leibert 20 ton unit shorted to ground

[jim4237]

Hey all. I can't believe I'm asking this, but I just want to make sure. I have a Carlyle compressor in a Leibert 20 ton unit. Blown contactor and fuses. I've got correct Ohms between legs, but I also have Continuity to ground on each leg. I know this isn't right, but is it common to have a short to ground on every leg; Or am I missing something.

[valentyn]

I know this isn't right, but is it common to have a short to ground on every leg; Or am I missing something.

Yes, its common for 3 phase motor,
if one leg short to ground other short too.

[WhoIsThat?]

Did the first leg to short cause the other two shorts?

[Domcort]

Hey all. I can't believe I'm asking this, but I just want to make sure. I have a Carlyle compressor in a Leibert 20 ton unit. Blown contactor and fuses. I've got correct Ohms between legs, but I also have Continuity to ground on each leg. I know this isn't right, but is it common to have a short to ground on every leg; Or am I missing something.

Jim,

When you say a blown contactor, What do you mean?

I have seen many a circumsatnce that technicians do not change badly pitted contactors and then what to know why they lost a compressor. When it was obvious that the contacts welded together and ran the compressor into oblivion or unitil she just shot the bed. Because of a 30 dollar part the lost a 4000 dollar compressor, it just don't make sense.

But it is common for the high voltage to short together, to ground, or too the internal overload which would cause more damage running high voltage thru the control circuits.

Domcort

[mattthehatt80]

yes it would be all three if melted contacts but im surprised there isnt any open windings then at least one

[jim4237]

I was testing fire alarms and it shunt tripped the hvac units. After resetting breakers I noticed it was getting hot in space. The contactor on compressor 1 was fried; burnt wires, etc. I replaced contactor and fuses and restarted without checking motor. It blew all the fuses again immediately. Seems like L3 fuse was hotter than the other 2 legs. Isolated motor and OHM'd out each leg to ground and got resistance on each. And also got resistance between each leg.

[Domcort]

I was testing fire alarms and it shunt tripped the hvac units. After resetting breakers I noticed it was getting hot in space. The contactor on compressor 1 was fried; burnt wires, etc. I replaced contactor and fuses and restarted without checking motor. It blew all the fuses again immediately. Seems like L3 fuse was hotter than the other 2 legs. Isolated motor and OHM'd out each leg to ground and got resistance on each. And also got resistance between each leg.

Jim,

Burnt wiring, smybolizies that there may have been a loose connection(s).

Anything can happen internally to the compressor, shorting phase to phase and then to ground can happen, shorting high voltage to the internal overload can also happen, which is low voltage.

Looks like a replacement compressor is needed, if you have the original compressor rebuilt you may get a better understanding of whta happened internally.

keep us posted,
Domcort

[WhoIsThat?]

Burnt wiring, smybolizies that there may have been a loose connection(s).

if it's within a few inches of the connection. Crispy the whole length means overload.

[Domcort]

if it's within a few inches of the connection. Crispy the whole length means overload.

I would agree with that, the fuses protect the wiring and the device i.e, the load.

Domcort

[WhoIsThat?]

20A through a bad connection having 0.02 Ω contact resistance is 8 W. If the connection has a small surface area [e.g., that of a pea] it will get very hot.

I had a half volt drop @10A through a badly installed wirenut connection. I was pulling 10A to check for bad connections just like this one.

[BFG6868]

Disconnect the wires from the compressor terminals and check there to rule out an external wiring or contactor problem. I would bet the compressor is toast.

[hvac-tech-lane]

Hey all. I can't believe I'm asking this, but I just want to make sure. I have a Carlyle compressor in a Leibert 20 ton unit. Blown contactor and fuses. I've got correct Ohms between legs, but I also have Continuity to ground on each leg. I know this isn't right, but is it common to have a short to ground on every leg; Or am I missing something.

Just to clarify, the short to ground is most likely or could be at just one location or area of on of the three independent windings of the motor. the motor windings are connected internally at each of the power connestions, if you were to designate the windings with letters as A,B,C, then terminal 1 would have the " input" lead of winding A and the "output" of winding C connected to it,terminal 2 would have the " input" lead of winding B and the "output" of winding A connected to it, terminal 3 would have the " input" lead of winding C and the "output" of winding B connected to it.

Therefore, if the short to ground is anywhere in the motor you will read it on all three motor terminals.

Hope this helps.

[The Doctor]

when you say "continuity to ground", do you mean low resistance?
Typically if your standard multimeter is ringing to ground then yes, it's gone. But, I'm just looking for you to clarify a bit.

What are the values of each leg to ground?

Are you talking like Megohms or are you talking 10, or 800, or 27K ohms?

[thump_rrr]

Before condeming any semi hermetic due to a suspected short circuit I remove the terminal plate and disconnect the wires to test the windings with a megger.
The service valves must be front seated and the refrigerant recovered from the crankcase prior to removing the terminal plate.

Carlyle Service Guide

From the Thermacon Compressor Guide

Compressor Testing Guide
Please use this guide if you suspect a faulty compressor
To verify basic compressor function in a field environment the following will
demonstrate whether further investigation will be necessary or not.
1 Earth Test Using a 1000v Megger check each field winding
to earth. 1st check the earth connection is
sound by an earth to earth test & repeat this
following the motor test.

If reading < than 2 MÙ Stator probably burnt out,
but do not rule out a contaminated / damp
terminal plate.

Reading 2 MÙ - 20 MÙ Probably not burnt out, terminal plate
contaminated or damp.
Separate terminal plate from main casting &
repeat check to casting. If fault clears then
terminal plate is faulty.

Reading > 20 MÙ No earth Fault

Precautions Do not effect Megger checks under deep vacuum.
Do not Megger overloads.

2 Field Balance Using an Ohmmeter set on Ohms verify balance
3ø motors only of motor field coils.
If balance is out by more than 10 % suspect
motor is defective.
Separate terminal plate & repeat measurements,
if readings do not improve rewind is probably
required.

[heavymetaldad]

great procedure thumper

[thump_rrr]

great procedure thumper

Thanks, and get well soon.

[valentyn]

Application Engineering Bulletin
AE-1294 August 1, 1992

MEGOHM VALUES OF COPELAND COMPRESSORS

......There are many factors that affect megohm
readings including contaminated refrigerant, oil
level, refrigerant in oil and current leakage through
electrical fusites or terminal plates.

Any external electrical components connected to
the compressor terminals also affect megohm readings.
Wires, contactors and relays all leak current
and will decrease compressor megohmeter readings
if not disconnected.

As mentioned earlier a single megohm reading
cannot be used to condemn a compressor since
many other factors are involved. However, limits can
be placed on megohm values that dictate action be
taken. Copeland has found that these limits are
related to the rated voltage of the compressor. Megohm
values equal to or greater than 1000 ohms per
volt are probably acceptable. For example, a 460 volt
compressor might show a megohm reading of 460,000
ohms or 0.46 megohm. Compressors with rated
voltages of 208 to 230 volts would then be operable
at megohm values of 0.208 to 0.230 megohms; for
simplicity, Copeland has set the limit at 0.5 megohms
before a compressor is condemned.

[Sun Dog]

Application Engineering Bulletin
AE-1294 August 1, 1992

MEGOHM VALUES OF COPELAND COMPRESSORS

......There are many factors that affect megohm
readings including contaminated refrigerant, oil
level, refrigerant in oil and current leakage through
electrical fusites or terminal plates.

Any external electrical components connected to
the compressor terminals also affect megohm readings.
Wires, contactors and relays all leak current
and will decrease compressor megohmeter readings
if not disconnected.

As mentioned earlier a single megohm reading
cannot be used to condemn a compressor since
many other factors are involved. However, limits can
be placed on megohm values that dictate action be
taken. Copeland has found that these limits are
related to the rated voltage of the compressor. Megohm
values equal to or greater than 1000 ohms per
volt are probably acceptable. For example, a 460 volt
compressor might show a megohm reading of 460,000
ohms or 0.46 megohm. Compressors with rated
voltages of 208 to 230 volts would then be operable
at megohm values of 0.208 to 0.230 megohms; for
simplicity, Copeland has set the limit at 0.5 megohms
before a compressor is condemned.

Thanks! I bought a megger a few months ago. Hadn't had a chance to figure out how to use it. This helps me get a feel for it. This thread is long out of play, so don't know if it will be seen, but what Megger setting recommended?

[maxster]

smell the freon off the suction it went NUKE..your cooked

[jpsmith1cm]

moved thread to Tech to Tech commercial