Are you using the right phases for your AC power?

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Are you using the right phases for your AC power?
« on: 1 Apr 2024, 06:43 pm »
I am auditioning some AC power cables right now, and I'll post my experiences in the next month.

At the same time, I wanted to check the electricians work to make sure nothing was fishy in my Media room.
What I discovered is that he had a shared breaker for two of my dedicated runs, and the TV was on the opposite phase
from all of the other outlets in the room.  I needed to make room for another breaker in the panel for my
third dedicated run in conduit, so I rearranged things. 

Checking to see if your AC outlets are all on the same phase is simple:

Usually, the panel has odd and even breakers from top to bottom.  Left and right adjacent breakers are on the same phase.
Once you determine the phase that your audio gear is on, you can check to see that the breakers are only odd or even from top
to bottom.  You can do this without taking the panel apart.

You can also use a voltmeter that has a 500VAC or 750VAC range and test between the hot on each of the outlets.
All should measure zero or a few volts.  If any of them measure outlet to outlet 240VAC, then they are on two different
phases.  The shorter slot in each outlet is the hot.  The longer is the neutral.  Measure shorter to shorter between outlets.
Use well insulated leads and probes on the voltmeter.  You can also plug a cord into one outlet and put the IEC near the other
outlet and put the probe into the IEC connector.  Do not touch the metal on the leads.  You may want to protect yourself
from accidents by standing on a pile of rubber extension cord.  Never hold one probe in one hand and the other in the other hand.
Always plug one in and hold the other with one hand.

You can also remove the outer panel on the AC panel and check between breakers, but do this at your own risk
and always stand on a pile of rubber cord.  Not worth it to die over this.

Another problem I had was a slight buzz in the tweeters of my speakers when the house lights were on and worse when they were dimmed. 
I changed this breaker to opposite phase from the audio outlets and it seems to have reduced the buzz.  Where the Neutral is connected
may also have an effect, but this is dangerous to mess with unless you are qualified or the panel has a main breaker you can turn off.

Steve N.


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Re: Are you using the right phases for your AC power?
« Reply #1 on: 2 Apr 2024, 02:54 pm »
Note that some low budget Digital Multi-Meters (DMM) have probes that are NOT safe to use measuring AC line voltages.