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208Y backup generator for 240 high leg

Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I'm getting ready to install a new backup generator for a small sewage pump station. The service is 240V high-leg delta, and the generator that is already set is 208Y. What should I look out for when wiring this setup? The main load is a couple of pumps, but there are also some lights, receptacles, etc. I'm assuming the generator supplier did account for higher amps at 208. I did confirm the ATS is a switched neutral.
TIA
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Electromatic said:
I'm getting ready to install a new backup generator for a small sewage pump station. The service is 240V high-leg delta, and the generator that is already set is 208Y. What should I look out for when wiring this setup? The main load is a couple of pumps, but there are also some lights, receptacles, etc. I'm assuming the generator supplier did account for higher amps at 208. I did confirm the ATS is a switched neutral.
TIA
Click to expand...

First check to see if the generator can be reconfigured to provide 240V high leg. 12 lead alternators are very flexible, and if the controller supports it you might be able to easily reconnect the generator.

If you can't change the generator for 240V:

Any 120V loads will likely be fine; both systems provide the same 120V L-N.

Next check the pump motors. Are they direct of the line or are they VFD controlled? If they are direct off the line, check the operating voltage rating. The pumps might be rated for 208V, in which case you are fine. If they are VFD controlled, then you will have to check the VFD settings for operation at reduced voltage. You might have a situation where the system will work but at reduced capacity.

-Jonathan
 
dkidd

dkidd

Senior Member
Location
here
Occupation
PE
winnie said:
Any 120V loads will likely be fine; both systems provide the same 120V L-N.

-Jonathan
Click to expand...
That's not true. I have seen at least 2 similar installations where they turned up the line to line voltage to 240, resulting in 138 volts line to neutral frying equipment.
 
Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
The pumps are across-the-line starters--no VFDs. I believe the pump motors are standard 230/460V. Obviously there will be increased amps and possibly less GPM output at 208. I don't see anything catastrophic that would occur with this setup.
(I may have to tape the ATS load side B phase orange AND red! ;))
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
Electromatic said:
I'm getting ready to install a new backup generator for a small sewage pump station. The service is 240V high-leg delta, and the generator that is already set is 208Y. What should I look out for when wiring this setup? The main load is a couple of pumps, but there are also some lights, receptacles, etc. I'm assuming the generator supplier did account for higher amps at 208. I did confirm the ATS is a switched neutral.
TIA
Click to expand...
Since this is a new install, the supplier needs to provide the correct generator, end of story. Sounds like somebody down the line ordered the wrong generator. If it was a temporary rollup generator, most of those rentals have a connection switch that can be turned to the correct voltage. If I was the inspector, I would turn it down.
 
H

hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
zbang said:
Can the ATS deal with 240v on one source and 208 on another? (So many questions.....) A 4-pole transfer switch might make things easier than a 3-pole but I haven't thought about that too closely.
Click to expand...
Usually there is a pot or a programmable set point that can be adjusted for pick up and drop out on both sources on a commercial or industrial transfer switch. And I think a 3 pole or 4 pole transfer switch would not make any difference.
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
dkidd said:
That's not true. I have seen at least 2 similar installations where they turned up the line to line voltage to 240, resulting in 138 volts line to neutral frying equipment.
Click to expand...

Fair enough. If the supply remains 120/208V, then the 120V loads will be fine. If the generator is adjusted to give 240V then the L-N voltage will be excessive.

-Jonathan
 
W

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Electromatic said:
The pumps are across-the-line starters--no VFDs. I believe the pump motors are standard 230/460V. Obviously there will be increased amps and possibly less GPM output at 208. I don't see anything catastrophic that would occur with this setup.
(I may have to tape the ATS load side B phase orange AND red! ;))
Click to expand...

If the voltage to the motors is too low, they may stall or not be able to come up to speed. Starting current will be reduced, but duration of the start may be significantly increased. Agreed that running current will be increased, perhaps excessively if torque is not sufficient for the motor to accelerate to low slip properly.

-Jonathan
 
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