Dedicated circuits

FWIW:

jea48

3,919 posts

06-07-2022 at 08:04pm 

@kijanki

+1

 

Please explain what happens if the power transformer’s secondary winding voltage is lower feeding the rectifier, due to a quick AC mains VD event, and the electrolytic capacitors voltage is higher. Just going from memory the rectifier will not conduct and the caps do not get recharged for that "(millisecond pulse)" in time.

 

Jim

Response:

kijanki

4,296 posts

06-07-2022 at 08:46pm 

@jea48   You are right - there will be no current thru rectifiers until capacitor voltage will drop below rectifier supplied peak voltage.  Theoretically it is possible to build LPS where capacitors keep average instead of peak voltage, but it requires huge inductor in series (in order of Henries) made with thick wire and AFAIK nobody is doing it.  One problem is lower rail voltage (average instead of peak) while the other is dependency on the load current.

http://www.r-type.org/articles/art-144.htm

I prefer Aluminum armored solid conductor 10 - 2 with ground MC (Metal Clad) cable for branch circuit wiring. MC NOT AC metal clad cable.

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Current doesn’t always go up when voltage goes down, it’s a little more complicated than that.

That is true. For AC induction type motors if voltage goes down due to Line voltage drop, current go up.

Not so for audio equipment power transformers. If voltage drops so can/does current as well as wattage, (VA)... In the case of a power amplifier lower wattage, lower power...

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if a 15A breaker was in front of a circuit that was made of 12-2 Romex and 20A outlets, wouldn’t that be safer? I mean, the 15A breaker would trip way before the 12-2 or the 20A outlet got hot enough to catch fire, right?

No you can not put a 20A duplex receptacle outlet on a 15 amp branch circuit. The breaker handle rating determines the size of the branch circuit, not the wire. The wire could be #10 and if the breaker is a 15A the branch circuit rating is still 15 amp.

You can put two 15 amp receptacles or a combination of 15A and 20A receptacles outlets on a 20 amp circuit, (20 amp breaker). You can install one 15 amp duplex on a 20 amp circuit. (Duplex is two.)

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@immatthewj

Myth is a breaker will trip when the current passing through the breaker reaches its handle rating.

NEMA requirements says a breaker must trip in less that one hour if overloaded 135%. It also says a breaker must trip within 2 minutes if overloaded 200%.

15A breaker X 135% = 20.25A. Can take up to an hour to trip.

15A breaker X 200% = 30A. Can take up to two minutes to trip.

Both calculations above are for constant, continuous, load current.

In most cases the branch circuit wiring is 14 gauge with an ampacity rating of 15 amps for a 15 amp circuit, breaker. (The breaker amperage rating determines the size of the branch circuit. (Not the branch circuit wiring.)

(Old white paper but still holds true for a regular type breaker.)

https://goodsonengineering.com/wp-content/uploads/2017/08/CircuitBreakerMyths_web.pdf

FWIW, in most cases spec grade or better 5-15R (15A receptacles) use the same internal contacts as a 5-20R (20A receptacle). The only difference is the face plate.

For cord and plug connected appliances and equipment NEMA has requirements that manufacturers must follow. To be able to use a 15A plug the FLA of the appliance or equipment can not exceed a continuous load current of 12A. (Continuous is defined as three hours or more.) For most consumer made products manufactures make sure the FLA is 12 amps or less. Why? Because the majority of wall duplex receptacles outlets in residential dwellings are 15 amp... Even though the kitchen, laundry, dinning room, bathroom, and garage, branch circuits are 20 amp, 15 amp receptacle outlets can be used. NEC, two or more on a 20 amp branch circuit. (A duplex receptacle is two.)

If the FLA is greater than 12A continuous the plug must be a 20A. NEMA Says the FLA can not exceed 16A FLA Continuous for a 20A plug .

The face plate on the 15A outlet makes the outlet idiot proof. A 20 amp plug will not plug into it... It prevents a possible 16 amp load from being connected to 14 gauge copper wiring in the wall. A continuous 16 amp load probably would never trip a 15 amp circuit breaker.

FWIW, what you did is electrically safe,... It just doesn’t meet code.

where to buy a magnetic breaker?

You won’t buy em for your electrical panel... Only T-M, Thermal-Magnetic, breakers are available. The Thermal protection unit of the breaker is for overload protection of the branch circuit wiring. The magnetic unit provides short circuit protection. It usually trips the breaker open in a matter of milliseconds. An electrical short circuit can cause a dangerous electrical explosion if not cleared quickly...

The only place I can think of where a Magnetic circuit breaker is used is on a piece of equipment. It is never used to protect branch circuit or feeder wiring...

Per NEC, UL, NEMA, only the manufacture’s breaker type/stye can be used in an electrical panel. A label on the back side of the electrical panel’s breaker cover door lists the manufacture’s type/style(s) for the breaker(s) that can be used in the panel. Using the wrong breaker will void the UL Listing.

Here is a video of the inside of a circuit breaker and how it works. Note the circuit breaker that is used for the demonstration is a EATON type/style BR breaker, not a Square D QO circuit breaker. A Square D QO breaker works on the same principal but in my opinion is of a better build quality.

The guy making the video does a pretty good job except, imo, when it comes to his personal electrical safety.