#LO to #6 jumper??

[CDR]

The schematic and TM says "When selecting position 120V, 1 PH unit is in 2 wire conf iguration. A situation can/may exist in allowing a double fault to occur. To eliminate this possibility the reconnection switch will be rewired by using an AWG #4 wire jumper between terminals #LO and #6 of section ."


I read every post and I still don't understand. Last weekend I ran my 20amp air compressor in 120v and it worked perfect. I don't under stand the double fault.

1. If I wire it like this will I have to take it out each time I use 240 or 3 phase??

2. Why would the military design something like this?

3. Does any one have clear directions on how to do this? all seems vague

Thanks for the help!
Dave

 

[Speddmon]

The schematic and TM says "When selecting position 120V, 1 PH unit is in 2 wire conf iguration. A situation can/may exist in allowing a double fault to occur. To eliminate this possibility the reconnection switch will be rewired by using an AWG #4 wire jumper between terminals #LO and #6 of section ."


I read every post and I still don't understand. Last weekend I ran my 20amp air compressor in 120v and it worked perfect. I don't under stand the double fault.

1. If I wire it like this will I have to take it out each time I use 240 or 3 phase??

No, you do not need to take it out each time you use the generator in a different configuration.

2. Why would the military design something like this?

The Military didn't design it like this, someone in the military did however find that there was something wrong with the OEM set-up, hence the TB was issued to rectify the situation.

3. Does any one have clear directions on how to do this? all seems vague

Thanks for the help!
Dave

I have a copy of the TB, but it is still not terribly clear. I have done about 6 or these, but I only did them be having another box that was already done to go by (that was before I had the maintenance advisory to look at). That reconnection switch is a very complicated beast.


From the Maintenance advisory (Tech Bulliten)

SUBJECT: Maintenance Advisory Message No. 88-01, Clarification of receptacle rewiring procedures, 5/10KW DED generators, MEP-002A, MEP-003A
A. Technical Manual (TM) 5-6115-584-12
B. TM 5-6115-585-12
C. Technical Bulletin (TB) 5-6115-584-30-1
D. TB 5-6115-585-30-1
E. TB 5-6115-584-30-2, dated Aug 26, 87
F. TB 5-6115-585-30-2, dated Aug 26, 87
G. MILNET Msg. AMSTR-WLT, 5 Jan 88, SAB
H. Maintenance Advisory Message 87-41

1. This is a maintenance advisory message and has been transmitted to affected units under your command. please ensure dissemination of this message to all applicable using units.

2. Ref. C, D, and G (above) notified the field that convenience recepticals (CR) should be disconnected because of problems with more than expected voltage at the CR when the gen set is placed in the 120/240 volt single phase mode and less than full expected voltage at the CR when the gen set is placed in the 120 volt single phase mode.

3. CR wiring must be carefully inspected prior to proceeding with wiring changes. Some CR's may have been re-wired and later disconnected, and some may have never been changed.

4. After inspection following the procedures of Ref. E, F and H (above),

First, connect CR as outlined in applicable TB (Ref. E or F) paying special attention to paragraphs 98 (7) thru (12).

NOTE 1. Dependent on the manufactured configuration of the generator, the instructions of para. 98 ( 8 ) and (9) or para. 98 (10) and (11) are followed. Where para. 98 ( 8 ) and (9) apply, there may be some deviation in locations of terminals on the switch from the instructions in the message.

Second, connect the jumper (AWG Nr 4) between L0 and NR. 6 of section 9 as outlined in ref. H.

NOTE 2. Terminal nr. 6 of section 9 is located on the 10th ring (the first ring is a cover, count from the control panel end) of the switch. The correct terminal will have wires X6A8 and X6B12 attached. Wire number X6B12 was added during performance of TB instructions. You may encounter wires with old markings (X12L12) or incorrectly marked conductors at this location.

L0 is located on top of the switch at 11th, 12th, and 13th rings of the selector switch with wire X13B8 connected to the 13th ring with bare copper jumpers from rings 13 to 12 and 12 to 11.

5. Re-assemble and check for proper operation IAW applicable TM and the following:
1). Close CB-3 (CR circuit breaker)
2). During operation and in each position of the reconnection switch, you should have zero (0) volts AC between the CR neutral terminal (wide slot) and ground (gen set frame) or the CR grounding terminal (U shaped).
3). During operation and in each position of the reconnection switch, you should have 120 VAC between the line terminal ("hot" - narrow slot) and the neutral terminal (wide slot) of the CR or the CR grounding terminal (U shaped).

6. The reconnection will only be accomplished at intermediate level maintenance.

7. Change to the above TMs, ref. A and B (above) will be distributed 3rd qtr FY88.

8. Addressees will confirm receipt of message to this office, if applicable. Point of contact at this command is Mr. Dave Long.

 

[CDR]

Lucky you that you saw one already done! I have no idea what #6 is on the switch looks like a wiring mess in that box

 

[dependable]

Are there more updated bulletins? Looks like the ones on the forum are from the late 70s. Am guessing that if CR tests at 120V in all reconnection switch positions this has already been done or is not needed?

ps to Speddmon, not sure your TM links form profile work anymore.

 

[CDR]

Here the bigger question what happens if I can a double fault?

 

[Speddmon]

ps to Speddmon, not sure your TM links form profile work anymore.

You are correct, must be an issue from the crash/server change. I'll fix it, thanks.

 

[LuckyDog]

Here are some pictures of what I did when I put the modification on my 002A.

Dis Way

Hope that helps.

 

[storeman]

I think I'd just rather just die standing at attention at my generator control panel, having been stricken by a "double fault".

Based on almost 31 years of service in the Army of The United States, as enlisted and commissioned, this sounds like an amber alert for an isolated incident, issued by a bureaucrat doing CYA. Otherwise, it would not be so vague and hard to understand. It is a sure bet that no one in his supervisory chain reviewed the guidance he/she was issuing to the world or it would have been challenged. Remember, TMs are supposedly written for 8th grade level.
Even the esteemed Speddmon (not to mention some engineering geniuses) has difficulty, with the instructions.


I'm not even going to look under my hood because I wouldn't recognize the problem OR the fix.

May the gods of lightning keep me safe now that my gennys are producing again. Come at me winter!

 

[dependable]

The reconnection switch is indeed a 'complicated beast'. The 003 I was having trouble with earlier this year clearly had this modification done to it, as there is a black 4awg jumper added in the reconnection switch wires and lots of wire numbers marked in pencil on switch. Something is still not right with it in R-3 circuit. If this double fault only affects the CR, I am tempted to ignore this on my working 002s. What would a double fault look like?

Has anyone ever seen the updated TM 'to be issued in 3rd qtr FY88' that is mentioned in that maintenance advisory?

 

[Triple Jim]

I finally took the time to look at this jumper, L0 to terminal 6, and what it does. It appears that it simply ties L0 to L1 in the single phase mode. In both the 3-phase mode and the 120/240 single phase mode, L0 is already tied to terminal 6, so the jumper does nothing in those modes.

In single phase mode, L0 is not connected to anything by the reconnect switch, but the bonding wire, if installed, connects L0 to the generator frame. The load is supposed to be connected to L1 and L3. I believe one reason for the jumper is that without it, if someone puts the generator in 120v single phase mode and accidentally connects the load to terminals L0 and L3, the load would connect L3 to L0, and since the bonding wire connects L0 to the generator frame, it effectively makes L3 a sort of neutral, with L1 floating. The load would not operate, and nothing bad would necessarily happen, but there is potential there for trouble. The jumper ties L0 to L1, so that if the load is accidentally connected to L0 and L3, everything functions normally, and the size #4 jumper would then carry all the load current to L1 where it belongs.

Another reason for the jumper is that with the load correctly connected to L1 and L3, the jumper connects L1 to L0, keeping L1 (neutral) at ground potential, rather than letting both sides of the 120V line float relative to ground, which from a safety standpoint is important.

Figure 2-4 in TM5-6115-585-12 is the diagram showing the generator windings and how they get connected in the three modes, and helps in visualizing what's going on.

 

[steelypip]

So basically if I never operate in 120V single-phase mode, I don't need to worry about this. And if I do, I'm OK as long as 1) the reconnection switch is wired correctly and 2) I pay attention when connecting to the load terminals.

Thanks for digging into this.

 

[Triple Jim]

Well, yes, except if you do use 120v-only mode, as far as I can see, without the jumper neither side of the 120 is referenced to ground or neutral, so they're floating. This is very non-standard. It means a 2-wire device that relies on a polarized plug to keep 120 and neutral in the right places might not see what it expects, and even 3-wire devices that expect one of the 120v wires to be neutral could have trouble.

Of course if the generator is wired to a house, the house would force the neutral to the correct potential, as long as the neutral were bonded to ground at the house's entrance panel, etc..

By all means, others should double check me to see if I missed something.

 

[Speddmon]

To do it simply, if you want to run your generator in 120 single phase only mode and you are not sure if the jumper was installed or not, when you run it in 120 only mode just put a jumper from L1 to L0 at the connection lugs. Just be sure to remove it when you change modes to something else.

 

[dependable]

If there is continuity between L0 and L1 when reconnection switch is in 120 single phase, would that indicate modification was already done?

I guess there could be low load continuity though other circuits that would show up on multimeter but not carry sufficient load. ?

 

[Triple Jim]

If the jumper from L0 to 6 were in place, you'd certainly see a dead short, zero ohms, in 120V-only mode. I *think* you'd see an open circuit if the jumper were not in place. If there were any control circuit devices trying to get power between L0 and L1, they wouldn't work in 120V mode, so I don't think there are any.

 

[natem]

If a double fault occurs will it damage the reconnection switch?

 

[Triple Jim]

No, the double fault refers to things like both sides of the 120 volts floating (not referenced to ground with one neutral).

 

[natem]

Thanks, now I know to look for other reason for the switch to lock in 120/240 after switching from 120 only.

 

[Triple Jim]

You didn't switch it with the generator running, right?

 

[natem]

Not running, I did read the instructions (this time). I wired it for 220 1 phase and switched to 120/240 from 120 only. Then I started and noted only about 50 hz at any speed and 120 volt output.
The switch moves clock wise under spring pressure but will not move counter clock wise at all (I broke plastic knob trying).