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Onan LTD100-4 Transfer Switch


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  #1  
Old 10-07-2017, 03:00:02 PM
whiteblaze whiteblaze is offline
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Default Onan LTD100-4 Transfer Switch

Hello All,

I got a transfer switch with my 15 kw RJC. The generator is rewired to single phase, and tested. I'd like to see if I can use this for single phase and / or if it's worth the hassle. I don't see any single phase wiring diagrams so I have my doubts. Pictures attached below!
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Old 10-07-2017, 04:18:48 PM
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Default Re: Onan LTD100-4 Transfer switch

I will check my files. But that one may be hard to do. Being 208.
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Old 10-07-2017, 07:05:17 PM
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Default Re: Onan LTD100-4 Transfer switch

Here is the build sheet and wiring diagram note Billy the coils re 208v as well as 240v
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Old 10-07-2017, 07:31:26 PM
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Default Re: Onan LTD100-4 Transfer switch

Would you think it would be possible just not to use the 3rd phase of the switch and still have it work properly? Still plan on going through it before use. Looks like it's in great shape, but there are a few marks on the inside top of the cabinet that seem a bit burnt.
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Old 10-07-2017, 07:55:22 PM
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Default Re: Onan LTD100-4 Transfer switch

Ok,
Just answer my question... looked at the diagram. Looks like relays k5, k6, and k7 are voltage sensitive (see attached). I just priced the 240 version and they are $700+ a pop.
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Old 10-07-2017, 11:58:52 PM
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Default Re: Onan LTD100-4 Transfer switch

I believe the voltage sensing wire has to be moved from C Phase to A or B. I believe the relays as stated on the drawing are 208/240. Someone will correct me if Im wrong.
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Old 10-08-2017, 11:26:18 AM
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Default Re: Onan LTD100-4 Transfer switch

As MBB stated, the drawing does state in the "Note" that the coils operate on 208-240VAC.

However, as you've correctly surmised, there are still some differences. If you wanted to use this switch, I would replace the three phase voltage sensors with a single phase sensor such as this: http://time-mark.com/shop/voltage_fr...tors/16-1-h-s/
I would suspect this module is probably in the $170-$200 price range.

This device would provide you with under and overvoltage protection, with a buffer time delay to prevent rapid switching.

Per the drawing the drawing, on three phase, the only thing "C" phase provides is a single wire 7, going up to power one coil leg on sensors K6 and K7.

Adding the suggested sensor above, you would remove the three existing sensors, mount it, then:
* take wire from old K5 (L2) coil leg as one power input (originates from wire #6, "B" phase)
* take wire from old K7 (L2) coil leg as other power input (originates from wire #4 "A" phase)
* Install a jumper from the wire #6 power input on landed above in first step, to one of the Normally open contacts
* take wire from old K7 sensor output contact that goes to a K4 contact, and land on the other Normally open contact
*(NOTE: This relay module would need to be calibrated--you could do that by using variable AC power supply, or bench calibrate it using a generator capable of 240 VAC, and has adjustable voltage. Suggested settings would be: 210VAC for under volts, 260 VAC for over volts)

Also, per the drawing, it appears that the K3 instant transfer relay is voltage specific-- they are listed separately in the parts table on the drawing. If the relay does not specify 208/240 volt rating on the coil (if still legible), then that would need to be replaced. Relay K3, PN 307-1083 is still listed, at around $77.

The fact that this is a mechanically-held contactor set up on utility and generator, was a desirable feature for these old switches. When (if) you power it up, make sure that when the utility contactor closes, that the utility contactor closing coil isn't still humming. There is an adjustable cut-out switch on these, that breaks the input power to the coil, as the plunger is in motion and the mechanical latch is falling into place. Have had to adjust these more than anything else on these old LT's.

Presuming at this point that K4 is dual-voltage rated (208/240), R2 could be adjusted slightly to change the pull-in voltage level, if needed. (Again, this is best done on a bench, or isolated power test set up, to get an accurate reading. Manual spec's are it should pull in at 85-90% of rated voltage.)

Do keep in mind this is an old switch, and has multiple power relays that are normally energized all the time. Those relays on that door are all fairly expensive to replace, so take in to consideration what a new switch that size will cost, versus potential upfit and maintenance repair costs over the next several years could possibly be.
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Old 10-08-2017, 03:49:48 PM
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Default Re: Onan LTD100-4 Transfer switch

Onan did use A&B phase as a single phase system. Some of the relays could be used. But as Eric said some would have to be replaced. Costly and hard to find unless you used an updated version. The main contactor set was obsolete over twenty years ago. Last one I changed out was replaced by a Cutler Hammer set.

To me the main problem with using the old switches. You must take better care of them than you might have back in the old days. Parts can be hard to find. But on the good side there is a reason you find. 50 year old switches still working.
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Old 10-10-2017, 09:58:18 AM
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Default Re: Onan LTD100-4 Transfer Switch

Thanks all... I think I see the writing on the wall with this one. If anyone is near the Scranton / Poconos (Pa) region and would like this switch, let me know. It's in fantastic condition for the age, which is why I was hoping to use it. ASCO here I come.
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Old 10-10-2017, 10:18:39 AM
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Default Re: Onan LTD100-4 Transfer Switch

I would love to have it. But to far for me. Great shape and I see it has been converted. To the one screw holding the control door shut.
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Old 10-10-2017, 02:15:09 PM
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Default Re: Onan LTD100-4 Transfer Switch

I was laughing at that myself... if it weren't close to 100 lbs, I'd ship it.
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