Yeah... most of us are off grid, but wow... 40Amps would leave a mark!
Looking closer at the meter, I think it is 4 amps... I wish he measured the voltage... most likely 120V, since it is residential Canada, but who knows?
Grounding and a possible danger from Neutral lines.
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Yeah... most of us are off grid, but wow... 40Amps would leave a mark!
Looking closer at the meter, I think it is 4 amps... I wish he measured the voltage... most likely 120V, since it is residential Canada, but who knows?
Hedges
I See Electromagnetic Fields!
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"A different 3-phase circuit used neutral of this circuit as the shortest path"
I don't like having more than one neutral as return, and I want it parallel to, twisted with, its hot line connections. Not forming a large air loop or going around a piece of steel.
But their grid wiring apparently offered multiple neutral paths.
I guess if they connect utility circuit to transformer at both ends after going through a neighborhood it can balance, share paths depending on how loads distributed. And keep many/most customers up even if there's an open circuit. That may be what happened here. It is a "grid", not a "tree", after all.
As you said, wish he measured voltage. Because he didn't get a huge flash, very likely it is quite low voltage, just a parallel connection that reduces IR drop from maybe 10V to 5V or the like.
Within our house wiring we can have separate neutral for each circuit, and (in some areas) neutral bonded to ground at service entrance.
When a single transformer on the pole serves multiple residences with drops of L1, L2, N, I think they each have their own neutral to ground bond together with ground rod. Some open circuit faults could cause current to flow between homes in the earth.
I don't like having more than one neutral as return, and I want it parallel to, twisted with, its hot line connections. Not forming a large air loop or going around a piece of steel.
But their grid wiring apparently offered multiple neutral paths.
I guess if they connect utility circuit to transformer at both ends after going through a neighborhood it can balance, share paths depending on how loads distributed. And keep many/most customers up even if there's an open circuit. That may be what happened here. It is a "grid", not a "tree", after all.
As you said, wish he measured voltage. Because he didn't get a huge flash, very likely it is quite low voltage, just a parallel connection that reduces IR drop from maybe 10V to 5V or the like.
Within our house wiring we can have separate neutral for each circuit, and (in some areas) neutral bonded to ground at service entrance.
When a single transformer on the pole serves multiple residences with drops of L1, L2, N, I think they each have their own neutral to ground bond together with ground rod. Some open circuit faults could cause current to flow between homes in the earth.
Aaron_85
New Member
I'm not sure what kind of earthing system they use in Canada, but the "multiple earth nuetral" (TN−C−S) system we use in Australia is only very safe when the multiple neutral part of it is intact, the integrity of the neutral is paramount for its safety. Once you get a broken neutral, it can become more dangerous than no protective earth at all
Multiple grounds connected in a loop can be a hazard . I rented a commercial building with 2 sources of power from opposite side.
One 3 phase delta (center leg to ground ) and the other single phase. When I wired 3 phase to single phase side I got a jolt from
touching the two ground sources. Definite problem. Fixed it by totally disconnecting the single phase service and its ground to prevent
any looping transformer effect .
I live in Northeastern Ohio and the "The Powers to Be" still allow using metal conduit as a only ground source .
One 3 phase delta (center leg to ground ) and the other single phase. When I wired 3 phase to single phase side I got a jolt from
touching the two ground sources. Definite problem. Fixed it by totally disconnecting the single phase service and its ground to prevent
any looping transformer effect .
I live in Northeastern Ohio and the "The Powers to Be" still allow using metal conduit as a only ground source .
Hedges
I See Electromagnetic Fields!
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Do you think the two grounds were at a different potential?
Meaning if you plugged an electric drill into one of them and stood on a wet floor, the grounded chassis of the drill would be high enough potential relative to earth that it would shock you?
Of course getting a shock from simultaneously touching grounds of the two systems means current would flow when connected.
There are a few different kinds of delta and grounding.
Can be corner ground, center of one side, middle of delta.
Even if galvanically isolated, capacitive coupling through a transformer might present voltage on what was supposed to be the ground connection.
1) Yes
2) I don't know the proper term , but the center leg was connected to the ground ,Measured #1)240to #2) 240to #3) and 240 to 1 and 3.... 240 center voltage connected to ground #2) being ground
Hedges
I See Electromagnetic Fields!
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Two legs having 240V to ground, one zero volts to ground.
Given symmetry in the transformers, if some capacitive coupling I would expect the geometrical mid point between the three phases to want to be ground (like 208Y and 480Y). The corner ground would try to drive some current. If separate ground rods, current would flow in the earth, producing losses. If connected by copper wire, would be an out of phase reactive load.
Could be that hardwiring the two grounds together would be the safest thing to do. So long as that doesn't carry excessive currents, a fault.
If transformers have an electrostatic shield, sheet of copper between windings that is grounded, would greatly reduce capacitive coupling.
Some transformers have windings on two adjacent bobbins, some one layer over the other. For isolation of high voltages (1kV or 12kV primary) I would expect not on top of each other. For smaller transformers used in EMI testing (noise injection) I've seen different signal amplitude at one end of secondary winding vs. the other.
What is an “Electrostatic Shield”?
Electrostatically shielded (Faraday Shield) transformers provides a copper electrostatic shield between the primary and secondary windings. The shield is grounded and thus shunts some noise and transients to the ground path rather than passing them through to the secondary. Transformers having a...
www.hammondpowersolutions.com
Power Problems: Common mode noise attenuation reduction
Power Problems: Common mode noise attenuation reduction
The 240 Delta had 3 transformers on the pole and the lead was connected to ground inside my disconnect box.Two legs having 240V to ground, one zero volts to ground.
Given symmetry in the transformers, if some capacitive coupling I would expect the geometrical mid point between the three phases to want to be ground (like 208Y and 480Y). The corner ground would try to drive some current. If separate ground rods, current would flow in the earth, producing losses. If connected by copper wire, would be an out of phase reactive load.
Could be that hardwiring the two grounds together would be the safest thing to do. So long as that doesn't carry excessive currents, a fault.
If transformers have an electrostatic shield, sheet of copper between windings that is grounded, would greatly reduce capacitive coupling.
Some transformers have windings on two adjacent bobbins, some one layer over the other. For isolation of high voltages (1kV or 12kV primary) I would expect not on top of each other. For smaller transformers used in EMI testing (noise injection) I've seen different signal amplitude at one end of secondary winding vs. the other.
What is an “Electrostatic Shield”?
Electrostatically shielded (Faraday Shield) transformers provides a copper electrostatic shield between the primary and secondary windings. The shield is grounded and thus shunts some noise and transients to the ground path rather than passing them through to the secondary. Transformers having a...
Power Problems: Common mode noise attenuation reduction
Power Problems: Common mode noise attenuation reductionwww.aelgroup.co.uk
We have here 208Y in a commercial voltage (stores) and 3p240 and 3p277/480 as industrial voltages. As for the inside , all copper wire. As for
the 240 delta went out of favor 30 years ago, because of the grounding problems.
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