Wiring a 3 kw set to house

[m139h2otruck]

Tried to wire the 3 kw set into the garage to test for possible use during a power outage. The terminals show the correct voltage of 240 volts between the L1 and L2 terminals with the switch in the correct position, so I wired up the L1 and L2 terminals to the hot legs of the fuse box and the ground to the ground. When we tried to run the garage, it acted like a low voltage on one or both legs, burnt up the heater PC board and overloaded a couple of motors that were on (but no problems). Anyone got any ideas? Unit works great on 120 volts with a plug hooked to L1 and L2.

 

[nickd]

Using an electrical meter, take voltage readings while the generator is running before attempting to hook it up to the garage.

 

[rmgill]

Did you unhook the power from the utility? Your garage may not have a neutral bonded to ground which is correct IF it's a sub panel off of the house.

If you didn't disconnect from the utility, you could have been out of phase and really horked things up.

If you don't know about bonding neutrals and grounds and phases and the like, you REALLY need to talk to an electrician to get this done right. Doing it wrong with a generator set can no only kill or hurt you AND burn your house down in the process, it can also kill a power worker who's working on a line that should be isolated from the substation (known as a backfeed).

 

[m139h2otruck]

All good points.
1) Yes the garage sub panel was disconnected from the house/main. Garage is single phase 200 amp box 240 volt.
2) Yes the voltage was checked at the L1 and L2 terminals and showed 240 volts between them and 120 volts from hot terminal (either L1 or L2) to ground. Gen set was set on the 240 volt single phase position.
3) Yes the sub panel has the neutral and ground bonded inside the panel.
4) While I am not an electrician, my father was, and worked for a local power utility for almost 40 years. I have been in the construction industry for over 35 years, & I think I have a reasonably good working knowledge of power panels and distribution. But as I said above, all good and very valid points.

Have done this exact same hookup before with a different set with no problems, so I can't see why this unit will not work. Was looking to load the unit for a test. Guess I will have to talk to a friend @ the local Cat dealer to see if they have a small load bank I can borrow.

 

[mangus580]

240 single phase setting on the 3 & 5kw gensets is NOT like the single phase in your house!!!!

You need to set it in the 3phase setting and only use 2 of the 3 phases....

 

[m139h2otruck]

So, 240 volt single phase mil is not 240 volt single phase std? This could be exactly the problem. Any further explanation for why this is so on this type of gen set?

 

[mangus580]

No clue why its like that.... but its so

 

[Recovry4x4]

You will end up with a ground leg and a 240 leg instead of 2 120 legs.

 

[JasonS]

Power comes off the line through a center tapped secondary transformer. This is how you get 120-n-120. How are you getting the 'neutral' off of the generator? Without this, the voltage line to neutral will be established by the individual loads and will be unstable.

 

[Oldvw2]

240 single phase setting on the 3 & 5kw gensets is NOT like the single phase in your house!!!!

You need to set it in the 3phase setting and only use 2 of the 3 phases....

Friend of mine found this out the hard way too after BBQing some household appliances. After talking with some guys knowledgeable about these sets we found the best way to power the transfer switch and emergency panel was to use the 120/208 3 phase position. We used two of the three hot lugs plus the neutral. We found 208v was plenty for most 240v applications. As mentioned, the 240v position is 240v line to line without a neutral. I have read that there is a neutral available on an inside terminal when 240v is selected but this would require some wiring changes. Hope this helps.

 

[JasonS]

240 single phase setting on the 3 & 5kw gensets is NOT like the single phase in your house!!!!

You need to set it in the 3phase setting and only use 2 of the 3 phases....

I don't think that this will get you what you want either. The two legs of three phase will not be in phase. This will affect your 240V appliances. Your 120-n-120 is in phase.

 

[acetomatoco]

And only 3 KW is hardly enough to bother with hard wiring... Just rig a mini panel on the gen set out side and run a couple of extension cords into the garage.. for a load test just plug a couple of battery chargers into the 110 plugs on the set and charge some batteries

 

[mangus580]

240 single phase setting on the 3 & 5kw gensets is NOT like the single phase in your house!!!!

You need to set it in the 3phase setting and only use 2 of the 3 phases....

I don't think that this will get you what you want either. The two legs of three phase will not be in phase. This will affect your 240V appliances. Your 120-n-120 is in phase.

Agreed... but in alot of industrial buildings... it is done in this manner...

 

[Oldvw2]

I hope I haven't confused anyone...

Based on my experience wiring one of these to a transfer switch, the closest you are going to get with the 3KW set in its stock configuration is to use the 120/208 setting. Any hot to hot will get you 208v and hot to neutral will get you 120v. Check your 240v loads to make sure they will work in this voltage range - most will list acceptable input voltage. You will still need to use two hot lugs and the nuetral lug(not ground). In the TM wiring diagrams, you can see an internal terminal that you could use to add a neutral for the 240v position and then you would have 240v hot to hot and 120v hot to neutral.

ACE's idea on the mini panel is a good one too as you can get full power from the generator via the output lugs on the side of the set vs. the 120v duplex outlet.

 

[m139h2otruck]

Now, since the 240 volt position on the selector switch is not usable on a home system without additional work, what about the 1.5 kw sets? I just got one of these too, (not picked up yet) and am wondering about the wiring for these units.

 

[mangus580]

Same thing. The only set that has a usable selector position is the 10kw.

 

[OPCOM]

The statement that you have to access the internal connection is correct. There is a thread on this somewhere, with diagrams. Once wired right using the internal connection it will be fine.

 

[rmgill]

240 single phase setting on the 3 & 5kw gensets is NOT like the single phase in your house!!!!

You need to set it in the 3phase setting and only use 2 of the 3 phases....

I don't think that this will get you what you want either. The two legs of three phase will not be in phase. This will affect your 240V appliances. Your 120-n-120 is in phase.

Right, they'll be 120 degrees out of phase. Their sum being 208 volts. Most 240 volt appliances work just fine with this. Some VERY home purpose items might have issues. Computers are just fine with it. I have a data center FULL of 208 consuming systems that are just like anything else. As long as it's able to take 240 volt with an autoswitching power supply it doesn't have a problem.

 

[dmetalmiki]

On the subject of generators..does anyone know if the ex army/airforce onan 10.K.V.A. 28/120/240 volt set is switchable between 50 and 60 hertz? (c.p.s.) or just 60 cps.... the 3.5 kva onans 240v only are 50 hertz. (cps). ok for blighty!

 

[OPCOM]

The Hz is determined by the engine speed and number of poles in the alternator. On the Onan, it may well be the same engine and alternator, only the speed is lower for 50Hz and the regulator may be different or adjustable since the lower the speed, the lower the voltage in some cases. There's no switch, you have to mess with the speed. You should be alke to try it with no ill effects. Watch the voltage, that it does not rise excessively.

If it is the same engine, you can try raising the speed. If it is a (2-pole alternator) 3000RPM one for 50Hz, it will have to be 3600RPM for 60Hz. The low speed (4-pole) ones will be 1500RPM-50Hz and 1800RPM-60Hz.