I am installing a subpanel in the basement. The main service is in
the garage. The main service has its ground wire runs to the basement
and it connects to the cold water pipe as it enters the basement from
the outside. This location is about 5 feet from the subpanel
I know the subpanel needs to be grounded to the main service panel
using a correctly sized wire.
My question is whether I can ground the subpanel to the same cold
water pipe at about the same location that the main service connects
to the pipe. Since they both ground to the same grounding item, would
this be allowed in the NEC?
(My appologies to any pros that may be cringing at my terminology).
Thanks in advance,
As long as you run a properly sized Equipment Grounding Conductor in the
wiring method you use to supply the sub panel then establishing an
auxiliary grounding connection from the sub panel's Equipment Grounding
Conductor buss bar, but not from it's neutral buss bar, to the
underground metal water piping will do no harm. In that case you will
be using the metal water piping as a Supplementary Grounding Electrode.
It is important to note that you must keep the grounded current carrying
conductor (neutral) aloof from ground at all points beyond the service
disconnecting means and that definitely includes in your sub panel. You
must not bond the neutral to ground in that sub panel. Any bonding
screw or strap that is supplied with the panel to connect the neutral
buss to the panels cabinet must be removed and discarded. The Grounding
Electrode Conductor (GEC) must not be terminated to the same buss bar as
the neutral or otherwise connected to the neutral within the sub panel's
cabinet. If you fail to keep the neutral and EGCs isolated from each
other in the sub panel then neutral current will be flowing on the
Supplementary electrode GEC and on the Service Equipment's GEC under
normal operating conditions. Please take my word for it that that is
not a good thing.
(B) Conductors of the Same Circuit. All conductors of the same circuit
and, where used, the grounded conductor and all equipment grounding
conductors and bonding conductors shall be contained within the same
raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable,
or cord, unless otherwise permitted in accordance with 300.3(B)(1)
250.54 Supplementary Grounding Electrodes.
Supplementary grounding electrodes shall be permitted to be connected to
the equipment grounding conductors specified in 250.118 and shall not be
required to comply with the electrode bonding requirements of 250.50 or
250.53(C) or the resistance requirements of 250.56, but the earth shall
not be used as the sole equipment grounding conductor.
Subpanels need to have their grounds go back to the panel/service feeding
You need 2 hots a neutral and a ground conductors going back to the
SER cable is the stuff you want if you do not use conduit.
P.S. I run a ground in every foot of conduit.
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