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Travel Forum / Travel Types / RV Travel / August 2004shock from Onan genset ground
Hi, world. I bought a used Onan genset, model 15.0JC-18R/17164AB. When it arrived, it was wired for three phase power. According to the automatic transfer switch it has about 600 hours on it. It looks good...no burned spots, no arcing, no smell of burned insulation, but I never saw it run...it was already on a pallet when I first saw it. Using the diagram printed on page 20 of the "Onan YD Generators and Controls Service Manual" (number 900-0184), I rewired the generator for 120/240 60Hz single phase (labelled "nameplate voltage code 18", the "double delta"). I then connected wires for house neutral to "L0", one hot to "L1" and the other hot to "L2". I also connected a 4G ground wire from the lug inside the wiring box of the generator to my house ground. I have a disconnect at the outside of the house to disconnect the two hot wires from the automatic transfer switch (per fire deptartment regulations). This disconnect was off (disconnected). The genset is natural gas powered, btw. On the first time I tried to run the genset, as soon as the genset began to run I got a nasty shock from the genset's "start/run/off" switch. While my hand isn't calibrated, it felt more like 115VAC than 12VDC. Which means either: a - I miswired the T1-T12 wires, b - I'm using the wrong diagram to wire the genset. c - there is something wrong inside the generator head d - something entirely different that I don't understand is happening. I'm sure the problem is not "a" above...I've triple checked that. I' don't think its "b" either since the diagram I'm using is also printed inside the door of the genset's power-connection box (where the T1-T12 wires are). I don't think its "c" since Onan builds solid hardware and this unit hasn't been run much. Frankly, I suspect the problem is "d" above, which is why I'm asking you folks. I'm hesitant to run the genset again if it is putting AC onto my house ground. Not only will this play havoc with my AC powered loads, I'm afraid it will fry the genset or melt the ground wires! There is, of course, also the charming possibility that the ground voltage might ignite the natural gas supply. Any suggestions will be greatly appreciated. --Jon > Hi, world. > [quoted text clipped - 51 lines] > > --Jon This is a prime example of the old saying......... "A man should know his limitations." Hopefully, you have a prepaid burial plan for yourself and other residents of your house. Also, you better pray that your insurance company doesn't figure out that it was you who managed to burn the house down. > This is a prime example of the old saying......... "A man should know > his limitations." Yes, you should. And do, apparently. Good boy. > Hi, world. > [quoted text clipped - 51 lines] > > --Jon Ok, Jon - let's take one thing at a time. First, disconnect your leads from the connections you have made and use an ohmmeter to check for continuity between any lead T1 thru T12 and the generator frame - you should have no continuity indicated. Second, redo your connections - L1 should connect to T1 and T6, L2 should connect to T8 and T10, T3 should connect to T5 and be insulated from everything else, T9 should connect to T11 and be insulated from everything else, L0 should connect to T2, T4, T7, and T12 as well as to the ground lug inside the genset wiring box. An additional ground wire should run from this lug by as short a path as practical to a -good- earth ground - ask your local electrical inspector, but usually 2-3 8' ground rods driven flush into the ground and interconnected. The genset ground should -not- be tied to your 'house' ground. (The NEC requires neutral to be grounded _at the source_). If your windings checked good, this -should- take care of your problem. Note, also, that depending on what three-phase voltage the genset the generator was originally set for, you may need to move the W10 jumper lead on the voltage regulator board - for your desired output, it should connect from V1 to V4. Alan > Ok, Jon - let's take one thing at a time. First, disconnect your leads from > the connections you have made and use an ohmmeter to check for continuity [quoted text clipped - 3 lines] > insulated from everything else, T9 should connect to T11 and be insulated > from everything else, L0 should connect to T2, T4, T7, and T12 OK so far...this is what I did per the diagram on page 20... as well as to > the ground lug inside the genset wiring box. Shazam! Here is the mysterious missing part, the bit not in the manual, the assumption on the part of the Onan folks. Makes sense, though...if the generator produces 120/240 VAC, that has to be potential relative to something. I had assumed it would be relative to the house ground, but creating a local ground makes more sense. So coming from the generator I will have L0 (neutral), L1, and L2. No ground. These connect to a disconnect outside the house. That disconnect must be grounded, but should it be at house ground or genset ground? Following the external disconnect is the automatic transfer switch...that _must_ be at house ground, right? > An additional ground wire > should run from this lug by as short a path as practical to a -good- earth > ground - ask your local electrical inspector, but usually 2-3 8' ground rods > driven flush into the ground and interconnected. The genset ground > should -not- be tied to your 'house' ground. To quote Homer, the patron saint of stupid mistakes: Doh! A theoretical question: currently (no puns intended) the house is grounded via an unshielded copper 8g connected from line neutral inside the meter box to a grounding stake. Next in line after the meter box is the fused line disconnect, where the neutral is connected (unswitch, unfused) to a bus from which all the house ground and house neutral depend. OK so far...this is all per code, btw. So enter the genset, which has its own local ground, two hots, and a neutral. That neutral is at genset ground. It connects to the house ground. The genset is 50' from the house, making it possible for there to be a voltage between the genset and house grounds. So here's the question: have I created a ground loop or some other potential disaster (again, no puns intended)? (The NEC requires neutral to > be grounded _at the source_). If your windings checked good, this -should- > take care of your problem. > Note, also, that depending on what three-phase voltage the genset the > generator was originally set for, you may need to move the W10 jumper lead > on the voltage regulator board - for your desired output, it should connect > from V1 to V4. ack. Checked and is OK. Thank you thank you thank you. I will try these things. I am a computer engineer in NC...if I can return the favor, please tell me. > Alan <snip> > from everything else, L0 should connect to T2, T4, T7, and T12 as well as to > the ground lug inside the genset wiring box. Hi, Alan. I just called the local electrical inspectors and was told: yes, use grounding stakes at the generator and ground the generator at the lug in the wiring box yes, connect the genset ground to house ground no, do not ground neutral at the genset. He specifically said the only place the neutral and grounds should connect is in the fused disconnect between the meter box and transfer switch. Thought you might be interested... > <snip> > [quoted text clipped - 15 lines] > > Thought you might be interested... Ok, no problem - I agree that you should only have one point that neutral is tied to ground. I'm more used to commercial work, where (locally) the inspectors require that the transfer switch also switch the neutral - so neutral is either tied to ground at the genset, or at the meter box disconnect depending on which is providing power. With his setup, you _do_ need to connect genset ground to house ground. Sorry - late at night forest/trees syndrome. Which brings to mind another point - if you're using the original 3-phase auto transfer switch to switch L1 and L2, on older Onan switches the control logic only looked at two phases - so you'd need to make sure you are using the appropriate connections (_probably_ L1 and L3 - just check to see which poles have extra little wires hooked to them). Alan <snip> > Which brings to mind another point - if you're using the original 3-phase > auto transfer switch to switch L1 and L2, on older Onan switches the control [quoted text clipped - 3 lines] > > Alan According to the manual for the transfer switch, the relays that control which power source is used do have contacts for three phases. If I'm only routing two phases, then I'm supposed to use the lefthand two contacts. Neutral from the genset is tied to a neutral bar (not grounded) and ground from the genset to a ground bar. Neutral from line is tied to the neutral bar and line ground to the ground bar. I haven't tried the transfer switch yet, however. One crisis at a time: with the genset running, I measured its output voltage at the external disconnect (between genset and transfer switch). The disconnect was open (disconnected), so there was no load on the genset. Output was 54VAC between L0/L1, 56VAC between L0/L2, and 110VAC L1/L2. This is pretty much exactly half what it should be. Any suggestions as to why this might be? I did have to experiment with the natural gas "main adjustment" screw to get the genset to start, so the idle may be off a bit, but by half? Or is this a no-load issue? Another question: how hot should the exhaust pipe be? I built the exhaust from 1.5" galvanized plumbing pipe, and it turned black within a minute of starting from the heat. Not that I care what color it is, mind you, I just am interested in not burning the exhaust valves and have never run a natural gas engine before. > <snip> > > [quoted text clipped - 15 lines] > mind you, I just am interested in not burning the exhaust valves and > have never run a natural gas engine before. I don't have the manual for this here at home, so will have to look at it at work tomorrow - but since this is a 'broad range re-connectable' set, which uses the same voltage regulator for all variations, I suspect that you've either got the wires for the reference voltage to the voltage regulator hooked up wrong, or you need to change the connections from the reference voltage transformer to the voltage regulator board, or change a jumper on the board. When you got it, what voltage were the output leads connected for? You won't be able to verify your mixture adjustment until you can put near rated load on it, but the pipe -will- be quite hot in any event. As long as the genset is running, and not at wide open throttle, the governor should be holding the engine at about 1800rpm - the genset doesn't have an 'idle' speed when no load is applied, it just opens or closes the throttle to try to maintain 1800rpm regardless of load changes. Alan > I don't have the manual for this here at home, so will have to look at it at > work tomorrow - but since this is a 'broad range re-connectable' set, which [quoted text clipped - 4 lines] > the board. When you got it, what voltage were the output leads connected > for? update: when I went to adjust R26, the voltage adjustment, the output jumped to 120VAC. I suspect this unit has been unused for decades and the adjustment pot had some corrosion in it which was wiped off when I turned the pot. I suspect the shock from the ground might have a similar cause. Either way, the genset is running fine now. I still haven't tested the transfer switch yet since I have yet to find fuses for the external disconnect...class R knife-edge fuses are, apparently, uncommon in this area. > You won't be able to verify your mixture adjustment until you can put > near rated load on it, but the pipe -will- be quite hot in any event. Thanks! That means the system is doing what its supposed to do and is not causing itself damage. Well, hopefully. As > long as the genset is running, and not at wide open throttle, the governor > should be holding the engine at about 1800rpm - the genset doesn't have an > 'idle' speed when no load is applied, it just opens or closes the throttle > to try to maintain 1800rpm regardless of load changes. Cool. That explains the adjustment algorithm: lean it until it starts to run badly then enrich it slightly...a vague description at best! Despite a rocky start, I'm very impressed with the Onan quality...this thing is a tank! > Alan > update: when I went to adjust R26, the voltage adjustment, the output > jumped to 120VAC. I suspect this unit has been unused for decades and > the adjustment pot had some corrosion in it which was wiped off when I > turned the pot. I suspect the shock from the ground might have a > similar cause. Either way, the genset is running fine now. Sounds good - you might want to 'adjust' the voltage every now and then to make sure it's ready when you need it. > I still haven't tested the transfer switch yet since I have yet to > find fuses for the external disconnect...class R knife-edge fuses are, > apparently, uncommon in this area. Go to your local electrical supply house - if they don't have them, they should be able to order them. > > You won't be able to verify your mixture adjustment until you can put > > near rated load on it, but the pipe -will- be quite hot in any event. [quoted text clipped - 11 lines] > starts to run badly then enrich it slightly...a vague description at > best! The best way I've found is to apply about half load, lean it till it runs badly/loses a little rpm, richen -just- till it starts to run smoothly again, then test by pressing on the throttle linkage to slow it down slightly (to about 55 hz), then release - richen the mixture just until it picks back up smoothly. On the gasoline sets, you go halfway between running badly lean and running badly rich, but that doesn't work as well on the NG or LPG versions - they'll still run pretty well when -quite- rich. > Despite a rocky start, I'm very impressed with the Onan quality...this > thing is a tank! Tell me about it! The engine was designed and built by Onan specifically for industrial duty - emergency services here in town has one on a trailer that was built for Civil Defense in the early sixties - they had me give it a tuneup just before Y2K, and at that time it had something like 9 thousand hours on it, was still running strong, was rated at 12.5kw but would easily handle 14kw load. If you maintain it, you'll probably pass it on to your grandkids. > > Alan Hi, Alan A new delima, if you will: everything seemed to be working fine, but the genset kept coming on when line power was on. I have an automatic Onan transfer switch (LTLEA 60-39 U/262 04G) which was originally set up for three phase. The switch is the problem, apparently. It contains adjustable relays (K4-K9, of which K7 and K8 are not adjustable), including K9, the "generator side voltage sensor" and K6 the "phase sensor/voltage sensor line side". When the set arrived, these two relays were unplugged and loose in the bottom of the switch (???perhaps they were shaken loose in transit, but perhaps they were bad???). There are also three switches on the control circuit board: A1S2, A1S2, and A1S3. S1 defeats the K5, making the genset stop instantly on switching back to line power from generator power. S2 defeats K4, making the transfer to line power instantaneous when line power comes back on after a power outage. Both are set to allow the relays to control transfer. S3 is not documented, but is labelled on the circuit board as "sensor bypass", by which I assume means it controls K6 and K9. If this switch is "off" and the transfer switch is set up for automatic transfer, the genset starts and the switch transfers to generator power even if line power is fine. Moreover, once I manually turn off the genset, the transfer switch relays stay stuck in the generator position so I have no power at all. If I switch A1S3 to "on", the transfer relays switch to line power. In short, I have to keep the transfer switch set to "manual crank" to keep the genset from running constantly. One more data point: inside the transfer swtich is a set of four plugs: J21-J24. They are located on the inside of the door of the transfer switch, beside the exerciser clock. They are labelled: J21 480V, 3ph J22 230V, 3ph J23 240V, 1ph J24 208V, 3ph When the transfer switch arrived, there was a set of wires connected to jack J22. Since all four have identical female jack configurations, and since I was rewiring the genset for single phase, I moved the wires to J23. These jacks are completely undocumented in any of the Onan literature I have seen. So, questions: is this problem of the transfer switch constantly "seeing" the line power as missing a 3-phase/1-phase change problem? Should I just resign myself to having, in effect, a manual transfer switch? Next question: the manuals on the transfer switch, aside from being scanty on detail and missing some crutial information (eg, A1S3, J23, etc), talk about adjusting K6 and K9. Specifically, the manual says "Approx Pickup Percent of Normal Voltage" as a function of the dial setting. But it also says "Dropout values of the relays are" and goes on to perform a percentage calculation. So, does the relay cause a transfer when the voltage drops below the setting? Why are there two relays? If the genset voltage drops, what can the transfer switch do about it? Again, I thank you for sharing your knowledge. You are much more informed than the local Onan dealership, which insists the only possible solution is to throw lots of parts and an onsite visit at the system. If I can return the favor, please let me know how. Jon Edwards www.StoneTurtleSoftware.com > Hi, Alan > > A new delima, if you will: everything seemed to be working fine, but > the genset kept coming on when line power was on. I have an automatic > Onan transfer switch (LTLEA 60-39 U/262 04G) which was originally set > up for three phase. <snipped> > So, questions: is this problem of the transfer switch constantly > "seeing" the line power as missing a 3-phase/1-phase change problem? [quoted text clipped - 18 lines] > Jon Edwards > www.StoneTurtleSoftware.com Jon, This is one that I'll have to do some research on - I don't have the manuals for transfer switches here at home, so may take a few days before I get back to you. It definitely sounds like it's having a problem sensing the line-side voltage. Whether that's a problem with the wiring, the sensing relay, or ??? is too early to tell. Alan |
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