Ohm my goodness... (ME)

[Deleted User]

ME

[Deleted User]

Honeywell V8043 series valve...

Wallies, I ran into a problem yesterday while trouble shooting a job. Actually, I discovered numerous problems with this job which I will discuss.

In the process of investigation, I had to ohm out the windings on a Honeywell V8043 series valve with a 24 volt motor. The motor is rated on the cover of the valve as .32 amps. When ohmed, it shows 22 ohm potential. Using Ohms law, amperage is found by dividing voltage by ohms, so, 24 (verified) divided by 22 ohms (verified twice on other valves) gives us 1.09 amps, not the .32 amps listed on the cover.

Could you wallies do me a favor and grab one of these devices and double check me. I called my partner in the office and had him grab a new one off the shelf and check it, and he confirmed my findings.

The other problem has to do with a Taco 406 ZVC. The owner suspected that we had 2 zones cross wired, which is entirely possible. This part of the house has always been kept turned down to 60 degrees F on all 5 zones. So, in an effort to correct the mistake, I flip flopped the wiring between the two suspect zones. I test drove the first circuit, and it worked OK. Tested the second circuit, and when I went for shut down, it would not release. I pulled the TT wires off completely and it STILL would not release. Suspecting a bad zone control, I decided to move station 5 (the non releasing station) over to the unused channel 6. I did, and when I powered up the control, the power light went real dim, and the secondary fuse blew...

****,O...

Grabbed my multi meter and started testing. Unwired the 6 conductor at the zone valve (4 for motor, 2 for t-stat) and did a continutity test between all four conductors going to the motor. They came back clean, no shorts between them individually, and no shorts to earth ground. Just to confirm I was working on the right wire, I twisted all four wires together at the remote manifold/zone valve station, went to the other end and confirmed continuity through all 4 wires, and still no connection to ground...

Replaced the fuse and as I touched each wire individually to the screw contacts, output terminal 2 on the ZVC, when connected to one of the motor leads would ARC real bad, indicating a dead short. Double checked it against ground, and it was still disconnected on the other end. No short seen on the ohm meter, but again, when I touch it to the terminal, it tries to take out the fuse. If I touch that wire to the right hand TT terminal on the same channel, it lights up the zone call (yellow) LED.

I went back and triple checked all wiring for continuity with and against each other and against ground potential, and the only anomoly I found was 1 volt of stray power as a potential from each wire to ground. I suspect that our installers paralleled the stat wire too close to the 220 volt circuit serving the compressor motor (GSHP) because when the compressor is off, I have ZERO voltage potential, and there was never any voltage potential between the individual legs of the 4 C going to the zone valve motor.

****, O....

I am going to have to jumper terminals 3 and 4 so I can use the end switch wires for the motor wires and abandon the motor wires, but what the devil is causing this? One of my window electricans said I should megger the circuit because I may not be able to see a partially grounded circuit (staple through the jackets) without putting some decent juice to it. I've never used a megger before. Anyone care to educate me on the use of a megger? From waht I can see, replacement would be a bear of a job...

Baffeled in Denver.

ME

tim smith

Re: short

Mark, when you say you shut off compressor and stray voltage went away, did you then try connecting wires to the zone valve and it did not short fuse??

Rich L.

Meg

Mark, we have a megger that we use on compressors and motors. Basiclly it's a small "box" with two test leads, a hand crank, and analog scale. When testing say a single phase motor both test leads are hooked respectivly to black and nuetral on the motor, unwired from power of course, and wind the crank. When the crank is wound you are inducing a high voltage low current situation to the windings of the motor. If there is a weak spot on the insulation, or in your case a staple through it , in the wires the high current tries to "jump" to ground. If you get a reading of infinate resistance on the ohm scale your windings are good in your motor. If the reading is less than infinate you have some leakage through the insulation. I would think you could test the leads in question by taking both ends loose from their connections, wire nut one end together and connecting the other to a megger. I've never tried it before on control wires but don't know why it wouldn't work.

Good luck, Rich L

Rich L.

Meg

Mark, we have a megger that we use on compressors and motors. Basiclly it's a small "box" with two test leads, a hand crank, and analog scale. When testing say a single phase motor both test leads are hooked respectivly to black and nuetral on the motor, unwired from power of course, and wind the crank. When the crank is wound you are inducing a high voltage low current situation to the windings of the motor. If there is a weak spot on the insulation, or in your case a staple through it , in the wires the high voltage tries to "jump" to ground. If you get a reading of infinate resistance on the ohm scale your windings are good in your motor. If the reading is less than infinate you have some leakage through the insulation. I would think you could test the leads in question by taking both ends loose from their connections, wire nut one end together and connecting the other to a megger. I've never tried it before on control wires but don't know why it wouldn't work.

Good luck, Rich L

[Deleted User]

Still shorted...

even with the compressor in the OFF position.

TIA

ME

[Deleted User]

Thanks Rich

Guess I'll see if I can borrow one from one of my electrical aasociates.

ME

tim smith

How far away from manifold to zvc

Is that how it runs, t stat to manifold and 6 wire from zvc to manifold. ?? Most electricians won't have a megohmeter. A/C refer guy or motor shop. Maybe simpler method, stretch a wire from where it starts to manifold, try quick test and see if problem goes away, sounds to me you have a staple barely through insulation of wire and just barely touching. Tim

MIke_Jonas

Future megger

Look into the Fluke 1587. I got one, use it all the time, love it.

[Deleted User]

Yes...

As the crow flies, probably 20 feet from point A to point B. But it goes vertical, through an attic with 2' of loose fill fiber glass, then down the wall of the mechnical room to the ZVC.

ME

jp_2

Ohm's Law & AC

mark,

ohm's law only kinda works with AC in your situation. it does work 100% but you have to look at reactance, the inductance and capacitances here Xl and Xc.

off hand, the winds of that motor look like more resistance to AC than the ohm reading you get with a meter(DC).


more tools:
sounds like you could use an amp probe clamp. need to look at the actual current draw of that motor.

David Nadle

jp's right

If you have a meter that can measure inductance L then you can measure the total impedance of the motor by the formula Z = R + 2 pi f L (for 60 Hz, Z = R + 377 L).

Alternatively, if your multimeter has a seperate socket for measuring current you can connect the meter in series with the motor to measure the operating AC current. Be careful; if you connect your meter that way across power without a series load you'll blow the internal fuse.

A probe clamp is convenient when you can get it around a single conductor.

don_185

Me too

I also would have to agree with other a amp meter is a great tool when chasing shorts.

I would also check low voltage wiring inside the gshp and see if they did not tie the circuit into the lock out relay.
I have seen guys tie in well pump relay and circ at the contractor coil.If the system goes out on safety for any reason your lock out relay will energize and you will lose one side of your 24 volts.Also depening on where they tie the voltage in could also give you a short as well.

jp_2

1 stray volt

no need to worry about a stray volt in that sort of wiring, I've measured 50V stray without trouble in a machine control system, this goes away when connected to a low resistance.

sounds like a bad motor.

Rich W

Possible short in the end switch circuit and that got cross-wired to term 1 and 2 on the zone outputs...I think supco has a new clamp meter that shows both amps and voltage at the same time. This will show a short very quickly- current up and voltage down. I do the same thing with two meters now, this will be easier. These are a pain in the butt to find....but so cool when you do.Good luck.

Rich2

[Deleted User]

I own an amp clamp....

somewhere...

Thanks for the education David and jp.

ME

jp_2

whats the outcome ME?

what did you finally do to fix it?

[Deleted User]

Spare pair...

Old addage. If 2 will do, run 4. You NEVER know when you will need the others.

Fortunately, the installers had run an 8C wire. THe spare pair were tightly wrapped around the base of the cable. All's well that ends well..

BTW jp, where can I find additional information on the subject that you broached?

Thanks for your input.

ME

jp_2

college town nearby?

go to a good used book store, I'd start with an intro into electronics book. or buy new.

Paul B._2

Additional reading at Fluke website

Hi Mark,

Book mark Flukes website, the "Fluke Technical Papers" alone - in "Application Notes" will make the site worthwhile.

http://us.fluke.com/usen/support/appnotes/default.htm

Paul