Backup Generator Wiring

Ted DuPuis said:
Like I said, I wouldn't do it myself, but I'm probably overly paranoid about that stuff since I used to run these things on dynos. :)
Click to expand...
You mean like using pterodactyl fuel in a brontosaurus? :D

You're not THAT old, Ted!
 
Sac Arrow said:
Power in the distribution grid normally comes as three phase 480v, and the two phase legs will usually be split between housing blocks to even the load. Three hots = 480V, two hots = 240V, and hot to neutral = 110V.
Click to expand...

This is incorrect. Residential distribution power is usually two or three wire 7200 volt and transformed to two wire 240 volt with a neutral for service laterals to homes. One leg of the 240 volt service and a neutral produce 120 volts for household receptacle and lighting loads. Ovens, dryers, and A/C units use 240 volts.

Three phase 480 from utilities is a delta configuration, and has no neutral. The voltage between any two phases is 480 volts, not 240. Three phase 480 delta is primarily used to power motor loads like air handlers and chillers or manufacturing plants. It has to be run through a 480 delta/480 wye transformer to produce a neutral.

One phase of 480 wye paired with a neutral results in 277 volts, not 110. Most commercial office building lighting is 277 volt, which is just about the only thing it's used for. All buildings served with 480 delta have a 480D/208Y transformer for receptacle loads. One leg of 208Y and a neutral produce 120 volts.
 
Last edited:
3393RP said:
This is incorrect. Residential distribution power is usually two or three wire 7200 volt and transformed to two wire 240 volt with a neutral for service laterals to homes. One leg of the 240 volt service and a neutral produce 120 volts for household receptacle and lighting loads. Ovens, dryers, and A/C units use 240 volts.

Three phase 480 from utilities is a delta configuration, and has no neutral. The voltage between any two phases is 480 volts, not 240. Three phase 480 delta is primarily used to power motor loads like air handlers and chillers or manufacturing plants. It has to be run through a 480 delta/480 wye transformer to produce a neutral.

One phase of 480 wye paired with a neutral results in 277 volts, not 110. Most commercial office building lighting is 277 volt, which is just about the only thing it's used for. All buildings served with 480 delta have a 480D/208Y transformer for receptacle loads. One leg of 208Y and a neutral produce 120 volts.
Click to expand...

"Most commercial office building lighting is 277 volt, which is just about the only thing it's used for."
Yeah we use 277 for tunnel lighting here on my job as well. In fact, it's the only time I've run into 277V equipment. Here it makes sense because our ventilation fan motors are 480V, so we tap off of the same transformers to feed the tunnel lighting, eliminating the need for additional transformers as well as allowing more lights per circuit.

We are supplied three 13KV feeders from Con-Ed in NYC and three from PSE&G in NJ, (six feeders in total), which we step down to 480/277 and 208/120 here at the facility.
Multiple 3-phase transformers in various locations throughout.
This gives us ample redundancy to keep the 84 fans running and the tunnel lit during a loss of power from either supplier. The only time we've lost all six feeders since I've been here, was during hurricane Sandy!

Sac Arrow said:
Presumably, he (RJM62) is feeding two-phase 220V from the generator to the main feed, hence the distribution between 220 and 110 should take care of itself in the breaker box. With the appropriate interlock, and wired correctly it should be safe.
Click to expand...

Single phase.
 
Last edited:
RJM62 said:
All done and load-tested. Works great. Basically, it will power anything in the house -- just not all simultaneously.

Here are some more pictures.

Here's the junction of the Romex to the THWN. You have to use wire rated for wet areas in an exterior conduit. I chose THWN because it's less bulky than UF-2. It's also THHN rated, so I technically could have gotten away with 8-gauge from the junction box to the generator inlet. But I used 6-gauge anyway (except for the ground, which is 10-gauge) for a bit of extra safety margin and future-proofing.

8.jpg


9.jpg


I have to label this box.

10.jpg


Next picture is the backfeed breaker.

11.jpg


Next picture is the contraption to affix the backfeed breaker to the panel. This is required by code, presumably because the backfeed breaker becomes the "main" when in use. The label is also required by code.

12.jpg


The next picture is the interlock switch installed. It's a simple device. It physically prevents the backfeed and main breakers from being energized at the same time. That makes it impossible to energize the power company's lines (and possibly electrocute a lineman) from your generator. The labels are required by code.

13.jpg


And here's the little generator powering the house.

14.jpg


As I mentioned, with this setup, I can power anything in the house. I just can't power everything at the same time. It's a good setup if you have enough common sense to manually manage your power use.

Rich
Click to expand...
Nice job! Almost makes me want to get my hands dirty again.:D
 
Barely related but...

I'm wiring my 220v bifold door to be able to plug into a generator if the power goes out and I need to open or close the door. Here's the layout:

45032986212_84203bd771_z.jpg


The idea is the door will generally be plugged into the generator receptacle. Power goes out, I'll unplug it from there and plug it into a generator.

(this was an idea a friend had to avoid needing a rather expensive transfer switch)

The door has 3 wires running to it: two "hots" and a ground, no neutral. I'm wiring to the generator outlet/plug which generally assumes a neutral.

Question: could this cause any problem for the generator, when it doesn't sense a neutral? If so, could a cheater adapter that bonds neutral and ground at the generator help without undue risk?

Thanks in advance.
 
FastEddieB said:
The idea is the door will generally be plugged into the generator receptacle. Power goes out, I'll unplug it from there and plug it into a generator.

(this was an idea a friend had to avoid needing a rather expensive transfer switch)

The door has 3 wires running to it: two "hots" and a ground, no neutral. I'm wiring to the generator outlet/plug which generally assumes a neutral.

Question: could this cause any problem for the generator, when it doesn't sense a neutral? If so, could a cheater adapter that bonds neutral and ground at the generator help without undue risk?

Thanks in advance.
Click to expand...

Many portable generators already bond neutral and ground, so as long as the cord is grounded or the generator frame is grounded all should be well. Even if not then it still shouldn't be a problem as the motor would already have to be properly isolated to use 240V without a neutral, unless the control circuitry is 120v and using the ground as a neutral that would be bad(tm). The generator shouldn't care. (Which reminds me I need to look at my hangar door and see what I can do there.)
 
Last edited:
chartbundle said:
Many portable generators already bond neutral and ground, so as long as the cord is grounded or the generator frame is grounded all should be well. Even if not then it still shouldn't be a problem as the motor would already have to be properly isolated to use 240V without a neutral, unless the control circuitry is 120v and using the ground as a neutral that would be bad(tm). The generator shouldn't care. (Which reminds me I need to look at my hangar door and see what I can do there.)
Click to expand...
That would be my only concern as well. What voltage is the control circuit. For example, our original motor control cabinets consisted of both 480VAC 3-phase for the motor contactors, as well as 120VDC for the control circuits. The relay coils were DC, fed by a 125VDC system that included a series of backup batteries and a 125VDC charger. This has all been upgraded and replaced over the last decade with Siemens solid state equipment.

This is why I seldom give wiring advice online without having the schematic to examine. But as you said, the generator shouldn't care as long as the output is rated to 240V (single phase).

Speaking of which, it is a common novice mistake to assume that two hots = 2-phase. Both hot conductors share the same Sinusoidal (sine) waveform.
Thus, making it single phase. As was mentioned by 3393RP, a neutral is a center tap from the same winding. So, both hots as well as the neutral share the same sine wave (in a single phase circuit).

True 2-phase is obsolete, it was replaced by 3-phase because 3-phase is more efficient, especially with induction motors.
 
Last edited:
Redbird said:
We are supplied three 13KV feeders from Con-Ed in NYC and three from PSE&G in NJ, (six feeders in total), which we step down to 480/277 and 208/120 here at the facility.
Multiple 3-phase transformers in various locations throughout.

This gives us ample redundancy to keep the 84 fans running and the tunnel lit during a loss of power from either supplier. The only time we've lost all six feeders since I've been here, was during hurricane Sandy!
Click to expand...

I would like to see your incoming feeder switchgear. I built large data centers before I retired, and the most complex service I was involved with had four 8 mW 4160 volt feeders and four 2 mW 4160 generators.
 
Industrial and airport power isn't residential. Sure, when I was in facilities at an Army Base and at the State University we had 13KV lines that we'd step down to 277/480 or 120/208, But you ain't going to see that in a residential neighborhood most likely and hardly germane to anything with regard to residential backup generators.

I've seen a few pretty flamboyant things at the high tension sides of things over the year, only one of which I was directly responsible.
 
Thank you to both chartbundle and redtail.

I will look at the installation manual and actual install to see if there’s 120v supplied independent of the 220v.

That would make things a little more complicated, requiring a second cord to provide the 120v. But all I’m doing here is rerouting the 3-wire combo supplying the 220v to the main panel.

But something I had not considered, so thanks again to you both.
 
flyingron said:
Industrial and airport power isn't residential. Sure, when I was in facilities at an Army Base and at the State University we had 13KV lines that we'd step down to 277/480 or 120/208, But you ain't going to see that in a residential neighborhood most likely and hardly germane to anything with regard to residential backup generators.
Click to expand...

Are you saying this thread went off topic?

That never happens here.
 
My current idea is to build a combination shed / baffle box so I can leave the generator outside near the inlet box. The biggest concern is that it would have to be rodent-proof. That's the only reason I don't just toss a canvas cover over it and leave it there.

I'm wondering whether if I put hardware-cloth air inlets about three inches high around the whole enclosure at the bottom, and a hooded vent on the top, the convection would be enough to provide combustion air even without an exhaust fan. I suspect it probably would be in the winter, but maybe not in the summer.

Rich
 
FastEddieB said:
Thank you to both chartbundle and redtail.

I will look at the installation manual and actual install to see if there’s 120v supplied independent of the 220v.

That would make things a little more complicated, requiring a second cord to provide the 120v. But all I’m doing here is rerouting the 3-wire combo supplying the 220v to the main panel.

But something I had not considered, so thanks again to you both.
Click to expand...
Good idea to take a close look at the manual and any print available before proceeding. The other possibility that comes to mind is, there could be a small 240V transformer enclosed, lowering the control circuit voltage to 24V (or another reduced value).
If so, there would be no need for 120V (no neutral wire).

Something like this

Pri: 240V, 208V.
Sec: 24V
https://www.amazon.com/Goodman-0130...38718722&sr=8-3&keywords=240v+24v+transformer
 
Last edited:
flyingron said:
Industrial and airport power isn't residential. Sure, when I was in facilities at an Army Base and at the State University we had 13KV lines that we'd step down to 277/480 or 120/208, But you ain't going to see that in a residential neighborhood most likely and hardly germane to anything with regard to residential backup generators.

I've seen a few pretty flamboyant things at the high tension sides of things over the year, only one of which I was directly responsible.
Click to expand...
True.
Guess I got all excited by the incorrect reference to polyphase AC systems (2-phase/3-phase).

As the youngins say....
My bad:D
 
Last edited:
I enjoyed the detour. I didn't know large airport lighting was powered in that fashion. I knew it was 4160, but not the details, especially the constant current source. The image in your post was great.
 
redtail said:
Good idea to take a close look at the manual and any print available before proceeding.
Click to expand...

I’m back at the property and will look.

Examining the physical installation, it appears the only power in is the two hots and the ground. There is also the single dual breaker at the breaker box marked “bifold door”, though it might be possible that 120v could be piggy-backed onto another circuit. I suppose I could verify that by turning off all the breakers other than the one for the door and confirming it still works.

I’ll report back once I check the manual.
 
FastEddieB said:
I’m back at the property and will look.

Examining the physical installation, it appears the only power in is the two hots and the ground. There is also the single dual breaker at the breaker box marked “bifold door”, though it might be possible that 120v could be piggy-backed onto another circuit. I suppose I could verify that by turning off all the breakers other than the one for the door and confirming it still works.

I’ll report back once I check the manual.
Click to expand...

If it just needs a simple 120V for a control box of some sort, that could just be plugged in on another 120V receptacle or mixed circuit. It wouldn't have a labeled breaker in the panel (labeled as bi-fold door, anyway). Look around the unit for a box that has the 220V wiring going into it (and out of it to the motor, probably near the motor) and see if it has a plug. If so, then you need to power that as well. If not, you're good with 220V as you've described. It could be that simple with a couple of limit switches.

John
 
3393RP said:
I enjoyed the detour. I didn't know large airport lighting was powered in that fashion. I knew it was 4160, but not the details, especially the constant current source. The image in your post was great.
Click to expand...
Yeah when you mentioned the 4160, I thought it would be an interesting tidbit to share with fellow aviators who happened to be discussing electricity and probably never give thought to something we all use. However, I should have started a separate thread.
 
Last edited:
The journey begins.... MEP803a mil genset. Military-rated at 10kw, this one load-tested at 14kw continuous for 4 hours, prior to purchase. No capable generator receptacles I can find (50 amp max so far), so probably will have to hard-wire it directly to the generator breaker (125 amp) inside the main breaker box. Woohoo!

Blessed by the military for both diesel and JP8 (jet fuel, baby!)

Jim
 

Attachments

  • Genset.jpg
    Genset.jpg
    217 KB · Views: 15
Last edited:
Jim Rosenow said:
The journey begins.... MEP803a mil genset. Military-rated at 10kw, this one load-tested at 14kw continuous for 4 hours, prior to purchase. No capable generator receptacles I can find (50 amp max so far), so probably will have to hard-wire it directly to the generator breaker (125 amp) inside the main breaker box. Woohoo!

Blessed by the military for both diesel and JP8 (jet fuel, baby!)

Jim
Click to expand...

The military does tend to rate things rather conservatively. Have fun!

Rich
 
Jim Rosenow said:
The journey begins.... MEP803a mil genset. Military-rated at 10kw, this one load-tested at 14kw continuous for 4 hours, prior to purchase. No capable generator receptacles I can find (50 amp max so far), so probably will have to hard-wire it directly to the generator breaker (125 amp) inside the main breaker box. Woohoo!

Blessed by the military for both diesel and JP8 (jet fuel, baby!)

Jim
Click to expand...

Very cool! You'll definitely have to direct wire it in, no receptacle for that amount of current.

If you don't mind sharing, did you grab it off of eBay or elsewhere and what'd the total damage end up being?
 
There are plenty of receptacles for higher current, Cooper has up to 125A in this line: http://www.cooperindustries.com/content/public/en/wiring_devices/products/pin_sleeve_devices.html

It's almost certainly more trouble than its worth as you'd still need to source a cordset and everything else. The 100A inlet alone looks like about $280.

Oh, if you need more current, here's the ones up to 400A, I don't even want to think about the prices:

http://www.cooperindustries.com/con...industrial_plugsreceptacles-nonhazardous.html
 
I found it fairly locally on craigslist, Ted. The man I bought it from is in construction, and had been buying groups of them and updating them for resale. A recent change to government policy is driving a bunch of people who did that out of business. Previously, if Fort Schmuck had a dozen gens to get rid of, they would sell locally. I'm told that now, you can only pick them up two places in the country. But I digress....

The one I have is a MEP803a, 10kw nominal (load-tested to 14kw), 2011 with 4005 hours on it. Onan 4-cyl water-cooled diesel, 1800 rpm...parts available at the RV places. At around 4000 hours the military does a full IRAN on them (if the ash tray's full, get a new ash tray sort of thing). They did this to it, and then it sat, properly moth-balled, til the guy I bought it from purchased a group of them. (Ironically, our 182RG went thru a similar process with the FBI...at 4000 hours the entire airplane was brought up to 'new' standards, including replacing some control surfaces.)

The guy I bought it from put in all new filters, upgraded the rubber gas lines, new fan belt, changed the oil and radiator coolant, ran it for 5 hours at load, then put an ad on craigslist. You could literally eat off the inside of this thing. He provided a full set of technical/parts/maintenance/whatever digital manuals with it.

I didn't feel bad paying $4000 for it, even though I'm sure it's way more than he had in it (did I mention there was no shipping :) The $4k includes him coming over to install the remote start kit when it arrives. (There are both an auto-start and remote start modules for the gens available...around $450 each. Didn't want to pay for the automatic transfer switch that auto-start would require when I already have a manual TS).

So...paint it to match the house, put it on a suitable base, make the wiring changes, and we're golden. The procedure if the lights go out will be...go to the basement, flip the gen start switch beside the breaker box, warm up the gen, then flip the line/gen switch. Reverse to shut down. It's quiet enough (mil designated 'tactical quiet') it will actually sit outside our bedroom window, with 'suitable security' available out the window. Nobody's gonna run off with it...1200 pounds full of fuel. :)

The 9 gallon internal tank should run our house for awhile (.9 gallon at full load, .25 gallon at 2kw load). In the event of a longer outage, I have a 55 gallon drum that will be filled and ready. The gen unit has an external fuel pump that will suck fuel out of the drum into the main tank when the fuel level dictates. It's a pretty nifty set-up. Oh...and to avoid wet-stacking, several milk house heaters will be employed to load it up occasionally.

More than anyone, ever wanted to know about this!....questions?

Jim
 

Attachments

  • Genset.jpg
    Genset.jpg
    217 KB · Views: 12
Last edited:
That sounds like you got quite a good deal that ought to work out well for you, Jim. That 9 gallon internal tank probably will be sufficient time wise too.
 
....and of course you know this means the power will never ever, forever go off at our house! :)

Jim
 
Matthew K said:
No one seems to have asked about this so...what are you powering to need a 80KVA generator?!
Click to expand...
The screwball engineers punted on my instructions of separating the essential circuits to a separate panel to be fed with the ATS, and just spec'd the big generator.
I can run my complete house which is pretty much all electric other than the generator (there are a few gas appliances like the two Rinnai's), I've got geothermal heatpumps, etc..
 
You must log in or register to reply here.
Back
Top