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Old 10-01-2009, 03:17 PM   #1
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grounding of main panel and sub panel in older house


I have an old house in Seattle. It has a main panel outside and three sub panels (100, 100, 60). Although the panels are a modern type with circuit breakers (GE), existing wiring runs inside the house are mostly ungrounded. I have been trying to update the wiring piece by piece. The sub panels do not appear to have a separate grounding cable. Since they are connected to the main via metal conduit, I'm assuming that it serves as the ground? Question: is this an adequate method of grounding by today's standards? If not, should I run #6 awg copper from each of the sub panels back to the main? I'm assuming that this cable can be connected via a bus bar adapter and the run could be left exposed without any conduit or other protection (basement installation)?

Next, I looked at the main. It has a #6 grounding cable on the same bus as the neutral. This cable runs just a couple of feet inside the house and clamps to the copper pipe. Unfortunately, the pipe entrance is on the opposite side of the basement from where they decided to clamp it. They clamped the cable to the pipe approximately 25' from where it enters the basement wall. The pipe is continuous with a few intervening brass shutoff valves. It is copper in the basement and appears to be copper through the wall into the ground. It's another 25 feet underground to the water meter at the street. I think I'm good as far as the 10' underground pipe rule. Another grounding cable runs outside into the concrete driveway. I believe that it is connected to a 4' grounding spike (not 8' as currently required by code).

Do I need to run #4 from the main panel all the way to within 5' of where the copper pipe enters the basement? I know it's required for new construction, but is it worthwhile for an old house? Should I continue this same #4 outside and install an 8' grounding spike?

Aside from the copper water pipe, the house has an old cast iron waste pipe that exits through the basement floor. It is not currently grounded.

Basically, I just want to make sure that I have a decent ground so that all of my hard work installing grounded outlets + wiring is not wasted on a faulty ground.

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Old 10-01-2009, 04:18 PM   #2
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grounding of main panel and sub panel in older house


The ground system you are describing has nothing to do with the ground prong on a 3 wire receptacle. Your water line and ground rod are there for high voltage events like lightning strikes.

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Old 10-01-2009, 04:34 PM   #3
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grounding of main panel and sub panel in older house


House runs:
Yes - metal conduit can & does serve as the ground as long as it is complete & the device is grounded to the metal box
Many places require conduit (Chicago for one unless they changed)

Grounding a sub I am not sure, today a 4 wire feed is required
So I would add a properly sized grounding wire, it must be green

Copper pipe must be grounded to Main within 5' of entering the house
Would I run a new ground ? Yes

I've never seen a waste pipe grounded, mine isn't

Ground rod is usually is from the panel outside
I would not extend the water pipe clamp/ground outside
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