I installed a subpanel when I switched from an electric stove to gas. I
used the 40A 220V breaker that formerly served the stove to power the
sub panel. The cable is #4 with two conductors and a ground. I have 6-
15 amp breakers in the panel providing branch circuits for my kitchen
and other areas of my house. The grounds and neutrals all share the
common bus bar in the sub panel. Everything has worked fine for years
now. Can someone explain why I read that ground and neutral are to be
isolated in the sub panel? Please don't answer because of the NEC since
that does not explain why. What is the risk of my current situation?
While I agree that what's there is correct and functional "circuit wise"
I think the reason the code requires a separate ground conductor is this:
That common ground/neutral might develop an open between the sub panel
and the main panel because of a "loose connection" at one end or the
other. If that happened currents returning on the neutrals of those
"new" branch circuits would lift the whole "ground" of the sub panel off
true ground and would create a dangerous situation by making things like
the grouning slots in recepticals rise above ground to dangerous voltage
On 27 Nov 2006 13:25:38 -0800, email@example.com wrote:
Essentially, because the ground wire is connected to things
that people are expected to touch.
When you connect the nuetral and ground together, you create
the possibility of the ground becoming hot, and energizing
things like the outside of your refridgerator. This is bad.
The probability of this happening goes up astronomically
if there is a nuetral/ground interconnection anywhere
but in the main service entry.
Aside from the chance of something coming loose and putting
some random voltage between 105 and 240 volts on the
outside of your bathtub, there's also the problem that
your ground wire is not zero resistance, which means that
if you touch both it and another path to ground, at least
some of whatever current is on it will choose to go through
you. (This is why, for example, you can get a shock
from the casing of a malfunctioning appliance, even if
The Reason is that there is current goes through a nuteral and no current
goes through a ground and if the ground and nutural are tied together they
both have current passing through them and the only time that current should
go through a ground is when there is a short or something similar...
but to make thing even moree confusing is then why is the nurural and ground
tied together at the main pannel and that is to bond the nuural to the earth
OK, so the ground is bonded to the neutral at the service panel.
What about the transfromer at the pole? Is the neutral center-tap in
the North American System bonded to the transformer enclosure? Is
this point often connected to a ground wire running down the pole and
into the earth?
Also, why in the US systems is the top wire on the pole the hot wire
(for the transformer primary) and the neutral is usually several feet
below this? Is this arrangement not more prone to lightning damage?
That was the old way - keeping the hot wire as far from people/animals
as possible. The vast majority of new installations will put the
ground wire on top.
But what about the rural Canadian systems where there is only a hot
wire with no ground at all? Are they any more susceptable to lightning
than a US hot top wire system?
The neutral (white) is a return ... it carries the same current as the hot
wire (black). The ground wire is a non current-carrying safety wire (often
bare copper). The purpose of the ground wire is to reduce voltages in the
case of lightning or an accident (wires falling across other wires outside
of your home and raising the voltage with respect to ground to a dangerous
level). The ground wire only conducts current in the case of a fault.
Ground fault circuit interrupters need the ground wire to detect such faults
and open the circuit when they occur.
People are often shocked and even electrocuted with voltages with respect to
ground ... one is standing on a wet basement floor ... one is touching a
faucet ... one is in the tub or shower. The voltage with respect to ground
is the big issue here (for safety reasons).
An ungrounded electrical system in your home would allow voltages to rise to
thousands of volts above ground and fry you if you happened to be grounded
(in a tub or standing on a wet concrete floor).
When a ground is available at an outlet with a GFCI it is preferred
(and required) that it be installed,
However, where there is no ground the NEC still recognized that a GFCI
can still provide protection by detecting an imbalance in currents
between the neutral and hot wire. In this case, the user must be
informed (with a small sticker on the outlet) that the GFCI is
Actually, they don't.
See section 210-7(d) in the NEC, and section 26-700(9) in the CEC.
GFCIs are a legal substitute for a grounded outlet in an existing
installation where there is no ground available in the outlet box.
Very well [*]
What it does is measure the current leaving the "hot" lead and
compares it with the current returning in the "neutral" lead. If those
are different by more than a few milliamperes, there is a Ground
Fault, that is, current is finding its way to ground through some
other path than "neutral". If that is the case, the GFCI Interrupts
(the "I" part of "GFCI") the Circuit, very, very quickly, so that no
damage is done to whatever caused the Fault (that could be a human
body). The test button simulates a fault.
[*] I had it work once for me. I didn't know it had until the
lamp I had dropped into water wouldn't come on again.
"What do *you* care what other people think?" --Arline Feynman
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