ground/neutral at sub panel

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enireh

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Canyon Lake,TX
when grounds and neutrals are separated at sub panel there will still be continuity between them because they are not separated back at main panel. right?
 

infinity

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Yes. As long as the main bonding jumper is in place there should always be continuity at any point in the system.
 

infinity

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then what is the difference if they are not separated at sub panel? resistance?

If they're connected at both ends they're in parallel which makes the EGC system (included EGC's, metallic raceways and enclosures) all current carrying conductors. The EGC should only carry current under fault conditions.

56314d1345965726-2-similar-gfci-but-one-tests-open-ground-objectionable-current-mike-holt.jpg
 

Dennis Alwon

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then what is the difference if they are not separated at sub panel? resistance?
The equipment grounding conductor is only supposed to carry current during a ground fault so tying it to the neutral in the sub would have it carrying current all the time and would be a parallel path as Trevor stated.
 

kwired

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NE Nebraska
And to add to what has been said - once you start to carry current on any conductor you have voltage drop. May not be much but it does increase as the current increases.

This can leave you with the equipment grounding conductor operating at a voltage above ground and that will increase shock hazards when touching equipment that is connected to the equipment grounding conductor.

So that equipment grounding conductor that remains isolated from neutral conductors all the way back to the main bonding jumper has very little to no voltage to earth/other grounded objects. The one that has been connected to current carrying neutrals along the way to the main bonding jumper is carrying neutral current and has a voltage rise to ground that is equal to the voltage drop in the current path. Voltage drop (voltage rise on the EGC) of 2 or 3 volts can go unnoticed pretty easily, but in the right circumstances is very noticeable. You will feel that in and around swimming pools or other similar areas.
 

enireh

Senior Member
Location
Canyon Lake,TX
And to add to what has been said - once you start to carry current on any conductor you have voltage drop. May not be much but it does increase as the current increases.

This can leave you with the equipment grounding conductor operating at a voltage above ground and that will increase shock hazards when touching equipment that is connected to the equipment grounding conductor.

So that equipment grounding conductor that remains isolated from neutral conductors all the way back to the main bonding jumper has very little to no voltage to earth/other grounded objects. The one that has been connected to current carrying neutrals along the way to the main bonding jumper is carrying neutral current and has a voltage rise to ground that is equal to the voltage drop in the current path. Voltage drop (voltage rise on the EGC) of 2 or 3 volts can go unnoticed pretty easily, but in the right circumstances is very noticeable. You will feel that in and around swimming pools or other similar areas.

thank you
 

zcanyonboltz

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Location
denver
The equipment grounding conductor is only supposed to carry current during a ground fault so tying it to the neutral in the sub would have it carrying current all the time and would be a parallel path as Trevor stated.

Say you have a main breaker only panel with no sub, the grounded and grounding conductors are tied together, how is the EGC not able to carry current? How is current being able to be carried on the grounded or grounding conductor any different in a main or sub panel? The main has a parallel path between the two conductors right?
 

GoldDigger

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The answer is that the EGC will only carry fault current.
When the normal current on the neutral reaches the panel it can go onto the POCO neutral or it can go through the GEC to the ground electrodes through the earth and back through the POCO ground electrodes to the transformer secondary. But it has no reason to go back over the EGC to get anywhere.
When you connect the EGC to the neutral in both main and sub the two wires are in parallel and some (up to half?) of the normal neutral current will flow through the EGC.
Again, in case you missed the distinction, current from the bond at the main panel will flow through the Ground Electrode Conductor (GEC) which is OK. Not through an EGC, which is not OK.
 

ActionDave

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Say you have a main breaker only panel with no sub, the grounded and grounding conductors are tied together, how is the EGC not able to carry current? How is current being able to be carried on the grounded or grounding conductor any different in a main or sub panel? The main has a parallel path between the two conductors right?
You need a complete circuit to light a light bulb and to trip a breaker.

Think about it this way.... electricity leaves the panel on the black wire, goes out and makes the the light bulb glow, and comes back on the white wire. The light bulb has resistance so the breaker doesn't trip. We want to keep that electricity, current more specifically, on those two conductors.

The Equipment Grounding Conductor is an "extra neutral" but it is not connected to any light bulbs. If everything is done right it is not part of the normal circuit. It's just there in case the black wire touches anything metal that is not part of the normal circuit, the stuff we hook up the white and black wires to, so that tons of current will flow for the blink of an eye and the breaker will trip.
 
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