Generator backfeeding question

[mendozer]

I currently have a transfer switch with 6 circuits installed by the previous owner. When I actually needed it last winter, I found out the hard way that only one circuit really worked. Not only that, but three that are wired into the panel aren't labeled at the breaker. So that's great.

Hence...I'm going to put in an interlock switch and backfeed with my generator. What I was curious about though, was if I could install a watt meter to monitor the draw of circuits being fed by the generator.

I have a 7kw gen, nothing too big. But in the event of an outage, all I really need to run are my water heat, furnace, stove (all gas), and my refrigerators, of which I have 4 (kitchen, spare, freezer, and project fridge for salamis). I don't intend to crank on my table saw or anything. We have LEDs everywhere as well, so our house draw probably isn't very much to begin with. I was looking at stuff like this:

Option 1

Option 2

Option 2 isn't as **** and you'd have to add it up but it's conveying the same wattage information.
I like Option 1 for the sake of amps as well, but IDK.

Any other options I haven't thought of?

 

[larry4406]

Watt meters are still on my to do list as well. Here is a similar thread I started.
https://www.garagejournal.com/forum/showthread.php?t=409827&showall=1

 

[ihateminimumwage]

...so our house draw probably isn't very much to begin with.

You'd better put a load calculation together on how many watts those appliances will actually take to run, or have an electrician come out and figure it out for you.

Fridges do draw a lot more wattage starting than running, and that's a lot of refrigeration going on...

 

[FarmerPete]

If you did Option 2, you'd need two of them, one for each leg. I personally like option 1 myself, and most of the solutions I've looked at either involve that or a similar part. You may want to get a slightly larger model in case you want to go with a 8k or larger generator down the road (assuming your wiring/plugs support bigger than 7500watts).

Have you checked to see if an interlock is available for your box, and is approved by your municipality? I know that not every box has an approved one available, and some municipalities don't allow them regardless.

 

[Dagny]

Refrigerators should say what they draw on the data plate. You should be fine though. It is very unlikely all 4 will start up at the same time.

 

[mike93lx]

I have meters built into my Reliance Panel. They can be nice, but in a power outage, you aren't going to be screwing around with balancing unless you are having problems with your generator keeping up. Make sure you do it before

 

[sberry]

I bring some of it on at a time. I have a big well, also a lot of fridge and I pump the well first.

 

[nafterclifen]

For whatever it's worth...

I installed a mechanical interlock in my panel for my generator. I have an Eaton Cutler Hammer (CH) panel and instead of buying an aftermarket breaker interlock kit, I was able to purchase a replacement Eaton CH panel cover with the interlock built-in for just a little bit more money than the aftermarket kit. Not sure what panel you have but something to consider.

 

[FarmerPete]

Refrigerators should say what they draw on the data plate. You should be fine though. It is very unlikely all 4 will start up at the same time.

As long as you turn off circuits before you turn on the generator....

 

[wyliesdiesels]

Option 1 only has 1 CT, so 120v loads that arent run through that leg will not be metered.

 

[wes73]

Option 1 I believe would require two devices. Option 2 will only require 1 device. I like to keep it simple when it comes to emergencies.

I have two of the reliance meter boxes (option 2) installed at 2 different locations. They work well. But it is best to make sure your loads are balanced prior to the time you need to use the gen.

 

[Bert_]

Option 1 only has 1 CT, so 120v loads that arent run through that leg will not be metered.

Could pass both legs through opposite directions.

Honestly a couple amp meters would be the simplest and best. Put a mark on the meter that shows the max for your generator. KVA is more important than KW in this situation.

 

[MBfreak]

Installing a Watt meter ( Watt=U*I*cos fi* maybe sqrt3) will tell you the active power loading the generator.
However it will not tell you the current in the stator generator windings, which is what limits the VA output of the set.
The heat load in the generator stator winding is almost directly proportional to the square of the stator load current.
I would install an Ammeter (in each phase) and monitor that.

Best regards

Ola

 

[JOE.G]

If I got 2 of option one, would that measure everything I need? I have a interlock on my box and my generator feeds my whole panel.

 

[zak77]

I'd skip the watt meter. I've run my house off a 7500watt generator many times which powered basically everything in the house including my well pump(biggest draw), microwave, coffee maker, 2 fridges, large standup freezer, boiler, lights, tv, and even a 6K btu AC. Obviously not all at once but with a little planning and thought, it can easily be done.

 

[theoldwizard1]

First, don't use the term "backfeed" for a generator interlock. Most people would think you are going to use a "suicide cord" !

Watt meters are really NOT required ! They are cool to look at, but once you have established that L1 and L2 are reasonably equal they are not useful. If you really want one, use a non-contacting "current transformer" type like #1.

(P.S. And now you know why I think those 6 circuit "transfer switches" are a waste of money ! You have ONE CHANCE to guess which circuits you want covered !)

 

[mike93lx]

(P.S. And now you know why I think those 6 circuit "transfer switches" are a waste of money ! You have ONE CHANCE to guess which circuits you want covered !)

Huh I had no idea. Here I was thinking that you could rewire circuits at any point. /s

Why would anyone be guessing? That makes no sense at all.

 

[JOE.G]

How does the first link style get hooked up?

 

[checkthisout]

With your load and 7000 watts, you don't need to monitor current draw.

You have 3500 watts per leg. Just make sure you don't run a coffee maker and hair dryer on the same leg.

 

[nafterclifen]

How does the first link style get hooked up?

If you have to ask, then the answer is "by someone else."

 

[JOE.G]

If you have to ask, then the answer is "by someone else."

I am sure I can figure it out, but it never hurts to ask and if I felt I could not do it then I would hire on someone, I like to learn and learn right.

 

[nafterclifen]

I am sure I can figure it out, but it never hurts to ask and if I felt I could not do it then I would hire on someone, I like to learn and learn right.

Turn off breaker, remove wire from breaker, slide sensor onto wire, connect wire to breaker, turn on breaker.

Is that really what you were looking for? If not, please be more specific with your question.

 

[JOE.G]

That is what I was looking for, Would this give me all the information I would need to balance my system?

 

[mendozer]

Wow lots of responses. What I don't quite get is how to balance the load since the power is going from the gen into the panel. When I turn on other breakers one by one, wouldn't the power just be split automatically? The reason I thought about installing the meter was for me to know what truly used 7500 watts at the max so I know what circuits to turn on.

 

[mendozer]

oh and the interlock switch I got is made by Siemens for my panel. It was $55 which for a piece of metal is expensive, but it sure ain't the aftermarket InterlockKit $175.

 

[checkthisout]

Wow lots of responses. What I don't quite get is how to balance the load since the power is going from the gen into the panel. When I turn on other breakers one by one, wouldn't the power just be split automatically? The reason I thought about installing the meter was for me to know what truly used 7500 watts at the max so I know what circuits to turn on.

You can't balance the load because you have no way to toggle the load between phases.

Just look at each individual circuit and know the wattage of what is on and operating on that circuit.

240 Volt stuff pulls evenly from both phases but 120V stuff is on one phase or the other.

Big draws on a single phase are hairdryers, space heaters, coffee pots, microwave.

The breaker on the generator will pop if your're having trouble figuring it out and your load gets too high.

 

[mendozer]

So, when running 120 on multiple circuits, there's no way to know which side of the generator the 120V phase will come from? This confuses the hell out of me haha.

Or are you saying that no matter what the balance is, as long as both meters don't go up to 7500W?

I don't have that much draw for my major appliances. And in an outage, I'm just going to use lights, cook with my gas range, and let the furnace and water heater continue along with refrigerators.

 

[checkthisout]

So, when running 120 on multiple circuits, there's no way to know which side of the generator the 120V phase will come from? This confuses the hell out of me haha.

Or are you saying that no matter what the balance is, as long as both meters don't go up to 7500W?

I don't have that much draw for my major appliances. And in an outage, I'm just going to use lights, cook with my gas range, and let the furnace and water heater continue along with refrigerators.

With a 7000 watt generator you have 3500 watts per phase.

So if your 240v stuff is pulling 4000 watts, that leaves 1500 watts on each phase.

You can tell which phase each breaker in your panel is on if you take the cover off and look. They alternate.

Nevermind all that. The load you're saying you're going to run makes it of no consequence. Just hook it up and run it. If the breaker pops, turn something off.

 

[mendozer]

ok I got you. Each phase corresponds to which side of the bus the breakers on. So each hot wire supplies one phase of 120V to the central panel. Thanks!

 

[mike93lx]

ok I got you. Each phase corresponds to which side of the bus the breakers on. So each hot wire supplies one phase of 120V to the central panel. Thanks!

No.

The "phases" alternate from breaker to breaker on each side. Look at the buss bars and how breakers connect in the panel

 

[mendozer]

oh so the (sine?) wave is essentially pictured with how the bus bar wiggles down?

 

[mike93lx]

oh so the (sine?) wave is essentially pictured with how the bus bar wiggles down?

Sure

 

[checkthisout]

oh so the (sine?) wave is essentially pictured with how the bus bar wiggles down?

What choo talk'n bout willis?

 

[mendozer]

Reviving this old thread since I am now finally going to get this done before winter.

I know some of you said monitoring it wasn't necessary...but I already bought it back when I posted it. So I already have (two) of Option 1, the digital ammeter. So just to review and clarify:

1. One hot line will run through each of the meter coils, black and red for each 120V feed.
2. Neutral was going to just run to the neutral bar on my panel but the wiring diagram suggests it comes back to this device on one of the terminals. (they list a little black and red from the coil for the top two terminals), then neutral going to a terminal, and the same load (after the "device") to the 4th terminal. The example they show is a light bulb but for my the device is the breaker and neutral bar on my panel.
3. This will be in a little project box mounted on the wall under my panel on the other side of the generator, which will be sitting outside of the wall.

One thing I want to double check is...if they're saying to feed neutral and load back to this little thing, it's just a tiny wire also coming out of the neutral bar and breaker port right? I'm not running the 10 gauge wire back to this for one it won't fit, but two, I imagine it's simply to power the device which has a very low draw.

 

[AP514]

How about uploading the Diagram....and your examples.
from the Amazon pics it looks like just slip over 1 wire and 2 other connects get power from a load and a neutral.

 

[nadogail]

IMHO, It appears that this whole discussion is an argument for the purchase of a clamp on Ampmeter.

 

[mendozer]

Forgive my crude drawing. This is extrapolating from their diagram (to the left).

But I want to see both legs as listed above in the discussion...so instead of black going directly to the breaker like I have...would it go through the second coil like in the second one?

Also, what splicing tool would I use to join the two wires? I've used the clamp down ones in car wiring before.

 

[Noltz]

IMHO, It appears that this whole discussion is an argument for the purchase of a clamp on Ampmeter.

Apart from OP having a failed inlet, yes it does. When you're on generator you'll want to be cautious no matter what. What worries me is OP has 4 fridges he wants to run. They have significant startup load. He will have to be careful switching the circuits on slowly.

 

[mendozer]

the clamp on ammeter would give me circuit loads at that time, the moment I'm checking it, right? That's not going to help me with real time balancing. but that's still a good tool to have and they're not expensive so I'm not opposed to that. I raise that issue because I can clamp it on a circuit to see amps but if the compressor's not booting up, then I'm not going to see the real limit.

Three fridge/freezers are on one circuit, the other is on another. Now I'm not expecting full house function here. I only need my furnace/water heater (which is propane but has low level electrical functions), refrigeration, and lighting (which is LED). I'm not looking to watch TV while making popcorn and stuff. It's just to keep things from spoiling during an outage. If I wanted full function, this wouldn't be a discussion and I've have a whole house generator plumbed to my propane tank.

I could bypass this monitor altogether, just thought it would be nice to see the usage so I know what's running real time

 

[checkthisout]

the clamp on ammeter would give me circuit loads at that time, the moment I'm checking it, right? That's not going to help me with real time balancing. but that's still a good tool to have and they're not expensive so I'm not opposed to that. I raise that issue because I can clamp it on a circuit to see amps but if the compressor's not booting up, then I'm not going to see the real limit.

Three fridge/freezers are on one circuit, the other is on another. Now I'm not expecting full house function here. I only need my furnace/water heater (which is propane but has low level electrical functions), refrigeration, and lighting (which is LED). I'm not looking to watch TV while making popcorn and stuff. It's just to keep things from spoiling during an outage. If I wanted full function, this wouldn't be a discussion and I've have a whole house generator plumbed to my propane tank.

I could bypass this monitor altogether, just thought it would be nice to see the usage so I know what's running real time

Again, you can't balance because you have no way to toggle between phases (the two hot wires) in your panel.

Figure out what you want to run.

Get a kill-a-watt meter and measure each devices draw by unplugging it and plugging it into the kill-a-watt and measuring it....write down your numbers.

Now figure out which circuit each device is on.

Then figure out which phase (which hot wire) in the breaker panel each circuit is pulling off.

Then look and see how many watts will be on each phase running the stuff you want to run.

If each phase is below 3000 watts, you're good. If not, you will have to juggle breakers needed with the easier way maybe just running a cord from the appliance to an outlet that is on the opposite phase.

If you don't understand this then hooking up those Chinese volt amp displays so they work and work without being a fire hazard with proper fuses and such is well beyond the scope of your skills. (not trying to be a jerk).