as well. )
 
  #11  
Old 01-01-13, 08:22 AM
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Furd, is our pay now per word instead of per post? Grin.

Best of the new year.
 
  #12  
Old 01-01-13, 04:20 PM
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The two power (hot) legs are 180 degrees out of phase from each other. So why do we not call our utility power two phase?
 
  #13  
Old 01-01-13, 04:25 PM
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Two-phase electric power - Wikipedia, the free encyclopedia
Two circuits were used, with voltage phases differing by 90 degrees. Usually circuits used four wires, two for each phase. Less frequently, three wires were used, with a common wire with a larger-diameter conductor. Some early two-phase generators had two complete rotor and field assemblies, with windings physically offset by 90 electrical degrees to provide two-phase power.
The single phase power we use is a single circuit 180 degrees apart so there are two differences.
 
  #14  
Old 01-01-13, 04:49 PM
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Confusing replys IMO.... Too much typing.



Your gen is 5500 watts.
The gen has two windings.
Each winding produces 2250 watts.
2750w/120v = 22.9 amps per leg

Max watts you can draw on each side of panal is 22.9 amps or 2750 watts.


Is my 30 Amp Inlet Box a max of 30 Amps? Or is it more?

Max draw through that inlet is 30 amps per leg. It is allowed to exceed this for surge since its temporary.

A breaker would most likly trip if you exceeded 2750 watts or 22.9 amps anyway.

To the pros... Is this a reasonable reply to the OP as in not to confuse him?

Not sure why the 2 phase argument this probably isn't the place.....


 
  #15  
Old 01-01-13, 05:04 PM
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I think the OP can expect to get 20 amps or more from each 120 volt leg. So yes, the total current can be 40 amps or more without his 30 amp dual breaker tripping.
 
  #16  
Old 01-01-13, 05:14 PM
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I think the 30 amp breaker will trip at 2880 watts or 24 amps which is 80% of the breaker rating, no?

And the gen probably has 20 amp breakers so I assume they will trip at 1920 watts 16 amps?

Not an electrician. Just basing it on my knowledge. I may be wrong but just trying to simplify for the OP.
 
  #17  
Old 01-01-13, 05:46 PM
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Not sure about breakers but a fuse will hold it's rated current for many hours. I would guess a breaker would be the same.
 
  #18  
Old 01-01-13, 06:00 PM
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Max draw through that inlet is 30 amps per leg.
The inlet is rated for 30 amps maximum.

lawrosa

I think the 30 amp breaker will trip at 2880 watts or 24 amps which is 80% of the breaker rating, no?
No, the 30 amp breaker will trip eventually if the 30 amp rating of the breaker is exceeded or if there is a direct short on the load side. You shouldn't load the breaker more then 80% of it's rated capacity for continuous use which is defined as over 3 hours.
 
  #19  
Old 01-01-13, 06:09 PM
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The inlet is rated for 30 amps maximum.
So Joe does that mean one can draw only say 20 amps from one side of my panel and 10 amps from the other for max?

No, the 30 amp breaker will trip eventually if the 30 amp rating of the breaker is exceeded

Thant gen will never exceed 30 amps right? The gen breaker will trip first if its a 20 amp..???


Hmmm the OP may of gotten scared away.....









 
  #20  
Old 01-01-13, 06:23 PM
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So Joe does that mean one can draw only say 20 amps from one side of my panel and 10 amps from the other for max?
No. The voltage of the rating of the inlet is 120/240. There are two hot legs and one neutral leg. You can draw 30 amps from either hot leg to neutral (120 volts), 30 amps from each hot leg to neutral (2-120 volt circuits) or 30 amps across the two hot legs (240 volts).

Thant gen will never exceed 30 amps right? The gen breaker will trip first if its a 20 amp..???
Yes.
 
  #21  
Old 01-01-13, 06:36 PM
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The breakers will hold their full rated current for many hours. The breaker trip curve will show that as the current goes up in the time to trip goes down. A breaker can hold 125% for quite a while, but at 2x the current will trip quicker.
 
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