50A shore cable a/c question

white-eagle · August 01, 2007, 07:47:07 AM

we just noticed last nite that neither roof a/c unit worked at home when they did just work on the way home with the generator. i checked all the breakers etc., then fired up the genset and they worked fine.
we have a 30A plug at the house. i run the bus 50A cable into a 50/30 adapter cable, then plug that into the 30A 25' extension to get to the house plug. i knew the week before, i had the 50A extension cable plugged into all this the week before and it worked, so i replugged everything as before, and it all worked and the a/c came on.
so the question is: why did the a/c work with the bus cable plugged into the 50a extension, then adaptor, then 30A extension, but not when the 50a extension removed?

Dreamscape · August 01, 2007, 07:52:02 AM

I had a similar problem yesterday. I installed a new 50 amp cable to the bus panel, bought a 30 to 50 dogbone, plugged it into a 30 to 15 cord. Nothing worked even when I had 120v to the breaker. I tore apart the 30 amp receptacle and found the neutral wire was attached to the ground. After installing the wires into the proper place, all worked great.
Don't know if this helps or not.

Happy Trails,

Paul

Dreamscape

edroelle · August 01, 2007, 07:59:26 AM

Tom,
If you have an automatic relay between generator and shore, it may be sticking. If you don't have an automatic (and I hate to suggest this), did you remember to manually make the switch?

I have had relays stick, and, I have done some real dumb things.

Ed Roelle
Flint, MI

white-eagle · August 01, 2007, 08:18:53 AM

thanks for the possible answers, but let me explain further.
we don't have an auto transfer. We never plug the shore power in, then use the genset. the genset would power the shore line. We have a short shore line that has a round 4 prong plug that goes into the bus with the standard 50 amp male on the other end. Jack Conrad hooked it up for me when the original transfer switch failed before i bought the bus.
all i did to correct the a/c problem was to add the 50a 25' extension cord between my 15ft 50a bus cord and the dogbone.

somewhere, i was thinking that a leg wasn't connected to anything solid with the dogbone, but is connected with the 50a extension??

Dreamscape · August 01, 2007, 08:29:33 AM

Do a continuity test on all blades of each piece. Something is not hooked up right. Are the plugs molded or take apart?

Paul

Buffalo SpaceShip · August 01, 2007, 09:50:15 AM

Quote from: Dreamscape on August 01, 2007, 08:29:33 AM
Do a continuity test on all blades of each piece. Something is not hooked up right. Are the plugs molded or take apart?

Paul

Agreed. All the dogbone does is tie the two hot legs of 50a together for 30a. Neutral and Ground should remain isolated on all cordsets (to be within code). Remove all power and continuity test everything. Check for neutral ground bonds while you are at it (should bond at the genset, at the inverter, and at "the pole" only... anything else is dangerous).

I'm assuming that there's not 220v items on your coach.

HTH,
Brian B.

Stan · August 01, 2007, 12:09:57 PM

manasst: If I understand this correctly, this is what you have:

Doesn't work: Shore Cord - dogbone - 30 amp cable - 120 volt 30 amp receptacle

Works OK: Same shore cord - 50 amp cable - same dogbone - same receptacle

I would say you have an open in the 30 amp cable.

Sean · August 01, 2007, 02:22:25 PM

I can think of only one way this exact set of symptoms could occur, which leads me to ask the following questions:

(1) Is the 50a<->30a adapter a store-bought item with molded ends, or "home built"?

(2) Does your bus make use of both incoming legs of the 50-amp cord (12,000 watts) or does it only use one leg (6,000 watts)?

On a separate note, if your setup is such that running the generator will back-feed the shore cord, you have some serious issues that need to be addressed. Setting aside, for a moment, the code violations and potential for killing someone upstream of your coach should the generator start while the shore cord is connected, the fact that there is likely a permanent ground-to-neutral bond in the generator means that you will have a double-bonding issue when on shore power, thus returning about half off your shore current through the ground -- another potentially lethal situation. Also, it likely doesn't do the windings any good to have them connected to an external source of power, and I think you'll find the genny head is heating up while you are on shore power. FWIW.

Let me know the answer to the two questions, and I think I can tell you where the problem lies.

-Sean
http://ourodyssey.blogspot.com

white-eagle · August 01, 2007, 05:05:17 PM

first: stan, the 30 amp extension stays in the loop. the only change was adding the 50a extension. with the 50a, a/c works. without the 50a extension, no a/c. same shore cord, same dog bone, same 30a extension, same shore plug at the garage. bus shore ->50a > dogbone> 30a>house 30a plug = A/C.

2nd. Sean, i believe there originally was an auto switch on the bus. when i bought the bus, no shore power at all since switch didn't work. Jack Conrad fixed it by taking out the switch and putting in just a plug for shore power which needs to be unplugged when the genset is on or else you have a set of hot leads at the shore end of the cable. i never power the genset when i'm plugged into anything, nor do i leave the cable out, always rolled up and put away.

i'm not exactly the electrical expert as you can tell. i suspect the dogbone (purchased with molded ends) is not putting any kind of juice on one leg so the a/c circuit doesn't power up. all other circuits including hot water do seem to work.

obviously, i cannot run the hot water, and both a/c units when i'm plugged into 30 amp without blowing the breaker in the house.
i have not run any continuity tests yet on any connections. Do i unplug the power before i run the continuity tests?
just joking, i'm not an expert, but i'm not that ignorant either.
thanks for the pointers on what to check. i will post results.

Buffalo SpaceShip · August 01, 2007, 05:26:41 PM

Quote from: manasst on August 01, 2007, 05:05:17 PM
...and putting in just a plug for shore power which needs to be unplugged when the genset is on or else you have a set of hot leads at the shore end of the cable. i never power the genset when i'm plugged into anything, nor do i leave the cable out, always rolled up and put away.

You should fix this immediately. The hot prongs on a male plug are destined to short out something (or someone!). The age-old "manual transfer-switch" still works: put a receptacle on your genset output. Then, you either plug your shore cord into it or the shore receptacle. No hot leads, no back-feeding, no hot windings... no tragedies.

HTH,
Brian B.

Sean · August 01, 2007, 05:49:14 PM

OK, take your voltmeter and check the voltage on your dogbone -- you should read ~117 volts between each of the outer two slots and the center slot. You may need to wiggle the test leads a bit.

If you read voltage on both sides, then my guess is that your dogbone is simply worn out. By chance, the blade on the 50A extension makes good contact in the worn slot on the dogbone, but the blade on the shore cord does not (possibly one is bent slightly differently than the other).

If you read voltage on only one side of the dogbone, then the dogbone has an "open" internally, and your 50A extension is swapping the hots between plug and receptacle (not really kosher, but not unheard of either).

In either case, the cure will be to replace the dogbone.

Once you get this fixed, though, you will definitely need to attend to the other issue -- it's an accident waiting to happen.

-Sean
http://ourodyssey.blogspot.com

JackConrad · August 01, 2007, 06:35:34 PM

Tom,
It has been a while, but I think I repaced your bad transfer switch with a new one. I think each of your ACs is on a separate leg of the 50 amp cord. Jack

white-eagle · August 02, 2007, 02:04:17 AM

no transfer switch or at least not any automatic one. Jack, see the note i sent you.

i remember trying to get hold of the auto txfr switch company listed on the old broken one and they were out of business, so i kept the shore connection the way it was. the air conditioner breakers are on opposite sides in the "fuse" box, 100amp breaker main. is that what you meant about separate legs?

i also found out the other day when i called powertech for a manual that my genset is a 12kw, not the 10kw marked on the outside cover, so maybe that's why 100amp main breaker?

i'll check more on the volts and stuff later today per some of the previous tips. and do some more checking on just what the electrical boxes in genset compartment actually do.

Sorry for not explaining well, but there was no manual or documentation with this bus. Mr. Schofield said he never intended to sell, and he knew where everything was. i've been trying to document (and learn)as needed when i'm correcting or fixing or enhancing. and moma said "if it ain't broke, don't fix it".

JackConrad · August 02, 2007, 05:33:24 AM

Tom,
I got your message. My memory just isn't what it used to be. I remember we tried to get it going as quickly as possible so you could get on the road. Go to Ebay and search for 50 Amp transfer switch. I found one similar to the one we removed from your bus. I think I paid around $50-$75. Jack

white-eagle · August 02, 2007, 08:03:15 PM

ok, did some measuring and now i'm more confused. on the 30a shore female plug at the house, 123v between the primary and ground, primary and neutral, 0v on neutral and ground. the female end of the 30a extension shows exactly the same. the female 50A end of the 30/50 dogbone shows 123v on the left primary between it and ground, or it and neutral. the right primary shows 119-129v between it and ground, or it and neutral. there is no voltage between neutral and ground. the bus end shore plug is a round L1430c lockable. it shows the same as the dogbone whether i connect it to the dogbone directly or insert the 50a extension cable. but the A/C only works when the 50A extension cord is in use.

i don't see any difference to justify the a/c issue? they seem to read like i think they should??

one good thing is i took pictures of the power relays where the genset and shore lines connect to bus breaker box, opened up the breaker box and took pics, and found the 12v connections (not labeled). None of it is documented, but at least i don't have to keep opening the boxes to verify what i saw. i also know that the washer/dryer is on the same breaker as the bedroom, and that i have a magnetek converter/charger that may have a recall due to fire hazard.