subfeed

[domnic]

When you install a subfeed the neutrals and the EGC must be separated why. what could happen if not, ?????????????????????????????????????????????????????????????????????

 

[don_resqcapt19]

The EGC would be in parallel with the neutral and become a current carrying conductor.

 

[electrofelon]

I can give you a good practical real life example of why they should be separate. Years ago I was running new MC feeder cables to feed panels in an Old Mill building that had been converted to live work lofts. The panels had been energized temporarily with 6/2 NM
With the main bonding jumper installed in all the panels, just quick and dirty for work power and lighting purposes. When installing the mc, typically I would connect it to the unit panel board with a connector and then work it back. I planned to get everything secured and landed on the supply end for minimal downtime when I would switch everything over. So the MC cable sheath became a conductor for neutral current, and would spark when running against other utilities such as water lines, other MC cables, and other grounded metal objects. Now there was probably not more than a few amps flowing so they were low energy Sparks, probably would be tough for them to start a fire, but it could certainly happen with just the right conditions. Now imagine during a fault where you might have hundreds of amps flowing....

 

[domnic]

If i run conduit from sub to main panel, the conduit and EGC would carry current and would be in parallel with the neutral.

 

[don_resqcapt19]

If i run conduit from sub to main panel, the conduit and EGC would carry current and would be in parallel with the neutral.

If the sub-sub panel is correctly installed (no neutral to enclosure or EGC bond) the conduit and the EGC are not in parallel with the neutral and only carry current under fault conditions.

 

[LarryFine]

If i run conduit from sub to main panel, the conduit and EGC would carry current and would be in parallel with the neutral.

IF you bonded the neutral and ground in the sub-panel, yes, which is why you shouldn't do it.

The hazard is metal surfaces expected to be at zero volts to earth suddenly becoming energized.

 

[domnic]

If the sub-sub panel is correctly installed (no neutral to enclosure or EGC bond) the conduit and the EGC are not in parallel with the neutral and only carry current under fault conditions.

YOU ARE WRIGHT THANK YOU !

 

[domnic]

IF you bonded the neutral and ground in the sub-panel, yes, which is why you shouldn't do it.

The hazard is metal surfaces expected to be at zero volts to earth suddenly becoming energized.

so the only reason we don't bond the sub feed, is if we loose a neutral the sub box becomes energized ?

 

[LarryFine]

so the only reason we don't bond the sub feed, is if we loose a neutral the sub box becomes energized ?

I wouldn't say "only" but it's a big one. Think about the old 3-wire major-appliance circuits.

Or feeding a receptacle with one conductor for both grounded and grounding purposes.

 

[domnic]

I wouldn't say "only" but it's a big one. Think about the old 3-wire major-appliance circuits.

Or feeding a receptacle with one conductor for both grounded and grounding purposes.

What is the main reason for this ???????????????????????????????????????????????????????????????????

 

[LarryFine]

What is the main reason for this ???????????????????????????????????????????????????????????????????

I don't understand your question.

 

[domnic]

I don't understand your question.

Why do we not bond the sub feed?

 

[LarryFine]

Why do we not bond the sub feed?

Then, yes, what we have explained and what you understood is the main reason.

As I said, its why we don't use one wire for both a circuit conductor and grounding.

Your service does, but its established as the zero-volts reference for the premises.

Years ago, a customer's son was badly shocked because the neutral wire in the 3-wire range feed pulled out of the lug in the range's wiring compartment.

 

[electrofelon]

What is the main reason for this ???????????????????????????????????????????????????????????????????

There are multiple reasons. If you lose the neutral stuff becomes energized, current flowing in raceways which raises the potential from ground,. Neutral current taking paths that it's not intended to, sparking between different paths with different resistances.....

 

[domnic]

Then, yes, what we have explained and what you understood is the main reason.

As I said, its why we don't use one wire for both a circuit conductor and grounding.

Your service does, but its established as the zero-volts reference for the premises.

Years ago, a customer's son was badly shocked because the neutral wire in the 3-wire range feed pulled out of the lug in the range's wiring compartment.

If you lose the neutral at the main service, the conduit to the sub and the sub panel will become energized . with 4 wires or 3 wires ?

 

[LarryFine]

If you lose the neutral at the main service, the conduit to the sub and the sub panel will become energized . with 4 wires or 3 wires ?

If you mean ahead of the service disconnect, which affects everything, a sub-panel wired either way could become energized. Earth alone is not conductive for made electrodes to prevent this.

If the neutral/grounding bond remains intact, there will still be little to no voltage between the neutral and the EGC, whether pipe or conduit. (If both, they should be bonded together everywhere.)

In a metal water-pipe neighborhood, such a break could remain undetected for some time. Otherwise, you get the bright and dim lights from the classic broken-neutral caused voltage imbalance.

 

[timmermeier]

If you mean ahead of the service disconnect, which affects everything, a sub-panel wired either way could become energized. Earth alone is not conductive for made electrodes to prevent this.

If the neutral/grounding bond remains intact, there will still be little to no voltage between the neutral and the EGC, whether pipe or conduit. (If both, they should be bonded together everywhere.)

In a metal water-pipe neighborhood, such a break could remain undetected for some time. Otherwise, you get the bright and dim lights from the classic broken-neutral caused voltage imbalance.

If you lose the neutral at sub feed on a 4 wire , no problem .other than 120 volt things wont work?

 

[LarryFine]

If you lose the neutral at sub feed on a 4 wire , no problem .other than 120 volt things wont work?

Not exactly. Any difference in load current between the lines will cause the voltages to shift. Voltage on the neutral will rise from zero, causing some loads to receive too little voltage and others too much.

 

[timmermeier]

Not exactly. Any difference in load current between the lines will cause the voltages to shift. Voltage on the neutral will rise from zero, causing some loads to receive too little voltage and others too much.

If you lose the neutral at the main panel the main panel and the 3 wire sub the sub panel surface becomes energized . with 4 wire the sub panel surface will not become energized . if you lose the neutral at a 3 wire sub the surface will become energized

 

[ggunn]

You guys are omitting the #1 reason why he must not bond neutral to ground in the sub panel: the NEC says so.