# Backup generator question



## 480sparky (Sep 20, 2007)

What voltage?


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## telecom_guy (Mar 26, 2009)

sorry, 120/208


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## walkerj (May 13, 2007)

I don't believe the genny will be able to handle that start up.

What is the LRA of the motor?


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## telecom_guy (Mar 26, 2009)

The LRA is about 110, or so im told. I have not checked the motor myself so im not sure what the specs are on it. This motor is for a fire department air siren which has been used with this genset in the past. It is actually the second one put in because the contractor ordered the first one too small for the siren load. The first one was a 23 or 24kw as I was told, and when they ran the siren, it ramped up to about 108amps and the generator quit. Anyone ever see a really big genset have a sudden dead short? I've heard that they can flip over, ripping out any anchoring.


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## william1978 (Sep 21, 2008)

telecom_guy said:


> I've heard that they can flip over, ripping out any anchoring.


 I would like to watch this. Any body got a video of this happening?


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## micromind (Aug 11, 2007)

I didn't get to see it, but fixed the results of a generator problem similar. 

Several years ago, a road contractor bought several hot plants (asphalt mixing plants). They also bought several generators to power the plants. these gens were from 1000KW to 1500KW. 

A hot plant needs a small amount of power 24/7 to keep the hot oil circulation system going. Usually this is a small diesel boiler with about a 5 or 7-1/2 HP circulating pump. Not a good idea to run the big gen for that small of a load. 

I installed a small gen (around 40KW) in the same trailer as the big gen. The hot oil system is powered by the same MCC as the rest of the plant. Since there is no synch system, I installed 24 DC shunt-trip coils in both gen breakers. There is a speed switch (idle-full) on the big gen. Whatever position this switch is in, it shunt-trips the other breaker. I also left instructions to completely turn off the running gen before starting the other one. 

One day, they burned up the breaker on the small gen. Not wanting to pay anyone to replace it, they did it themselves. A couple of days later, I got a call about a problem with one of the gen vans. When I got there, the small gen was laying on its side! Rubber mounts ripped apart, fuel lines ripped out, not a pretty sight!

It seems that (no one will admit to it) the big gen was running, they started the small gen, and closed its breaker. Normally, this would have caused the shunt-trip to not allow the breaker to close, but it seems that the replacement breaker had a 120 AC coil. 

I wonder if they still think of all the money they saved by replacing the breaker themselves!

Rob

P.S. Most turbine generators I've seen have shear-bolts on the shaft couplings. That way, if the breaker is closed in while out of synch, it'll shear the bolts rather than destroy the turbine and gearbox.


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