Need help wiring Generac GTS to Cummins c25 genset

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Pdexter1210

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Location
Texas
Occupation
Engineer
Hello, I'm looking for someone who might be able to help point me in the right direction on hooking the subject transfer switch and genset together. I have run contacts from 178 and 183 in the GTS out to the genset and landed those on TB5 (Remote Start) and TB1 (Ground). Have tested the generator in manual, it starts and runs just fine, generates electricity as it is supposed to. When we disconnect utility service and hold down the Fast Test Mode switch, the generator starts, comes up to speed and the GTS transfers power to the load. This has the appearance of working as it should, however if we don't disconnect utility service ahead of time, the transfer switch seems to feed power through both the utility and the generator (as noted by the nearby a/c unit ramping up dramatically when we tried the transfer). The transfer switch mechanism is working, so I don't how to explain why it seemed like we were sending electricity from both sources, but it does. We have disconnected the utility service, started the generator manually and manually transferred the GTS and that works fine. I have manuals for both the GTS and the Genset, but haven't been able to diagnose my issue yet, so I thought I would check the forum. Also note, when we put the GTS in Normal Test Mode, nothing happens (although I'm not sure yet whether this is simply a timer that we have set too long, or if it is a further issue). Licensed electrician working on this, just not one that is familiar with this GTS.

Any thoughts on where we might have stumbled or ideas on what to look for would be appreciated. Thanks in advance.
 
Following up on this post to see if anyone has experience with a Generac GTS transfer switch? The electrician got everything working today with the exception of the Normal Test Mode switch, it still will not start the generator. All other functions are operating correctly, transfer upon loss of utility works great and transfer back works fine.

If anyone has a wiring diagram of a GTS (I only have the installation manual which doesn't have wiring diagrams), I would appreciate it if you could post that so that we can try to diagnose the cause for why the GTS doesn't want to work in Normal Test Mode. Thanks in advance.
 
I'm not a generator expert, but I thought only Generac brand TS would go with Generac generators and vice versa.


What is a GTS?
 
Thanks for the response, GTS is the model of Generac transfer switch, circa 2015 vintage or thereabouts. It's a two-wire start transfer switch that has a number of additional features like CT's to monitor amps/volts/Hz, has built in timers for exercise as well as adjustment for timing of switching the utility/gen sources and other bells and whistles. They're typically found on larger genset systems coupled with water cooled generators like found on communications towers. On the pairing of Generac brand only, a two-wire start signal is all that is required to start this Cummins genset, so it's agnostic to what brand of transfer switch that is sending the closed contact signal. If using the big box store variety Generac air cooled systems and ATS, mating is probably a little more impactful for install purposes. This application is just closing an open contact and the generator starts, which works fine under Automatic mode and Fast-Test mode from the GTS. My issue specifically is that I cannot get the GTS to operate the generator (meaning closing the same set of contacts that is closes under all other modes) when in Normal-Test mode. This mode is there so you can flip a toggle switch and operate the generator without transferring utility service (basically a maintenance function). Not critical at all, but is definitely puzzling and is likely something really trivial that I have missed.
 
Pictures would probably be helpful. Physically the generator and utility cannot be connected at the same time unless something is wired wrong. Bringing utility into the load output lugs with utility input connected to the load lugs can cause the generator to backfeed the utility, but then the load would not have power. If it was an Onan switch, the switch would require the 12 volt positive and negative, along with the remote start wire, as that transferswitch controls are powered by the generator battery. I’m not familiar with that style of Generac switch, so I don’t know if it requires the positive. Kohler switches do not.
 
This sounds very fishy. A normal GTS should not be able to simultaneously connect both inputs. It is a device made of simple components, they need to be looked at one at a time. Service manuals are freely available for the older stuff. The basics are still the same.
 
Looks like that switch uses the same contactor as the Cummins/Onan air cooled switches. Just replaced one last week where one of the poles failed to transfer back. The plastic actuator had broke after 25 years.
 
Sorry, check my second post, all other issues have been resolved other than the Normal Test Mode. The unit is NOT sending power from two sources. That issue was a simple fix made by increasing the time to switch back from generator to utility power once utility is restored. The transfer switch setting was too fast (0.01sec) and the electrical loads (a/c units in this case) did not like the instant transfer. We increased the timer to 3 seconds and now the contacts open and then close and the equipment all responds well.
 
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