Always test your electrical dog bones

[Chad Heiser]

I came across an interesting issue today and thought I would share with the group.

I am helping a friend sort out some electrical issues in his 5th wheel while I install an inverter/solar set up for him.  His trailer was getting some very odd line voltages.  His trailer has a female marine twist lock 50 amp cord connection in a small compartment at the back of the trailer on the driver side.  He uses a short 50 amp marine twist lock to 50 amp standard male dog bone to then connect to a standard 50 amp power cord to go from the trailer to the power pedestal.  Because the compartment where the twist lock connection is located is so small, the short dog bone connector had to be almost folded in half to allow for connections on both ends.  Well, that caused an issue over time.  The cabling broke internally in the dog bone and was sending 240 volts over one line in the trailer.  After a few minutes of troubleshooting, I located the issue and recommended replacing the dog bone.  I also remounted the marine receptacle so the new dog bone wouldn’t have to be folded over to make both connections.

Here’s the interesting part.  When the new dog bone arrived, we connected it up and everything worked as expected.  No more 240 volts on one line (yeah!).  But, me being me, I wanted to test everything.  I metered all the connections and it started out fine.  120 volts on line one, check.  120 volts on line 2, check.  240 volts between line 1 and line 2, NO.  What?  I got 0 volts between line 1 and line 2.  Not good.  I tested the power source and everything worked as expected.  Back to the dog bone and still 0 volts between line 1 and line 2.  There is only one thing in my mind that can cause this, so I ran an additional test.  I test continuity between the ends on the dog bone.  Line 1 to line 1 at both ends, good.  Line 2 to line 2 at both ends, nothing.  Line 1 at one end to line 2 at the other end, good - huh???

The manufacturer of this particular dog bone decided to jumper the lines between 1 and 2 internally at one end of the plug rather than run them from one end of the plug to the other.  In other words the dog bone works and puts 120 volts on both line 1 and line 2, but it is the same source for both lines in the trailer (like a 50 amp to 30 amp dog bone would be wired).  This means whatever is hooked up to this dog bone only has the potential for 50 amps total between line 1 and line 2 rather than 50 amps on each of line 1 and line 2 (for a total of 100 amps available).

Obviously, this dog bone is getting returned in the morning and will be replaced with a properly wired one.  I really would like to cut this one up to see exactly what the manufacturer did, but I don’t want to spend the money on it.

I don’t have the manufacturers name handy right now, but I will get it in the morning and post a picture of the dog bone for reference.  I guess I know why this one was cheaper than the others now.  😜

[lappir]

Interesting, very interesting. 

 

Rod

[Kirk W]

54 minutes ago, lappir said:

Interesting, very interesting. 

Yes, the entire story. 240V on one leg and  0V on the other?

[oldjohnt]

Chad, fun and interesting post, thanks. FWIW I have seen (own one but never need it) 50 Amp Male to 30 Amp Female Dogbones used so a 50 Amp RV owner can plug into a 30 Amp Receptacle AND HAVE ONE PHASE OF 120 VAC FOR BOTH LEGS. IE they jump/connect L1 and L2 together. Of course, there's still ONLY ONE 30 AMP LEG OF PEDESTAL POWER AVAILABLE, NOTTTTTTTTTTT  TWO legs of 50 Amp 120 VAC 180 out of phase with each other.

 Similar, such a dogbone CAN NOT produce 240 VAC L1 to L2 they are tied together !!!!!!!!!! IT WOULD BE ZERO VOLTS L1 to L2. 

As said you cant make a silk purse out of a sows ear lol sooooooooo if the pedestal ONLY has ONE leg of 30 Amp 120 VAC, a Dogbone (with jumper L1 to L2)  CAN NOT produce TWO legs of 120 VAC (180 out of phase so its 240 L1 to L2) at 50 Amps. The 30 Amp RV Pedestal has a 30 amp circuit breaker so even a Dogbone IS NOT going to supply 50 Amps !!!!!!!!!!!!  and IS NOT producing two 120 VAC legs 180 out of phase with each other. 

PS I obviously haven't see every brand of 30 Male to 50 Female dogbone nor their wiring diagrams SO I CANT SPEAK TO ALL OUT THERE NOR THE ONE YOU TESTED (I ONLY reported on the ones Ive seen) Sooooooo the above is ONLY theory and only way I have seen them wired ..........

Good troubleshooting Chad, take care best wishes let us know what you find.  It would be interesting to see any other methods/schemes/procedures to produce two 180 out of phase legs of 120 VAC from ONLY ONE single leg 120 VAC source   I CANT IMAGINE ANY SUCH !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! 

Also, if one were plugged to 30 amp 120 VAC (Not sure what source was so I cant say from here) where's any 240 VAC coming from ?????????????????????

If you actually found   "The cabling broke internally in the dog bone and was sending 240 volts over one line in the trailer."  from a 30 amp service ????? now that's a serious problem !!!!!!!!! Better check the source/pedestal  wiring !!!!!! How would even a faulty dogbone produce "240 volts over one line" if plugged into a 30 amp 120 VAC "CORRECT WIRED" receptacle ?????????????  hmmmmmmmmmm

NOTE One way I can imagine to get your reported  "and was sending 240 volts over one line in the trailer" is there would have to be a pedestal/junction/box/circuit that first of all actually had two lines L1 & L2 with 240 VAC Line to Line,,,,,,L1 would have to be on the Hot/Line of the 30 Amp supply and L2 would have to be impressed upon the Neutral IE L1 TO L2/Neutral = 240 VOLTS.....BETTER CHECK THAT BOX/PEDESTAL !!!!!!!!!!!!

Oh well not being there its hard to speculate over the net, sounds like you're working on it LET US KNOW what you find Chad

John T 

Edited January 8, 2021 by oldjohnt

[Chad Heiser]

Here are the pictures I promised.

Edited January 8, 2021 by Chad Heiser

[Chad Heiser]

17 hours ago, Kirk W said:

Yes, the entire story. 240V on one leg and  0V on the other?

He was actually getting 240 volts between one of the lines (I can't remember now if it was L1 or L2) and Neutral.  

[oldjohnt]

6 hours ago, Chad Heiser said:

He was actually getting 240 volts between one of the lines (I can't remember now if it was L1 or L2) and Neutral.

YO CHAD, thanks for the update

YIKES  The 30 Amp connection only has Hot (L1) Neutral and Ground so the 240 must have gotten across Hot and Neutral. If there were L1 & L2 240 in the Pedestal/Box such as for a 50 Amp RV and the 30 Amp Receptacles was somehow mis wired it could end up as 240 L1 to Neutral. While not being there I cant speak to the dogbone, but I would be looking in the supply box for a wiring error since if the 30 Amp outlet was WIRED RIGHT you cant get 240 ?????????  If a 30 Amp male to 50 Amp female dogbone jumps L1 and L2 together (plus box wired right???) there would be ZERO L1 to l2 NOT 240...????

 Its a MYSTERY

John T

 

Edited January 8, 2021 by oldjohnt

[Kirk W]

I wish that I could be there with my own meter to take a few readings on the entire thing. After more than 40 years of electrical training and experience it is very clear to me that there is more to this story. 

[oldjohnt]

3 hours ago, Kirk W said:

After more than 40 years of electrical training and experience it is very clear to me that there is more to this story. 

AMEN Kirk I agree. 49 years of electrical engineering, RV ownership and repairs leads me to the SAME CONCLUSION !!!!!!!!!!!!! Were definitely on the same page on this one....Now hopefully Chad can get it figured out. 

PS I can see how ifffffffffff he had a 50 Amp Male to a 30Amp female dogbone to plug a 30 Amp RV into a 50 Amp outlet a way L1 and L2 240 Volts could (if miswired or faulty) be present......... 

As always, its a pleasure sparky chatting with you, take care now.

John T 

Edited January 8, 2021 by oldjohnt

[Darryl&Rita]

Sounds like a bad Neutral somewhere in the short adapter. Might be in the connections on either end, or the wire in between. Without an autopsy (necropsy?), only guessing.

ETA: the above is in relation to the original adapter. The replacement has been proven to be faulty, and the nature of the fault. That "fault" allows the manufacturer to save about 1 foot of wire per device, thus increasing profits.

Edited January 8, 2021 by Darryl&Rita

[Kirk W]

2 hours ago, oldjohnt said:

PS I can see how ifffffffffff he had a 50 Amp Male to a 30Amp female dogbone to plug a 30 Amp RV into a 50 Amp outlet a way L1 and L2 240 Volts could (if miswired or faulty) be present......... 

The only way to get 240V between and leg and neutral would be to connect in the same was as the old 3 wire dryer plugs that have no neutral. You have to measure between L1 and L2 or between the two bus bars of the distribution box in order to measure 240V. The supply leaves the pole from a center tapped transformer with two legs of 120V each that are 180° out of phase. There is no single lead in a home style of wiring that will measure 240V to a real neutral. Commercial wiring does have that capability but no household does. In a properly wired RV pedestal there is no one lead that will ever measure 240V to neutral or ground. You have to go between L1 & L2 at the pedestal. 

[oldjohnt]

4 hours ago, Kirk W said:

The only way to get 240V between and leg and neutral would be to connect in the same was as the old 3 wire dryer plugs that have no neutral.

Hey Kirk, for the most part you're understanding this pretty well so I will add just a bit in hopes of helping out the thread  HOWEVER  remember its s been yearssssssss since I practiced electrical power distribution engineering and I'm rusty on the latest codes grrrrrrrrrrrrrr lol but believe this to be accurate. See below our investigation of such an incident appeared to be what happened 

1) The old style 240 volt clothes dryers that had a three wire cord consisted of  1)  An UnGrounDED L1 Conductor      2) A second UnGrounDED L2 Conductor  (240 VAC L1 to L2)   3) A Third Wire Safety Equipment GroundING Conductor  YOU GOT IT RIGHT THERE WAS NO GROUNDED CONDUCTOR (aka NEUTRAL)

HOWEVER if the dryer contained any 120 devices ??? The Safety Equipment GroundiNG Conductor was at times used for carrying return current (Ive seen it)  !!!!!!!!!!!!!!!!!!!! The later codes required FOUR WIRES, Two Hots, Neutral, Ground   

NOT having any Neutral, if all was in place and wired correct, the ONLY two leads that had 240 volts across them would be L1 and L2 YETTTTTTTTTTTTTTT there would be 120 VAC from EITHER L1 or L2 to GROUND and why is that you ask ???? Because in the main panel (or another approved location) NEUTRAL AND GROUND ARE BONDED TOGETHER  

4 hours ago, Kirk W said:

In a properly wired RV pedestal there is no one lead that will ever measure 240V to neutral or ground.

YOU GOT THAT RIGHT and of course the key is your statement "IN A PROPERLY WIRED RV PEDESTAL"

7 hours ago, oldjohnt said:

PS I can see how ifffffffffff he had a 50 Amp Male to a 30Amp female dogbone to plug a 30 Amp RV into a 50 Amp outlet a way L1 and L2 240 Volts could (if miswired or faulty) be present.........

 Now let me explain my statement of how    "if mis wired or faulty"   240 Volts could be present between what was say for example supposed/used to be a Neutral and another Hot.  IE what Chad observed ifffffffff he measured 240 from a Hot Line to a Neutral. Not being there I can  NOT say

NOTE  I UNDERSTAND THIS IS WHAT CHAD OBSERVED (he claims 240) BUT NO WARRANTY THIS THREAD IS GETTING CONFUSING LOL

 1) The Neutral somehow got severed and disconnected from its source (connection came loose or there was a short in the box and it got burned off) 

2) The Neutral became stuck/welded/connected INSTEAD, OVER TO to one of the Hots (during shorting in the box and resultant heat and wire movement)

Sooooooooo now as Chad reported 240 VAC this is one way at least he could have observed 240 VAC  from one of the Lines to what used to be a Neutral that got burned off and up against THE OTHER HOT    There ya go 240 VAC from L1 to "Neutral"      BECAUSE The Neutral got burned/melted off and became stuck/welded to L2 !!!!!!!!!!!!!!!!!!!!

PS Our Engineering Department got involved in studying these types of electrical problems and best I recall (no warranty faded memory lol) once had a situation similar to this IT CAN HAPPEN  a wire shorted and burned resulting in a hot stuck to an open Neutral  YES WEIRD BUT OVER YEARS IVE SEEN SUCH HAPPEN   

AGAIN NO WARRANTY THIS TOOK PLACE YEARSSSSSSSSS AGO MY OLD HARD DRIVE MAY BE CONFUSED GRRRRRRRRRRRRRRR but hey I try my best

Thanks Chad and Kirk for the fun sparky chat I truly enjoy it even we bore the others lol

Best wishes and God Bless you both

John T  Free dry camping at Istokpoga Lake Canal Boat ramp near Lorida Florida 

Edited January 8, 2021 by oldjohnt

[oldjohnt]

4 hours ago, Darryl&Rita said:

Sounds like a bad Neutral somewhere in the short adapter

Yo Darryl, you may be onto something, see my post above. The Neutral got shorted/burned/severed and came into contact with the other Hot !!!!!!!!!!!!!!!!!!!!!

John T

[Chad Heiser]

The wires broke internally in the original dog bone.  As a result, the neutral wire was no longer neutral.  It was being energized by one of the hot leads.  Because of this, there was 240 volts between the neutral and the remaining good hot lead.

[Chad Heiser]

18 hours ago, oldjohnt said:

YO CHAD, thanks for the update

YIKES  The 30 Amp connection only has Hot (L1) Neutral and Ground so the 240 must have gotten across Hot and Neutral. If there were L1 & L2 240 in the Pedestal/Box such as for a 50 Amp RV and the 30 Amp Receptacles was somehow mis wired it could end up as 240 L1 to Neutral. While not being there I cant speak to the dogbone, but I would be looking in the supply box for a wiring error since if the 30 Amp outlet was WIRED RIGHT you cant get 240 ?????????  If a 30 Amp male to 50 Amp female dogbone jumps L1 and L2 together (plus box wired right???) there would be ZERO L1 to l2 NOT 240...????

 Its a MYSTERY

John T

 

There was no 30 amp receptacle involved.  The original dog bone was marine 50 amp twist lock to a standard 50 amp plug in and it was plugged into a 50 amp outlet.  This dog bone broke internally and one of the hot wires energized the neutral wire.  This allowed the 240 volt reading between neutral and the remaining good hot wire.

The new dog bone was also 50 amp marine twist lock to a standard 50 amp plug in.  It was wired like a 30 amp to 50 amp dog bone from the manufacturer in that it only passed one hot leg through to the trailer and energized both L1 and L2 from the same source.  This gave 50 amps total of available power to the trailer instead of 50 amps on each leg (L1 and L2).

[DJohns]

Would the progressive industries  EMS-LCHW 50 prevent 240 v from going through coach?

[oldjohnt]

6 hours ago, Chad Heiser said:

As a result, the neutral wire was no longer neutral.  It was being energized by one of the hot leads.  Because of this, there was 240 volts between the neutral and the remaining good hot lead.

EXACTLY same as one of the possibilities I described immediately above   Thanks for the update

 

6 hours ago, Chad Heiser said:

 This dog bone broke internally and one of the hot wires energized the neutral wire.  This allowed the 240 volt reading between neutral and the remaining good hot wire.

DITTO A hot wire got against Neutral,,,,Neutral burned off/open (or just was off by whatever reason)  from its source,,,,,,,,,,,,Neutral got against a Hot THEREFORE (If all conditions were one certain way) YOU COULD READ 240 ACROSS THE OTHER REMAINING GOOD LINE TO NEUTRAL   !!!!!!!!!!!!!!!!!!!!!!!!!!

By golly Chad this "maybe" is figured out

Keep up the good work Chad.

[oldjohnt]

25 minutes ago, DJohns said:

Would the progressive industries  EMS-LCHW 50 prevent 240 v from going through coach?

DJ, Ifffffffffff the EMS was in a location where those conditions (such as open Neutral, excess or no voltage etc) were indeed being monitored, I would expect it to catch and prevent such, but not having specs or data or a manual or location I cant guarantee that.

John T

 

[Kirk W]

4 hours ago, DJohns said:

Would the progressive industries  EMS-LCHW 50 prevent 240 v from going through coach?

It would as long as the problem was above it but if the problem were between it and the RV then it probably would not as it would not see the over voltage. I have used a Surge Guard line monitor since 2003 and I always connect it to our power cord and any adapters would be between it and the pedestal, just to make sure that it monitors any potential problems. I now have a 30a RV but even with the previous 50a version, I did that came thing so if I had a 50a to 30a outlet adapter with a fault, I would have been protected. 

[Kirk W]

4 hours ago, oldjohnt said:

I would expect it to catch and prevent such,

I gather that you have no experience with any of the line monitoring devices, Surge Buard, Progressive, Camco, or Hughes? 

[oldjohnt]

2 hours ago, Kirk W said:

It would as long as the problem was above it but if the problem were between it and the RV then it probably would no

 

6 hours ago, oldjohnt said:

DJ, Ifffffffffff the EMS was in a location where those conditions (such as open Neutral, excess or no voltage etc) were indeed being monitored, I would expect it to catch and prevent such

Correct as we BOTH realized it depends on the location, good job. Looks like what Chad found was similar to an experience I recalled (open Neutral shorted to a hot) and predicted above...

PS FYI the huge heavy iron laminated Buck Boost Transformers (Hughes makes some) are more for voltage dips sags or spikes etc. UNLIKE an EMS which monitors for faults such as an Open Neutral or Hot/Neutral reversal, faults or voltages.

ALSO WORTH NOTING there are Surge Protectors,,,,There are full fledged EMS,,,,,,There are Buck/Boost Transformers and each type and even brands have different parameters and offer different protection. What they can or can not protect or prevent depends on their design plus where in the circuit they may be so as to monitor current, voltage, faults and leaks..

 Hope this helps, best wishes my sparky friend a pleasure chatting with you

John T  Currently free dry camped at DuPuis on Lake Okeechobee, Florida

Edited January 9, 2021 by oldjohnt

[DJohns]

19 hours ago, Kirk W said:

It would as long as the problem was above it but if the problem were between it and the RV then it probably would not as it would not see the over voltage. I have used a Surge Guard line monitor since 2003 and I always connect it to our power cord and any adapters would be between it and the pedestal, just to make sure that it monitors any potential problems. I now have a 30a RV but even with the previous 50a version, I did that came thing so if I had a 50a to 30a outlet adapter with a fault, I would have been protected. 

My EMS is mounted in the rig not at the pedestal.   The first thing to see power is the EMS so I should be OK?

[Kirk W]

4 minutes ago, DJohns said:

The first thing to see power is the EMS so I should be OK?

Yes you should be. With your set up it sees power after all cords and adapters. That is probably the best possible way because some type of failure in those devices would be detected. As long as your EMS is one of the major brands and is working then you should be well protected. Frankly, I have never before heard of anything like the problem described. 

[oldjohnt]

1 hour ago, DJohns said:

My EMS is mounted in the rig not at the pedestal.   The first thing to see power is the EMS so I should be OK?

DJohn, Great question, here's an engineers response:

Short answer YES, now for a deeper explanation:

 NOTE just "where at" in the rig I do not know, but for now I will proceed such as its just before your AC Power Distribution Panel.

  Iffffffffffff the EMS is in line to where it can monitor measure and protect the power just before your main distribution panel, if there were faults in say a dogbone (as in this thread, it happened to Chad it appears) or other wiring or cords or plugs or electrical service IT (subject to design) WOULD BE PROTECTED..... 

    That's one reason I prefer an EMS be a hard wired unit inside the RV as its better protected from the weather and less likely be stolen.

NOTE If the RV has an onboard genset and a transfer switch (utility versus genset) "SOME" people configure the EMS to protect ONLY Utility power while "SOME" configure it to protect EITHER Utility orrrrrrr Genset. There are advantages and disadvantages either way, but that's NOT part of your question.........

Hope this helps, post back any more questions, best wishes and God Bless

John T  Dry camped and even AFTER coffee and microwave and toast already by 10:30 my batteries are at 100% SOC   Yayyyyyyyyy gotta love Solar