ECN Forum Forums General Topics of the Trade General Discussion Area Residential Main 200A breaker trips and humms

For the record, and too late for this matter:

Booster circuits are optional for heat-pumps.

They have no utility in mild climates, those that never get below 45 degrees Fahrenheit. Such places do exist, just not anywhere close by.

The industry standard is to provide 0,1,2 and perhaps 3 booster modules for a given heat-pump scheme.

Here in Sacramento, a single booster is more than enough to handle occasional dips below 32 degrees.

When running in heat-pump mode (reverse air conditioning) the exterior coils evaporate refrigerant -- even down below 20 degrees. This does not cause massive ice dams because the air is already dry -- naturally. Other factors can intrude, however. Any, local, saturated air would cause ice to form over the coils. A good design addresses this, one way or another.

Because of the limited size of the coils, when the refrigerant is evaporating at 20 degrees, the exterior air ejected by the unit is still quite a bit warmer... say 10
to 13 degrees. This temperature 'head' represents thermal resistance during the fluid to fluid heat transfer. (Air and liquid refrigerant are both deemed to be fluids.

This temperature head, coupled to the physics of suitable refrigerants, means that it's no longer possible to extract heat from the outside air once it falls below 30ish degrees.

If your weather is like Sacramento, then a single booster will get you over the hump -- if the grid can handle it. (Mass adoption of heat-pumps would overload any grid during a severe cold snap.)

The greater portion of the lower 48 American states can get by with just two boosters. Both are typically twins, and can be retro-fitted at any time. Their slot is typically exposed -- on the same side as the air filter.

Some, not all, designs permit a third booster coil assembly. This, when added, provides BTUs to take you through the worst storms. However, your e-meter will be spinning.

If you've never seen what a booster looks like: think of an oversized toaster grid/ ancient e-overn. Some strongly resemble blade-style server computers: they can be shoved into place almost as fast.

These boosters do present an issue to electricians during the build. The disco has to be sized to allow for them. Further, protection is also needed for the rest of the machine. what ever is done must not impede HVAC service (filters, boosters, etc.) while still attaining NEC standards. That can really require clever work as the HVAC industry thinks we're miracle workers.

No it does not.

Information from Schneider Electric - history of HACR
http://ecatalog.squared.com/pubs/Ci...Case%20Circuit%20Breakers/0600DB0102.pdf

"...additional investigation was done including tests to determine that the circuit breaker provided appropriate protection for the circuit components of typical heating, air conditioning, and refrigeration equipment."

"It was found that all circuit breakers that passed the normal UL 489 tests also passed the special HACR testing without a special design."

HAPPY ELECTRICIAN:

When you measured the Current at the Line Side of the Main Disconnect (200/2), did you have the "Peak/Hold" feature on the Ammeter enabled?

That may explain the high Load reading when the Heat Pump became an included Load
(the Locked-Rotor Amps drawn by the Compressor during Start were held as the Peak reading on your Ammeter)

Looking at the FLA on the Line Side of the Main Disconnect:

A: Without Heat Pump Included:
Line 1 = 22 Amps,
Line 2 = 33 Amps.

B: With Heat Pump Included:
Line 1 = 115 Amps,
Line 2 = 130 Amps.

Largest Load through the 200/2 Main is 130 Amps, and as such, the Main Disconnect is not Overloaded... unless:

a.: The Ammeter is not able to read "True-RMS" Amperes, and there is a considerably large level of Scuttle Current involved - which would read > 200 Amps total Load Current by a True-RMS (Non-Averaging) type Ammeter,

or

b.: A Fault (L-G Ground Fault, L-N or L-L Fault) occurs on a Branch Circuit, and the Main 200/2 has a higher Load than the Branch Circuit with the Fault.

If the Time-Trip Current Curve Characteristics of the Main 200/2 are exactly the same as the Branch Circuit Overcurrent Device with the Fault, the only Device which will open will be the Main 200/2... The Branch Circuit Device will remain Closed.
At times where the Branch Circuit is Loaded to near Maximum Capacity, then a Fault occurs during this heavy Load State, the Branch Circuit OCPD _AND_ the Main Breaker ahead of it, will both Trip.

Nevertheless, the Trip problem experienced with the 200/2 Main appears to be from Contact Seating issues, rather than Overcurrent Trip Activation (as pointed out by "HotLine1").
The Heated Case/Conductor, along with the "Buzzing", would be indicative of Contact Issues.

The culprit might be Internal, at the Breakers' Contacts; or partially Internal/External, at the Termination Points.

An In-Series Voltage Test will help determine if there are any Contact-Related issues with the Main 200/2.
This is done by measuring the Voltage Drop across the Breaker, between the Line Side and the Load Side of each Pole, using a Volt Meter (High Input Impedance type Volt Meters - such as the typical DVM's, are helpful with these Tests).

--Scott (EE)

Scott35:

It's nice to see that someone agrees with my opinion.....

"The culprit might be Internal, at the Breakers' Contacts; or partially Internal/External, at the Termination Points."

Thank You!