ONT Grounding Discussion (via e-mail 12-2009)
We continue to have internal discussions regarding the necessity of grounding ONTs. I would
like some input.
When the ONT and battery are on the outside of the house (and especially if they are mounted
adjacent) I think we need to follow a strict interpretation of the NEC and NESC and bond to the
power ground and, if the distance to the power ground is over 25’ insert a ground rod.
However, if the UPS / battery is inside the home, the only power coming to the ONT is 12 volt
DC (assuming the drop cable is di-electric and a locate wire is terminated only in the mainline
ped, if at all). I think you could make the argument that in this case it is actually more
dangerous to make a path to the power ground than to let the ONT float. This might save the
Telco at least $50 per premises and actually increase the safety of the system.
Comments?
Mike Riley
----------------------------------------------Mike,
On the St. John project we did it exactly as you have mentioned above, except we put a ground
rod in no matter how far we were from the power ground on outside installations. On the
indoor units we just floated them.
Glen Gines
----------------------------------------------Mike
We have not use outside batteries but at one location for a multi family which we grounded to the
power MGN without question. (110AC and DC both)
But if you review the schematic of the inside power supplies you will find that most of the ground
connections are common on the dc circuit feeding and alarm wires to the ONT’s. Also all power
cords to power packs are of the grounded type. This would allow any voltage potential on the
MGN to appear on the dc circuit at some point. Also, most any ONT’s I have inspected over the
years had a ground connection on the ONT housing. The actual current carrying capacity of the
locator wire or the DC power source wires is much smaller but anyone outside that make be
testing their phone will most likely be standing on earth and it could also be on the damp side. My
concern is first for people and second for equipment. Also some of the vendors like Occam push
for a heavier wire so the ONT get proper current levels. You may also have one of the station
wires feeding an AC potential back to the ONT. All these conditions scream for protection. I
cannot think of any condition that would justify not having a MGN ground connection except at a
Power substation for safety alone. Our company use to do insurance claims for people hurt or
killed from improper grounding so we have heard some pretty strange stories about what should
never happen. Once they are powered by light we can remove the ground. I have been trying to
find out what Verizon FIOS standards are but have had no luck to date finding out. Once the
Codes catch up with the industry I believe it will be clearer that a ground is required.
Joel Williams
------------------------------------------
Joel brings up a good point; the AC and DC circuit grounds at the power supply may be
common.
- Mike
ONT Grounding Discussion (via e-mail 12-2009)
------------------------------Hello to all,
Below is a transcript of an e-mail received from Washington regarding a bonding and
grounding question on our Indiana project, namely the tracer wires.
-John Walker
"As Joe indicated, we do not have requirements for the drop tracer wires. Whenever we
revise PC-5, we intent to require that the tracer be grounded at both ends for safety.
When you ground just one end at the pedestal, then would have two ground references at
the ONT, or nearby the ONT. You can just ground one end, but you are taking some risk
and undefined liability by not grounding at both ends. In my opinion we should not
compromise safety for equipment design’s short comings."
"Do you ground the power supply at the electric circuit with a three prom plug? I read
once in a technical description of line card for a PBX system that “continued and
extensive studies of line card failures due to lightning damage indicates the best
protection is to have a separate earth ground for the power supply and not to use the
adjacent or easily available AC circuit for this purpose”. Perhaps grounding the power
supply and ONT at the same point might help. This should be run through the
manufacturer. We need to get the manufacturer involved to find a solution before we
compromise safety."
Regards,
Norberto