View Full Version : Compressor Terminal Arcing

07-04-2016, 06:28 AM
Hi Guys , i have a brand new comp that has failed its earth resistance test. I pulled the terminal plate and found arcing between a terminal post and the plate.
Has any one seen anything similar or know how this may of occurred ?

07-04-2016, 10:23 AM
Your pictures won't load.

07-04-2016, 10:31 AM
Pics attached again hopefully.

monkey spanners
07-04-2016, 06:57 PM
As a guess, moisture or lightning. I'm sure others will have some better ideas!

07-04-2016, 07:42 PM
Hi normally when this happens when everything tight
(1)the insulator in the terminal plate is tracking and faulty
(2)when the terminal plate is bolted down the crimp is very close and arcs

07-04-2016, 08:06 PM
Hi Andy

I've never seen anything like that before.

I am thinking along the same lines as monkey spanner, moisture in the terminal box.

Moisture in the terminal box might have started it, but once you get the carbonation (if that is the correct word) residue across the insulating agent between the terminal and the body, it creates a conducting path that makes the problem worse.

the initial problem could be moisture, or an abnormally high starting current, or a combination.

As a solution:

Clean the terminals and put heat shrink tubing over the terminals to cover them all the way down to the insulator.


07-04-2016, 08:40 PM
Hi All , thank you for all your replies . Just one thing to clarify , the arcing is on the internal side of plate so im sure moisture should not be an issue. Will wait to here from manufacturer about what they think.
Thanks again.

07-04-2016, 10:22 PM
Is this arcing due to someone testing when the compressor was under a vacuum?

install monkey
07-04-2016, 10:32 PM
the lug on the terminal isnt as bent as the other 2

08-04-2016, 08:42 AM
Voltage drop on that phase when under load. The other 2 connections are showing signs of excess heat.

22-04-2016, 09:45 AM
Hi all , its been established that the damage to terminal block was caused by testing insulation resistance while the comp was under vacuum.
Thanks for all your comments.

22-04-2016, 03:33 PM
Thank you for providing the update.

22-04-2016, 06:35 PM
Hi all , its been established that the damage to terminal block was caused by testing insulation resistance while the comp was under vacuum.
Thanks for all your comments.
Andy you are living proof as to what happens whereas many have disputed that in a vacuum this could happen.
Well done and as Brian says Thanks for the update.

23-04-2016, 04:52 AM
Hi Andy.
again from others , thanks for reporting back on actual cause of problems.
Out of interest what level of meg testing was actually done , voltage value etc., that created the problem, was it an electronic meggar type test instrument, or an electronic multi meter.

23-04-2016, 08:51 PM
Here is an article on resistance of a vacuum. Interesting stuff.

Magoo, 500v megger.


Glenn Moore
24-04-2016, 03:04 PM
Hi Andy
This type of fault happens more than you think, as ive seen several instances of this whilst doing compressor warranty work. I'm convinced this is a situation which happens when different trades are involved on the same installation, and a lack of inter trade knowledge can cause system issues such as this.
playing devils advocate lets see what happens.
Main Contractor (A) REFRIGERATION , installs the fridge system and pipe work, SUB contractor (B) ELECTRICAL, installs the Control panel and the associated wiring. The fridge installation is now pressure tested etc, and then the system is evacuated. The electrical installation is now finished . The electrical system is now check and metered for integrity, continuity and insulation before being signed off. Does the electrician Know that the system is under a deep vacuum? does he know that meggering a semi or hermetic compressor under a deep vacuum can damage the compressor motor ? or simply manually pushing a compressor relay in, to kick the compressor over whilst its under a vac can also damage the motor. Many electricians ive spoken too have no idea that in the fridge trade that testing or running a compressor under a vacuum is a total NO NO.
The Refrigeration engineer should know this but the electrician ?.
I had a situation recently where I went to look at a new coldroom which was nearing completion. The Electronic expansion valve hadn't been set up correctly. While I was on site the sub contract electrician was fitting the Flourescent lamps inside the cold room. The electrician had made a fantastic neat installation of the lamps inside the room. Their was one large evaporator at one end of the room ,the lights had been installed in pairs every 1.5 metres down the long room. Unfortunately he had mounted them in line with the evaporator across the ceiling, which would totally destroy the Coanda Effect of the air being blown down the room, which would have caused bad air circulation and hot spots in the room. When I told him what effect fitting the lamps in that configuration would have on the operation of the room he was angry that no one had explained this to him before, I explained it was up to him if he left them as they were or if he changed them as I had no authority on the site, but he could see the problem and turned all the lamps 90 degrees so the air flow was no longer impeded. He later thanked me for the advice, and said how was he expected to know that !!!! Good question. This is the blame game, or get out of jail free card.

24-04-2016, 08:11 PM
Glenn, I totally agree with you but have one question,
Shouldn't there be a position of supervising? One skilled person that knows what anyone's else's job?
What to do and when?

Seems strange to me as I have an electric license and do all the controls and electricity myself. [up to a certain cold room size]

charlie patt
24-04-2016, 08:14 PM
I had a similar issue where I was called to a site that had lost three comps on a new install three decent engineers had installed comp very good install engineer with a torr gauge but sometimes he was a bit keen to leave on a Friday anyway it was again diagnosed another comp blown history as follows
Installed may 2002 r404a chiller room 6mx 3m room medium use correct size kit
On install after 24 hrs blew trips engineer went to site comp gone comp fitted
Two days after comp install trip blows again engineer visit new comp needed
Four days after that trip blew engineer goes to site comp blown
Then I got the call to fit new comp and find out what's going on so called install engineer who advised room on wrong breaker a type b and he advised on site sparky to fit a c so any way I role up with a very upset customer so fit a comp change a breaker no debris in system ran system all pressures temp oil levels good until it pumped down and it pumped into a vacumn so I set it up and ran and done nothing else so I called the three previous engineers who fitted comps and asked was comps dirty inside or smelly and all three said no .....now right or wrong I reckon the room was blowing trip because wrong breaker to small and wrong breaker I believe all units where pumped into a vacumn and when insulation tested which then fried comp all three of um ...... that room still running on same comp now which is a bit rich but averages a comp every 4 years so not to bad now anyway just proves bit of time cup of tea bit of thought and all is cure able what I am really saying is Glenn I agree with you ta charlie

24-04-2016, 09:38 PM
Your right Charlie,when you change any compressor find out why the old one failed,and on semi hermetically always change the contactor/overload and starting kits on single phase oh and always monitor while drinking a few good cups of tea and hobnobs!

Glenn Moore
24-04-2016, 10:30 PM
Thanks Charlie
Hi Chemi Yes your right there should be someone who is an all rounder supervising the site, but due to costs many large contracts are subbed out to contractors for electrical and pipe work, and the only time anyone with any real fridge knowledge gets to site , is when the commissioning engineer arrives and he then has to sort out the mess left by others.
One large industrial contractor regularly used to call me out during the commissioning stage complaining that the Danfoss valves in the system would not work or were letting bye etc. The pipe work contractor uses a grinder to cut the steel pipe , and on one site there was even shingle (stones) inside the valves which had come via the pipe work from the site walkways and carpark. Rule 1 in refrigeration CLEANLINESS Rule 2 Cleanliness

25-04-2016, 12:02 AM
Sadly pricing is the downfall ,and others have to correct the mess a now retired top engineer used to call them cowboys they ride into town shoot the sheriff then ride off into the sunset with the loot,great products like danfoss tried tested and respected in the industry get blamed for others incompetence !

25-04-2016, 07:30 PM