Neutral on main and subpanel

[bdogg5656]

2 questions

I have been reading online that the main panel needs neutral and ground connected together, But sub panel cannot be setup like this.

Is this true?


my second question is i watched a video on youtube where a guy shows a basic setup from panel to lightbulb and he puts a current meter on black which shows 2 amps while bulb is on, and 2 amps on the neutral going back to panel.

So whatever the load requires, the same amount of current is on the return end? meaning if im drawing 2 amps from load, i'll have 2 amps on neutral?


thanks for any input

 

[hj]

What would you expect. In fact, if you have a split circuit with a common neutral, it will be carrying the SUM of the two circuits, if they are on the same phase, and the difference if they are on opposite phases.

 

[Sponsor]

 

[bdogg5656]

What would you expect. In fact, if you have a split circuit with a common neutral, it will be carrying the SUM of the two circuits, if they are on the same phase, and the difference if they are on opposite phases.

i dont understand your resonse. can you explain it as if your explaining it to a kid

 

[Reach4]

i dont understand your resonse. can you explain it as if your explaining it to a kid

The white wire carries the algebraic (signed) sums of the hot wire currents.

A kid who does not know algebra?

The white wire carries the leftover currents.

 

[Jadnashua]

For any electrical circuit to work, it needs what is called a complete circuit...think of a circle. WHatever power goes out one side, must come back to the other. A short circuit is where the power doesn't go the intended path and takes a shortcut, which can often overload the supply that is protected by either a fuse or circuit breaker. AN example might be where the hot lead, instead of going through the load, got accidentally connected to ground or neutral - maybe by hammering in a nail to hang a picture and puncturing the cable hidden in the wall.

We don't really have 120vac coming into the house in the USA...we have 240vac from one side of a transformer to the other. WHen power is going out one side of the transformer, it's going into the other end. At about the middle of that transformer is what is referred to as neutral...so, it's 120vac from one side to the middle, and 120vac from the other back to the middle or 240 from one end to the other. When measuring things, it helps to have a reference. On our power, we use the neutral as the reference, and to give it a further reference, we attach that to ground. If you were to measure a 240vac circuit on one side to neutral, you'd get 120vac and the same on the other, but across the two leads (not using neutral), you'd get 240vac. A 240vac circuit does not use neutral. A safety ground is still often used. Many of the household things that run on 240vac also need 120vac, for example, an electric stove. IT uses 240vac for the heating elements, but often, will use 120vac for things like the oven light to make it easier since not everwhere carries 240vac light bulbs. Ground is for safety. There should not be any current on the ground, but it gives an alternate path for current if there's a fault to blow the fuse or trip the circuit breaker.

In an alternating circuit (ac), across a transformer, when power is coming out of one end, it is going back into the other. From one end to the middle, it would be doing the same, but in different directions. That's why in a shared neutral circuit, the actual current in the neutral might add up to zero, but the current would be functionally flowing from one end of the transformer back to the other end with the neutral point being balanced out to nothing (thus the neutral).

You're reading things correctly...there should only be the neutral connected to the ground at the main panel and separate wires run from there to any subpanel. This is to prevent there being ground loops.

Anyway, that's the thumbnail explanation, and there's all sorts of info on the web if you want further investigation.

 

[bdogg5656]

For any electrical circuit to work, it needs what is called a complete circuit...think of a circle. WHatever power goes out one side, must come back to the other. A short circuit is where the power doesn't go the intended path and takes a shortcut, which can often overload the supply that is protected by either a fuse or circuit breaker. AN example might be where the hot lead, instead of going through the load, got accidentally connected to ground or neutral - maybe by hammering in a nail to hang a picture and puncturing the cable hidden in the wall.

We don't really have 120vac coming into the house in the USA...we have 240vac from one side of a transformer to the other. WHen power is going out one side of the transformer, it's going into the other end. At about the middle of that transformer is what is referred to as neutral...so, it's 120vac from one side to the middle, and 120vac from the other back to the middle or 240 from one end to the other. When measuring things, it helps to have a reference. On our power, we use the neutral as the reference, and to give it a further reference, we attach that to ground. If you were to measure a 240vac circuit on one side to neutral, you'd get 120vac and the same on the other, but across the two leads (not using neutral), you'd get 240vac. A 240vac circuit does not use neutral. A safety ground is still often used. Many of the household things that run on 240vac also need 120vac, for example, an electric stove. IT uses 240vac for the heating elements, but often, will use 120vac for things like the oven light to make it easier since not everwhere carries 240vac light bulbs. Ground is for safety. There should not be any current on the ground, but it gives an alternate path for current if there's a fault to blow the fuse or trip the circuit breaker.

In an alternating circuit (ac), across a transformer, when power is coming out of one end, it is going back into the other. From one end to the middle, it would be doing the same, but in different directions. That's why in a shared neutral circuit, the actual current in the neutral might add up to zero, but the current would be functionally flowing from one end of the transformer back to the other end with the neutral point being balanced out to nothing (thus the neutral).

You're reading things correctly...there should only be the neutral connected to the ground at the main panel and separate wires run from there to any subpanel. This is to prevent there being ground loops.

Anyway, that's the thumbnail explanation, and there's all sorts of info on the web if you want further investigation.

 

[bdogg5656]

If the neutral is grounded at the main panel, how is it fed back to the electric company? wouldnt it ground out?

 

[Reach4]

See if either of these help.

https://en.wikipedia.org/wiki/Split-phase_electric_power

Note that if you disconnected the neutral from ground, the system still works. The ground connection makes it safer.

 

[bdogg5656]

ahhh. because he clearly states because of the high resistance to earth?

 

[Jadnashua]

It's all about the reference point. Way back when, I used to repair high voltage power supplies for a radar system. The filaments on it used 5vdc. The tube used 5,000v. If the filaments were referenced to ground, because they were close to the plate (at 5,000v), it would have arced over sort of like a lightning bolt. But, instead of ground, it was referenced to the 5,000v, so really was at 4, 995v (a 5-volt difference), and that's what made it safe. Reference points when measuring things can get you into trouble if you don't understand what's going on. Doesn't matter whether it's electrical, distances, weights, etc. Even at say your butchers...they'll zero the scale (or at least should) so you aren't paying $10/pound for the packaging materials. Reference points...

The power company references the neutral to ground, so it can be connected. Power should not be running on the ground lead as the ground is NOT connected to the power company. If the power is perfectly balanced on each leg of the 240vac, the current on the neutral would equal zero since half would be going out on one leg's path, and in on the other's. That rarely happens, so neutral does have some current, but back at the power company, YOUR ground is not connected to THEIR ground, so there's no current flow between them, but neutral is sent from their transformer to your house and has the same conductivity as the two other power leads required to achieve that 240vac.

Because the wires don't have perfectly zero resistance to them, you only want to make that reference point at one location in your home, otherwise, you can measure voltage (and thus, get current) on the ground lead at a subpanel.

A little searching on the web will bring up all sorts of discussions on this topic...here's one of them: https://www.bluesea.com/support/articles/AC_Circuits/86/Current_Flow_in_120_240_Volt_AC_Systems