120V 2-pole generator

[FoxValleyRob]

I'm confused about how to connect a 120V emergency generator into a normal power distribution system. I see in the wiring diagram that in order to obtain the 120V (NOT 240V), they have jumpered the line side of the circuit breaker together. That means that you would have to read 0V on a meter from L1 to L2. This is on the emergency generator side. The problem I'm having is that when you measure the same leads (L1 and L2) on the NORMAL side, you'll have 240V. When the transfer switch goes to emergency, the only way I see this working is that the phase of one of the lines has to switch 180 degrees. What happens to a load when it suddenly sees a 180 degree shift in its voltage? If I'm way off here, please let me know...

Thanks a bunch!

 

[jim dungar]

Ignore the internal wiring of the generator except for its 120V two output terminals.

Are you really trying to feed a 3-wire 120/240V load with only a 2-wire 120V source? Or do you plan to feed only some of the 120V loads?

 

[FoxValleyRob]

A followup - I have finally learned that a 240V system is not in fact 180 degrees out of phase...something I should have learned a LONG time ago. So all is cool. The existing system is a 120/240V single phase system, and the emergency generator is 120V, so any 240V loads under normal loads will not function under emergency load.

I didn't want anyone to waste time answering my uninformed question...Thanks!

 

[hurk27]

I have done this through a manual transfer switch only, when wiring the transfer switch, place a jumper from line 1 to line 2 on the E (generator) terminals only. put the load on the L terminals, and the utility on the N terminals

No 240 volt loads will have power but all 120 volt loads will work if the generator is large enough to supply the load, when the transfer switch is in the normal (utility ) mode it will supply the full 240/120 to the load, but when in the back up side only 120 volt loads will be supplied.

 

[hurk27]

A followup - I have finally learned that a 240V system is not in fact 180 degrees out of phase...something I should have learned a LONG time ago. So all is cool. The existing system is a 120/240V single phase system, and the emergency generator is 120V, so any 240V loads under normal loads will not function under emergency load.

I didn't want anyone to waste time answering my uninformed question...Thanks!

most 240 volt supplies in the USA will be 180? out of phase, only where you have a 240/139 Y will you have a 120? phase differance. but that is a rare installation. for the most part any 240 volt supply will be 180? from L1 to L2/ and L1 to N and L2 to N, it is tha additive of these two windings that is dependent on the 180? phase shift that gives you the 240 volts.

 

[Rick Christopherson]

Make sure you're not feeding any multiwire branch circuits. You'll burn the neutral.

 

[hurk27]

Make sure you're not feeding any multiwire branch circuits. You'll burn the neutral.

good point, didn't think of that when I posted.

 

[LarryFine]

In my opinion, the fix here is a genny-load sub-panel with proper interlock, supplying only 120v loads, with the lines compliantly jumpered on the genny side.