Electrical question

[joeu235]

But anyways, I picked up 10 gauge THHN this morning since that's what code requires.

 

[Industrial Toys]

So on a Y, the centre is neutral? And at 600, any outer point to neutral is 347?

I built a 600 rotary converter wired in Delta and wondered how to get a ground reference?

 

[CobyRupert]

208V is most always a 3 phase system. 208V can be measured between phases A&B, B&C, and A&C. This is usually made when the transformer's (3) secondary coils (which each generate 120V across them) are connected in a "Y" (wye) fashion, the common center point of the Y (wye) is the "neutral" (which is usually grounded to earth; it doesn't have to be but that's another subject).
So now you have 3 phases, with each phase 120V to neutral (or ground), but with 208V between each phase.
Why do (3) 120V transformer coils connected this way result in 208V between each phase? That's a bit more complicated.

Note that the relationship of 208 to 120 is 1.73 (which is the square root of 3)

The voltage sine wave being induced on each coil is 120 degrees out of phase from the voltage sine wave on the other 2 coils. (+120, 0, -120)

(They're 120 degrees separated because back at the generator, 360 degrees of rotation was divided into developing "3 phases", 120 degrees apart from each other (I digress, don't be distracted)

There's a lot of mathematical ways to prove that vectors separated by 120 degrees of rotation have a "square root of 3" (1.73) relationship. (120/208, 277/480V, 347/600V)


I think it's easiest to see how like this:
Look at the letter "Y", where each "leg" of the "Y" is rotated 120 degrees from the other. Imagine the length of each of the 3 "legs" are 120 units (volts, or inches, miles, whatever). Now measure the straight line distance between the end of one "leg" to the end of another. This distance is 208. Thus you can "see" how (3) 120 units have a difference of 208 units between them when 120 degrees apart. Example: a 120/208V, 3 phase system. (120 units to the center (neutral), 208 units between each leg (phase)).



A 347/600V system is a similar 3 phase (grounded wye) system. (600 volts between phases, 347V from each phase to neutral). 277/480V systems is common in U.S. (when there's a neutral).
Note "square root 3" relationship.

 

[mbohuntr]

50amp wire will never melt or fail. It is thermally protected .

Thermally protected by what?

 

[LD1]

But anyways, I picked up 10 gauge THHN this morning since that's what code requires.

No idea if thats right or wrong. You never gave any detail as to what you were working, load requirements, etc. So if you are looking for someone to verify you are doing things correctly......sorry, you are on your own.

If code requires 10 gauge and you are certain you are right (since without details we have no idea), what was the purpose of this thread?

 

[Industrial Toys]

Sorry about derailing your thread.

In a sense, everything is thermally protected. If it gets too hot, it will melt, opening the circuit. Any resulting fire, is a mere side effect.

 

[buickanddeere]

So on a Y, the centre is neutral? And at 600, any outer point to neutral is 347?

I built a 600 rotary converter wired in Delta and wondered how to get a ground reference?

Could do a corner grounded Delta but they are a weird configuration and not the first choice .
Center of the Wye where the neutral is connected has a bond to earth. Contrary to common belief the bond is only to hold the Center Wye point and the neutral to a close to earth potential as possible . No other neutral to earth bonds anywhere else or neutral current will flow in the ground system . That is undesirable and possibly destructive .

 

[buickanddeere]

Thermally protected by what?

Fla on the motor is 40.0 amp. Motor thermals are set at 115%. The 50amp Wiring can稚 be over heated as it is thermally protected . The breaker is only there to provide short circuit protection and isolation.
I copied those numbers straight out of Table D16 from the 2012 code book.

 

[buickanddeere]

Sorry about derailing your thread.

In a sense, everything is thermally protected. If it gets too hot, it will melt, opening the circuit. Any resulting fire, is a mere side effect.

I am getting a notion that the difference between short circuit protection and thermal protection is not well understood by most members here.
I would assume that googling Canadian electrical code and table D16 may show the chart. A picture is worth a thousand words .

 

[Industrial Toys]

It's a real problem on generators, mostly portable. Breakers are chosen for temporary motor start loads and generally made as 10, 15, 20 amp and so forth. The next highest rating being chosen. So people keep loading up the sets, thinking they are protected and fry the windings.

I have more question about three phase, but won't ask them here. Thanks.

 

[CobyRupert]

So on a Y, the centre is neutral? And at 600, any outer point to neutral is 347?

I built a 600 rotary converter wired in Delta and wondered how to get a ground reference?

"So on a Y, the centre is neutral?" Yes, (but in U.S. it's the center that is neutral. :laughing: -Canadian joke)).

"And at 600, any outer point to neutral is 347?" - On a 600V, 3 phase (wye) system (3 phase, 4 wire), the phase-to neutral voltage will be 347V. I think this is what your asking.

"I built a 600 rotary converter wired in Delta and wondered how to get a ground reference? " It's important to know the difference between ground and neutral. You cant get a neutral reference from a delta. On a delta system, when you talk about 600 volts, that's between phases, period. You can't speak of, or reference, this voltage to the voltage you would measure to "ground" (earth) if you had a voltmeter between the phase and earth. This voltage could be anything (600 volts, 50 volts, 300 volts, etc..). This is because it's not like a "Y" wye connection where the center neutral is grounded to earth.

Why do you need a ground reference?

 

[Industrial Toys]

The more I think about it. The more confused I get. Not a big fan of 600 volts. So the thought of not having a system where if a live 600 volt leg touches a (grounded) metal cabinet, or conduit and a breaker trips, troubled me.

 

[joeu235]

If code requires 10 gauge and you are certain you are right (since without details we have no idea), what was the purpose of this thread?

I was confused thinking about how a load draws half the amps when its converted from 120 to 240.

 

[LD1]

Loads as most think of them are typically measured in watts.

And doubling the voltage does indeed cut the amps in half.

A 100w 120v light bulb will draw twice the amps as a 100w 240v bulb.

A 2 hp 120v motor will draw twice the amps as a 2hp 240v motor.

 

[mbohuntr]

I am getting a notion that the difference between short circuit protection and thermal protection is not well understood by most members here.
I would assume that googling Canadian electrical code and table D16 may show the chart. A picture is worth a thousand words .

I am quite aware of thermal overloads, They are listed as a 49 type device, and we test them frequently. I was fishing because there is a world of difference between a 240v table saw, and a motor on a 480-600V MCC with overload protection. I.E..."HEATERS"


I believe the OP was talking about residential single phase wiring. Does the 240V 100 amp breaker circuit you describe offer the homeowner thermal protection? Or should you fall back to the "Size the conductor to the FLA expected, and the breaker to protect the conductor?

Not trying to pick a fight Buickanddeere, but I believe your info is more for a business than a homeowner.

 

[mbohuntr]

I was confused thinking about how a load draws half the amps when its converted from 120 to 240.

Watts is a unit of measurement that in it's simplest form equals Volts x Amps... 2000 watts / 240 volts = 8.33 amps used. 2000 watts/120 volts = 16.67amps.

Less amps = lower electric bill..

 

[mbohuntr]

The more I think about it. The more confused I get. Not a big fan of 600 volts. So the thought of not having a system where if a live 600 volt leg touches a (grounded) metal cabinet, or conduit and a breaker trips, troubled me.

If a conductor touches the inside of the conduit, it will trip. Those systems are required to be grounded and the breakers have "instatrip" functions where the huge momentary current will trip the breaker in thousandths of a second. A lot different than your house breakers which are mostly thermal.

 

[buickanddeere]

The more I think about it. The more confused I get. Not a big fan of 600 volts. So the thought of not having a system where if a live 600 volt leg touches a (grounded) metal cabinet, or conduit and a breaker trips, troubled me.

Why any difference if a live line grounds out on 120,240,277 or 347 ? Ever see how many sparks a 12V battery can throw ?

 

[prichard]

If a conductor touches the inside of the conduit, it will trip. Those systems are required to be grounded and the breakers have "instatrip" functions where the huge momentary current will trip the breaker in thousandths of a second. A lot different than your house breakers which are mostly thermal.

Not true. His system is ungrounded. Without a ground there is no current flow to this metal surface. Any one leg can be grounded, but only 1. If you ground 1 leg them a second touches you get instant trip.

 

[mbohuntr]

Not true. His system is ungrounded. Without a ground there is no current flow to this metal surface. Any one leg can be grounded, but only 1. If you ground 1 leg them a second touches you get instant trip.

Do you have a link to that? I have never heard that, and every conduit and frame we have is house grounded. We even have floating "isolated" transformer grounding on the main gens. I would love to read up on that. Thanks