Troubleshooting Problem

Status
Not open for further replies.

The Iceman

Senior Member
Location
Florida
I went on a service call this morning to a veterinary surgical center. They claim that in the last couple months they have fried two computer monitors both on separate circuits and on surge protectors, sanitizing equipment keeps plowing fuses and a technician said there?s nothing wrong with the equipment, and other computers shut down throughout the building and need to be turned back on. I have checked all wiring from the meter to each receptacle and can?t find any problems. POCO is on site now and checking their end, they said they have been out there before and have not found any problems. The veterinary center has added a lot of computers, copiers, printers, and fluorescent lighting in every room and it is a large building. Could this be happing because of harmonic currents? If POCO comes back with a clean bill of health again today what else do you all recommend I check? I would appreciate any help on this matter
 

brian john

Senior Member
Location
Leesburg, VA
One check for open neutrals particularly on the service end as it is happening facility wide.

I would doubt harmonics as harmonics generally are a lets blame it on them attitude from a lack of knowing what really is happening.

While there are sever utility men on this site and I mean no harm to their fine firms. I NEVER RELY ON WHAT A UTILITY lineman tells me. They basically are assembly line installers and have little or no trouble shooting experience and I am including their service technicians.

What I would do.

Infrared
Line disturbance analyzer
complete visual inspection
 

cadpoint

Senior Member
Location
Durham, NC
Every circuit that blow a piece of equipment is suspect, I'd chase everything down, I'd look at the main, I'd look for the first nasty box out side the panel, I'd look for the first nasty box above the equipment.

I'd think about putting in a AFCI breaker and see if it holds that will tell you if you have a bootleg neutral that you didn't ID...

Does the inrush of the sanitation equipment demand its own circuit ?

I'd then ring then all out, and meg everything out that was orginally suspect.
 

charlietuna

Senior Member
Without a certified data recorder on the problem circuits everything is just a guess. The data recorder will tell you what and when is happening to this equipment and allow you to confront the power company if it happens to be their problem. Consider investing in this equipment -- your customer will be impressed with a computerized explaination of the problem without "guessing". Two units can narrow it down to which side of the service it's on!
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
090930-2130 EST

I am with others on the possibility of a neutral problem.

However, some new computers operate from 90 V or so to over 240 V for the main supply. These use wide range switching regulators.

Several years ago we had voltage problems. Three phase open delta with a wild leg. Edison put a recorder on the system and never detected the problem when it occurred. Obvious the recorder was not capable of detecting the problem based on what ultimately was found to be the cause.

I did some limited monitoring and saw substantial dips. But I was not monitoring both sides of neutral. One day by chance I saw a light flicker, and in addition a floor fan sped up. Got Edison back out and it was near dusk. While one truck was waiting for another the driver noticed arcing at the transformer terminals. When they climbed the pole they found bad joints at both the neutral and one hot line. Two new transformers and no trouble since.

A useful test I have suggested for detecting this type of problem is to connect a light bulb, 50 to 100 W on each side of the 120-0-120 supply. If the neutral is bad one light will brighten and the other dim. This is a very low cost detector and sensitive to short duration voltage changes. Obviously some eyes need to be seeing the lights.

If there is a neutral problem you would likely see it by applying a substantial load on one 120 V phase. Try a 12 A load first (1500 W heater). If that produces very little flicker, then try a 1.5 HP induction motor with substantial inertial load. About a 70 A load. With these known load changes monitor line voltage with a good DVM that reads to 0.1 V at 120 V.

.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Good idea

Good idea

A useful test I have suggested for detecting this type of problem is to connect a light bulb, 50 to 100 W on each side of the 120-0-120 supply.
You could even make a 2-socket contraption and fit it with a dryer plug for easy use. :)
 

wankster

Member
a loose neutral of a MWBC can cause voltage to rise above phase toground volts

i recently had this problem in my house. a long chain of receptacles were reading 85-100 volts with one ominous receptacle reading 130 volts. turned out to be a disconnected neutral @ a lighting J-box:roll: The low outlets were playing hell with our electronics while the one high outlet caused the incandescent it was feeding to be extra bright!
 

wptski

Senior Member
Location
Warren, MI
090930-2130 EST
A useful test I have suggested for detecting this type of problem is to connect a light bulb, 50 to 100 W on each side of the 120-0-120 supply. If the neutral is bad one light will brighten and the other dim. This is a very low cost detector and sensitive to short duration voltage changes. Obviously some eyes need to be seeing the lights.
.
Recording each side of the 120-0-120 supply with a two channel scope with something like the Fluke 120 Series.
 

BAHTAH

Senior Member
Location
United States
System Wide Problem

System Wide Problem

I would bet on the bad neutral. Be there when the utility company shows up. Over the years I have found bad neutrals in the meter sockets, loose splices at the weatherhead and open neutrals on underground services. This is something that may not show itself unless the load is high enough so I would be looking at the checking all the utility connections just to be sure they are ok.
 
Status
Not open for further replies.
Top