Equi=Core Hum & Other Issues

I’ve owned a Core Power Tech Equi=Core 1800 for 6 months. Recently the transformer has started to hum inside the chassis. It happens when components are on and also when sources are powered down. The transformer hum is intermittent. It ranges from multiple times per day to 3 or 4 days without any hum. I never had DC on my dedicated lines before, so I picked up a Klein Tools AC/DC tester... https://www.kleintools.com/catalog/electrical-testers/electronic-acdc-voltage-tester-12-240v-ac-15-2...
and when plugged into wall receptacles it indicated overload. Line voltage is steady at 122VAC and always has been.
What am I doing wrong, and how should I test for DC on the power line?

I discovered another problem when testing the Equi=Core duplex receptacles; they indicate inverted polarity. All house outlets measure correct polarity.
I’m looking for some assistance in diagnosing this hum. I’m not sure if it’s due to DC offset or if the torroid itself is vibrating in its mounting.

I know this is becoming a long thread, but I must mention that the Equi=Core now trips the breaker at the panel when powered on. It trips several times in a row, eventually allowing power-up. This is a 20A dedicated line from a subpanel which I’ve had for years.
Any advice is much appreciated.

New service drop.
New meter socket.
New service entrance conduit and wire from meter socket to a new electrical panel.
(Including breakers). 
System grounding up date as needed.   
Electrical permit.

$1900..... That’s a good price.


I wanted you to see the new installation. And I was wrong about conduit; code does not require it.


No more transformer hum.

@ lowrider57

Glad to hear the new electrical service solved your hum problem.

As for the service entrance cable the electrical contractor installed.
Yes, it meets NEC, Article 338 of the code. And it is obviously approved for use by the AHJ (Authority Having Jurisdiction) in your area. The AHJ has the final say.

In the Capital City, metro, and surrounding suburbs cities in my State conduit is required for the electrical service. I’m not sure if any counties or cities in my state allows service entrance cable use for an electrical service. Though I do not know that for a fact.

I decided to install a whole house surge protector; a Square D to mate with my new service panel.

The instructions state that a 2-pole 20 amp breaker is required. OK, fine.
Now here's what I don't understand; if the surge protector has its own breaker wired to hot, neutral, ground on both phases, how is it going to absorb a spike before other circuits? Won't a surge trip other breakers as well as the surge protector?
There is no point of least resistance.
Feel free to comment.

Post removed 

The instructions state that a 2-pole 20 amp breaker is required. OK, fine.
Now here’s what I don’t understand; if the surge protector has its own breaker wired to hot, neutral, ground on both phases, how is it going to absorb a spike before other circuits?

The SPD protects the whole electrical panel from high voltage transient surges/spikes.
The Square D SPD uses multiple MOVs to protect the panel from high voltage surges/spikes transients. During a high voltage transient surge/spike event the MOVs limits the high voltage and absorbs or diverts the high current to ground. That is why the electrical service entrance neutral conductor connection to earth is so important. (The Grounding Electrode System.) The lower the grounding electrode resistance to earth soil the better. (Grounding electrode? Ground rod/s, metal main incoming water service piping, foundation footing concrete encased rebar.)
IEEE recommends 5 ohms or less.

It is very important where the electrician mounts, installs, the SPD to the outside of the electrical panel enclosure. (Do not install the SPD inside the panel.) Make sure he installs the 2 pole breaker for the SPD wire connections in the first two spaces below, near, the panel’s main breaker. Doesn’t mater which side just so it is in breaker spaces 1, 3 or 2, 4. The electrician more than likely will have to relocate a circuit/s load breaker/s to make room for the SPD 2 pole breaker. I would relocate the lighter load circuit/s breaker/s. The SPD connection wires must be kept short as possible without any sharp bends in the wires.

Square D HEPD50/HEPD80 SPD user guide and installation

NOTE:To enhance the performance of the HEPD50/HEPD80, twist and keep the conductor length as short as possible by trimming down the wires (do not loop or coil the wires and avoid sharp bends). Always connect the HEPD to the circuit breaker(s) found in the closest proximity. Increasing the HEPD conductor length will degrade its performance.
See page 4 and page 6, figure #3.

Why is keeping wires short so important?
Here is a great video on the why.

I attended a seminar a couple of years ago and seen the demonstration first hand.
Inches do matter.

Going from memory don’t you also have a sub panel for your audio equipment? If yes you should install an SPD on that panel as well.

For added protection of your audio equipment a Type 3 SPD should be installed to plug your audio equipment into. Make sure it has a minimum 1449 3rd edition listing. Newer Type 3 SPDs may have a 1449 4th edition listing. (Read the specs wording carefully. Minimum 1449 3rd edition listed).

That's all great information; the position of the SPD relative to the main breaker and how using short wiring will clamp surge voltage. There are plenty of knock-outs available to do this correctly.
Your explanation of having a low grounding electrode resistance to earth helps me understand the entire concept.

Now, regarding the subpanel, why is a SPD needed? Wouldn't a surge be clamped by the SPD on the main panel?

As always, I appreciate your thoughtful comments.