INSPECTING
THE
SUBPANEL
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Inspecting a subpanel is very
similar
l to inspecting a service
panel with the exceptions of
panel,
a few interior red flags.
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Subpanel
1.
The hot wires, red and black, are each connected to a lug on th b b
the bus bars. 2.
The neutral wire (white wire) are connected to )
the neutral bus bar. 3.
The ground (bare) wire is connected to the
is connected to the ground bus.
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REMEMBER THIS RULE: DO NOT GROUND THE NEUTRAL AFTER THE MAIN DISCONNECT
DO NOT GROUND THE NEUTRAL AFTER THE MAIN DISCONNECT. THE NEUTRAL MAY NOT BE USED TO ACCOMPLISH GROUNDING.
COMMON SUBPANEL FAULTS::
COMMON SUBPANEL FAULTS
• BONDING JUMPER CONNECTED TO THE NEUTRAL BAR
• GROUNDS AND NEUTRALS SHARE THE SAME BUS GROUNDS AND NEUTRALS SHARE THE SAME BUS BAR
GROUNDS AND NEUTRALS SHARE THE SAME BUS BAR
• Neutral wires not isolated from the subpanel
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Subpanel
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Remember: In a panel
or a subpanel,
subpanel each
screw on the neutral
bus bar can only hold
one wire.
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NEUTRAL BUS BAR
When this panel is used as a sub‐panel,
sub panel
the neutral (white) wires are
connected here.
Note the S‐shaped piece of metal
secured by a green screw. This is called
a "bonding strap" and is used to
connect (or "bond") the neutral bus to
ground (the metal case) only when the
panel is being used as a main panel.
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If the bonding strap is used, the strap is inserted into one of the
strap is inserted into one of the neutral terminal points. BUT WE CAN'T DO THIS... If the panel is used as a sub‐panel. The neutral and ground wires MUST be Th
t l d
d i MUST b
connected together, but ONLY at the main panel.
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10
Safety Hazard
f y
SUBPANEL WITH BONDING STRAP NOT REMOVED
SUBPANEL WITH BONDING STRAP NOT REMOVED
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Why not connect the neutral Why
not connect the neutral
and ground wires in a subpanel?
path for electric current could be
Because if a neutral wire became disconnected,, the return p
along a ground wire. While that itself may not be a hazard, if that ground wire also became
disconnected somewhere, parts of the ground system could be energized. That's not EVER
supposed to happen.
The neutral wire is essentially a "low‐risk" return path for the electric current in that branch
of the system. All of the neutral wires all have the same electrical potential... nothing. At
least, no potential compared to ground. There is, of course, 120 volts of potential difference
between a neutral wire and any hot wire in the residential system.
If you touched the metal part of a live neutral wire you should not receive a shock. (But don't
try it!) By tying the neutral to ground at one point,
point half of the conductors (in a typical 120
volt circuit) have no dangerous electrical potential. Of course, the hot wires are still
dangerous.
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OLD CERAMIC FUSE BOXES ARE OBSOLETE AND POSE A RISK OF SHOCK OR ELECTROCUTION BECAUSE OF THE EXPOSED ELECTRICAL CONTACTS.
C OC O
C S O
OS
C C CO
C S
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Old ceramic fuse blocks are a safety
Old ceramic fuse blocks are a safety hazard
safety hazard
hazard. 14
Old ceramic fuse blocks are a safety hazard. 15
• EQUIPMENT GROUNDING CONDUCTORS IN SUBPANELS MUST
BE ON THEIR OWN GROUND BAR.
• IT IS NOT ACCEPTABLE TO SIMPLY BUNDLE THEM TOGETHER
AND RUN ONE CONDUCTOR TO THE PANEL ENCLOSURE.
• THE SUBPANEL NEUTRAL MUST BE ISOLATED AND MAY NOT
BE USED FOR GROUNDING.
• THE GROUND BAR MUST BE BONDED.
• ALL METAL ENCLOSURES CONTAINING LIVE ELECTRICAL
WIRING, INCLUDING SUBPANELS, MUST BE GROUNDED SO THEY
REMAIN AT ZERO VOLTAGE POTENTIAL TO GROUND,
GROUND AND SO
THEY HAVE AN EMERGENCY GROUNDING CONNECTION TO
CLEAR POSSIBLE FAULTS.
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REPORT
SUBPANEL
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SUBPANEL
In a subpanel, the white
neutrall and
d the
h equipment
i
grounds must not be
bonded together.
The neutral MUST be
isolated from contacting
the metal enclosure and
any equipment grounds.
Bonding these conductors
is hazardous as it creates
another path for current.
X
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Report
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Report
What kind of panel is this and how many things are wrong?
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Report
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Report
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Report
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Report
SUBPANEL
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Report
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Report
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Subpanels
REPORT
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