Buzzing noise

Merry Christmas
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JdoubleU

Senior Member
Every time the building heat pump kicks on for the first second there is a loud buzzing noise that seems to come from the inside of the emt conduit any suggestions. The machine works fine.
 

iwire

Moderator
Staff member
Location
Massachusetts
Turn up your radio. :grin:



A couple of pretty sure fixes.

Replace the conductors with larger ones.

Put a soft start unit on the heat pump.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I would consider turning up the radio as one of the fixes.

The high current flow creates a magnetic field which can cause conductors or EMT to vibrate. You hear this noise, but the noise is not much of a problem unless a paying customer objects to it. Breakers can also buzz during acceptable overloads.

-Jon
 

JdoubleU

Senior Member
winnie said:
I would consider turning up the radio as one of the fixes.

The high current flow creates a magnetic field which can cause conductors or EMT to vibrate. You hear this noise, but the noise is not much of a problem unless a paying customer objects to it. Breakers can also buzz during acceptable overloads.

-Jon
Thanks for your ans. If the breaker buzzes load would the breaker be bad.
 

billsnuff

Senior Member
shader coil

shader coil

this thread just woke up an old grey cell......keeps saying contactor coil hum = bad shader coil. think these were a DECO brand or something like that. industrial not resi. just an aside.
 

JdoubleU

Senior Member
brian john said:
No a buzzing CB in not necessarily indicative of a bad CB, but it warrants investigation and testing..
Sorry to be probeing so much on this topic, but what would you suggest to do for testing? I am new at troubleshooting and want to give an educated ans. to those it concerns. I've checked all the connections that I know of.
 

brian john

Senior Member
Location
Leesburg, VA
We would first perform a FOP test (see below)

Then we remove the CB and high current test it, megger it and ductor/micro-ohm (contact resistance measurement).

This is an old post. I keep some I write as questions often reappear. have you ever thought about ground up, ground down?

Oh and always ASK, better to ask then not know.

We are often called by electrical contractors to investigate why fuses are blowing or CBs are tripping. Many times the cause is a high resistance connections resulting in sufficient heat to effect the thermal element in the fuse or CB.

A simple method to isolate the high resistance connection and thus the source of the heat is the Fall of Potential Test Method, commonly referenced to as the FOP test. To perform this test, one simply needs a multimeter with a millivolt scale, and an amp clamp.

There needs to be a load on the device to be tested, preferably a balanced load or close to balanced load. In the case of a fused safety switch (FSS). One would measure current across all three phases, then measure from line to load of one pole/phase of the conductor strands (if exposed) for each pole of the FSS. If one phase has a higher that average millivolt measurement (actually the voltage drop across the device under test). Your next measurement would be from line conductor to line of the fuse, if all readings are close to equal move to the next components of the FSS, in this manner you an isolate the high resistance connection.

With an arranged outage repairs can be implemented and a repair FOP measurement taken to verify repairs.

Our thermographers perform this test as part of their IR Scan to isolate to high resistance issue. As sometimes it is not possible to determine from a picture if the issue is a CB connection to the bus or the CB. Additionally it is not feasible to use a DLRO (Digital Low Resistance Ohm Meter)/ Micro ohm-meter to take measurements on small CBs and FSS due to contact point spacing of the test instruments, so our technicians take pre-repair and post-repair measurement s to verify repairs.


An example we IR?d a 200 amp CB this weekend with 155 amps per phase (average), millivolt readings were 38mv, 91mv and 42 mv. The readings were taken from the bus stabs of the CB, negating any possible issue with the CB to bus connection or conductor termination connector to CB connection. B phase had an issue, when we replace the CB we will do further testing and open the CB to see if visual thermal damage has started.

This test can be performed on single pole CB, or any 3-pole devices, we have used this on 4000 amp bolted pressure switches.

As with any testing of exposed energized parts, all safety cautions must be observed, wearing of PPE, isolating the area to be worked in. One issue we have had over the years is customers taking FLASH photography as we are taking measurements. We no longer permit customers to take photos, without prior notice. This minimizes heart attacks.
 

cschmid

Senior Member
first how big are the pumps? what is the voltage? are they on starters? A few more details please..when the wires humm in the pipes and the pipes shake you normally need to up size your wires and maybe even your starters..But normally the contactors a very little and this is a sign of a bad contactor..one that has burned contacts..so unless you can change the contacts you need a new relay..coils normally fail with out notice and smell real bad..So if you can smell it it needs to be changed..:grin: :D kind of like a Poppy diaper..:) :smile:
 

Cellardweller

New member
Location
Goodyear, AZ
I've got a similar issue, but it occurs only on the start-up of the motor. It's a 30 HP, 460VAC motor with a DOL starter. The incoming voltage is 482VAC. I'm thinking that the inrush is dropping the voltage at start-up enough to increase the amperage draw to cause the wires to buzz for a moment in the conduit. The contactor has been replaced and full load amperage is normal. The first location is 10' upstream of the motor near a junction box located just before transitioning through the wall to the disconnect. The second location is just downstream of the breaker panel feeding the unit, which is approx a 100' away. The wire size is more than adequate at 1 AWG (copper). Measuring the voltage at start-up using a Fluke 787 w/ the hi-low-avg record feature on, captured a low voltage of 448VAC. I know that the actual voltage probably dipped way below this but was not caught by my meter. But it doesn't appear too excessive to me. My reaction is that the voltage is causing the issue, but I don't feel I've got enough evidence to support my conclusion. Anyone?
 
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