3 Phase Question

Im not electrician, so bare with me. Here at work, we have one warehouse that has to maintain 60 degrees year round. To do this we have a total of 4 chiller units. 2 are more or less back up, and had seldom came on except on very hot days. They are older units that work, but cant keep up with 60 degrees. 2 bigger units were installed in the 70s, and one has just been replaced with a new outside unit and air handler. The other has had the outside unit replaced both within the last 2 years. Now, the older units are on a seperate transformer outside from the new units. No issues there, but the new units heat up the main breaker inside to the point it trips. Old units have line from the transformer, to meter base, to inside breaker, and from there to each unit, where it has its own breaker for both inside and outside units. The new ones, well, heres the point ofthe post. The guy who installed the new units came by to check the untis, and determined the source of the heat in the breaker was from the fact the new units pulled more amps, and possibly the age of the breaker as well, is whats causing it to trip. So he was going to install a new breaker inside. He pulled the meter outside, checked for power and there was still power to the breaker. Heres what he found: The lines from the transformer go to the building, there is some type of setup attached to the outside wall of the building that has 3 "blocks" for a lack of a better word, that has a hole in the center of each block. The wire wraps around the blocks going through the hole in each, then comes to the inside breaker. From the bottom of the breaker, 3 wires go to meter base, and from there to the chiller units, where each has its own breaker for each unit. Boss said the original units were installed in the 70s, and as far as he knew, no other work has been done or needed. So finally my question: Why would the "hot" wires from the transformer been connected directly to the breaker?

(If I could post pics from work I would. I may try this evening from home.)

sounds like rom your description that there was power to everything without a meter measuring power to bill correctly ..gonnabe interesting to see all responses ,,.

I guess that you are thinking that meter is being bypassed? It isn't. When currents are large as in industrial situations, the current is too high to meter directly, so current transformers are used. The main conductors loop thru the current transformers ( the loop is actually the primary winding) and the secondary winding feeds the unfo to the meter for registering.

GOOGLE "Current transformer metering".

That is called a "CT" meter. Very common on industrial electrical power. If he is not aware of that, he has NO business fooling around with it!

Without being there, sounds like CURRENT TRANSFORMERS to me. They SHOULD NOT drop voltage or inhibt the flow of current. Sounds like perhaps excess current flow due to line voltage drop or just aging or faulty equipment. If a new breaker doesn't cure the problem its time to look at voltage drop and what the actual current flow is. It may be time for some electrical upgrades such as bigger conductors or service capacity. I usually fed a main service entrance panel (such as 200 or 400 amp) from the utility transformers and then used individual branch circuit breakers to feed motor loads.

John T

I am no electrician but owned and operated a shop with three phase and am somewhat familiar. I agree with JMOR but also believe it is time to het everything on one transformer and install proper breaker panels. In time the savings on the utility bill will pay for the update. If John T. responds he will likely rename me "Bubba"

My son has a large building that was wired with those current transformers. I had a lot more capacity than he would ever use working in there by himself. I can do single phase but until this job knew nothing about 3 phase so I found a fellow who works for the electric dept to help us out. The wiring in the building was a real mess I think Thomas Edison may have done the original installation.and others worked on it in the last 100 years and really messed it up. My friend looked it over and decided to completely overhaul everything, whole new service entrance and rewired the whole building. Cut the electric bill in half from about $800 per month to $400. The job has paid for itself already.
Hire someone who knows what he's doing and do the job right.

So this is normal, ok, and it does make sence to me now. Im sure the guy workig on it knows whats what, I just didnt understand why it was like that. As alaways, thanks!!!!

Usually with CTs you get a little free power if you are not drawing much through them. They let a bit of current get by without picking up on it.

No I'm not, you sound too smart to be called Bubba lol UNLESS you and your brother in law wired your own home while you downed a case of beer !!!!!!!!!!!!

John T

Current transformers are used often to reduce the metering voltage down from actual line voltage. I can check a gauge at work and read 119 volts, and know that translates to approximately 4160V on our standard pump buses. Much safer than having 4kV hooked to the gauge. Also comes in handy for accurate metering of three phase power usage, especially in light industrial, where the three phases of 120 are split for lights and smaller equipment use (120/208).

Using a qualified, licensed individual is always the best and safest idea. Not always the route I choose, though.

(quoted from post at 14:47:07 06/14/16) Current transformers are used often to reduce the metering voltage down from actual line voltage. I can check a gauge at work and read 119 volts, and know that translates to approximately 4160V on our standard pump buses. Much safer than having 4kV hooked to the gauge. Also comes in handy for accurate metering of three phase power usage, especially in light industrial, where the three phases of 120 are split for lights and smaller equipment use (120/208).

Using a qualified, licensed individual is always the best and safest idea. Not always the route I choose, though.

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Nope. CT's do not output 120V . A CT outputs 0-5amp on the secondary . Just choose the PT ratio and the proper Ammeter scale. Voltage would be 1 or 2 at the most.
DO NOT ever energize the primary side of a CT with the secondary side open/disconnected . The results are flame, arcing, smoke, equipment damage, injury or death.
The PT secondary output at full rated voltage is 120V. Choose the PT ratio to match the primary voltage of 240, 416, 480 or 600V. Choose the meter scale to match the PT ratio.
Metering PT and CT's are more accurate and more $$$.
As previously stated . This is not a job for Bubba and his Brother-inlaw/cousin/step brother Billy Bob.

JohnM,
Bad breakers and defective buss bars where breaker connects can cause heat and trip breakers.

One place with high ambient temperature, we had to blow cold air inside the box to keep from tripping breakers.

Bottom line both excessive temps and bad contacts where breaker connects to line and cause problems too. Not to mention excessive currents. I can't remember the exact amount but you don't push a breaker much past 80%.

Use an IR thermometer and look for a hot spot and measure current. geo

I totally agree with you B&D.

An IMPORTANT thing to remember is that CT's must be shorted if the circuit is opened, or they WILL explode.

CT's (current transformers) don't reduce voltage, but amperage, generally for metering. PT's (potential transformers) step down the voltage
Pete