Trane Screw comps

[Rob S]

Got a couple Trane chillers with CHHB1007NG0N119A helix screw compressors. All 4 compressors are reading 13 to 9 mega ohms to ground @ 500V. I find it odd all 4 would be reading such a low mega ohm. And none showed any acid.
Do these just use mag. wire with poor insulation or what?

M# RTAA2004XG01A1DOB

[US Iceman]

Off the top of my head I'd say this sounds like the system is wet. Have you checked the site glass to see the moisture indicator color?

Perhaps they have only been this way for a short time, and acid has not developed yet?

[Rob S]

Always... As green as the top bar on these forum posts. Hence my curiosity as to why.

[US Iceman]

Ok, now I'm going out on a limb.

Is the area around the motor terminals wet from condensation? In the past I had the unfortunate experience to work on some Dunham-Bush equipment that caused me to learn a lot of different things to solve the problems.

One of those was the motor terminal box was always wet from condensation due to the cold suction return gas through the motors (semi-hemetic).

You couldn't get decent megger reading for nothing.

Shut the compressors off, went to a store to get a hair dryer. Shut off the power, and removed all of the electrical connections and terminal blocks. Dried all of the terminals, terminal blocks, etc.

Used a spray on electrical sealer around the terminals and all over the inside of the terminal enclosure being careful to not get any spray on the terminal posts.

Used the hair drier to speed up the curing process on the sealer.

When the sealer was hard, I re-installed all of the wiring, etc.

Meg the motors and guess what? A decent reading. None of the low stuff like you are experiencing.

Now, I'm not saying that's the solution to your problem, but it did solve mine.

Hope that helps.

[Rob S]

Possible.. however don't remember seeing any sweating in the terminal boxes. I'll look at it again when I change out a cond. fan.

[Chris Burton]

I would suggest iceman is correct,i think the terminal box sits horizontal on top of the compressor & if the terminal box lid is leaking you will get tracking. A similar problem used to happen with the carrier 06D box which would fill up with water, you'll come along find the contcator blown to peices but the compressor windings fine. I've seen those trane screws with about 1/2 inch of water in the box. Also with the RTAA or RTAB if you get HP trips in winter & LP trips in summer we used to fit an HP switch to 1st stage condensing fan as UCM uses the saturated condensing temperature sensor which can be wildly inaccurate at start up until system settles down.

[NoNickName]

I think the terminals were tightened over their rated torque, and the bolts cracked the insulation laquer where the bolts cross through.
It once happened to me, and I almost got mad trying to sort out why that compressor was not passing the electrical stiffness test.
Also do the meg testing WITH gas, because vacuum is a good conductor.

[US Iceman]

I think the terminals were tightened over their rated torque, and the bolts cracked the insulation laquer where the bolts cross through.


That's another very good possibility too. It's essentially the same problem.

Chris Burton mentioned "tracking". That's a term I have not heard for quite some time. I have seen this in contactors too. In that case I believe it was called carbon tracking. Sometimes you can see a very faint line from one pole to another.

This is similar also to flash arcs across the starter contacts. When you look at the front of a starter, the contacts have a little plastic shield/plate over them. This is the flash guard to prevent arcing across the contact. Say L1 to L2, etc.

Does the EU have anything for flash suppression on large motor starters or switchgear? There has been a BIG push here to train people on this, and prevention methods.

[NoNickName]

Yes, they call it "flame chimney", and they are commonly found on big contactors.